Engine driven electric power

Discussion in 'Electric Bicycles' started by professor, Sep 27, 2009.

  1. professor

    professor Active Member

    I heard in NY now, 250 watts is legal and gas engine driven is not.
    I got a 250 watt 24v motor and parts from an old scooter to fit to my Mongoose. I am thinking that I could power a re-worked alternator off a 2 stroke to make a power source for the electric. Still would need a very small battery to power the field circut in the alternator, I don't mind that.
    It is said a car alternator needs 5 thousand rpm to produce 120 volts (unregulated) at full field amps. So to make 24 volts (or a little more) much lower rpm would do (there is a low limit for where the alt. begins to make anything- older ones kick in lower than the newer high output ones). I am thinking of gearing down a weedwacker engine to run the alternator and that would feed the electric motor. Also, I'm thinking controlling the field current lower would let the engine rpm control output- eliminating the need for a controler.
    Thus, I woud be totally legal in NY and would NOT need to deal with batterys and charging ( maybe could step down some alternator power to charge the little field battery. This is how diesel electric train engines drive the wheels. Why not a bike? The weight would not be much or any more than battery power.
    I am not looking for speed - 15-20 mph is plenty, just want assist.

  2. safe

    safe Active Member

    Working around the laws is hard work... I know...

    (but it's reality)

    I was looking into using alternators as motors and learned that they create their own field currents separately from the stator currents.

    Anyway... the more I investigated that the more I found that the "high tech" alternators were using permanent magnets. (not field currents) This is because if you can afford permanent magnets they do work better and for less weight. (less hassle too)

    So here's the idea:

    Maybe you buy TWO 250 watt permanent magnet motors... the first acts like a generator taking the power from the gas engine and the second actually drives the bike. Maybe a small battery exists or some capacitors to provide some buffering. The two motors can be on different places on the bike. Maybe a hub motor is used as the bikes main drive and a little standalone 250 watt motor is used near the gasoline engine.

    Most automotive hybrids do the opposite... they have a smaller gasoline engine and a larger electric motor and they then use batteries as a way to even things out.

    In this case the gasoline engine could be really, really small. (maybe like an RC gasoline powered engine)


    An even more "surreal" idea would be to eliminate the battery/capacitor entirely and eliminate the CONTROLLER too! The idea would be to directly connect the generator to the motor (the two 250 watts motors) with a straight set of wires. You then CONTROL the vehicle through the throttle of the gas powered engine. Some way to deal with over-power and under-power needs to be thought out. When the gas engine is at idle the bike would need to stop and when the gas engine went too high it would need to be scaled back.

    The easiest way to do the over-power is to create a circuit that measured the voltage and current flowing between the generator and the motor components. Whenever the power exceeded 250 watts it would automatically "pulldown" the gasoline engines throttle.

    It's the under-power situation that is the hardest... at idle the electric powered motor will want to creep. (somehow at closed throttle you need to be able to disconnect the power from the generator running at idle)


    Buffering seems the easier way to deal with control... if you can create a large enough buffer between the generator and motor then you can use simple PWM as the control scheme.

    Maybe you need a way to simply "dump" excess energy?

    If you had a constant stream of 250 watts (more like 350 watts before losses) and could either use it or lose it, that would work. Maybe run some useless extra fan or something when there is excess energy. Actually a fan that cooled the gasoline motor when at idle isn't a bad idea... anything to keep the buffer from overflowing.
    Last edited: Sep 27, 2009
  3. professor

    professor Active Member

    Thanks for the input Safe.
    I definitely want no controller on this thing.
    A clutch on the wacker motor would achive a zero speed when idling.
    Good call on using another 250 watt motor to power the drive motor, but how fast can you spin one before it blows up?
    An alternator (for generating power) can go up to super high rpm with no problem + it has very robust bearings. So rpm would not be an issue. A switch on the field would cut output too for idling/ coasting.
    I am one to spend almost no money on these gizmos. I have a wacker engine, some spare alternators, the scooter parts and the bike.
    I choked up a bit when I got to the,"Buy" word in your post :sweatdrop:
  4. safe

    safe Active Member

    Small permanent magnet motors are cheap for the generator:




    You will have to decide about things like "motor through chain" verses "hub motor" for the power delivery side. Going through the chain is better in that you can then take advantage of multispeed gearing, (widening the powerband substantially) but the complexity of all the geardowns and getting the rpms to match is difficult. The hub motor gets you operational quickly, but the results are less spectacular.

    As for generator speed... these motors run at 2500 rpm and that's not too far from where the gasoline motor might run. It should be possible to run these motors above their normal maximum up to about 4000 rpm without problems... but that's about it for brushed motor. Eliminating the controller would mean that it's a direct drive from generator to motor and that makes things much easier.

    To remain really legal (and to prevent burning up your electric motor) you need to be able to measure the current and voltage that flows from the generator to the motor. That's tricky to do because the generator will produce a different voltage and current depending on it's rpm. Alternators in cars use fancy stabilization techniques where they feedback information to the alternator and that reduces the field strength when it's not needed... this is better than "energy dumping" in that it doesn't bother to produce the energy in the first place.

    Actually maybe the alternator isn't that bad... you could cut the field strength to zero when the throttle is off (gasoline at idle) and you would cut the power to the motor that way. Alternators are designed to maintain a constant 12 volts to the battery and yet for this hybrid bike you need to be able to vary the voltage from zero to about 24 volts... so they are different situations. (though I can see how the alternator option might work well if adapted) Standard 12 volt alternators would not give enough voltage, but if you "tricked them out" they might. The bummer about alternators is that you need to have a battery... and you didn't want that. (so maybe not... hmmmm)

    :D Permanent magnet generators are linear devices... rpm/volt. This actually more closely matches the linear nature of the motor you want to drive.

    :D Alternators create a controllable output voltage based on the field strength, (so control is external) but in order to "bootstrap" them they need a battery to create the field.

    If you used the permanent magnet motor you could just have a switch that dumped the wasted energy during idle into a cooling fan. A simple switch could be enough to solve the circuit demands.

    Otherwise it's going to take some circuit design for pretty much any technique you try... are you up for that?

    After the last few years I've come up to speed on the circuits and understand them better now, one good thing is to set yourself up with some free SPICE software which allows you to simulate circuits on your computer so you can be sure it works right. Ever tried a SPICE program?


    ...I use this to verify every idea now. (better than guessing)
    Last edited: Sep 28, 2009
  5. safe

    safe Active Member

    The Simple Design

    Permanent magnet brushed motor of about 350 watts to act as a generator.

    Permanent magnet brushed hub motor of 250 watts to act as main power drive.

    Cooling fan connected with a circuit that says:

    "If throttle is off (idle) then divert 100% of motor power to a cooling fan, otherwise all power goes to the motor as direct drive." This could also be done with a mechanical device that disconnects a belt drive to the generator. (less elegant, but possible)

    Circuit that checks for peak power... this could be an rpm based tachometer that limited the gasoline motor to a specific rpm. (or maybe even a physical throttle limit... just set your throttle so that full will not allow more rpms than is permitted) Ideally the gearing would be set up so that peak power of the gasoline engine occurs at an rpm below this limit.
    Last edited: Sep 28, 2009
  6. professor

    professor Active Member

    My own legality issue is visual. To be seen as electric is all that is necessary.
    Rpm- the weedwacker engines run pretty fast, not sure but probably over 6000 if not limited in some way, so the alternator deal could be run with a Lovejoy coupling directly. Having to have a small battery would not bother me at all.
    Alternators -I've got. Every project (or old car) brings some spare parts to the inventory shelf.
    I took electrical shop before there was anything called IC- the very thing I want to avoid.
    I am considering an interior car light dimmer to control the field current? House dimmer switch? Something I can understand.
    Then, engine rpm would set the motor speed after both field amps and max engine rpm is detirimined.
    All this can be set-up on a bench test plate, then transfered to a bike rack. Which would then be in a sound enclosure after making a decent muffler and intake. I still want stealth.
  7. safe

    safe Active Member

    Don't forget that alternators are designed for 12 volt operation. I'm sure that you could find a way to modify them to allow 24 volts (and above) but that's something to consider.

    The easy way is as I suggested... two brushed permanent magnet motors connected together directly with a wire and the only real issue left after that is controlling the gas engine.

    The easy way to deal with idle is just to dump the excess energy to a fan...

    But if price is the higher issue than simplicity then the alternator is your path... but sometimes things end up more complicated and expensive when you choose the cheaper solution by the time you get finished.


    For about $50 there is something called a "WattsUp" meter that could allow you to simply calibrate the motor power by reading the meter as you ride. After a little fiddling you would be able to get an average power level that is within the 250 watts range you want and that can also be used as a way to show law enforcement that it's being limited. Without some measureable proof (and no baseline to point to like battery voltage or amps) you could be using 500 watts and no one would know either way. (it would be a black box)
    Last edited: Sep 28, 2009
  8. professor

    professor Active Member

    I'm making real headway. Pulled an alternator off the rack from an '86 Mustang (kept as a spare for my '83 that I drive everyday (NO computer! - a car i can fix and no emissions check in NY). Anyway, this unit is a remote style regulator type alternator.
    I chucked it up in my vise, cut a bit of hex rod to drive it with my drill (2speed) and spun it.
    There are 3 wires in back- the big red one (power out) and one marked F and a ground. I connected a meter to the big one and to the case, then fed a ground to the ground post on a battery and to the case.
    Then connected the F alternator post to + batt. ( got a bit of a spark) And spun it with the drill= 25V. I also experimented with connecting the 24V motor and a car dimmer on the "F" line (maybe from an old heater), the voltage would go down some as I turned the dimmer.
    Note- the motor would turn even at very low rpm of the alternator so a disconnect for the field would be needed at engine idle.
    Not a problem- a switch in line with the throttle that energizes only when gassed up some.
    I am thinking that there must be some way to drop running voltage into the battery so that it charges while scooting down the road.

    How many lights do you think you could run with a set-up like this? I don't ride at night but could be an option for a night rider.

    This looks real promising. Oh, and as long as the motor says 250Watts, I think I am fine.
    The likelyhood of an old guy putting very quietly along at slow speed being even noticed is remote.
  9. safe

    safe Active Member

    One idea might be to have the gasoline engine run at a constant rate and then just adjust the field current when you get above idle. Lights? No problem you just increase the field current more in order to increase the load on the gasoline engine and generator without changing it's speed any. By running the gasoline motor at constant speed you can optimize for efficiency.

    You could create a circuit where if the throttle is off, then the electric motor is disconnected from the generator... but you still need to do something with the extra power even if it's relatively slight when the field strength is zero. Ideally if the power levels drop to zero when at idle you have one less thing to worry about.

    Let me ask this...

    When the field strength is zero (no voltage being added to the motors field) how much does the alternator still produce from the power wire? At idle? At peak efficiency gasoline engine rpm?

    If that energy "waste" is small enough you could just dump it... there are many ways to dump energy and if it's just during idle it should be okay.

    At zero throttle the excess energy needs to get dumped and the gasoline engine needs to be taken to idle.

    Hmmmmmm.... keep up the good work...
    Last edited: Sep 28, 2009
  10. professor

    professor Active Member

    With the field wire disconnected from the battery I spun the alternator at full drill motor speed and there was no movement at all from the little 250/24V motor until I touched the field wire to the battery, then the drill would hit resistance and try to turn in my hand (against the alternator), the scooter motor would spin and the voltmeter start shooting up to around 25. Don't know the drill rpm. Take away the connection to the battery and the voltmeter goes to zero and motor coasts to a stop. Couldn't be better.

    I am thinking you are right about setting the engine rpm constant and then varying the field current for speed control. The only thing I see with that is this particular engine lacks a governor to maintain constant rpm with different loads.
    The 6 hp Techumseh on my 24inch mountain bike post (Toro 622s) would be better suited for this because it has a governor on the carb that operates the same way as all lawnmower engines. You need a governor, so constant rpm is out.
  11. safe

    safe Active Member

    Heck, if you can get a constant speed gasoline engine that is able to cruise along at a moderate pace and have a governor that automatically adjusts for motor load and at the same time be able to vary the alternator field strength to control bike speed, then you have it all worked out.

    So the basic points are:

    :D Gasoline motor with automatic load adjustment by governor. (mechanical)

    :D Alternator that goes from zero volts output up to the maximum you need for a 250 watt motor all controlled by a simple field current. (should be from 0 - 24 volts output)

    :D Throttle that acts to control the field current of the alternator.

    :D Electric motor to drive bike which is directly connected to the alternator output.

    ...you will need a battery to supply the field current, just like with a car, but it would likely not need to be that big as long as you have the ability to feed some of the alternator power back into battery charging. This is what the standard voltage regulators do on cars already... so if you just salvage the voltage regulator from a car and use it then you are set.

    This will be interesting... be sure to include digital images on this thread to record the progress. (we want to watch you build it)
    Last edited: Sep 29, 2009
  12. professor

    professor Active Member

    Safe, when I get done with the off road bike, I will start on the gas/electric.

    Was talking to the sparkey guys at work who gave me some tips also.

    Here is how the alternator works - the diode bank turns the AC into DC.
    The field spins, the field becomes a bunch of magnets as you send current thru their slip rings.
    The amount of current you send thru detirimines the output that comes off the big wire to feed everything. The regulator controls the amount of voltage the whole thing puts out.
    The faster you spin the thing - the higher the voltage would be IF it wasn't regulated somehow. At full field current (3 amps of 12 V or so) I saw 25 V @ 3300 rpm. Spun at 5000, it is said, voltage goes up to 110.
    It sure looks like a goverened engine (3500 rpm) would work real well to just leave it there and tweak the field from zero up to what you need to get 24V.

    For my application, I will be setting the field current at some level, probably with something like a dimmer switch and limiting engine rpm under load @ 24V.
    For idling another switch would be at the throttle lever somewhere to cut field power until the throttle is opened again.
    It would be great to be able to find a car-type regulator that would have it's preset level at 24. My friends tell me that a regulator is available to take a range of input voltages up to around 38 and get a fixed output of one to three amps 12V (dependong on which regulator I get- there are a lot of them and they do not cost much) This could not be used to set field current but could be used to charge the battery while running.
    So far everything looks viable.
    One of the guys is doing a windmill. He disassembled an alternator and placed rare-earth magnets in the part that spins- eliminating the need for energizing that field section electrically...he is wild about that set-up, but it would need a clutch to use it on a bike.
  13. safe

    safe Active Member

    Once I made the mental connection of "throttle" and "field voltage" it all made sense. The idea seems very good... you use the variable field strength as your way to control the electric motor.

    No need for a PWM controller... it's sounding very good.

    Throttles are usually either Hall Sensors (most ebikes) or Potentiometers. (Magura) The dimmer is actually some type of PWM using some really basic circuit which I don't know much about. Dimmers are for AC household 120 vac to my knowledge so I'm not sure if they will work with DC or AC that isn't 120 volts.

    The field voltage is a DC voltage, not AC.

    Are you sure about the dimmer idea?
  14. professor

    professor Active Member

    I did use a rotary devise that looked like a reostat. It was from a car and it did change the power to the field, thus dropping voltage. I am thinking the dimmer switch controls current the same way.
    BUT, I have been studying alternators. One of the connections on the back is the "S" terminal (on Delcos) and on Fords the "S" spade on the remote regulator, in both cases the "S" stands for "Sensing". This line feeds system voltage to the regulator.
    When the regulator receives lower than (a built in standard refrence) voltage- the regulator sends more juice to the field, to bring that voltage up to the standard refrence point.

    I am now thinking- what if that line would have a resistance built into it? Could be a resistor, reostat, or light bulb?.
    Wouldn't the regulator fire up more juice to the field until it got it's end of the sensing line to register 14.5 volts?
    But in reality, the alternator is putting out my desired for 24 volts. The alternator would be functioning totally normally- limiting voltage- except that now the limit is where I want it.
    At this point, being that the voltage is now set and limited to 24, engine throttle position would detiriimine output.

    There is one unknown to me and that is- the wacker may need to rev more than the alternator. In this case, I would fool the regulator again by placing a resistance on the field line as it goes to the alt. Not a big deal, the engine then would rev higher to make the desired output. Far as I know the wacker can rpm real high but I only want to rev as much as needed to get full power to the drive motor.

    Battery charging would be able to be done with a different regulator which takes alternator output and sends a set amp signal at 12v to the battery. But 12v would not charge the battery, it needs a couple more.

    Have been looking at the weedeater engine/ means of mounting and driving the alternator. Don't see any problem here. The engine weigns about 6#, the ford alternator 6, drive-motor 2or 3, jackshaft and chains/guards about 3. Mounts, a rack and small battery, maybe 10#, the bike was 34. A quiet muffler and a milk crate to cover the generation rack.
    Should be under 60 #.
  15. safe

    safe Active Member

    Light dimmers are Triacs:



    This results in a bidirectional electronic switch which can conduct current in either direction when it is triggered (turned on) and thus doesn't have any polarity. It can be triggered by either a positive or a negative voltage being applied to its gate electrode (with respect to A1, otherwise known as MT1). Once triggered, the device continues to conduct until the current through it drops below a certain threshold value, the holding current, such as at the end of a half-cycle of alternating current (AC) mains power. This makes the TRIAC a very convenient switch for AC circuits, allowing the control of very large power flows with milliampere-scale control currents. In addition, applying a trigger pulse at a controllable point in an AC cycle allows one to control the percentage of current that flows through the TRIAC to the load (phase control).

    So it does tend to suggest that you need AC current for a generic "dimmer" to work...
  16. safe

    safe Active Member