Adding a generator in bottom bracket to charge battery

[Hummina Shadeeba]

My bike has just a throttle and the pedals/cranks are floating on bearings and do nothing. I want to add a generator in the bottom bracket shell to charge the battery while pedaling.
Mainly I want to build resistance as I’m getting cold n fat while riding.


I know there’s a thread about what I’m trying to do but I lost it


I think this should be pretty simple and I was going to make a 3-phase generator/motor by adding some magnets to the bottom bracket axle and a huge amount of 3-phase coils glued into the bottom bracket shell to create a very low kv so even a slow pedal rpm would produce a voltage higher than the battery’s. The details on the motor design I can figure later but assume the greater the number of poles the smoother the resistance


The three phase output needs to be rectified and caps to smoothen it and that’s it, right? And I’ll add a fuse.


What “three phase rectifier” is appropriate? If it meets my voltage n current needs are there other considerations?

@fechter i know u had posted this circuitry in the other thread I can’t find.



I’d rather get the rectifier with smoothening caps and anything else already built. It needs to convert my pedal-turned generator (producing 90v or greater and I imagine very little current) into dc. Smaller the better to fit in the seat tube.

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Use common sense when mounting the rectifier! Mount it in an enclosed box that is designed to handle electronics and that can NOT be accessed by children or anyone else! Continuous Duty 35 AMP Three Phase Bridge Rectifier.

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[thepronghorn]

Hey this is a cool idea and one I've also been interested in especially since Also released the details of their TM-B.

I know you said you could figure out the details of the motor later, but I don't think a motor exists that can put out 200W at 100 rpm that's only the size of a bottom bracket. You'll need to either gear up your pedal rpm to the motor or get/make a much bigger motor.

For the rectifier, I don't think a 3 phase diode bridge will feel very good to pedal without some significant inertia in the system since it will only be able to generate power at the peaks of the AC waveform when the EMF of the motor/generator is above the battery voltage. Do you have an extra 3 phase controller sitting around? Maybe start with that as your rectifier then realize that you'd prefer to turn the controller on and set it to regen power from your legs back into your battery.

 

[Hummina Shadeeba]

Hey this is a cool idea and one I've also been interested in especially since Also released the details of their TM-B.

Aha interesting and hadn’t seen rivian are doing it

I know you said you could figure out the details of the motor later, but I don't think a motor exists that can put out 200W at 100 rpm that's only the size of a bottom bracket.

I’m saying it would be a motor in the bottom bracket (small) but wound to a super low kv to produce a voltage higher then the battery’s. The amount of actual power producible by the pedaling …who knows. I’d do a powder core and pot all the windings into the bb shell

You'll need to either gear up your pedal rpm to the motor or get/make a much bigger motor.

I’d make the motor simple by gluing magnets to my square taper bb and potting MANY coils in the bottom bracket shell. Being so small a motor and also a super low kv is challenging but I see no obstacle

For the rectifier, I don't think a 3 phase diode bridge will feel very good to pedal without some significant inertia in the system since it will only be able to generate power at the peaks of the AC waveform when the EMF of the motor/generator is above the battery voltage.

I think smoothening the resistance would be the challenge. Making the motor a very low kv with as many magnet poles and coils and maybe capacitors too to help smoothen..is all I can think to do.

Do you have an extra 3 phase controller sitting around? Maybe start with that as your rectifier then realize that you'd prefer to turn the controller on and set it to regen power from your legs back into your battery.

I wanted to make it as simply as possible and with just a rectifier n caps if possible. If I can wind a motor to produce a smooth resistance from very low rpm that’s all that’s needed



surely this has been done but I can’t find a thread. Thanks for ur input and if u have any other advice please tell me.