I'm considering to buy a bafang cst 250w kit. My only consern is if it will overheat on long steep hills? how long hills does it handle?

 

What happens when it overheats? Does it have overheat protection? Will the motor be useless after it is overheated, or do I simply need to wait for it to cool down?

I doubt that you'll get problems of over-heating, except that any motor will over-heat if you don't treat it properly. The motor max RPM and voltage affect it's efficiency, so we'd need to know what they are to give exact info. Also, we'd need to know the conditions under which you'll run it.

 

The 250W CSTs that I've seen have been 250 rpm (19mph) at 36v. The one I tried ran OK at 22 amps but didn't seem to give any more torque when I increased it to 30 amps. The 500w one is much better if you can get a battery that'll give 30 amps. On the other hand, if you want to run the 250W one at lower amps, it'll be nice and smooth and quiet.

 

The SWX motors can handle a one mile 7.5% hill, with bits up to 18%, so the 250 RPM 36v CST should manage it easily without over-heating as long as you pedal too.

I will use con62 from greenbikekit:

http://www.greenbikekit.com/250w-36v-electric-bicycle-hub-motor-controller.html

 

It has over-current protection at 14±0.5A

 

The hill I will ride every day is 4km with up to 10% grade

If the info is correct on greenbikekit.the motor is 265 rpm.And if the info on elifebike.com also is correct.Then their cst 250w motor is 205 rmp and better for hillclimbing

If the info is correct on greenbikekit.the motor is 265 rpm.And if the info on elifebike.com also is correct.Then their cst 250w motor is 205 rmp and better for hillclimbing

That would be true. The lower the RPM, the better the hill-climbing. 205 RPM will max out at just over 15 mph, and power will reduce from about 12 mph. At 5 mph, it'll have an efficiency of about 55%, so will give output of 15amps x 36v x 55% = 297W. If you can pedal with 100W, it'll go up a 15% hill at 5mph without overheating. The 265 RPM one would have an efficiency of about 47% at 5mph, so output power would be 253W. On the 15% hill with 100W of pedalling, it'll overheat in about 15 minutes. You'd have to pedal with 200W at 7 mph to stop it from overheating.

With this simulator I get similar results:

http://www.ebikes.ca/tools/simulator.html

 

But it does not say which versjon it is. Is the 250w and 350w the same engine with different amp?

 

If I set ths simulator to bafang cst and 15amp, It will take me up a 8% hill without overheating. 10% with light pedaling.

 

If this is correct? I will get safely up most hills in my town. And I will stay sway from the once over 10%

You can't use the simulator like that. The only way you can use it directly is if they have exactly the same version of the motor as you.

 

The main thing that affects the motor is its RPM (speed), so you need to customise the voltage to get the maximum rpm or speed the same as yours. Then you need to compensate by changing the current in the same proportion, i.e. if you decreased voltage by 20%, you need to increase current by 20%. Then you can play with it to see how the motor will perform under different circumstances. It's not exact, but it's close enough to help you.

 

For the 250w 205rpm CST motor, you'd set voltage to 23v and current to 22A for a 36v 14A controller and battery.

 

One last thing. There's a new small Bafang CST motor. For climbing, you need the big one, which is actually the 350w one marked 250w. You need to make sure which one you're getting. The small one is about 120mm dia and the big one is about 180mm.

One last thing. There's a new small Bafang CST motor. For climbing, you need the big one, which is actually the 350w one marked 250w. You need to make sure which one you're getting. The small one is about 120mm dia and the big one is about 180mm.

Got any spec's on the new motor, or is it not released yet? I can't find it at any of the usual suppliers for info.

Not really. It was shown at last year's Eurobike, and then again at the Shanghai show.

7th photo down here:

https://www.endless-sphere.com/forums/viewtopic.php?f=3&t=53059&start=25

I will definitely go for the 205 rpm version.

 

Now, what happens if it does overheat? Will the motor be completly broken after it is overheated. Or do I simply need to wait for it to cool down, and pedal faster next time?

I can't remember anybody that burnt out a motor from normal use. People here run motors at double and triple the ratings, and still they don't burn. Only if you have very long steep hills is there a risk. You'll be OK. No need to worry.

I am also interested in the BBS01. Which of these engines (BBS01 vs CST 205rpm, both 250w ) will have the best performance, and what speed can I expect in an 8% grade hill.

for a total weight rider + bike = 100kgs, I estimate that the CST (with 20A controller) will go up 8% hill at 10mph on maximum throttle alone, the BBS01 (15A), also on maximum throttle alone, will trounce the CST at 11mph if you use gear 5, 18T cog at the rear. On any other gear, the CST will win.

You need to check whether that 205 rpm CST is the normal large one.