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  #1  
Old 04-19-2002, 10:53 PM
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Default A Dumb Alternator Question...

This is probably a dumb question...but the same mind that brought you the "Corded Cordless Drill" has a new idea....

SO! Are alternators omnidirectional? Can they go "both ways?" hehehe

I think they can go either way...but I wanna make sure before i spend time on this...

thanks,
-remy
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Old 04-19-2002, 11:17 PM
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Default Re: A Dumb Alternator Question...

Yes. Just makes an AC wave 180 degrees out of phase of the other direction. Since it is single phase and the diodes change it to DC, guess what? It won't matter. This extra knowledge is provided because I feel that lately I have not been providing a good service by just answering the questions that are being asked. Quality control must be in effect on the board!!
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Old 04-19-2002, 11:18 PM
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Default Re: A Dumb Alternator Question...

Sorry they are not omnidirectional, they are bidirectional-didn't read your question good enough. Now those QC guys got another hit against me!
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Old 04-20-2002, 12:40 AM
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Default Re: A Dumb Alternator Question...

I've seen the guys gut a battery and solder a 12 volt lead to it, and connect it to their battery.
It seems to work OK, but most cordless batteries are under the rated voltage for the drill...
IE: you would be better off with a 14 or 16 volt drill on a 12 volt vehicle battery...
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Old 04-20-2002, 02:57 AM
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Default Re: A Dumb Alternator Question...

Thanks Aaron...but I did that two weeks ago...

My stupid question of the week is about the alternator. Does it matter which way I turn the pulley, or does it have to turn a certain way? I dont think it matters, but I wanna make sure before i strat thinking about this too much! (smile)

-remy
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Old 04-20-2002, 08:11 AM
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Default Re: A Dumb Alternator Question...

Electrically, it just doesn't matter. The only hitch would be if the slip rings that carry field current to the armature were designed to go one way only, but I can't even think how they could do that. Spin it by hand both directions. If it spins with the same drag both ways, you're in business.
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Old 04-20-2002, 11:33 AM
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Default Re: A Dumb Alternator Question...


For DC applications, you have to watch for fan rotation or the unit will not cool properly.
Straight blades will work either direction but are less efficient than angled blade fans.
Angle blade fans are either clockwise or counter clockwise (unidirectional), and should spin so the blades draw air Out of the case, not trying to force air into the case...

Alternators are directional (technically).
Having said that, it doesn't matter what direction you turn them to the mechanicals of the alternator except for the cooling fan.
Common automotive alternators produce synchronized (120 Degree intervals) 3 Phase AC Current.
If you turn an alternator 'Backwards', the three AC Phases are reversed.
So if you plan to do 3 phase AC, beware...

This doesn't matter a damn to the DC output.
The rectifiers don't care how the AC current arrives, it converts anything and everything that arrives into DC current.

If you are planning on using the AC taps to power something, take care...
If you are planning on using the DC taps to power something, No difference what so ever...
There are both clockwise and counter clockwise fans for the common Delco SI series alternators, and if you find a fan with straight blades, it works both directions...
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Old 04-20-2002, 10:20 PM
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Default Re: A Dumb Alternator Question...

Car alternators are three phase? Really? Not arguing, just never would have thunk that. That means there are six diodes in there to go bad. I only thought there were two. I stand corrected, didn't realize they would go through the extra effort for a car. Again the master who has torn everything apart that is humanly possible-TR
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Old 04-21-2002, 03:52 AM
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Default Re: A Dumb Alternator Question...

Aaron,

I was going to use it for DC, but now you said the magic words "AC" and got me thinking...no good can come of this.

I knew that alternators put out AC then converted it to DC, hence "alternator", but I never thought about HOW MUCH AC power you can extract. And how do i extract it...

Electricity is one of those things I've always wanted to learn about...but have yet to find a local Socrates of Current. Maybe you can throw some pointers my way? How much (and How do I) AC can I get, from say, a typical GM CS alternator..say...~85amp?

thanks,
-remy
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Old 04-21-2002, 07:35 AM
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Default Re: A Dumb Alternator Question...

As Sundance said, "You keep thinkin' Butch; it's what you do best."

Alternators have three windings, so the AC they put out is three-phase, which would be nice for running a three-phase motor. Not so nice for anything else. For single phase, like house current, you would tap one winding, and get 1/3 of the total output potential.

Second, it's regulated to around 15-16 Volts so that after it's rectified to DC you've got about 14 Volts. The regulator could be disabled, but I doubt the internal insulation could tolerate 120 Volts very long, even if it will produce that much Voltage.

The frequency is proportional to alternator speed. When the alternator is spinning 3600 rpm you will get 60 cycles per second on each leg, so you would need to control engine speed carefully for anything that was AC frequency sensitive.

As for how much you can get out of it, alternators are rated in Amps. A 60 Amp alternator will put out 60 Amps DC, a little more AC because there's not the (minimal) loss in the diodes, but that's on all three phases combined; you'd get 20 Amps on each leg. But that's at 16 Volts. As voltage increases the maximum current will drop dramaticly. I'm sure somebody on the board has experimented taking AC out and knows what they can do.

For about $30 at Sam's Club you can get an electronic inverter that will connect to a 12V battery and put out 400 watts of 120V 60 cycle. That's enough to run a small TV and VCR, or a 3/8" drill if you don't push it too hard. It's the size of 3 or 4 paperback novels stacked together.

Inverters are available in sizes up to huge, but they get pretty pricey. That one at Sam's is relatively cheap because Sam's ordered huge quantities of them.
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