Gas powered electric- a measure of sucess

Discussion in 'General Questions' started by professor, Nov 25, 2009.

  1. professor

    professor Active Member

    Here is what didn't work- driving a dc motor (as a generator) to propel drive motor on the bike. Engine at full rpm and creeping down the road. Back to square one. Bike has a 250 watt electric motor driving the back wheel with a chain. Gearing 19 to one and battery power speed 13 mph.
    Phase II >
    Weighty HF 79cc (20#) on rack (6#) driving an alternator (9#) (non-regulated with a small battery to energize the field) making 37 volts at 3600rpm = it goes, but does not have the snap the battery alone had. Would get up to speed but was sluggish. Motor pulley was smaller than the one on the alternator.
    Phase III >
    Changed the motor pulley to run at a one to one ratio= 50 volts at full rpm and the drive motor now acts almost as snappy as the battery on initial take off. Have to throttle back to almost idle going down the road to keep from going faster than the battery powered formerly went.

    Here is what I think- motors typically draw a multiple of running amps on start-up, and the battery would supply that extra juice. But the alternator doesn't have that deep reserve for starting, hence the high rpm and big voltage fills that need. But once going down the road, it is necessary to drop the rpm (volts) down to the motor's design voltage.

    The next phase will be to remove the HF and replace it with a 50cc Techumseh which weighs 11 pounds less.
    The current rack set-up is totally unusable but might be OK at the lower weight. (If the HF and alt. would fit in a cruiser or streched frame- I think it would be OK).

    My question is, will the smaller engine start OK with the extra pulling effort of the alternator connected to it, the HF does fair in this regard. You definitely know the alternator is there- about double the pull effort- lots of inertia to overcome. This is with the field wire un-attached.

    What I need to find is a regulator i can tap off of the big power output to charge the 12 volt field battery (remember the big power is connected directly to the drive motor- the battery that powers the field is separate).

    So far-so good.
    I have a pic but this new computer uses Linex and I can't figure out how to get the pic to photobucket!
    Last edited: Nov 25, 2009

  2. AussieJester

    AussieJester Member

    Sorry if i missed something here (highly likely) But what ah of batteries are in the setup (if any at all) The principal of ICE running generator to power electric motor is how the Haul Pacs drivetrain is setup IIRC?

  3. professor

    professor Active Member

    I edited the first post for clarity- sorry for the confusion.

    I used one 9ah battery to power the field.
    I have figured out (while reclining in the bathtub) the reason why home generators are so heavy- they must use really big permanent magnets.

    In my case, the rotating part of the alternator is an electromagnet, so it must be charged from something, hence the battery- doesn't have to be a big one though.

    I am now thinking a regulator from a small engine (a universal snowmobile reg.from MFG supply) would work to charge the battery, from the big power- two wires, I think those engines produce AC from their stator but don't see why the regulator wouldn't work with DC.

    Any knowledgeable input is welcome!
    Last edited: Nov 25, 2009
  4. ibdennyak

    ibdennyak Guest

    Hey prof....Denny here, the guy that seems to have started all this nonsense. :grin5:

    Trying to wrap my aged mind around what you have there. Sounds like you are running an alternator full bore and controlling voltage by rpm. Then running it through the rectifier. I have a schematic to build a regulator that could be setup to deliver any voltage up to the max of the alternator, but that would also limit the voltage to your big power. I would google dc to dc converter. Drive one side with your 36 volts, and pick off 12 volts to charge your battery. You could probably drop your voltage with resistors, but that would be very inefficient. Hope this gives you a few ideas.

  5. AussieSteve

    AussieSteve Active Member

    I don't quite catch the purpose. Using a ~2HP, (~1500W) motor to produce 250W of rear wheel power.
    On the electrical side, a standard DC motor has very poor torque at low RPM, even using a switching DC-DC converter for voltage/speed control. They're jerky and horrible to control well. A brushless motor and controller are far better. Also, your system will only work well with storage batteries. Varying petrol (gas) motor speed to control the DC motor will not give any start-up torque, as you described.
    Sorry to be the Devil's advocate.

    You are on the right track in a way, in my opinion. I have an electric bike, (200W) and a small, petrol (gas) emergency charger, say 6" cube or smaller, to fit in a backpack etc, would be great. It would only need something like a model aicraft style engine or slightly larger. Small line-trimmer maybe.
    With a 36V 10Ah Lithium battery, I only get about 32km range, (20 miles). A quick mid-trip charge, (or two), would be great sometimes.

    ... Steve
    Last edited: Nov 25, 2009
  6. professor

    professor Active Member

    You got it Denny, except I didn't get to the rectifier part yet. I am not good with electronics, so I want to tap a regulator on the big power (leaving the big power to vary with throttle, like now) to keep the battery up while going down the road.

    Steve- here is the deal. In New York, it is now legal to run an e-bike.(which I recently made out of scooter parts and a new Mongoose).
    I want nothing to do with stuff I know nothing about, like brushless,controlers. electronic gizmos. I can do simple stuff, like hooking up wires too and from the alternator and switches. I am good with engines and fabrication.
    Everybody knows the issues with batterys. Issues I am seeking to bypass. Besides that, I have some ethnic in me that doesn't like to spend much on toys. You know what that means.

    As for the engine size vs drive motor- I tried 2 weedwackers in direct drive ratio to the alt. and neither had the umph to do the job. Probably geared down to get them in their power range, they would work. But I also really like quiet and a screaming 2 stroke (even muffled a lot) might bother me. The HF engine was cheap, easy to mount, strong and absolutely does NOT sound like a chainsaw- pretty quiet, even though I would add a cigar muff to quiet it even further (stealth).
    I did not realize just how heavy it would be on the back. BUT with that as a baseline, I now know the alternator powered drive motor will work.

    If there existed a generator that was light and could output 24volts at, say 700 watts- that would be ideal, especially in conjunction with batterys. The HF 2 stroke generator(for example) is over 50 pounds.
    An alternator can make good power and be relatively light because (I think) it uses electromagnets rather than permanent ones.

    As an aside- once you start your car, you are running it off the alternator- put too much load on the system (like an electric winch) and you will fry the alternator and the battery will be OK.

    By the way, running on batterys (twin 9ah) the 250 w scooter motor surprised me on how much off the line snap it has. I weigh 135 and the bike was around 60.
    It is geared to go 13 mph flat out- bike speed. I have a 450 w motor waiting to go on with a bigger motor sprocket on it and to keep up with the spandex guys for a bit might be interesting.
    My goal is not speed but to duplicate bike action with less effort.` I want to attract NO attention. Just another peddler. I am afraid the speed and noise of gas power that is so popular here will be what limits gas bikes all around.
  7. wheelbender6

    wheelbender6 Well-Known Member


    Here is a gen from Harbor Freight that could possibly be rack mounted. It weighs 42lbs!
    It produces 120AC, so it would run your battery charger as you ride.
    I have read posts that these little generators work well for power tools, but have not seen any posts on any site where anyone has actually used one of these
    on an ebike.
    Last edited: Nov 26, 2009
  8. professor

    professor Active Member

    I was off on the wt. of the HF generator, but 42 pounds is too heavy for a rack. Besides, it would have to put out big amps dc or you would have to have a converter to obtain dc OR use an ac motor. The very lightest thing I can come up with is using a 2 stroke instead of the HF. Am mocking up one now.
  9. wheelbender6

    wheelbender6 Well-Known Member

    Last edited: Nov 26, 2009
  10. loquin

    loquin Active Member

    The idea behind hybrid gas/electrics is to drive the electrical system from batteries, which are being recharged by the generator. The battery has the capacity to provide the high amerage for takeoffs and hills. The generator just needs to provide enough amperage to maintain speed once attained, and recharge the battery with the power needed to get the bike up to speed.

    Thus, the gas engine can be smaller than would otherwise be needed, as it can run in it's maximum efficiency RPM range. The battery stores the small excess power until it's needed. A regenerating controller can also convert some of the kinetic energy back into electrical energy when slowing down or going downhill and push it baqck into the battery, so that it's not all lost to heat.
    Last edited: Nov 26, 2009
  11. ibdennyak

    ibdennyak Guest

    Exactly.....that was my theory when I had my pusher. The generator was just big enough to keep the smaller batteries charged, and the batteries were big enough to absorb the higher power requirements of hills and acceleration. The smaller batteries provided the power and the genserator extended the range without needing the extra weight of the larger batteries.
  12. AussieSteve

    AussieSteve Active Member

    I designed and built a small regenerative controller for a DC motor a couple of years ago. From memory, it could handle up to about 750W, but was only 12V and had forward and reverse so wouldn't be suitable for a bike.
    With the 'throttle' centred, the vehicle was stationary. Dropping below centre went backwards while above centre moved forwards.
    Any time vehicle speed was higher than throttle position, (ie going downhill), excess energy was diverted back into charging the battery.

    I thought about buying a 450W upgrade for my electric bike, but decided against it because I'd need to double up on battery capacity to keep a decent range. (At about $500 a pop for the Lithium batteries, it's hard to justify)

    ... Steve
  13. AussieJester

    AussieJester Member

    There is a delta trike setup with a small honda generator on the back (forget if its on here or other motoredbike site?) Gets something ridiculous like 200mpg range, a fella that is legally blind built it...

  14. ibdennyak

    ibdennyak Guest


    Been kicking around the idea of using an electric trolling motor to power a bike. Have enough other ideas to stay occupied for years, but your controller sounds ideal for something like that. :idea: Reverse isn't necessary......but the cool factor.....:devilish:
  15. ibdennyak

    ibdennyak Guest

    Saw that too, but can't find it. Very useful contraption.
  16. AussieSteve

    AussieSteve Active Member

    I've been thinking about making a regenerative controller for my 200W electric bike. Problem is, it's a brushless motor and I've never built a controller for them, let alone a regenerative one. It would take a fair bit of research to get me started, so I haven't got past the 'thinking about it'stage.
    I've still got all the gear sitting here - circuit board design software and PCB etching equipment, just lacking motivation.

    ... Steve
  17. ibdennyak

    ibdennyak Guest

    I can understand that feeling......especially after eating like a pig. Dumb question for the you celebrate Thanksgiving??:jester:

    I have to admit I am appalled at the tight regulations the Aussies and Canadians have on their MBs. Just curious, how would they feel about the hybrid situation. After all, the bike is powered by just has an on board generator to charge the batteries. Could be a bad portend of things to come in the USA. :sweatdrop:
  18. AussieJester

    AussieJester Member

    Nope we don't ...

    I think regardless of if the motor is directly powering or 'indirectly' powering the bicycle the 200watt law would somehow raise its ugly head in the end of the day the motor is required for powered motion, if its over 200watt the would have a problem i think


    p.s that delta trike with a genie on it was also on Endless Sphere IIRC tried searching then no luck...
  19. ibdennyak

    ibdennyak Guest

    Figures. Loopholes only get one so far. Been watching your build.....great job. Like the fiberglass work.
  20. professor

    professor Active Member

    I am doing this exactly because of regulations.
    I have considered your mode of charging while going down the road Denny, but then I would need a controler and either somehow charge at 24volts or drop the whole system down to 12 and run the 450 watt motor at 1/2 voltage (giving about 250 watts at the alternator's 14 volt output.