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Oliver, Cletrac, Co-op & Cockshutt Tractors Discussion Forum
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gm alternator wiring question

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Jared Chaddock

06-16-2007 15:09:44




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I am an Oliver man all the way, but I am helping a friend wire an alternator on "another" brand...The tractor ( a Fordson, actually) has a retrofitted GM starter and alternator so the 85 year old owner can still enjoy it. Anyhow, because the tractor has magneto ignition, it doesnt have any sort of ignition switch or starter solenoid. My question is, what type of diode do I need to wire into the trigger wire of the alternator (a GM 10si) so I dont get voltage feedback? I can see on the MAD Electric website that they use an ordinary diode, but I cant see the color code to i.d. it...anyone have any ideas what to use? Thanks in advance

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Bob

06-16-2007 20:41:37




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 Re: gm alternator wiring question in reply to Jared Chaddock, 06-16-2007 15:09:44  
I am the originator of that photo, incidently.

Third Party Image

The 1N5408 diode is a GOOD choice, yet CHEAP. It is more "robust" than some of the other suggestions, making for an installation that will remain trouble-free "down the road".

Even WITH the diode, you will need a switch to apply power to the diode at, or after startup.

A "momentary-contact pushbutton switch" will work, but the SLICKEST way to do this an a machine with a MAG is to use a two-terminal N.O. oil pressure switch that switches "ON" at low PSI, typically in the 4-11 PSI range.

That way, the alternator will "excite" at startup, yet there is NO NEED to remember to turn anything "OFF" at shutdown, to avoid running the battery "dead".

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Jared Chaddock

06-17-2007 09:34:13




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 Re: gm alternator wiring question in reply to Bob, 06-16-2007 20:41:37  
Can I hook the battery side of the diode to the starter side of the starter button, so it will be hot when it is cranking? You see, on the fordson engine, it is spash oiling, with no actual "oil pressure" so the pressure switch wont work. Where can I purchase a 1N5408 diode? Is that the same as Radio shack part #276-1661 posted by "old"? Thanks again



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Bob

06-17-2007 11:53:53




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 Re: gm alternator wiring question in reply to Jared Chaddock, 06-17-2007 09:34:13  
You can TRY connecting it so it's hot when cranking. This MAY or MAY NOT work. If it doesn't, simply install a separate pushbutton switch, and press it after each engine start to "excite" the alternator.

The 1N5408 diode is available at industrial electronic suppliers. The RS diode will work, probably just fine, if you don't have a ready source for the more robust one. I repair alternators, and have NEVER had a problem with the 1N5408's, but have occasionally seen a lesser-rated diode fail, so I buy the 1N5408's in bulk, for less than $1.00, and keep a supply on hand.

If you can't readily find the more robust diode, try the RS one. You're not out much $ IF it ever does fail.

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Bob

06-17-2007 11:53:52




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 Re: gm alternator wiring question in reply to Jared Chaddock, 06-17-2007 09:34:13  
You can TRY connecting it so it's hot when cranking. This MAY or MAY NOT work. If it doesn't, simply install a separate pushbutton switch, and press it after each engine start to "excite" the alternator.

The 1N5408 diode is available at industrial electronic suppliers. The RS diode will work, probably just fine, if you don't have a ready source for the more robust one. I repair alternators, and have NEVER had a problem with the 1N5408's, but have occasionally seen a lesser-rated diode fail, so I buy the 1N5408's in bulk, for less than $1.00, and keep a supply on hand.

If you can't readily find the more robust diode, try the RS one. You're not out much $ IF it ever does fail.

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old

06-16-2007 19:06:43




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 Re: gm alternator wiring question in reply to Jared Chaddock, 06-16-2007 15:09:44  
Diode that is in Hals picture can also be a Radoi shack part #276-1661



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El Toro

06-16-2007 16:51:21




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 Re: gm alternator wiring question in reply to Jared Chaddock, 06-16-2007 15:09:44  
third party image

Here's one in this picture. Hal



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Kruse

06-16-2007 16:34:02




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 Re: gm alternator wiring question in reply to Jared Chaddock, 06-16-2007 15:09:44  
Go to your neighborhood Case/IH dealer and get a diode/rectifier with the part number 548239R2.
It"s a heavy duty diode that is shrink wrapped and has a male electrical spade on one side and a female spade on the other. It makes your wiring real simple.



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Goose

06-16-2007 19:52:18




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 Re: gm alternator wiring question in reply to Kruse, 06-16-2007 16:34:02  
NAPA also makes a wiring kit for ten bucks that plugs into the two pin socket in the GM alternator. One lead goes back to the hot post on the alternator and the other with a diode goes to anything than has 12 volts when the switch is on. A hot wire from the battery also goes to the main post on the alternator.

I just installed one on a D19 Allis diesel. The D19 has a hydraulic pressure warning light. One side of the light is hot whenever the switch is on, and the hydraulic pressure sensor makes or interrupts the ground to turn the light on or off. I just hooked the lead from the diode to the hot side of the hydraulic pressure warning light because it was easy to access. Works like a charm.

Goose

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