Just wondering if its doable - gas to run electric ?


just for kicks

I seen a small 4-stroke 2.5HP gas generator that puts out 1000 watts of power (AC with a low amp 12vdc plug) and wondered if it could be converted to use on an electric bike with front/rear electric hubs.

The generator would simply be used instead of batteries to supply the motors with power.
Or the generator could be used along with batteries to recharge them when needed and still be moblie by running off the generator.

I know the thought of a stinky, noisy gas engine on an electric bike is like fingernails on a chalk board to some people but I like the idea myself.

I know it's NOT an original idea by any measure but the small generator I seen looks like it would fit the bill perfectly for an application like that.
:cool:Just for kicks, i vote nay.
online stores sell generators for $190+ and they weigh up to almost 60lbs. they're not compact enough to fit midframe, rackmount is out(center of gravity too high). ya probably have to pull a trailer. since there are no batteries to store the charge, the generator would be constantly running.
if ya throw some batteries onto the bike, i might change my mind. maybe 36v per motor.
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JfK -- Yours is a great idea, as long as you can find a small enough of motor :) Our Happy Time bicycles produce over 1HP, which means they produce over 750Watt. If you can convert that to electricity efficiently, you've got an electrical generator.
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The generator I seen was at harborfrieght and was a lifan engine 4-stroke rated at 2.5HP with a 1000W AC output.

The biggest problem I see is getting the AC back to DC right from the generator.The generator itself was very small and the engine on it is the size of the 4-strokes being used on bikes right now.

I'll go back and write down the specs (couldnt find exact one on their website) but I think it was actually on the lightweight side and very compact but with a steel tube frame around it that would have to go.I'll try to sneak a picture (stores hate that).

The thing I like about electric motors is they have the torque right from the start.

Ultimately I think the whole setup would be less efficient but it might be a better overall ride performance.
I worked out a system for a Honda 1000W generator. The basic idea is to step down and rectify the voltage to the charge voltage for your battery system. The generator would run full time, but when the load is more than the generator can put out, the batteries would hold the voltage up and provide power, for example during acceleration.

I don't know if this is the right way to build a hybrid system, but I think it would work.

The Honda 1000W generator has a voltage regulator that will hold AC voltage at a certain level, for example 120VAC. When a load is added, it powers up the motor to compensate and maintain 120VAC.

A step down transformer is used to drop the voltage to approximately the charging voltage of the battery (adjusted for losses in rectifying the AC). For a 36V battery system, the DC target voltage is about 40V, which should charge the battery but not cook it (verify this). I estimate that you would want to drop the AC down to about 42.8V when you account for diode losses in the rectifier. You would have to build the system and adjust the number of turns to get the exact voltage that you want. Take some plumbers steel strap, wrap it into a circle to make a transformer core, then wrap 14 gauge copper wire for the 120VAC side and 12 gauge or 10 gauge for the low voltage side. 120VAC/42.8VAC means about 2.77 turns for the 120VAC wire to 1 turn for the 42.8VAC wire.

After the transformer your output is 42.8VAC. Run this through a bridge rectifier to get pulse DC with an RMS potential equal to about 40VAC due to the voltage drop in each of the two working diodes in the rectifier.

To smooth the pulse DC, use a coil-capacitor filter.

At this point, connect the DC output to the controller at the same point as the battery, in parallel with the battery.

The generator should handle most loads under about 1000W, but when loads exceed this, the batteries should prevent voltage drop. It would take some experimenting to get the perfect voltage where the generator circuit breaker did not shut off the system because the batteries took on the load at the right voltage.

You may not need a 1000W generator, its just that the Honda 1000W generator is a nice small package that is reliable. You might get by with 500W.

Its all theory at this point.
That little generator I seen was very small and light from what I could tell with it half strapped to the shelf.

If you were to use just the generator for the electricty, no batteries then it wouldnt weigh to much more than a bike with just batteries I think.But I think it would work best with a set of batteries also.

I got one more day of doctors then I'm free to roam friday, I'll check out that generator again ASAP.