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Alternator on SM/TA

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SDE

06-21-2006 19:46:43

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The alternator hadn't been working when Ed bought the tractor.We used Bob Melvilles wiring diagram to confirm that everything the previous owner had, was correct. Just when we thought everything was right, we found that we could not turn it off with the key. I remember that someone had posted that this will sometime happen and I don't remember what they had suggested the solution to be. Can someone please get that information please? Thank you, SDE

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SDE

06-22-2006 03:28:49

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Re: Alternator on SM/TA in reply to SDE, 06-21-2006 19:46:43

Thank you both for the replies. I was short on time last night aand I wanted to get this info for ED today. SDE

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John T

06-21-2006 20:13:56

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Re: Alternator on SM/TA in reply to SDE, 06-21-2006 19:46:43

In cases where an alternator like the 3 wire GM 10 SI was fed its lil No 1 terminal excitation voltage from the coils high input (NOT to distributor) terminal or the ignition switches IGN output (same point electrically) even if the ignition is turned off its possible for the alternator to backfeed voltage to the coil and they can run on even after the ignition is turned off.

One way to prevent that is to wire a diode (one way current flow check valve) in series from the coil or ignition switch to the alternators lil No. 1 excitation terminal. Assuming its Negative ground for the alternator, the diode MUST BE WIRED with its + anode to the coil/switch and its - cathode to the alternator. Its bigger then required but I use a 5 amp 50 PIV diode cuz the bigger leads are easier to wire. The diode allows current flow INTO the alternator to excite it but not OUT OF the alternator to power the ignition coil.

I recommend a 10 ohm current limiting protection resistor in the excitation circuit whereby the diode may not even be required but if thats in place n she still runs on, then I add the diode.

John T

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old

06-21-2006 20:11:55

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Re: Alternator on SM/TA in reply to SDE, 06-21-2006 19:46:43

Oh forgot to say it you use a diode theres a white line on them and it goes to the alternator side when you wire it in

Hobby farm

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old

06-21-2006 20:10:45

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Re: Alternator on SM/TA in reply to SDE, 06-21-2006 19:46:43

Theres a number of ways to fix that problem. My self I use a diode in the wire from the #1 terminal on the alternator to the switch. Some people use a small light bulb. And some people just add another switch in the system. Any of them works but the diode is the cheapest by far and so far I have never had one go bad and if the light burns out you have no charge and if you forget to turn on the switch you have no chagre either. I use Radoi shack part # 276-1661 cost is about $3 for a pack of 4. I keep a couple packs around all the time but I also do a lot of 12 volt upgrades for other people.

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