Anyone used motorized bike kit and hub motor for hybrid bike

[rudyauction509]

My lithium powered ebike blew up yesterday, luckily insurance is covering everything and the only things damaged when the 1,500 watt hour lipo pack blew is the bike (melted the entire aluminum frame!) and a low hanging branch of a nearby tree - good thing I always charge outside!. I'm thinking, instead of rebuilding another $2k lithium bike, I can use the new 9c hub motor and kelly controller with regenerative braking, and a generic 66cc gas engine to make a hybrid bike. The 66cc engine would be geared for top speed, the hub motor would be the front wheel, both would be used for acceleration and high speeds, while cruising only the electric motor (using locking clutch lever to disable the gas engine), or just the gas one and use regen to get some power back into the battery. Anyone ever thought about this? When I'm out of gas my range would be around 10 miles, yet I could ride as far as I wanted (upwards of 100 miles occasionally during the summer) without spending hundreds of dollars on batteries. I'd be using high charge and discharge rate lithium batteries for the electric portion, and the pack would be quite small and cheap, around 5 amp hours at 74 volts. Most power would come from the engine, but I'd have a small charger, to make it basically a plug in hybrid. In the future I may consider a computer throttle management system that I'd have to design myself.

 

[justin_le]

Hi rudyauction, first in regards to the LiPo battery blowing up, it would be really helpful if you posted another thread here explaining the full circumstances of that, with photos too if possible. Like what specific packs you were using, whether it was charging or discharging or just sitting there, if you had a BMS circuit or not etc. The more knowledge and awareness we have of ebike batteries catching fire then the better prepared people can be when their designing and using their systems.

But back to your main questions, with a proportional regen capable motor controller then this kind of system can work fine for sure, and we've helped a few people over the years with similar builds. It makes a lot more sense than the more commonly discussed approach of using a gas genset to charge the batteries on the fly, since in that case you are unnecessarily doubling up on the electric engines and ensuring a double conversion loss (mechanical to electrical, and then back from electrical to mechanical). Use the gas motor to drive the wheel directly to propel the bike, and then if you ever need to top up the battery as well then just dial up your controller regen to a suitable level, there are no issues or complications. Just make sure your battery has a BMS circuit onboard as a hard cutoff against possible overcharge situations.

Whether you enjoy riding with a noisy and smelly gas engine is another question altogether, and for 100 miles summer trips you can do that with a pair of high capacity lithium batteries. That will probably weight similar or less than the whole gas motor and drive contraption, but of course won't be as cheap.

 

[dogman dan]

IMO, the really cheap gas motor kits aren't up to the task of a 100 mile, continuous ride. You'd have to stop often to cool it I think. So to get the gas endurance you crave, you'd likely be spending a bit more on a 4 stroke, Subaru or Honda engine.

But it's true, a really reliable battery able to take you 100 miles can be spendy. Real bummer your original one caught fire.

I'm also very curious how that happened, even the very safest battery can still start a fire if a wire gets shorted. I had my truck burn in 1977 from a short on a 12v car battery.