I have alternator off of a Ford Excursion that I need to use in a specific application. Its just the normal OEM 95 amp stock alternator with a built in IC regulator. I need to know if the alternator will function correctly if spun the opposite way it normally spins. Please don’t ask why I need to do this because I don’t want to explain it.

 

Yes. The spinning makes three-phase alternating current that will be the same no matter which way it's spinning. The diode pack (six diodes) turn it into direct current. The polarity will be correct as well.

Pop

 

An alternator doesn't care which way it turns to charge. The only difference is the airflow on the fins. We use GM alternators from junk yards (cheap and available) on farm tractors and such all the time and they work fine regardless of which way they turn.

 

Don't count on it to put out rated amps tho. The heat sinks will only stand that for a few seconds. It may put out 30-40 amps continuous tho.

 

I thought the contacts were placed at an angle that wouldnt let it work right if it went backwards,,,,,,,,,,,,,just guessing

 

Is this a reference to the cooling fins?

 

No, the heat sinks themselves will not stand the power dissipation no matter which way they are spinning. This is one of the reasons they caution not to charge a dead battery with the new small frame alternators.

 

An alternator will charge spinning backward. The brushes will sometimes squeak and wear at an odd angle, especially if the alternator has been used in the correct direction previously. The output is less because the output is inverse to the internal temperature. Since the fans are centrifugal, they work, but less efficiently in the backward direction. I have enough challenge keeping alternators working in the normal direction. High under hood temps cause big alternator problems and don't forget radiant heat from exhaust mainifolds, or anything hotter than 200F. I want to use alternators to recoup some of the energy lost in braking and I was wondering how to use an alternator on each wheel without turning it backwards. Sort of a poor man's hybrid. jbbmw

 

You are thinking the same thing I have, a way to recapture the energy lost when breaking and convert it into electrical energy or with the use of an air compressor convert it into air pressure for pneumatic energy.

 

It’s a nice idea, but I doubt you could recapture much power with an alternator designed to take only a couple of HP to turn. You’d have to go to a much higher voltage to pull more power. I'm thinking best case: 12v * 50a * 4 wheels = 2400w. At 745w per hp you generated 2400/745= 3.22 hp By the time your done with the setup, it may be hardly enough to pull the extra weight you added. You need something that generates enough power to act as a brake. Then you need to worry about over braking and traction, not easy.

 

I was trying to stay with 12V components, but it looks like 120v would be the next most common voltage. The car I play with can get 50 MPG of diesel at 60 miles per hour. I wonder what my average horsepower usage is over an hour. I am quessing it would take at least a 5 hp electric motor to make a difference on takeoffs and hills and city. Maybe an Army surplus motor/generator combo. jbbmw

 

Any alternator will produce rated amps at speed (the diode pack will sort it out), but the problem is that the cooling fan blades will turn opposite what they are intended to - so they will be less effective.

It will probably burn out unless you change the pulley and fan.

Those fan blades are angled to draw as much airflow through the alternator as possible. Turning backwards they will be fighting against the normal flow.

 

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I suppose you could run a ram air duct from behind the grill, and use it to propel the alternator fan on a non-pulley mounted alternator. But that's kind of a reach...