Electric bike with a small 25-35cc generator?

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#11
What you really want is an angle grinder and a hf tailgate generator. The angle grinder runs off DC and AC and it has good power output properties. It can also be speed controlled and it comes with a threaded arbor. Perhaps one of the cheap drill master grinder
s. Use a float battery controller?
 


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#12
I considered that but I kinda just want one drive train to simplify the system and reduce drag. Electric also utilizes energy most efficiently. So, I think when I convert gas to electric and using that energy either as storage or sent directly to the electric hub motor is more efficient than simply running a belt/chain drive from the gas motor. This is done in real life with modern cruise ships where diesel engines generate electricity for electric propeller motors rather than drive the historical shaft propeller systems. I stopped by Menards/Home Depot and looked at some of the 25cc yard work engines. Damn, they are tiny. It would fit on the rear rack on a bike easily.

Also, I am going to have like a huge battery bank capable of about 50 miles at 30 mph or something like 2-2.5kwH. So, the gas generator is only a back up or incase I am at like 20% capacity I will turn it on. I really want to do this on a fat tire bike but those wheels have such high rolling resistance...
No offense but the gas directly connected is more efficient than having it power a Dynamo and then power a DC motor. That's 90percent effiency at the alternator x 90 percent inverter x 90 percent for the motor which is much less than 100 percent for a direct chain.
 

bakaneko

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#13
No offense but the gas directly connected is more efficient than having it power a Dynamo and then power a DC motor. That's 90percent effiency at the alternator x 90 percent inverter x 90 percent for the motor which is much less than 100 percent for a direct chain.
Yeah, after thinking about it a bit more 100W from a 25cc engine is abysmal. I am looking for a friction drive that will fit a fat tire 4" wheel. Not sure if such a thing exists.
 

LewieBike

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#14
Theoretically you should be able to get at least a half ~ 2/3rds kilowatt out of a basic 25cc two stroke. This engine should have a raw output at the shaft at least a Kw.

My 28 cc husky weedeater is rated at 1.2 kW.

...but you have to carry gasoline, run the engine on a governor, (complex and need to DIY..) and the best way to get electrical power out of the engine would be to drive a big, Hi Kv RC electric model aircraft brushless motor with the IC engine, then run the 3 phase output into a trio of low voltage drop Schottky bridge diodes of at least a 15 ~ 30amp ratings. It's going to be complex, troublesome and add another 15~25 pounds of weight.

The thing that makes Hybrid cars works so well is the engine and electric motor are linked electromechanically and the IC engine can always add power directly to the wheels if the batteries are low in charge. A couple years ago there were 49 cc pocketbike/MotoPed 2 cycle engine with a dynamo/starter on the pull rope end. There was talk about using the dynamo as a charger for additional battery boost to a hub E-drive. These were Chinese engines and not particular efficient or clean running.
 

LewieBike

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#15
P.S.

I'd be joining Endless Sphere and bumping this idea around, unfortunately they're pretty dead set against gasoline assisted E-power.
 

bakaneko

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#16
Theoretically you should be able to get at least a half ~ 2/3rds kilowatt out of a basic 25cc two stroke. This engine should have a raw output at the shaft at least a Kw.
Yeah, that is what I thought I am just surprised of all the weedwacker generator build videos I've seen they are getting like 60-100W, which seem miserable for a 25cc engine. My initial thought was to run a 200-300W motor at low RPM (sound) and feed that into a bulk converter with a charge regulator for the right voltage. I am also open to making a weedwacker friction drive for the fat tire bike, which would be most minimal. This is all as a back up for the electric bike incase I run out of juice or if I want to go on very, very long rides.

The Endless Sphere and green crowd is kinda annoying in this respect. I mean if you can get the efficiency of the gas generator to like 120+ miles per gallon and with all the environmental certifications. I don't see how that could not be a bad thing as a back up. It is only as a back up. Even if I build up a battery bank capable of 100 miles on one charge, I'd still want to have the back up especially if it can be very small, which a 25cc engine will be.

Anywho, this is all in the air for now. I hope to start on it this winter but who knows... I made a solar ebike over the summer but tore it down. Good and bad to it. I'll write something here to document and for people to learn from my mistakes.
 

CrazyDan

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#17
I thought you can't charge and deplete a LiPo battery at the same time. Might need an old school lead acid battery.
 

bakaneko

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#18
Yes, the way I think it will work is it will follow Kirchoff's current law with two currents (battery and generator). The load will draw from the generator first and then battery. A few scenarios on a 1000W ebike:

1. Off the line = load is 1000W, generator makes 300W, and load draws 700W from battery (1/8th of the time???)
2. Getting up to speed = load is 500W, generator makes 300W, and load draws 200W from battery (1/8th of the time)
3. Cruising = load is average 300W, generator makes 300W, and load draws 0W from battery (4/8th of the time)
4. Coasting or braking or stopped = load is 0W, generator makes 300W, and battery is charged 300W (2/8th of the time)

For a high power ebike, the 300W is not that amazing but remember that it is constantly providing a current for charging or reducing load on battery. This adds up over time that you are stopped at the light, coasting, braking or lightly pedaling and not using power. Especially, if you have an efficient ebike motor constantly running the generator helps.

 
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