3 amp diode will this protect alt???

replaced my alt (napa 2134508d) and it died after
hr of replacing it.

jim you say to use a 3 amp diode in excite wire

will this protect my alt???

coil and alt run off same side of the (on off) toggle switch. ... could the coil be spiking the alt???

by the way i bought a analog volt meter and i did
show that the alt was charging at the alt battery terminal...for a little while any way.

not

i am loading a picture so you can see the
hookup of the harness preveous owner used http://members.localnet.com/~woodslip/harness.jpg

red wire far right is the excite wire. that is the only wire used...yellow connector other end is where it connected to lead from switched side
of on off toggle. other wire was not hooked up at all.

looks like he used original wire going from alt bat term to starter solenoid.

funny didnt have problem till i changed the excite wire from alt bat term to the switched
side of toggle.

he put in a seperate toggle switch for the alt bat wire. told me to toggle it off or would drain bat....as it did.

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Give THIS a try...

You can use your choice of "MY" diode, "BobM's" "idiot light", or "JohnT's" resistor anywhere that's conenient in the wire feeding power from the ignition switch to the alternator's #1 "switched excite" terminal.

You only need ONE of those three options, and ALL work EQUALLY WELL.

If you want an "idiot light" in the dash, go that route. USe a #194 lamp, or one of equivalent current draw.

If you want to use a resistor, go that way, but be advised it will get HOT, if the key happens to get left on, so you need to mount it so that it can dissipate the heat without melting any wires.

That's why I almost always use the DIODE... it provides protection to the alternator if there's a problem in the high-current part of the charging system wiring, and prevents the engine from "running on" when the ignition is switched "OFF", but it doesn't get HOT, so it can simply be covered in heat shrink tubing, and taped up along with the other wires in the harness.

Questions?

The quickest way is probably to have a poor connection in the wiring somewhere between the alternator's output stud and the battery, causing wild voltage surges, and, if there's no diode, resistor, or "idiot lamp" in the "switched excite circuit", the alternator will attempt to charge the battery through the "excite" circuit, "killing" it's internal diode trio and/or voltage regulator. These diagrams show how that happens:

Also, if the alternator is poorly grounded, or the #2 "voltage sense" connection is not properly connected, possibly the alternator will "lose it's smoke".

I wish I could "autopsy" your failed alternators... that would give a good idea if it was just freak failures from a couple of "bad" alternators, or just WHAT is failing.

John T

Buttttt t Im not really that much of an alternator guy, Im more into DC generators so talk me through this if possible

Take care Jim

John T

The #2 terminal supplies battery + through a very low current (high resistance) voltage divider/zener diode biasing circuit to the base of a second transistor whose collector-emitter circuit shunts base-biasing 'on' current away from the first transistor, thus lowering field current when the battery voltage rises above an amount set by the zener diode and voltage divider.