Just wondering if its doable - gas to run electric ?

Discussion in 'Electric Bicycles' started by just for kicks, Aug 21, 2007.

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  1. 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.

  2. 5-7HEAVEN

    5-7HEAVEN Guest

    :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.
    Last edited by a moderator: Aug 22, 2007
  3. npk1977

    npk1977 Guest

    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.
    Last edited by a moderator: Aug 22, 2007
  4. 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.
  5. skyl4rk

    skyl4rk Guest

    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.
  6. iRide Customs

    iRide Customs Member

    Wouldn't the bike weigh a lot with a generator on it?
  7. But think of the coolness factor.
  8. 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.
  9. skyl4rk

    skyl4rk Guest

    Yes, and the transformer is a hunk of steel and copper. An IC motor alone will be lighter.
  10. 5-7HEAVEN

    5-7HEAVEN Guest

    :cool:dimensions are 17"L X 16"W X 13"H, 50.8lbs, costs $249 on ebay.
  11. Ok I measured it but just the engine and generator not the tank, control panel or frame and it is appr. 10"W x 16"l x 11"h.I still dont know exactly what the weight of it is but it is a bit on the heavy side.

    98cc engine, 4 stroke $199.99 on sale at the retail store for $162 and I only noticed it because I need something to put in our new enclosed trailer and was looking at the small generators but thought about a bike project also.:lol:

    It is part #94678 at harborfreight and I pulled it right up after typing that in so if you want a picture there it is.(I wont do pictures anymore)

    Might not be to bad tucked up in a trike with electric powered rear wheels.

    If it just had a manually engaged gearbox between the engine and generator for total drive options. (pedal, gas, gas powered electric, electric from batteries) ability to charge itself anywhere if needed although I doubt it would be driveable from gas power and be able to charge at the same time unless it was just trickle charging.
  12. I wonder if like a model airplane engine would work. That would be small enough to stick in your pocket.
  13. RLK

    RLK Guest

    I found this just last night

    These guys have made a DC generator from a lawnmower motor and a GM car alternator.


    They hint that an alternator with an external regulator could generate up to 70 volts depending on how fast it spins. If you could find a 40 volt external regulator and a smaller gas motor that would turn it you'd be set.

    I wonder if the Honda or other on-the-shelf generators with 120 volt AC output have DC to AC inverters built in. I'll bet a dollar that they do. If so, remove the included inverter instead of inverting your current twice.

    Food for thought.
  14. dbigkahunna

    dbigkahunna Guest

    A 2 wheel motored Hybrid

    As I was cruising around today your thread came to mind. How about a true hybrid. This would be based on the Cheetah frame. Have the electric to start out on them when up to speed, kick on the IC and turn off the electric. The electric could be a right hand chain drive and the IC could be a rack mount Golden Eagle, Staton, or a scrubber set up. Google Cheetah electric bike to see the frame. This would be a build it yourself thing. However you could have a honkin battery and a 40-50 cc engine. You can use the battery for around town and the IC when you head home.
  15. If I were to do it I'd want the front and rear hubs electric for the power and the compact/cleaness of it then mount the generator inline with the frame and the engine to the front so I could still pedal (with a widened crank if needed) and at hmmm, what was it 16" long it would take a long custom frame to hold it.

    The batteries could go on a rear rack or maybe even over the generator itself, actually there a few good places the batts could go.

    I bet something like that, while running on gas would get terrible gas mileage maybe even down to 30 or so miles per gallon and probably weigh around 225-275.With it weighing so much I'd need some seriously heavy duty hubs/wheels and a good solid frame but it would most likely ride like a cadillac at that weight.:lol:

    I'd still want to slide a transmission inbetween the engine and the generator so I could to it all.(pedal, gas, electric from batts, electric from gas generator)
    Last edited by a moderator: Sep 3, 2007
  16. vanilla ice

    vanilla ice Guest

    Seems the way to go is to have a drive for the gas engine to power the wheel directly. Its more efficient that way. Then shut it down an run electric when you can. In high demand situations you can run both.

    I mean look at whats been successful for cars. As far as I'm concerned it would be foolish to ignore the research that has been done in that area. I don't see any gas generator cars with only electric drive.

    Electronics are lighter and cheaper than ever. If you really wanted to I'm sure you could rig up a monitoring system to switch between the three modes automatically. Or if thats not your bag, theres always manual control.
  17. Maybe a trike would be a good platform for the first attempt just to make it easier to mount everything.
  18. vanilla ice

    vanilla ice Guest

    You're right about the trike. It would take a bunch of components. For one thing, you would want a clutch to disengage the IC motor from the driven wheel when you're in electric only mode- and a clutch between the IC engine and generator for gas only mode. Lots of electronics also I would think.
  19. RLK

    RLK Guest

    There are not cars with pure electric drive but that's the way all railroad locomotives made in the last 60+ years work. On the other hand, locos need to be as heavy as possible.

    In my mind I see the 36v front hub kit i've been running every day for ~6 months pulling a modified kiddie trailer with a gas fired alternator on board as well as some lightweight backpacking gear. I can leave my daily driver setup alone but have the option to hitch the trailer and have unlimited range.
  20. yep the old tried and true "diesel-electric locomotive" but I think they use the electric just for the shear torque they produce which is what they need to get those heavy train cars moving.
    :smile: I cant imagine how bad someone would smoke a clutch if it was in a train driven by only a combustion engine.

    I went back to harborfreights retail store and even the demo generator I had seen was gone off the shelf.
    I really do think it would work very well.
    Might have to be a late winter project.