Another alternator wiring question

Mathias NY · Oct 1, 2008

A few days ago (maybe weeks) there was a post on how to wire an alternator so that it won't drain the battery on the tractor. The easiest way to do this is to add a toggle switch. Would an appropriately sized diode prevent the battery drain, but still allow charging?

This would be much cleaner installation than a toggle switch and there is nothing to forget.

Janicholson · Oct 1, 2008

If it is a one wire style alternator it will not allow the exciter current to start it operating.
If it is a three wire delco, The #2 terminal connects to the big output terminal directly. The #1 terminal connects to the ignition switch terminal going to the coil. (assumes a distributor, not mag) In this wire place a diode with the flow of the diode going toward the alt, and the block direction going toward the switch (band on the end toward alt.) Should be a 3+ amp diode with 1000PIV rating. A alternator diode from the diode pack will also work. Be sure the coil is wired seperately and the diode is in only the wire to the #1 terminal. JimN

Bob · Oct 1, 2008

If you are working with a common 10SI or 12SI Delco 3-wire alternator, they need to have the "excite" current to their #1 terminal shut off when the machine is not running, or the battery will be drained.

If the machine has battery ignition or is a diesel with an electric fuel shutoff, the "excite" circuit can be set up so it's fed from the "ignition" switch, so it's "OFF" when the engine is "OFF".

If the engine has a mag, a DPDT switch can be wired so that it "kills" the spark and shuts off the "excite" circuit at the same time.

An alternative is to use a 2-pole N.O. oil pressure switch so the "excite" circuit is only powered while there is engine oil pressure (engine running).

John T · Oct 1, 2008

Mathis, Contrary to some opinions, use of a diode in typical Declo 10 SI Alternators IS NOT TO PREVENT BATTERY DISCHARGE its to prevent the tractor from still running even when an ignition switch is turned off (in typical wiring systems) .... Furthermore I prefer use of a 10 ohm current limiting resistor in lieu of a diode amyway, but thats another story.

The gents below have already described and Bob posts a picture as to how to excite the alternator in a way that DOES NOT discharge the battery (regardless if you use a diode or my resistor to prevent running with the switch off) and I think its easier then a toggle switch cuz you dont have to do ANYTHING no switching to be bothered with, although sure a switch (if properly wired) is okay if thats your choice

If you wanted to use an in line diode in the charging system (for some reason) it would have to be like a 50 amp or bigger but if the alternator is correct and wired correct it dont discharge the battery anyway

Best wishes

John T

JDemaris · Oct 1, 2008

Seems if someone doesn't want components to forget (like switches) - there is nothing simpler than installing a self-exciting regulator in the alternator and using the one-wire hookup.

I don't particularly like the one-wire setup - but it does make things easy. To be technical, most of the 10SIs and 12SI will self-excite but they have to be really revving to do so (over 3000 RPM). Not practical, especially on a tractor.

If you use a conventional externally excited 10Si or 12SI and an automotive type ignition switch, you don't need a resistor or a diode to prevent run-on with the key off. Just run the excite wire to the ACC terminal, and the igntion feed (or injection pump feed) to the IGN terminal. When the key is in "off" position, ACC and IGN are isolated from each other and run-on won't happen.

That being said, it's pretty easy just to add a diode or resistor that cost less then a buck.

Anonymous-0 · Oct 2, 2008

Years ago i used a push button, It was a diesel and had an amp meter..

MAY GOD BLESS THE USA

Another alternator wiring question

Mathias NY

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Janicholson

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Bob

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John T

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JDemaris

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Anonymous-0

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