hybrid power w charging via regen brakes ?

I'm thinking of increasing my range to more than my current 60km by building a bike with my 9C hub and one of those 2 stroke bike engine kits. I often travel to areas where it woudn't be prudent to use the noisy smelly gas engine so there I can use the electric. My idea is to be able to charge the battery by 'turning on' the regen feature of a controller during gas usage. A little like a hybrid car. My question is, how many amps can one expect from the regen, into a 36 volt battery ? The controller I have now does not have regen, so I can't test this.
Yes, I know the argument that I should just add battery of the same weight as the gas engine, but I want a LOT of range. Can't beat the energy per gram of liquid fuels. Thanks for any advice.

dudewheresmycar said:

I'm thinking of increasing my range to more than my current 60km by building a bike with my 9C hub and one of those 2 stroke bike engine kits. I often travel to areas where it woudn't be prudent to use the noisy smelly gas engine so there I can use the electric. My idea is to be able to charge the battery by 'turning on' the regen feature of a controller during gas usage. A little like a hybrid car. My question is, how many amps can one expect from the regen, into a 36 volt battery ?

Click to expand...

For a very rough estimate, use the simulator at ebikes.ca to see how much power you can put into your motor without overheating. That is about the same as the amount you can get out without overheating.

dudewheresmycar said:

I'm thinking of increasing my range to more than my current 60km by building a bike with my 9C hub and one of those 2 stroke bike engine kits.
My idea is to be able to charge the battery by 'turning on' the regen feature of a controller during gas usage. A little like a hybrid car. My question is, how many amps can one expect from the regen, into a 36 volt battery ? The controller I have now does not have regen, so I can't test this.

Click to expand...

How big is the engine? When regen is set high, the braking effect is pretty dramatic, so you likely will need to find a sweet spot where the engine is actually able to overcome the braking and propel the bike, while giving a decent charge rate. You could try riding the bike on gas only, and firmly applying the rear brake at the same time to get an idea about if the engine has enough power to propel the bike without bogging down.

Keep in mind that braking heats the motor, controller, and phase wires, significantly more than using it as a motor. Doing this continously to recharge the battery may cause overheating in one or more of these parts.

Its' also going to heat up the ICE more, as it loads it down quite a bit more heavily than just moving the bike with it; this will also use proportionally more fuel.


It also is less efficient as a recharge system than just plugging in somewhere to recharge, but that isnt' always an option.

What you might consider instead is using the gas motor system as a generator that simply kicks on automatically whenever the battery runs below a certain point, *but* this means it has to be large enough to supply more power than the electric system is using, so that it will fill the battery faster than the motor uses it. That may mean a larger generator setup, that would probably have to go in a trailer or sidecar.

The good news is that there are some pretty quiet generators, like Honda, that are probably a lot quieter than the typical ICE engines found in bicycle kits. If in a trailer or sidecar it could also be enclosed in a vented box with baffles to further mute it.


BTW, there are a number of hybrid threads, and other threads using regen for recharging, around the forum that may help you.

My inclination is why charge the battery? In other words, when going on these out of the way spots, just use the gas engine wherever you don't need to run the quieter electric motor, and thus always save some battery to use when needed.

Of course you could carry a small generator, but again, if you have gas for the generator, you may as well use it to run the gas engine you have on the bike.

And then you could carry a regular charger to use when you do have access to an outlet. Or a solar charger. Or?

I'm not against your regen idea. I have a friend that set up a bike exactly like you described with a 24V brushed hub motor on the front and a gas motor driving the rear wheel. He needed to run both, plus pedal, to get up the steep hill to his house, and, like you, used the electric motor in appropriate areas. He found the sweet spot where he could maintain the speed he wanted plus use the hub motor as a generator, mostly to top off the battery before heading up the steep hill. (he joined this forum for some unrelated advice and was disgusted with comments from purists concerning his gas motor and subsequently left the forum).

He has since removed the hub motor and added a 48V 750W BBS02, which will pull him up the hill without using the gas motor. And of course he no longer has regen with the free wheeling BBS02.

Good luck with your project, whatever you decide to do.

Edit: Here's another member thinking about doing the same thing:

https://www.endless-sphere.com/forums/viewtopic.php?f=1&t=100908