Nearly every retail electric bicycle and ebike conversion kit is listed at a specific power level, such as a “500 watt electric mountain bike” or a “250 watt ebike conversion kit”, yet often this power rating is misleading or just plain wrong. The problem is that manufacturers don’t use the same standards to name their motors, and consumers often don’t understand the differences.
What’s a Watt?
Let’s start with some definitions and a bit of a physics lesson. A “watt” is a unit of power, named for Scottish Engineer James Watt.
Watts can be used to measure the instantaneous power output (or input) of a machine, such as the electric motor on your ebike. The number of watts used by an electric motor at any moment equal the voltage supplied by a battery multiplied by the current flowing from the battery to the motor. So an ebike motor connected to a 24V battery being supplied with 10 amps of current would be powered at 24*10=240 watts.
As you can see, calculating the peak power of an ebike is simple. You just multiply the voltage of the battery by the maximum current the ebike can handle. The maximum current is determined by the ebike’s controller, and is usually somewhere between 15-30 amps. An ebike with a 48V battery and a 20 amp peak controller would theoretically be capable of a nominal 960 watts of instantaneous power.
This is where things get complicated though, because ebike manufacturers don’t always rate their parts this way.
Lies! Deception! Blasphemy!
This happens for a number of reasons. A common cause is to skirt importation laws. Many European countries limit imports to electric bicycles with a motor rated at 250 watts or less. 250 watts is not very much power by ebike standards. Professional cyclists can put out more than 400 watts on leg power alone.
So in order to clear their electric bicycles for import to as many countries as possible, many ebike manufacturers rate the components on their ebikes much lower than what they are in reality.
Meet “250 watt” motors.
Here is a great example of a 250 watt electric bicycle conversion kit. It comes with all the parts except the battery, a pretty standard motor rated by the vendor as “250” watts, and a pretty decent price of about $250 including shipping. But when we look at the specifications, we see the 36V controller has a peak current limit of 15A. Doing the math shows us that 36V * 15A = 540 peak watts.
This is very common in the industry. Ebikes sold with “250 watt” motors often come standard with 36V batteries and 15 or 20 amp controllers. As we saw, a 15 amp controller would mean the actual peak power supplied to the motor is closer to 540 watts and a 20 amp controller would be over 700 watts.
Yea, “250 watts” my tuchus!
How do ebike manufacturers get away with this? One way is to rate the motor for “continuous power” instead of “peak power”. The difference between continuous power and peak power is that continuous power essentially means power a motor can safely handle for an indefinite amount of time without damage or overheating the motor. A “250 watt continuous” motor, theoretically, could run forever at 250 watts without overheating, but any more power would cause it to eventually overheat. If the motor is truly a 250 watt motor by definition, then running this motor at 251 watts would eventually cause it overheat.
Is it ok for ebike companies to rate their motors this way? Technically yes, if the numbers are accurate. But most of the time a “250 watt continuous” motor can handle more than 250 watts continuously, meaning the numerical naming convention is inaccurate and misleading.
The problem here isn’t the morality of underrating ebike specifications (this is one of the few times you usually get more than you pay for), it’s that this often confuses customers and makes comparing different motors much more difficult.
a “250 watt” motor that I run at 500 watts
How can you best use power ratings?
When comparing ebikes or ebike kits, it is important to know first of all if you are comparing continuous or peak power. When someone advises that a 220 lb rider would likely need at least a 1,000 watt motor, he or she usually means 1,000 watts of peak power, as in the amount of power the ebike should be able to produce to drive the rider up a hill.
A 500 watt electric bicycle conversion kit may be listed as a 500 watt kit, yet a closer inspection could show that the kit comes with a 48V battery and a 20 amp peak controller. The math shows us that this kit is in fact capable of putting out 48V x 20A=960 watts, essentially a 1,000 watt kit. What might have initially appeared to be too weak (advertised as 500 watts) is actually an approximately 1,000 watt peak kit, perfect for our 220 lb rider we used in the example about above.
Lawmakers are ignorant about ebikes (among other things)
This is also an interesting example of how nonsensical many electric bicycle laws are. Limiting the wattage of ebike motors doesn’t necessarily limit how powerful they can be. Even though a motor is marked as 250 watts (and even if it may actually be a true 250 watt motor), anyone could connect it to a 48V battery and run 20 amps through the motor to achieve 1,000 watts of power. Of course this could eventually damage or destroy the motor, but it is still demonstrates how it is entirely possible from a practical standpoint.
In fact, direct drive motors such as the Nine Continent are often listed as 500 or 1,000 watt motors, but many people have had success running them at over 3,000 watts by drilling out the cover plates to provide additional air cooling to the motor. Other modifications such as increasing the gauge of the wires carrying power to the copper windings can help maximize the useful power output of these strong, underrated motors.
These examples should reinforce the take-home message here: when you are looking into an electric bicycle or ebike conversion kit, always calculate peak watts in your mind (volts x amps) to do a fair comparison of the actual power you can expect out of any ebike setup. That way you’ll know what type of power level you’ll really experience when you’re ready to twist the throttle.
We have bought two hub motor rating 60v and 2000w…we are using battery of 48v and 32amp. We want to give this to both the motar. We want to know the uncharging time. And importantly can we get the maximum speed?
the discharge time (the amount of run time) is impossible to calculate without knowing the conditions of the ride. You’ll have to experiment on that yourself. To calculate speed, determine the original speed the motor was rated at for 60V and multiple that speed by 4/5 (which is 48V/60V).
i have a 1000w motor and 48v battery with 30Amp controller
then i need to know the battery consumption of the motor according to the motor power when a certain load is applied on it . how can i calculate it
The instantaneous battery consumption (in watts) is equal to the instantaneous current (in amps) multiplied by the instantaneous voltage (in volts). So using your 30A controller, if you were using full power, like during acceleration or hill climbing, you’d multiply the 30A by your voltage. Your exact voltage changes depending on the current, but let’s just assume it’s right at 48V. So you’d have 30A x 48V = 1,440 watts. Interestingly, the wattage of the motor isn’t very relevant here, as long as it’s providing a load to the controller sufficient that the controller wants to give it full power (in the case described above) or any amount of power, such as during flatland cruising where you might only be pulling 10A (or 10A x 48V = 480 watts). Hope that helps!
i got it but i have to know the charge that is going to discharge from the battery when connected with respect to the time .
As in the watt hours? If your load isn’t constant then that is very difficult to calculate. With a constant load it is just Volts x Amps x hours = watt hours. But if your load is normal riding then you’re stopping and starting and going up hills. At that point you’d basically have to take the integral and get the exact VxAxH=Wh at every second and sum them up. Alternatively, you can just test this by using a wattmeter or cycle analyst.
If motor has a tag of 350w 48 v. Current controller is 48v 20 amps. Can controller be upgraded to 60 volts 20 amps? Can the motor handle it.
It depends. The controller can likely handle 60V but you’ll have to check the capacitors inside to be sure. Most 48V motors can handle higher voltages but if you use high power for extended periods of time then you can risk overheating the motor.
Hey Micah, I was wondering if it was possible to run my 48v 1000w rear hub motor @ 36v & 500w? Is it as easy as just plugging in a 36v battery and 36v controller, and will I run into any efficiency issues doing this?
My reason for doing this is so I can utilize my 10cell hobby charger and avoid a bms and also to have a slightly longer but slower ride. Is there any sense in this, keeping in mind I am stuck with a 48v 1000w motor?
Thanks!
You can definitely do that. Like you said, just use a 36V battery and a matching 36V controller. The downside is you’ll get about a 25% drop in speed by using 36V instead of 48V, but it will still work.
Hi Micah, Congratulations for your site is amazing and i have learn a lot with it. I leave in Europe and we have the 250v limitation law, so my question is related to the following and having in considering the bike features:
Range – 10ah – 25 Miles
Motor – Xiongda 2 – 6*36V*250W brushless geared rear motor
Controller – Tongsheng – 36V15A speed sensor, aluminium
Battery – Lithium Ion 36v / 10aH Yoku/Samsung with lock
I want to get more speed from the 250V engine so i need to increase the power to 46v so far so good, but instead of changing the controller or even the battery, can I increase the output power at the end of the controller to give more voltage to the engine, like adding a voltage multiplier or something of that kind ?
Kind Regards
Or i can buy one more battery with 12v 10ah and plug in serie and this way i will get the 48v 10ah, but will this will fry the controller?
To increase speed you’ll need to increase voltage. 48V is the next standard step up. Some 36V controllers can handle 48V, others will fry. To determine if yours will be ok, you’ll need to open it up and check if the capacitors are rated for 50V (not good enough) or 63V (should be fine on 48V).
You could either add a 12V 10AH battery in series to your battery as you mentioned in your other post (clunkier and more difficult solution) or replace the 36V battery altogether with a 48V battery (the cleaner, easier but more expensive solution).
I have two Hilltopper battery/controllers each 24V 6.6Ah with the 8fun 250 watt front wheel hub. I’m having troubles with hills and not range or speed. Can I combine the two battery packs in series (making 48V) to help on hills or will it not help me on hills? If it does, do you know offhand what controller Hilltopper uses for controller board components. I can’t find specs on the 8fun or the controller board. Would I need to buy a new 48v controller? If it does help on hills in series or parallel do I wire the batteries to one controller or both controllers? Thanks.
Yes it will give you twice the power which will help on hills, but the hilltopper controller is almost certainly not rated for 48V so you’d need to find yourself a 48V controller. Also, your motor will try to spin twice as fast, resulting in a faster ride, though if the motor doesn’t have enough torque to get up to the speed it wants to go, you’ll end up wasting lots of power as heat and potentially overheating the battery.
I’ve always found it comical that Clean Republic’s kits are called “hilltoppers”. They are fine kits, don’t get me wrong, but what they are best at is flat ground cruising, where they are one of the most economical options. They simply don’t have any power for “topping hills”.
Micah,
Great article, but not being an engineer, I’m still a little confused on the nuances of this.
For instance, I’m looking at a electric cargo bike. One of them is the Juiced which comes with three different battery sizes all connected to the same “500 watt” motor and 48Volt battery.
There is a 15AH, a 23AH and 32AH version of the battery. If I do the math using your article the 32AH battery will provide over a 1500 watts of power…is that right? Or am I confusing the AH of the battery with the amperage of the “peak controller”?
And then you have to consider the weight of the different batteries…my walnut sized brain starts to spin and things stop computing properly.
Can you help clear this up in my head. And please use easy words, I’m not that bright (at least according to my wife.)
Thanks.
Lloyd
” Or am I confusing the AH of the battery with the amperage of the “peak controller”?”
That’s exactly what you’re doing. AH is capacity (think gallons in a gas tank) and A or Amps is current (think the rate of flow of that gas into the carbs or fuel injectors). To get the power in watts you need to multiply the current (amps) that the controller is pulling by the voltage of the battery. Those different AH batteries are just like different volume gas tanks.
Tell your wife to go easy on you, I’m sure you’re plenty bright 😉
Hi mitch,
Wanted to ask, my electric scooter is a 48 v, 1000 watt scooter with 33 ah controller. had 33 ah batteries, but, i want to install fresh 42 ah batteries. Will i burn the controller or will i be fine?
Thank you
Increasing the amp hours (capacity) of the batteries won’t have an effect on your controller at all. Think of it like just installing a bigger gas tank… that won’t hurt the car’s motor, it will only allow it to run longer.
Hi ,
if i would like a ebike that is able to run 62mph on 72v 12ah lead acid batteries , what controller and motor specs would be approriate?
I’m sorry but that’s just a bad idea. A) 62 mph is ridiculously fast for an ebike and becomes dangerous unless you have a really high quality bike and know how to ride at those speeds, which is more like hanging on than riding… and B) at those speed weight is even more important and you don’t want a huge amount of lead acid on that frame.
I am not sure it is as simple as saying a motor’s power is the input watts = volts x amps of the battery and motor controller.
The power applied by the motor to the wheels are the actual output watts and this is how a motor should be rated in my view. The output power depends on the load the bike is under…. incline, weight of bike/rider the speed it is doing etc etc so very confusing and no straight answer as the efficiency of the motor varies (and the output power) with the load. The endless sphere wiki at
https://endless-sphere.com/w/index.php/EBike_Efficiency#Rating_By_Watts_Input_Or_Watts_Output
has a good write up on this. The writer concludes that motor output power is ~ 40% of input power according – the rest is lost in heat.
Phil, you are absolutely right. There are also a lot of parasitic losses between the motor and the ground. But it’s both hard to explain, account for and calculate the exact output power in every situation. The easiest and best proxy for comparison then is the input power to the motor. After that it gets very situational as you correctly explained.
Yeah, we want more power, 250w not much over ½ a person power, guess some 1 said ‘Let them have ½ as much as a moped’, but we ended up with ½ the speed, instead of the power of a 25cc engine. Cliché time ’20 is plenty’ (but let’s be naughty & go at 40).
WATT is that all about, he didn’t invent steam engine, he converted 1 of Newcoman’s to use ¼ as much fuel. So guess he reduced pollution, or did we just us 4 times as mean? & while I’m here, de Vinci didn’t invent the bike, was 4 wheeled powered + hands, OK?
Hi, Micah,
I recently purchased a little 24V / 250 watt ebike (Yukon Trail Navigator) and I’m considering upgrading the motor controller to a 36V / 500W and a 36V 10-12 Amp battery. I don’t have much info about the motor, it simply has a sticker on it that says 24V.
Do you suppose my motor can safely run at 36V? Or do I need to worry about replacing that as well?
Thanks!
Generally speaking, most 24V ebike motors can do fine on 36V. If you planned on riding up a really steep hill for a long time then you might get into overheating issues, but that would be an extreme case.
hi , I am planning to build friction drive ebike . I thought i would go with 42V and 6.8A. could you guide what would be the range i would be receiving in idle stage with configuration where i use 18650 3.4Ah batteries and my motor has 190Kv. These setup is been connect over normal 26 inch tire.
Looking forward for your valuable comment.
I’m sorry but it’s hard to calculate without knowing all of your parameters, some of which (such as the friction coefficient) you pretty much won’t know until you build the thing. Your best bet is to build it and see…
Hello Micah
I just purchased a ebike kit 5.2 ah samsung 10k 24v 250 w. Now I find that it is a 5 mile without paddle assist, and 9 mile with. thinking about increasing the range to about 30 miles. what would I need to know to do this, I will purchase your video, do it have a section or chapter to increase the range of the battery?. And where do i get the tools and batteries etc. your comments will be appreciated. Thank you
Basically you have two options: either buy a bigger battery (or more batteries of the same size to swap out) or open your battery and add cells in parallel. I’m currently working on a video to demonstrate this. In the meantime, watch this video but just imagine adding the cells in parallel instead of in series: https://www.youtube.com/watch?v=9KHo-T74IWA
Hi, for a 250 watt bicycle, instead making a 48V custom made battery kit drive with around 5 amp to archive
is there anyway I can use ten normal 2 port power bank like this https://www.anker.com/products/A1271011 ,
by theory can I series this ten power bank, with each using both port to output 4.8A, so i still can have 50V * 4.8A to archive 240 watt ?
it is possible?
I have no idea how to series the 10 power bank 😛
In theory yes, but in practice no. You’ll get a really wonky battery that can’t handle much power and will die incredibly quickly.
Hi,
What if I want high power but at low capacity (imagine e-bike sharing in hilly area)
200Wh of energy is enough but how do I realize this if the motor is dimensioned for 36V.
Would I lose power with a 25V/8ah battery (chemistry can handle 2C comfortably) or is for example 36V/5ah battery configuration with cells that can handle 4C discharge better?
I like the bafang “350W” (36V x 18amp).. the 500 to 600W of assistance is really necessary to comfortably do slopes of 5 to 10% but I think the batterypack 4P10S x ICR18650 is too big.. but these cells already lose a lot of their claimed capacity at 3C.
What is your advise on this matter?
Thanks in advance for your time!
http://ecolo-cycle.com/en/electric-bike/cargo-electric-bike/
i recently got this ebike from a buddy…but im very dissapoint about the speed and the look of it. im thinking about putting the electric component to a normal bike…and wondering how i can max out the speed of it…without spending too much. thanx
It looks like it’s got SLA batteries, no? The cheapest way to increase the speed would be to buy another 12V SLA brick and wire it in series to boost the voltage to 60V. That should give you about a 20-25% boost in speed. You’ll likely need a 60V controller though if that 48V controller can’t handle the overvolting.
Read about e-scooter I was thinking of buying, 1 could + 12 volts to get 60, (guess top speed 30 » 37½ mph ).
But controller would cut off fully charged battery @ 65 volts. So 1 could either turn lights on @ 1st, or use push switch left from starter on petrol engine to only switch extra 12 volts after journey started.
I have a 48v 1000watt electric bike front motor on a three wheel Schwinn. I run four 35ah batteries to get 48v. I average 40 miles but the motor is not powerful enough for what I’m looking for. I found a 48,60, or 72v option on a 3000 watt electric front motor. I’m trynna get the most pulling power not speed, so which will produce more power four batteries at 48v on 3000watts. Or 60v, or 72v on 3000watts. I’m confused just trynna get the most power not speed. My bike is 220 lbs with the batteries and 450 lbs with me on it. So I need more pull not speed. Any ideas on this will be helpful thanks…
The 3,000W motor on 72V will give you more pulling power than the same motor on 60V or 48V since power = volts * current (amps), but the higher voltage will also result in a higher top speed. What you want is a direct drive motor with a slow winding, meaning more turns of copper inside the motor. Check out the guys at Kinaye Motor Sports https://kinayems.com/ and ask for a 3,000W motor that has a very slow winding. Then run that sucker at high volts and you’ll be pulling stumps out of the ground if you can get enough traction!
Micah- Recently purchased your Ebike book. Excellent tool for the first time Ebike builder! My questions is about using a motor “Rated” at 48V 1000W 470RPM High motor efficiency 80%. I’m waiting for the kit to arrive, but I assume the controlled will probably be a 20A controller. Can I use this kit with a Bottle type of battery rated at 36V 10AH? I really like the simplicity of the Bottle type battery and I’m not looking for a lot of speed. My commute is less than 3 miles but in a hilly area. Would this set up be ok for my purpose? Or should I get a 48V 10AH battery? Thanks.
Glad you enjoyed the book! To answer your question, that motor could run off of that battery, albeit at a slower speed due to the lower voltage. However, that 48V controller won’t work with a 36V battery because you’ll be below the low voltage cutoff most of the time. You’d need to either get a 36V controller or upgrade to a 48V battery.
Hello im so happy i found your web site.I bought an electric scooter recently and my thurst about knowing whats happenning under it is breathtaking.Your info’s were great.I have a lead acid battery 48 v 12 ah and i want to convert it to lithium but i dont understand why chinese manufacters are recommending the type of motor for their lithium battery pack.Like for example a 48 v 20 ah battery pack -recommended 1000 w motor or under 1440 w the most.From your informations the controller does the hard work and math.Also if i have a 48 v battery can i connect a 2000 w motor 60 v and a recommended controller for that specific motor(60 v 2000 w-54 A ).Whats the math with the voltage of the battery and the other components?Also that amp hour thing.and the last question.The controller provides like 30 a to the motor from a battery with 48 v 12 ah .So u can calculate the time until it wil dry out?and from your calculating a 30 a controllor and a 48 v battery=1440 w,but i have a 1000 w motor .can it provide that power ?
To answer your questions:
Chinese manufacturers often suggest a certain wattage motor that would be appropriate for their batteries. I can’t say for sure, but I believe this is because most of the time their customers don’t understand that it’s largely the controller that defines how much power will be drawn from the battery. Instead, most people just think that a bigger motor (which usually means a bigger [i.e. higher current] controller), means more current draw from the battery. Which is usually correct, but it’s not the most accurate way to specify the parts.
Next, if you have a 48V battery, and then you connect it to a motor that is advertised as a 60V motor, you’ll find that the motor will spin slower than advertised, as the speed of the motor is defined by the voltage of the battery.
In order to determine the power of the ebike, you’d simply multiply the 48V of the battery by the current limit on the controller. For example, if you used a 30A controller then you’d have an approximately 1,440 W ebike.
To calculate the life of the battery you’d divide the capacity of battery (in AH) by the current being drawn. If you pulled 30A continuously, you’d get 12AH/30A = 0.4 hours of driving time. But you won’t be pulling 30A continuously. Maybe you’ll average 15A, considering some time at high current and sometimes at low current. That would give you 12AH/15A = 0.8 hours of driving time, on average.
Thanks for the answers.yes i went down on a paper and i calculate what u did after i send the reply.but If i have 4 batteries 12 v 12 ah that 0.8 hours multiplies by 4 or IT remains the same?
So u could drain the same amount of amps from a battery different motor if u mentain the same speed right?and another question.a company is selling an electric scooter with 1600w brushless motor and they say he can produce 1900 w power 70 km/h speed.that is from the controller combined with the fact that IT is brushless ?
It remains 12AH because you are wiring them in series. So 4 pieces of 12V 12AH in series becomes 48V 12AH. If you wired them in parallel instead you’d have 12V 48AH.
I was thinking 24 volts, 250w ~=10a, so going @ 15 mph I’d get 1½ miles for each Ah of the battery.
The Ah of battery is what you get using a constant current for 10 hours, so yes in theory, but would weight so much that you’d not get anywhere @ all!
Hi Micah,
Thanks for this wonderful post. I am a bit curious about your motor. At a local importer’s shop, I saw a 36V 350Watt motor just like your pic (250 Watt silver color motor), but I didn’t buy that motor because I didn’t find DISC BRAKE installing option (usually what we see is that 6 holes at one side of the motor). Is your 250 Watt motor capable of installing a disc brake? (both the motors look similar to me)
Some motors accept disc brakes and some motors don’t. You’re right about checking for those 6 holes. If you see 6 holes on the side of the hub in a circle then it should accept disc brakes.
Hello Micah,
I am in process to build my fisrt electric bike. I have an 36V-750 W Aotema front wheel with a peak of 1200W. The motor is brushless and senseoreless.
My question: Is the Controller wattage important? I found some offers with a 36 V controller and 30 AMPS but the wattage is 350 some others are at 500.
Thanks
Use the amps printed on the controller to get a better idea of its power level. The wattage is likely referring to continuous rating, not peak.
For example, the 36V 30A controller gives a peak power draw of 36*30 = 1,080 watts. The 500 watt rating means that it can handle 500W continuously, but if you tried to pull 1,000W for an hour continuously you’d probably burn the controller.
Hello Micah!
Hats off ! great article.I am just trying to get into the eBike scene. Ive seen many conversion kits available but in my country buying the bike from right out of the box is cheaper. Quality aside, i am not sure if this bike can haul my 85kg butt over hilly terrain say 6% gradient.http://stonbike.com.my/portfolio-item/bike-lan2601alumium/ .If i actually need more power then i might opt for the conversion kits. I have a standard bike which is use but i dread the days that i have to be drenched in sweat just to go into town to buy a soda. Your opinion is appreciated
Looks like a broken link?
This article refers to a watt as a unit of power, however, a Watt is a unit of Electrical power,not mechanical, so when a motor is described as 250W,this is the input power.
A 500w motor would roughly provide 1/2HP, because of losses in motor.
I have found that brushless DC motors are less efficient than commutator motors,the copper commutatotor and brush gear is a very efficient device.3 phase synchronous motors,(as now fitted to many vehicals) are the best,but need a vfd drive.
Hi Micah!
First of all, congratulations for your work here!
I’m Brazilian and I have a Electric Scooter Sonik Eagle King 1500W here in Brazil.
Unfortunately, we yet no have places for do repair on e-bikes here.
I have a problem with my motor controller and I will change this.
My battery is 60V 38A and my motor controller is 60V 35A.
Can I put a motor controller 60V 50A of 2500W for become more faster?
The manual sayd that the motor is 1500W but I not found this confirmation on wheels superficie.
Thank you My Friend!
It depends. If you are hitting the 35A when you are at top speed, then increasing the current limit on the controller will give you more speed but it is the current limit that is stopping you from pulling more power to go faster. If you aren’t hitting the current limit though, that is to say you are cruising at top speed and pulling less than 35A, then swapping your controller to a higher current limit won’t make you faster because your top speed isn’t limited by the current at that point but rather it is limited by the motor.
Hi Micah-
Currently own cyclamatic bafang 250 watt motor on a 24V 10Ah li-ion set up. For upgrade, I ebay purchased 48V 12Ah battery and a china controller that label reads 36/48 V – 18amps – 350 watts. The label confuses me? 48 X 18 = 864 peak watts. Where does 350 watts come into play? Is this based on a nominal amperage? Can some controllers have a preset wattage? Btw, controller has 7 mosfets. Great site! Thank you.
Hey Terry,
Good question. The difference here that is important to take note of is maximum instantaneous power versus maximum continuous power. If your controller is pulling 18 amps, then you’d multiply that 18A by whatever voltage you are running to get your max instantaneous power. On a 24V battery that would be about 432 watts and on a 48V battery that’d be the 864 peak watts you calculated. The controller is “under rated” at 350 watts because they are likely using a max continuous rating. If you were to pull 18A all day (for instance driving continuously up an infinitely long hill) then you’d probably burn out that controller. In reality you would get to the top of that hill and the current would drop back down to a reasonable level, probably in the low teens and thus under the 350 watt continuous rating.
Here’s another example: I’ve used been happy with this controller on a few builds. It’s rated as a 600W controller but has a current limit of 30A. On a 48V battery you’d pull about 1400 watts during extreme conditions, but when you factor in stops at traffic lights and normal flat land cruising, you don’t actually spend very much time above the max continuous rating.
We are looking to buy an eBike for the Rangers of our local state park to allow them to respond to emergencies on remote trails. Some of the trails in the park are moderately steep and in various states of repair. The Rangers wear full law enforcement gear, adding 30 pounds to their normal body weight (total maximum weight would be appox. 210 lbs.). Can you recommend an appropriate bike or provide guidance for our purchase? Thank you.
It sounds like you’re going to want a combination of a powerful motor, low gearing (for steep terrain) and a sturdy mountain bike potentially with full suspension (for the rough terrain).
A good option could be the Bafang BBS02 mid drive motor (or the even higher powered BBSHD), as it would allow a good amount of power and the ability to use very low gearing in an offroad environment. The best price would be getting it straight from China (http://s.click.aliexpress.com/e/i2bUrzNVR) or if you’d prefer to source the kits in the US, a company called California Ebike has excellent service and support. http://california-ebike.com/product/8fun-mid-drive-electric-bicycle-kit/
California Ebike also has a good geared motor kit that I’d also recommend.
If you are looking for a ready-made ebike, your options are a bit more limited and the price will start going up quickly. There aren’t many off-road capable, powerful ebikes on the market for an affordable price. The Optibike would be a great option, but it costs many thousands of dollars. That’s why DIY is such a good option – you could build your team equally capable ebikes for a fraction of the price.
I love it, from the title to the end!
My ‘450w’ currie pulls a measured 35A at 24V… a mere 840W!
The next discussion might be about range on a given Ah pack?
I see on other forums a seemingly random 20Wh / mile figure being
tossed around. That’s fine well and good, my bike with my chubby arse
(95kg) has been measured at 9.5-10A on flat ground with no wind, wide open.
That comes pretty close to the 20Wh figure (24 really). And since it’s 24v
it ends up being 1Ah per mile.
Almost everyone skips the part about how the x or y ah are rated.
I think most battery specs are measured across the full range of the pack
v-max to v-min at 20hour rate (unless otherwise stated).
This can be WAY below the cut off voltage of a bike PWM controller.
Keep up the good work, and Micah if you’re anywhere near Daytona, drop me a line please!
I also bought Currie e-bike, read some where = 450w, but even pedaling using its extra low gear & electric I still can’t get up this big hill. Could it be that it has no more power than my 250w e-bike that was stolen? Is it that the weight of the 2 batteries & motor is more than its power, & so I’d be better taking them off & using it as normal bike? I’ve old maths book that says ‘9lb could make bike go 20 mph’, that is; 9lb weight falling over cliff towing bike on level, (don’t try this @ home!).
Hi,
Thank you for the great article. I had a newbie question.
If I have a bag an motor rated 36v 500w can I mate it to a 48v battery? Is this bad? What exactly Is the difference between a 36v and 48v rated 500w motor?
Hope you can help thank you
Hi Ben,
Theoretically speaking, any DC motor can be mated to a 48V battery. The voltage just changes the speed that the motor spins. A motor that is “rated” for 36V means it achieves its intended speed at that voltage. If you run it at 48V, it would go faster (exactly 48/36 = 1.33 times faster). Practically speaking, the answer to the question of whether this is “bad” or not is more difficult to answer. The higher voltage you use, the more power you’re using as well. Moving up from 36V to 48V likely isn’t going to be a big enough difference to cause large problems, at least not immediately. If your motor has plastic internal gears, the higher power could cause those plastic teeth to wear out a bit faster over time. If you’re going up a large, long hill then the added power could cause the motor to overheat sooner. Generally speaking, I quite often overvolt to 48V gearless motors that are marked 36V. I have done the same for geared motors as well, but I often limit the current to cut down on the power, resulting in more speed but similar or only slightly higher power output.
My current bike has two 36V 350 watt motors that I’m running each at 52V and 10A, for about 500W at each motor. I don’t recommend that to everyone, but I live in a flat area and use a CycleAnalyst to watch my systems and make sure everything is staying at safe levels.
I hope that helps you!
No, it = 0·33 times faster, or a speed of 1·33 as fast.
I’ve 48v/1000w motor but only 24v battery, can’t find 24v/500w brushless controllor or it.
sos…I need help,i built a wagon that I want to go 35 miles per hour at a steady pace…………..I would like it pushed by a wheel on each side…so 2 ebike wheels.total load of me and wagon would be about 280lbs….im wanting 28 inch wheels,regular width….where do I order such a thing….battery size for both wheels ect
It sounds like you’re starting at square one here and have many questions, which is awesome, but I think the ebike forum Endless Sphere (http://www.ebikeschool.com/endless-sphere-use/) will be a more helpful place to ask these questions as you will receive advice and guidance from many different perspectives.
My initial two cents though are that you should rethink your design goals. 35 mph in a wagon sounds like a very unstable proposition. This could certainly be accomplished technically by two hub motors, likely fast winding direct drive motors at 48V, but there are many safety concerns for a vehicle like this.
Thanks again for the response and all the advice. Ive been online trying to figure out how to just make a battery, and controller. All seems like alot. After looking at the site i sent you im now convinced it doesn’t have a battery either.
Sucks but I did have these other sites as well. I hope you can give me your expert advice
The fusion says 70miles at 20mph. Which sounds OK but I wanted to build a folding motorcycle that looks like a bike and can do 50mph with some kind of switch to keep it 15, 30 and finally 50mph even if it was just the 30 and 50 but now I’m thinking about what your saying about the motor not fitting… I seen two folding bikes I would like to consider. Do you think any of these can maintain at least 30-40mph or am I just stuck with solid frame.. I seen one of those bikes pictured with a hub motor in the ninja star wheel (I don’t know what kind of wheel it is) but can that be done?
Online Shop Full suspension mountain bike folding bicycle scooter lithium battery car downhill mountain bikes|Aliexpress Mobile
http://m.aliexpress.com/item/1939754136.html
Fusion- High Performance Electric Bike | Indiegogo
https://www.indiegogo.com/projects/fusion-high-performance-electric-bike#/story
http://m.alibaba.com/product/60133611915/2015-new-design-24-speed-36V/specifications.html?s=p
I’ve been doing a bunch of research and I have some new ideas about building this bike….
Before anything Id like to thank you for hearing me out…
This build is on my mind a lot..
Anyway I’d like to take a folding bike and put 2 motors on it (a 2000w in front and 5000w in the back). Id like to also build a battery that can power both kits at the same time. Even though I’d like to put a switch that keeps the front one off until I feel I need that extra power.
Here’s where my real questions come in… if I want to say maintain 30-40 with the back one alone and 50+ with both. Am I going over board with a rear 5000w or is that the minimum?
Again I’d like to be able to do 50mph continuous for about 50miles or more. Or at least have the option to do so. More than likely the bike will operate at 30mph 80% of the time but doing so I’m expecting more than 50 mile range. Say 60 or 70.
Next question is and I’m not sure how much you know about batteries but I seen these at Batteryspace.com for $18
A123 System High Power Nanophosphate LiFePO4 26650 Rechargeable Cell: 3.2V 2500 mAh, 120A Rate, 8.0Wh – UN38.3 Passed
Not sure how this works but if I took 60 of these in series would that give me 180v at 7,200ah? Or am I calculating this wrong?
If you don’t know, it’s cool I’ll hit up you tube after this too.
Other questions are what kind of frame, ie aluminium, carbon fiber, steel ect… would you recommend I use for this. I’ve seen nice carbon fiber bikes on aliexpress but also seen nice aluminium frames.. does it matter what kind of frame I use if the bike has front and rear suspension?
Definitely Disk brakes but which are better, floating mechanical or hydraulic?
What kind of controller would I need for this battery?
Lot of questions huh?
Lol. My fault bro. I get carried away when I have an idea… any help or advice is very appreciated. Thank you again in advance.
You’ve got a lot of questions, which is awesome! But I want to recommend that you check out Endless Sphere and post some questions there. Endless Sphere is the largest online ebike community, and there are tons of people like me that can all answer your questions. That way you get more opinions than just mine, and other people can follow along and learn too. I wrote an article about ES here: http://www.ebikeschool.com/endless-sphere-use/
Now to try and answer your questions:
A dual motor ebike is a bit more complicated, but can be done. You’d ideally want to match the speeds of the motors, otherwise the slower one won’t be doing much good when you’re going faster than it is designed for.
Actually, if you put 60 of those cells in series, you’d have a 192V 2.5AH battery – which wouldn’t be good for really anything. You’d want to parallel and series them, so you get good capacity in addition to high voltage. I wrote an article on battery building that you might find helpful: http://www.ebikeschool.com/how-to-build-a-diy-electric-bicycle-lithium-battery-from-18650-cells/
I’d be very wary of trying to do 50mph on an aliexpress frame, or any folding frame for that matter. Folders are generally (though not always) less rigid. You want a good strong bike for those speeds. Trying to use a cheap bike on a 50 mph ebike build is a recipe for disaster. At those speeds you’re putting your life in the hands of your machine. Do you really want to be relying on cold welds and cheap tubing?
Hydraulic and mechanical disc brakes both have advantages and disadvantages. Hydraulics are generally considered higher level, but good mechanical brakes are plenty for most riders.
Again, I recommend checking out Endless Sphere due to the amount of questions you have and the amount of planning you still have left to do. That way many people can help you choose parts and plan out a safe, awesome ebike.
Reading MuertoInc’s plans causes great concern. Let me explain with a story.
I live on an island, and to get to town, we have to take the ferry. E bikes are allowed on the boat for free so when we get to the city, which is hilly, we have mobility and gridlock means nothing to us. My group has been active in promoting ebikes on the island, and now they are very popular.
One of our elected officials was riding her ebike to the ferry, not paying attention or going too fast and she managed to run over one of the ferry staff. So now the security force down there is forcing all riders to dismount for the final 100 yards are so. It’s a legal public road, and they don’t have the legal right, but we now have a fight on our hands because one bad apple (ironically an elected official) was riding irresponsibly.
When I read MuertoInc, a newby, wanting to build a 50 mph ebike on a budget, I see a dire threat to the freedom that we currently enjoy: the freedom is no registration, license plates, inspections, insurance or regulations, other than a wattage limit (which BTW is what the motor does, not what it says, so a 250 W that is boosted on a 48V battery is not a 250W motor anymore, and if it is involved in an injury crash, the police will throw the book at you).
MuertoInc, the other answers on this page are being nice. Let me be blunt. You will kill or seriously injure yourself putting 50 mph power on a bicycle you buy off Amazon. You may also kill or seriously injure someone innocent who happens to be in the wrong place at the wrong time. And when you turn into road meat, there will be a clamour with people saying “this is awful, we must do something about it”, and the laws on ebikes will get tougher.
MuertoInc, you want to build a motorcycle not an ebike. So build one. Get a motorcycle frame with a suspension made for 50 mph; with disk brakes made for 50 mph, proper headlights, turn signals and register and insure it as a motorcycle. Wear a motorcycle crash helmet, and if you are smart, wear protective clothing. Forget looking at Amazon. Do google searches like this one http://www.instructables.com/id/How-to-build-a-96-Volt-Electric-Motorcycle/ or look on Craigslist for an older but good running motorbike https://sfbay.craigslist.org/eby/mcy/5202954768.html. Or just buy a motor-scooter that will cost less than what you want to build.
One thing you have not disclosed is your age. You admit to being new to ebikes, and you clearly do not have a lot of money because you are looking at the lowest prices you can find. It sounds like you live 30 miles away from work or school on a highway with a 50 mph speed limit. Are you not old enough to get a driver’s license?
Anyway, you get my point. You know nothing about ebikes, have been reading the internet in hopes you can buy 50 mph speed for cheap, and you are focusing on whether two motors will hold up to 50 mph without cooking. Trust me, that’s not enough worrying. There is a reason street motorcycles and motorscooters are built the way they are: speed. Bicycles of the sort you are looking at are not made for those kinds of speeds.
If I haven’t convinced you yet, see this video: BMX Bicycle Wreck At 50 MPH! https://www.youtube.com/watch?v=di3fpS5cem8
Hey. Thanks for all the concern about my build ideas… you have a lot of points… after looking into this over and over again I’ve decided to go with the Montague paratrooper… it’s been proven to do the 50mph I want to do… mind you I am aware of the law and most likely will ride it at 30mph 90% of the time… building it with higher expectations would ensure me further distance. I’m glad I have critics.. again I’m new to this and welcome any questions or opinions…. I’m 33 by the way… yes I can get a license and have one but it’s also suspended. Parking tickets and fees.. always a fee… I paid off my van and still have to pay fees… wack… so I settled on the bike idea… I understand I can’t build a bike on a budget… I’m looking at about $2000. For a nice bike build… just so you know….
Also looking at the Crystalyte HS 3540 and the HT 2425.. both motors being very exceptional and Crystalyte being a great company… still looking at building my own battery because a 48v isn’t enough… would prefer a 72-96v.. each motor having it’s own 30 amp controller… 72×60 = 4320 ( good enough ) probably 40 mph continuous… I can live with that but 96×60= 5760 and I know that will do the 50 I want easy…. disk brakes I’m told work up to 70 MPH… not looking for that… just a foldable “motorcycle I can put in my girlfriends trunk… or work on inside the house outside the elements…. or take to work without waiting for the bus and 2 trains only to have to walk… a bike means no traffic, no looking for parking, no license, insurance, registration, tickets… car repairs… owned 6 cars in my time… all ends in headache and repair… ebikes are the future… if your scared of the risk, there’s always a bus… time is all we got…I’m using mine this way… ?
First I wanted to say thank you for the reply… again I’m new to this whole thing and still learning about the type of bike and motor I want to use… my main goal is getting the bike to do 50+ mph for 30 miles without burning out my motor.
This is the link for the motor.
http://m.aliexpress.com/item-desc/2038660299.html
Also this is the link for the bike I wanted to put it on. http://www.amazon.com/gp/aw/d/B00Q7EEO0K/ref=pd_aw_sim_sbs_468_2?ie=UTF8&refRID=0739D77FJC98DD5DC1FG
I’ve seen other kits but I think this one was again under $600. I’ve also seen this on aliexpress and m.made-in-china.com all posting similar ads and prices for 5000w kits.
Not sure if any are legit but if you have time to look at any of those links I’d appreciate it.
Also the link you sent me was a $349 3000w hub motor… wouldn’t $500-$600 be a average price for a 5000w. And do I need 5000w to do 50mph for 30miles?
That motor looks, at least from the outside, to be similar to the 3,000W motor made by MXUS and sold by Kinaye Motorsports. Since I haven’t used the one in your link, it’s hard for me to say definitely, but my gut is saying that motor can’t really take 5,000W continuously despite what they are saying. They also don’t include any graphs on power or speed performance, so without raw data, it’s hard to gauge exactly how fast it can go and what power level it can support.
Now about that bike you linked to: I’m worried about the dropouts in two ways. 1) they just don’t seem very beefy, and you’d need to include a good strong torque arm to keep that motor from twisting right out of the bike, and 2) that ad says the dropout spacing is 149mm, but most normal bicycles have a rear dropout width of 135mm. Forcing another 5mm is doable, but not 14mm. You’d be risking breaking the bike by trying to squeeze the dropouts apart to fit the motor in there.
Regarding that link I sent you, that one was for the motor bare (no rim, spokes, controller, etc). There’s a fee for having it laced into a wheel, though you get to choose the exact rim, spokes and everything. And all the other parts you’d need are available there on the other pages, like the controller, throttle and whatnot. When it’s all said and done though the price will be higher than that AliExpress link (though as I’ve seen Kinaye’s motor’s firsthand, I can vouch for them being top quality and able to get you to 50 mph no problem).
Again, I hate to be the barer of bad news, but when you’re talking about 50 mph, you’re in the realm of serious ebikes. Those bikes usually cost a couple thousand dollars, and require a good strong donor bike to be safe.
Hey what’s up. I have a question. I want to build my own ebike but I’m fairly new to this. I’ve seen kits online for under $600 claiming to go 50+ mph. The kit includes a low speed brushless motor >400w
Motor power is 5000w rated, 9000w Max.
Motor speed 900rpm/min
Motor design is brushless gearless
Wheel size, 16-29″ (they specify that they are double wall aluminium alloy wheels )
Motor drop out is 149 mm
Motor loading 300kgs
Controller is 100A sinewave programmable controller
Comes with a 48v-96v 5000w brushless gearless hub motor for electric bike , 5kw electric bike hub motor and shimano hydraulic disk brakes front and back…
I want to put this kit on a 26″ xspec 21 speed folding mountain bike that comes with High Tensile Aluminum FrameFront and Rear SuspensionShimano ST-EF51, Shimano RD-TZ50 Gear Index, 14-28T Thread FreewheelMechanical Disc Brake with High Grade 700c x 23c Tires, VP Head Parts, Neco BB, Folding Pedals, Alloy Stem
Can this kit work with this bike?
Will I do 50mph without burning out my motor?
If not, what kind of folding bike would you recommend?
Thanks for your time and any help or advice you have…
Not much, what’s up with you? 😉
For starters, a kit with those specs for $600 almost certainly doesn’t include the battery (which to power a kit like that, should cost nearly $600 itself).
Next, and to be honest, that kit sounds like it’s promising more than it can deliver, especially for that price. The good quality 3000W motors that I am familiar with cost more than that when laced into a rim and with a controller, throttle, etc. That sounds like what is probably a lower quality kit and is being advertised as having a power level higher than it is really capable of. It’s hard for me to be sure without seeing it, but with those specs at that price – it just sounds too good to be true.
For comparison, have a look at the motors here: http://kinaye-motorsports.myshopify.com/products/mxus-xf40-45h-45mm-3000w-motor-4t-9kv?variant=1212363124
Those are great quality, high power motors, that can easily hit 50 mph (depending on which motor you choose – some are slower and faster) and are sold by an American company with full support and warranties, etc.
When you are operating at those high power levels and speeds, safety and quality of components becomes of paramount importance. A good quality and safe ebike capable of 50 mph shouldn’t cost less than $2000.
I hope this doesn’t curb your enthusiasm, but I want to give you a realistic picture so you know what you’re getting into. As an alternative comparison, my 30 mph ebike cost me about $700 to build (which partly reflects my experience in knowing where to buy from for the best prices). That is nearing the cheapest you can do it for and still be safe. Most 30 mph ebikes cost closer to $1,000 to build, and many cost well more than that.
hello ! I am actually planning to build an e-bike myself. So I would like to crosscheck a few things and get some expert view to check if I am right.
I am planning to use a 36V 250W motor with a 36V 15 amp controller.
1. do you suggest a 20 amp controller with some air cooling facility with the motor?
* i am really not looking at climbing steeps more than about 10(ten) degree.
2. i am expecting a decent speed of about 20-30 Kmph (max) on flat road.
total ride weight will be around 250lb.
Most 250 watt motors are right at home with a 36V 15A controller. Bumping up to 20A should be fine for most motors as long as you aren’t planning on doing any long and grueling uphill challenges, which it doesn’t sound like you are. The best bet for cooling is to leave the controller somewhere exposed to passive air flow so that it cools naturally in the breeze.
Buy a Bafang BBS01 250W motor and battery kit from Paul, at em3ev. http://em3ev.com/store/index.php?route=product/product&path=45&product_id=183 . Paul is one of the most respected vendors on endless-sphere.com, the ebike forum. I have bought 33 motors and batteries from him. He (and his team) makes the batteries and they are far more reliable than other vendors who I used before I discovered Paul.
I pay Paul a bit more than from a Chinese vendor, but when I had a problem (which turned out to be shipping damage that cut a hidden wire on a MAC 500), he paid postage and fixed it no charge. He is an Englishman in China so he understands what backing his product means.
The motors are mid-mount. You remove the bottom bracket and install it. This means that it runs off your rear gears. With 250W you can climb in low gear with power, then on the flat shift to a higher gear, just like a car and go faster. On one bike I have a Nuvinci N360 hub and it is a fantastic combination. The BBS01 motor itself is very quiet. It is, in my opinion, far superior to hub motors. The controller is built into the housing, which means a lot less spaghetti wiring to cope with (and to have come loose).
I have no business relationship with Paul and do not get compensated for recommending him. But having had bad experiences with other vendors, including BMS battery and eLife, I recommend Paul.
Welcome to ebiking.
Hi Micah,
After a lot of research and not many findings, you’re article has been the most useful for what I want to do.
I have one of those conversion kits that states 250w, the motor looks identical to the shiny one on your article.
It runs on a 36v 10amps battery and 36v max current 15w controller.
My question is:
Is it possible to modify the insides of the controller, something on the mother board for it to boost to the actual 15w?
Or can I use another, still 36v, controller but with a higher max current to get more power/speed out of it?
I want to do exactly what you have done, run mine at around 400/500w.
Any suggestions for a controller are welcome.
Thanks in advance and congrats for the article.
Hi Zenry,
I’m glad you’ve enjoyed the article!
You mentioned that your bike includes a 36v 15w controller, but I think you meant “15A” (amps) instead of “15w” (watts), which is a very common sized controller. 15 watts would be very small indeed!
The answer to your question is: yes, technically you can make a fairly simple modification to increase the power of your controller. You can add solder to the shunt of your controller, which will trick the controller into allowing more current to flow through the controller and thus increase the power, though not the the flat land top speed. The problem is that it is easy to go overboard, add too much solder and thus cause your controller to burn itself out by trying to run at too high of a power level. For that reason, I don’t usually recommend this approach. To those that still want to try it, it is best to use a ‘little bit at a time’ approach by adding a small amount of solder to the shunt, then closing it up and testing the ebike until you get to a power level you want. That way you don’t miss it and go nuts with the power level. You can learn more about soldering shunts here: http://endless-sphere.com/forums/viewtopic.php?f=2&t=31643
Thanks for your response.
I had actually done that modification on the shunt in the meantime before you replied. However I didn’t notice any difference in the top speed, although I did it gradually like you suggested with small to large increments of solder. I even at last soldered a copper wire running from one end to the other on the shunt insertions and apart from a massive spark, no speed improvement happened.
As far as I understood, you also have a 250W motor, but you said you run yours at 500W. Would you mind if I ask how you did it? And also, what’s your top speed after the modifications?
Appreciate your help,
Cheers!
Hi Zenry,
You’ll notice that I said that the shunt mod will increase power, but not flat-land speed. That is because your motor has a top speed that is based on the voltage it is supplied, not the current it is supplied.
The shunt mod is only going to increase the current flow to the motor. This means that on hill climbing where your top speed is limited by the amount of power you have, you’ll see an increase in speed, but on flat land you aren’t pulling full power (i.e. full amps) so providing more amps doesn’t do anything for speed.
To increase speed of the motor, you’d have increase voltage, which means a higher voltage battery.
Regarding my motor, it is unmodified. The 500 watts is determined by the controller and battery I’m using. Remember, watts = amps x volts. So in your scenario, you said you had a 15A controller and a 36V battery. If multiply 15A x 36V we get 540 watts. In reality, some of that power is lost as heat and other parasitic loss, so we end up with something around 500 watts.
That brings us back to what I call “the myth” of ebike wattage ratings. Your bike comes with what is claimed to be a “250” watt motor. Yet at peak current draw (15A on your controller) you were actually pumping about 500 watts through that motor. That means it is actually operating like a 500 watt peak motor, even if the manufacturer calls it a “250 watt” motor.
Thanks for your response Micah. That was very clarifying as I’m not an expert in the topic.
I decided to not upgrade my battery and controller as it would add weight to the bike and Cost me some more hundreds fo the battery.
Your input was certainly the best I’ve had!
All the best!
Cheers,
Zenry
Great article, just found your site.
Question: I have an older stokemonkey from 2009. My battery is a 36V 15AH LiFEPO4. I noticed that sometimes I can get up to 800-900 watts. How is that possible? Shouldn’t I be limited to 540 Watts? Is this something to do with peak vs. continuous watts?
Sure this is a dumb question, so thanks.
Stokemonkey’s are nice kits, that should be a fun ebike!
It’s not a dumb question at all. The answer is in your controller, not your battery. It is the controller that actually decides how much power you’ll be pulling from your battery. I’m guessing that you have a controller with a peak current draw of around 25 amps (900 watts divided by 36 volts equals 25 amps). So regardless of whether your battery was 10AH or 50AH, your controller would still try to draw the same power from it. You mostly see peak current draw during acceleration and hill climbing. When you are cruising at constant speed, the power usually dies down to something more reasonable like 350-500 watts depending on factors like weight, size, terrain, etc.
The 540 watts you ask about is actually watt hours, which is a measure of energy, not power. 36V multiplied by 15AH is 540 watt hours (as opposed to 36V multiplied by 15 amps, which equals 540 watts). So you’ve got 540 watt hours of energy in your battery, but the actual amount of watts (i.e. power) being pulled at anyone time is totally depending on the controller.
Most LiFePO4 packs are capable of about 2C continuous current draw and 3C peak (2 times their capacity rating or 3 times for a few seconds). So your 15AH pack should be capable of putting out about 30A continuously or 45A in short bursts.
Lots of numbers!
Hello there
I have just bought a Sakura s200 electric bike. Hopefully, after my new batteries will come, it will work fine. But one thing makes me anxious: I just cannot find the controller for this bike, in case it would be faulty (it stood in garage for 4 yrs so its state is pretty unknown). Its brushless motor rated 200w and battery is 36v, but the closest controller I could find is 36v 250w.
Now, my questions are:
-could I use this controller instead of 36v 200w?
-or I could somehow add resistors to the controller so the output power would be lower than specified? If yes, how?
Regards,
Seb aka Maziu
Hi Maziu,
I’m not familiar with that ebike, so I did a quick search and actually found someone who replaced the stock 36V 200 watt controller with a 48V controller to get more power: http://endless-sphere.com/forums/viewtopic.php?f=2&t=15271
Generally speaking, 250 watts is such a small increase over 200 watts that you should be fine with upgrading to that level. The fellow that upgraded to a 48V system surely increased more than that.
You should know though that some of your connections might need to be redone for the new controller as the connectors are likely not identical. That’s just a matter of cutting off and resoldering a few new connectors, or even soldering the wires straight to the controller. Shouldn’t be too difficult.
Hello Micah,
thank you very much for your reply, now I am calmer knowing that.
I am familiar with soldering so changing connectors wouldn’t be a problem. But once again, thank you for your help, you are doing great work with this website and the information you provide, in a very clear way.
By the way, I quite enjoyed your article about making your own LiIon batteries, now Im poor like a church mouse (well, maybe not that bad), but maybe in the future I will do something in that direction.
Cheers and keep on going.
just bought a Chinese kit 250watt front geared hub motor (same as above pic)36v,can I use a 48v with the same speed controller?
Hey Ian, most of those motors can be run at 48V, though you should know that you will be adding more stress to the motor that way and consider taking it a bit easier on the throttle. I’m currently working on a bike which will have two of those motors (one in the front, one in the rear) running at 48V.
Regarding whether or not you can use the same speed controller, that will vary from controller to controller as there are many different types of controllers available. One quick way to check is by opening the controller and looking at the specifications on the capacitors. If they say 50V, then you can’t run a 48V battery because most 48V batteries actually charge up to 54.6V, which could burn up those capacitors. If the caps say 60V though, you’ve got a good chance of the controller working with 48V packs. The only issue is that the low voltage cutoff (LVC) will no longer work, as it is checking for low voltage on a 36V battery, not 48V. As long as your battery has a BMS with its own LVC (pretty much every BMS does) then you should be fine.
Hi
i had a question about a electric fat bike i am building. I have a 48v triangular battery which i have installed a 40A BMS board too. i am running a 1500w motor and i have had issues with the controller due to the large amounts of current running through it. the controller is rated at 18As and i know that this is probably the problem and i was wondering if i get a 45A controller to fix this problem is it going to be bad for the battery?
Any advise would be greatly appreciated!
Thanks
Zac
If your BMS has a 40A rating then the absolute maximum controller you want to use is a 40A controller. You can do this, but it leaves you no safety room. I like to have at least a 50% safety factor, meaning I wouldn’t try to run a 40A controller. You wouldn’t actually be pulling 40A all the time, but during acceleration and on long hills you could stress your BMS to the point of blowing a mosfet.