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Tractor Talk Discussion Forum

does an alternator turn just one way?

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GaryS TX

12-23-2004 08:56:18




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Does an alternator just charge by turning one way? Must you buy a "clockwise" alternator?




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martin(a curious boy)

07-28-2005 09:44:27




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 Re: does an alternator turn just one way? in reply to GaryS TX, 12-23-2004 08:56:18  
i have an old volvo alternator. the fan blades are angled but the wrong way for what i need it for. does it matter what way it spins



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rustyj14

12-30-2004 11:34:27




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 Re: does an alternator turn just one way? in reply to GaryS TX, 12-23-2004 08:56:18  
Seems to me, if ya turn the alternator backwards, it will take the "juice" out of the battery, won't it? RJ



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Mark - IN.

12-24-2004 22:14:53




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 Re: does an alternator turn just one way? in reply to GaryS TX, 12-23-2004 08:56:18  
Don't make this harder than you have to. Just turn the wheel on your tractor and drive in the opposite direction, that's what it's there for. Merry Christmas.

Mark.



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Pappy

12-23-2004 18:18:25




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 Re: does an alternator turn just one way? in reply to GaryS TX, 12-23-2004 08:56:18  
What are some of the applications that would require an alternator to run CCW. I was trying to think of some, but came up blank----- ---



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Paul Janke

12-24-2004 06:44:06




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 Re: does an alternator turn just one way? in reply to Pappy, 12-23-2004 18:18:25  
I once was working on a military 6x6 on which the generator had quit. We were using it as a logging truck with a self-loader on it. I took the guts out of the generator and mounted a belt drive governor and an alternator on it. The alternator ended up mounted on top of the generator facing the rear. It worked fine.



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buickanddeere

12-23-2004 19:39:58




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 Re: does an alternator turn just one way? in reply to Pappy, 12-23-2004 18:18:25  
Aircraft, boats and crowded engine compartments.



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buickanddeere

12-23-2004 16:25:27




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 Re: does an alternator turn just one way? in reply to GaryS TX, 12-23-2004 08:56:18  
A generator will change polarity if spun "backwards". Polarity not an issue with an alternator as previously stated.



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Gerald J.

12-24-2004 03:53:33




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 Re: Actually in reply to buickanddeere, 12-23-2004 16:25:27  
Actually a self excited generator run backwards won't do anything. Because the residual would make the output voltage opposite of the last field excititation the rising reversed polarity output will cancel the residual and there won't be significant output until its polarized. Then it should build properly until the direction is reversed again to the way it was originally.

There is a detail however, the brush position isn't the same for either direction of rotation because of "armature reaction" where the field of the armature current distorts the field of the simple generator. So to cut back on brush sparking the brushes should also be moved.

And then there is the directional fan on the generator that works better in the design direction than reversed.

Gerald J.

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buickanddeere

12-24-2004 13:34:57




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 Re: Actually in reply to Gerald J., 12-24-2004 03:53:33  
You are right. I keep thinking of MG sets with separatley excited shunt fields instead of the self excited units in older equipment. And PM excited generators used in some of the control feedback loops to indicate rpm.



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Jon H

12-23-2004 13:13:29




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 Re: does an alternator turn just one way? in reply to GaryS TX, 12-23-2004 08:56:18  
An alternator does not care which way it spins,but as others have stated,the fan sometimes does. Some have the fan blades angled for one rotation or the other. Some have straight blades so they work equally well either way. An alternator shop should be able to get whatever rotation fan you need for cheap. On the old 60's chevy/Delco alternator you would use a corvair fan if you wanted to reverse rotate it.
If the electrical load is not very high,the fan may not make any difference. On one tractor I repowered,I have run a Delco alternator turning CCW with a CW fan on it without problems for over 20 years. The backwards fan apparently is doing a good enough job to keep the alternator from overheating at the present load level.

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old

12-23-2004 09:19:05




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 Re: does an alternator turn just one way? in reply to GaryS TX, 12-23-2004 08:56:18  
They don't care which way they go but the fan on them if it has one does



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greenbeanman

12-23-2004 09:11:13




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 Re: does an alternator turn just one way? in reply to GaryS TX, 12-23-2004 08:56:18  
Just remember that there are cooling fans and in order to do their job properly must turn a certain direction.



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Don L Cress

12-23-2004 09:05:57




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 Re: does an alternator turn just one way? in reply to GaryS TX, 12-23-2004 08:56:18  
Alternators will charge both ways..... .....



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Bob

12-24-2004 01:20:06




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 Re: does an alternator turn just one way? in reply to Don L Cress, 12-23-2004 09:05:57  
....Until the pulley and nut unscrew....

Alternators with the pulley keyed to the shaft are a better choice if the alternator needs to be driven backwards.

At least, LocTite the pulley and nut, if driving it "backwards".



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