using a motor as a generator

If you want efficient, go with permanent magnet generation. You can get brushless dc motors sometimes from the surplus vendors, and it would cost (much) less than the alternator. It will mean keeping your eyes open and having patience until something shows up. Maybe a treadmill motor or something. A good web site for discussing these things is

Also, if you're worried about an i.c. engine burning up, just use a governor or a throttle stop.

Im not worried about efficiency for power in vs power out its more for dealing with heat, same thing but what i meant was would the alternator run cooler than your "average" permanent magnet generator. I didnt realize that treadmill motors were dc what voltage, i might pick some up just to play with. A problem though is this thing is supposed to be towed behind a bicycle so i think that might be too heavy. if its in the 10-15 pound range and not too big it might be perfect. Ive been looking around surplus places and my main problem is there are no specs sometimes they just show a picture and say "12vdc motor 3000 rpm 1.4 amps" should say "good luck" right after it too. I wasnt really worried about burning up the engine, I was saying that i dont think the

540 mabuchi motors would make a good generator because of heat handling, mine has .2 ohms of armature resistance so at 25 amps im looking at 125 watts of heat. I cant imagine a small motor like that dissipating this kind of heat. I plan on having the unit controlled with a pic microcontroller, with temperature sensors amperage shunt voltmeters etc , basically going as far as the resources in the pic will let me with 33 i/o lines and 8 k program i should be able to get good control. Anybody know of proven pmdc motors that take about 30-40 amps continuous ( that dont cost a million dollars nor weigh a million pounds). continuous power ratings also seem really really hard to come by for the average non industrial motor. I know it seems like im being difficult here but i cant find a good motor, i could just use the small car alternator but maybe there is a good motor out there that i dont know about.

I mooched around and found this with a brief Google search:

pm motors that are only a few inches in diameter and have 2.5 to 3 horses for $150. Doesn't say how much they weigh. Would be cheaper if you wait until they show up at some surplus house. I've never tinkered with this stuff, but I think you get ac from a brushless dc motor converted to generate electricity. Maybe you could use the diode pack from a car alternator to rectify it.

thanks for helping me out i really appreciate it they appear to have brush mounts so i wont need to rectify it, they appear to be hefty in size but are a lot cheaper than my drive motor, so i might just go for it, i dont have pedals anymore on this bike ( i know its a sin ) so the drive motor and brakes will just have to suck it up not me :-) im just hoping to find one on surplus the alternator sticks in the back of my head but regulating the voltage to do a charge cycle might end up being a task with the permanent magnet you up the throttle and the current goes up in proportion with the emf the voltage is self limiting by the coil resistance simple, the alternator will be a balancing act another thing i was thinking is if i dont use a clutch with the pmdc motor i can use it to start the motor no cords to yank! i appreciate your searching the site down your the only one who helped me

You're planning to put a 2KW motor on a bicycle? you're nuts! 500W will be heaps in a hybrid setup, (also about the right size for a 35A automobile altenator).

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Bye.
   Jasen

I hear this a lot from my dad "your nuts". Actually the motor that drives the bike is more than 2 kw.http://www.npcrobotics.com/products/viewprod.asp?prod=33&cat=20&mode=gfx thats 1 hp continuous 3.8 hp peak. Hill climbing and high speed cruising :-), im waiting for it in the post. 3.8 hp*750=2.85 kw

Go to ebay and type "treadmill motor" in the search window. most of them are less than $50

I checked out the treadmill motors, theyre 130 vdc and low amperage, pretty much the opposite of what i was looking for i saw an electric scooter motor in th 30 buck range claimed 500 watts

24 volts seems perfect anybody here think its actually 500 watts continuous(wow bad spelling) if so its just about perfect

You would be better off, energy-wise, to use the engine to drive the bike directly instead of using it to charge batteries to run the electric motor that then drives the bike. That would eliminate the weight and friction of the cart that tows the engine, which will knock the hell out of energy efficiency. That is a problem Toyota doesn't have - the vehicle has to be 4 wheels and large enough to contain the engine to begin with, so they are not adding a second vehicle just for the engine.

Ed

I realize this but I prefer the drive feeling of an electric motor over a gas engine, and this allows me to just have a gas engine on longer trips that the batteries cant accomplish.