Mr.Dangerous

So I am building a low rider chopper from scratch right now and I want to make it electric too. I have a 72V controller and a 48V Hub Motor (500 RPM rated) and I'm planning on buying a 60V battery. Will I fry the motor?

Thank you!

KPREN

Maybe you will fry the motor. If your controller has a temperature probe capability, its a good idea to use it. Electric motors have no real rating so using a 72V controller and a 60v battery will not automatically fry the motor. Make sure your display is also rated for 60V. Voltage determines the speed of the motor. a 60V battery will turn the motor 23% faster Amperage is what fries your motor and high amperage at slow speeds is how you fry it.
You can play around with the numbers over on Grin Technologies simulator and get a better idea of what to expect. Here is a link to the simulator. Good company to work with.
https://ebikes.ca/tools/simulator.ht...27.5i&axis=mph

2old

I have a "1000w, 48V" motor that I've operated with a 52V battery (58.8V fully charged; 14s X 4.2V = 58.8). It will attain 35 mph on the flat, no wind, 175 pound rider and 50 or so pound bike) and has never come close to overheating (but I don't ride it "wide open" for long stretches). If you're worried about overheating there are methods to minimize it (see endless sphere for adding materials to the inside or of the hub to increase heat transfer.or heat sinks to the outside for the same purpose). I'm assuming you'll employ a direct drive hub, and these transfer heat effectively.

andychrist

What brand hub motor? Because Bafang’s newer Intelligent displays such as their P850C allow the use of up to 60V batteries on their 48V motors. Like 2old, I’m just using 52V batteries on mine but it was easy to select voltage from the display menu.

spinnanz

You can use whatever voltage you like on any motor, you may just need to limit amps.

​​Voltage kills controllers, amps kills motors.

2old

I should point out that the "52 V" battery comes off the charger at 58.8 V (14s or 14 X 4.2 V per cell = 58.8 V).

veganbikes

You will likely have destroyed the frame before you get the chance to destroy the motor and other parts. Trying to cold set a relatively cheap steel frame that much 20mm is probably not super safe and then sticking a motor on it when it was not designed for any of that is a terrible idea. Plus add to all of this the fact most of those lowrider frames (at least all that I have seen over the years) are pretty much all coaster brakes which is not really good enough for a motorized bike.

This is all a bad idea and if you value life you won't do it. There are plenty of already built e-bikes out there some of them are of quality and some will work almost like your idea but at least slightly better because they were sort of designed to work together if not actually designed for that.

bgates2012

It depends of your controller type. You should check electrical specifications and perform simple math to calculate the maximum wattage it could handle.

skookum

Succinct and to the point.

Is it true?

KPREN

yes more or less.

chas58

kind of over simplified. For you and the OP, you can go to ebikes.ca simulator and find out exactly how hard you can run a motor before it overheats.
Spoiler - you can overheat a motor with volts or amps, but its true that at the same power level you will overheat faster with current than with voltage.

I have a tiny ass 36v battery, and I overheat controllers all the time. you can push a controller too hard without a lot of voltage or current if you want to. It doesn't matter too much how you configure it, if you are running noticeably less than 50% the no load speed at full throttle for long enough, something is gonna get too hot.

klevin

Actually, no. If you think back to your HS physics classes, you may remember EIR. Current passed through a wire is what leads to heating. Voltage is the means by which we get the current through the wire. So more voltage means more current which means more heating. (and note that voltage times current means power in watts!)

The job of your controller is to control the current going through the motor (usually by voltage modulation) and to vary the frequency for brushless motors, the most common these days. Your motor never directly sees your battery voltage. But the battery voltage may affect how much current (and therefore heat) goes to the motor. It all depends on the controller design and how hard the bike rider drives the system.

There are other factors, like how well your motor is cooled, but you can see there's no simple answer to your question. Does your controller allow you to set a current limit?

chas58

It's not really clear to me what you're saying no to. I understand your theory and agree with it but if you want to know the specifics you can still go to ebikes.ca simulator and find out exactly how hard you can run a motor before it overheats.

that simulator isn't Theory, they take each motor and run it to get those numbers

KPREN

You would normally be correct but your reference points are off. The programing on an e bike can manipulate both current and voltage. E bike controllers normally limit both voltage and current through programing, can manipulate both to alter torque as well. Generally speaking with an e bike, voltage determines top speed and current determines acceleration and ultimate load capacity.

E bikes are limited in power by regulation. Given the same motor, a road bike may be manipulated for higher voltage and lower current to achieve a higher top speed while a mountain bike may opt for lower voltage and higher current for hill climbing. Both bikes would put out the same power but the purpose and intended use are different.

Play with the simulator as suggested.

Leisesturm

Even if safe, 72V controller x 60V battery x 48V motor sounds ... chaotic. It doesn't sound well thought out. Not well thought out and single track vehicle out among the heathen = unwise. As I understand it, 52V is the dividing line between practical cycling applications and LEV (light electric vehicles). Motorcycles. If the o.p. wants to build an electric motorcycle they are limiting their options using a 'bicycle' motor. I imagine though there is a quantum leap in the prices of components built to LEV standards.

klevin

Not exactly. For any magnetically operated device like a motor, current rules. Voltage drives the current. Yes you can current limit, but that's actually done in practice by limiting the voltage!

It's easy to understand for DC motors, but more complicated for AC motors like these since you have reactive power and reactive current to deal with. Even the math becomes very complicated.

Your simulator program may or may not take all this into consideration. It's probably a good starting point, though.

chas58

good point.
the biggest issue may be that you are running the motor too fast - and if it isn't in its sweet spot, it will generate too much heat and something will melt.

To be fair, I do run a "24v" motor at 36v, which gives it a 50% increase in noload speed. It took a bit of calculation and simulation to ensure this is what I wanted, but it works great for me. Normally that kind of thing is going to cause a lot of problems unless you engineer it properly for the conditions.

For the OP (and klevin). If I did not make it clear above, calling it a "simulation" is almost a misnomer. It is based on actual physicals testing of physical motors to the point of destruction. Its very accurate. Ebike.ca is an amazing place and done more to support ebike makers than just about anyplace on the planet.

And to answer Klevin's question - in the context of the OP question, yes you can buy a matched controller to limit the current.

For example:
You can buy a 36v motor at an average of 10amps will give you roughly 350 watts.
The same motor (with different windings) can also be run at 500 watts by:
running it at 36v and 15 amps
or
running at at 48v at 10 amps.

There are plenty of motors that are off the shelf with configurations like this.

chas58

So, what did you decide?

KPREN

I am well versed in AC three phase motors. You really should go look at the motor simulator stuff. All of the equations and methods are listed and your contribution would be much better if you did. That said, I did just that this time. It appears that the bulk of the e bike controllers out there do modulate voltage to control the motor but not all. As well, most use square wave control but some use sine wave. Digging into the math this time through made more sense to me than just playing with different controllers on the simulator. I believe that what I have is a sign wave type voltage controlled. Of course I now want sine wave field/frequency controlled after digging further. I realized there was a difference but did not make the full connection in my mind until reading further.
You appear, like me, to know three phase AC but not as well versed in what is really e bike specific and the true types of controllers available. Most everything is built to a price point for cheap ass individual consumers. I realize I made some assumptions based on industrial experience. Will you realize the same? Fyou, now I have to spend more money. (said with big grin)

2old

Mr D, you haven't been back to comment, but you might explore Endless Sphere where the individuals have lots of experience with higher power systems. Personally, unless you already have the 48V motor or are trying t get by on the cheap, I'd recommend a motor like the 1500w Leaf (ebikeling has one that appears similar). Probably it's somewhat heavier, but not excessive for a chopper and (I think) has laminations that disperse heat better.