Diode

JD2840 · Jun 2, 2010

what kind of diode do i need to put on the exiter wire of this altinator?

i dont have any unless this one will work
http://parts.digikey.com/1/parts/412079-rectifier-50v-1a-do-41-1n4001-t.html

what im doing is taking off the key and solinoid and puting the old push button back. im told i need to put a diode on the exiter wire but i need to know what kind. and to make sure i dont mess up which wire is the exiter wire?
thanks

tjiniowa · Jun 2, 2010

The white wire is the exciter, I just use a diode out of a delcotron alternator. Just needs to be hot for a second and it will charge. The two red wires should be always hot.

John T · Jun 2, 2010

The diode is used to prevent the alternator from backfeeding the ignition coil so when you turn the switch off the tractors STOPS running.

About any diode rated at say 3 amps (a bigger rated is okay if thats all you have like a 5 or 10 amp or more) and with a voltage withstand rating of say 50 volts or more (again a higher voltage rating like 100 or more volts is okay) will suffice. NOTE its polarity sensitive and MUST be wired correct, the cathode towards the alternator assuming Neg ground.

I have used a 10 ohm or so (or larger) resistor instead of a diode as it can still prevent the backfeed run-on problem PLUS provides at least some degree of safety current limiting.

It (excitation circuit with diode or resistor) wires between the ignition switches IGN output or the ignition coils input (same electrically) and the small No 1 alternator terminal. I wire the other No 2 small voltage sense terminal direct down to the alternators big main output stud

John T

JD2840 · Jun 2, 2010

will this resistor work?
http://cgi.ebay.com/5W-10-ohm-10-Wirewound-Power-Sandblock-Resistor-12-/380235075508?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item5887c6cfb4

JMOR · Jun 2, 2010

(quoted from post at 14:06:06 06/02/10) will this resistor work?
http://cgi.ebay.com/5W-10-ohm-10-Wirewound-Power-Sandblock-Resistor-12-/380235075508?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item5887c6cfb4

ight be a little overstressed, as GM used 6.25 Watt/10 ohm, but if you don't sit around with the key on/engine stalled a lot, it will be fine, as it is only active when alternator is not putting out & key ON. Probably not going to be a problem, but if by chance your engine tries to keep running when you turn the key off, you will need to step up to a higher resistance, such as two of those in series. The reason that this "might' happen, is that your tractor ignition draws so little current compared to the drains on a GM automobile.
Try it and see....if keeps running, throw in the second resistor. Be kind & let everyone know, for future folks.

JD2840 · Jun 2, 2010

ok ill try it. i intend to take the key off and but the old iginiton button back with the old starter button. will this still be alright or do i need to find a different resister?

old · Jun 2, 2010

I use Radio Shack part #276-1661 on all the tractor I put and alternator on. Cost is around $2.50 for a pack of 4

JD2840 · Jun 2, 2010

i think ill just go pick up some of those

JD2840 · Jun 2, 2010

(quoted from post at 19:50:43 06/02/10) I use Radio Shack part #276-1661 on all the tractor I put and alternator on. Cost is around $2.50 for a pack of 4

when i wire it the band goes towrds the altinator right?

John T · Jun 2, 2010

The resistor doesnt care about what kind of an ignition switch you have. It's to provide sufficient current to initially excite the alternator but then limit current and drop sufficient voltage so the alternator dont backfeed the ignition coil so she quits when you turn off the key.

Like I already said, I use a 10 ohm or larger resistor there instead of a diode as it serves a DUAL PURPOSE to prevent backfeed PLUS it drops some voltage and limits some current.

It dont hurt if you use a larger wattage resistor (like a 10 or even larger watt, 10 ohms and higher) and it may even be easier to wire as it may have bigger leads

The 10 ohms 5 watt you mentioned will probably work fine, if it gets too hot it will open in which case the alternator may not excite butttttt its such a cheap and easy fix, just replace it with a 10 watt or more but I doubt the 5 watt will go bad.

John T

JD2840 · Jun 2, 2010

ill look for a 1o watt at radio shack

John T · Jun 2, 2010

YES, if you use a diode instead of a resistor, its cathode banded end is to the alternator if its a neg ground alternator

John T

buickanddeere · Jun 2, 2010

Simpler to just wire in a dash idiot light.

JD2840 · Jun 2, 2010

true but im looking to show this tractor later on

sasedivy · Jun 2, 2010

JD2840

Some SI alternators are Self-Exciting, (I don't know if yours is or not) but this website has both parts & information that you may find interesting if not helpful.

For those of you interested there is also information on converting your alternator to a Positive Ground system.

Good luck!

Scott
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