Newby needs charger help please

[deacon]

hi there I am building electric bicycles and I have a charger question I hope you guys can help with. The bike runs on a 24volt battery pack powering a front wheel hub motor. The big issue with an ebike is range for me. For some guys it's speed but I like puttering along. I would like to increase the range so I have an idea.

I know that a 24volt brush motor will also generate 24volts when turned without a power supply. I can set it as a friction drive on the rear tire and have it turn with the movement of the bike. Either with the front hub motor or coasting or even with the pedal power. Now that is all fine and dandy. The problem is that if I hook it to the power supply to recharge it. The motor will drain the power and become a motor again not a generator.

So what I need is a one way diode type device that will only allow the current to go in one direction. It needs to be capable of a max 25amps at max 27 volts. I doubt that it will ever reach that load but it would be my dream parameter. Most likely it will be a couple of amps at 24volts i hope.

If you can point me in the right direction I would be most grateful ... thanks. ps i can wire a circuit if I know what to put in.

 

[crutschow]

You can't expect to use a generator while running the motor and generate any net charge. The losses will always be more then the generator can supply (otherwise you would have perpetual motion). The only time you would want the generator to be connected would be when you are coasting downhill, or using pedal power.

You could use a large schottky diode (which have a lower forward drop then a regular junction diode) to isolate the generator so current will only go out, not in.

This brings up a question: Can the hub motor also be used as a generator?

 

[deacon]

Yes the hub motor does some generating when the battery is dead. I have noticed that when the batter dies it will revive after I pedal a few yards.
Thanks for the name of the product I need. I'll see if I cant find one.

And yes I had an inkling that I needed to lift the motor when the hub is running. to prevent additional drag on it. Im not even sure I can get enough rpms to make it generate much current even in the best case.

 

[colin55]

Take an extra battery with you.

 

[deacon]

Actually plan b is to take them all off and ride it home like a bike. I ran my friction drive this afternoon and it did about 80 of the hub motor's efficiency. I think I'm just going to scavenge the battery pack and leave the friction drive set up. just in case I need it. I can always move the battery pack back to it.

Thanks guys I think adding the generator was a pipe dream.