24 vs 36 volt

[schiller]

Good evening everyone. Inspired from the brompton builders (daniel.weck, jerrysimon, cwah among others) i want to convert the s-type i purchased recently. I would like to ask if there is any difference in the terms of torque and hill climbing ability between 24 and 36 versions of the same motor, same rpm -eg. 36v/240 and 24v/240.

By the way i want to thank you all for posting and thoroughly documenting your conversions, without them i wouldn't dare to start mine.
I want to try both the keyde and the larger tongxin, q85 is also is very good choice, but i'm afraid to remove another mm from the dropouts - it has a 12mm axle- (i have already ordered a q100 for the rear wheel of my city bike, thanks d8veh for the suggestions about the q motors).

Thanks in advance,
Greetings
Konstantinos

 

[patpatbut]

I am not a bike mechanics but I managed to file the dropouts nicely. Just a bit of patient. I would recommend Q series or bafang motor over keyde and tongxin in term of reliability. My ebrompton has run nearly 3000 miles without problem.


Also, use 36v system as the efficiency is better
Pat

 

[Deleted member 4366]

You get torque in proportion to voltage, so a 36v motor will have 50% more torque.

If you run a 24v motor at 36v, it will run 50% faster too, but this has a bearing on efficiency and efficiency also has a bearing on torque. Say you had a 20 mph 24v motor with a 15 amp controller, which slowed down to 10 mph up a hill. It's efficiency at 50% of its max rpm would be about 60%, so its power would be 60% x 15 x 24 = 216w.

The 36v one would have more torque, so might be able to do 13 mph up the hill, but its maximum speed would now be 30 mph, so its now only about 50% efficient. Output power now is 36 x 15 x 50% = 270w, so only 25% more, not 50%.

You have more power now for hill-climbing, but 50% of your battery power is heating up your motor, which is not good.

 

[Nealh]

This brommie wheel and kit currently on Fleabay, the hub has a Angyang label on it.

http://www.ebay.co.uk/itm/e-bike-electric-bike-hub-motor-brushless-electric-bike-wheel-BROMPTON-KIT-/331552933371?pt=LH_DefaultDomain_3&hash=item4d321845fb

 

[patpatbut]

Don't go for the rear motor for brompton as it is too much afford to get it right.

 

[schiller]

Thanks very much for your answers. I'll go for the 36v version then. Cwah, i think i can remove the extra mm for the Q85 but this will weaken the dropouts even more. That is my concern.

Rear motor for the brompton? OLD is about 110mm, i don't think there is such a motor currently available.

 

[Deleted member 4366]

This brommie wheel and kit currently on Fleabay, the hub has a Angyang label on it.

http://www.ebay.co.uk/itm/e-bike-electric-bike-hub-motor-brushless-electric-bike-wheel-BROMPTON-KIT-/331552933371?pt=LH_DefaultDomain_3&hash=item4d321845fb

That kit will most likely not be suitable for a Brompton because Chinese 16" wheels are too small.

 

[RobF]

Brommies have either a hub gear, a two-speed deraileur or a combination of both.

A motor wheel and a five speed cassette won't fit and would be a nightmare to engineer.

Mounting the deraileur so it doesn't scrape on the ground or compromise the fold is just one the problems.

 

[schiller]

Thanks very much for your answers. I'll go for the 36v version then. Cwah, i think i can remove the extra mm for the Q85 but this will weaken the dropouts even more. That is my concern.

Well i'm wrong: photos from bms battery site misleaded me to believe that the axle is round. It isn't. 12mm with flats, the same as the tongxin. This motor would be by far the best choice for me, but where can i get 36h rims? You have described how difficult is to get the tyre on the sun ones

 

[patpatbut]

Yes it is difficult not totally impossible. If you can go to your LBS I am sure they will be happy to help.