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51 8N ELECTRICAL ISSUE

A

Anonymous-0

Well-known Member
I HAVE A 51 8N THAT WAS CONVERTED TO 12V BEFORE I BOUGHT IT. I REWIRED IT USING A SCHEMATIC I FOUND ON LINE. IT STARTS RIGHT UP EVERY TIME, BUT IT WON'T SHUT OFF WITH THE KEY SWITCH, I HAVE TO PULL THE COIL WIRE. I DO HAVE A DIODE, (FACING THE RIGHT WAY) WIRED INTO THE ALTERNATOR ACCORDING TO THE SCHEMATIC I USED, ANYONE HAVE ANY IDEAS WHAT'S WRONG?? THANKS IN ADVANCE FOR THE TIME.
 
start it up,shut off key and ,pull wire on alternator with diode let us know if it dies.was it working before the rewire?
 
YES, IT WOULD SHUT OFF WITH THE KEY PRIOR TO THE RE-WIRE. I'LL TRY YOUR TIP AS SOON AS I GET HOME TONIGHT. MORE TO COME. THANKS.
 
If installed correctly, it"s likely the diode is shorted.

One of the fellows on the "N" Board suggests a 1 Amp, 50 PIV diode, and I"ve been chided for my recommendation of a 3 Amp, 1000 PIV diode as "overkill".

HOWEVER they only cost me about $.05 in bulk and I have YET to have one fail.

(The diode "sees" voltage spikes from BOTH the alternator and ignition systems and the greater the PIV the better, and 1 Amp is pretty meager for doing it"s job of "exciting" the alternator at startup.)
 
well.. if you rate the diode at 50% of its rated max capacity.. a 1 amp diode would run all day with a 500ma lamp..

so thats great as long as you never have any surges, and keep the tractor in a 70 degree air conditioned enviroment, never run it in high humidity.

a 3 amp is much more sane,, and 5 amp, would not be an overkill at 50 cents a piece.
 
I get them from an electronics wholesaler. Don't know what the shack has nowadays. You'll have to ask and find out. ANYTHING is better that the 1 Amp 50 PIV units. Do you have a part number/know what you have now?
 
I FORGOT TO MENTION, IT WILL SHUT OFF BY THE KEY AS LONG AS THE ALTERNATOR IS NOT EXCITED, ONCE I THROTTLE UP FOR THE ALTERNATOR TO EXCITE ITSELF, THATS WHEN I HAVE TO PULL THE COIL WIRE TO KILL IT.
 
On my alternator / generator test stand, those SI series Delco alternators draw about 3-4 amps in the #1 excite circuit, so Bob's 3 amp diode is not overkill.
 
yep..diode bad.some folks dont use a diode but a light,i use both a diode and a light.but i mow a lot at night and since guages arent lighted the light comes in handy.
 
Yes Sir, I use both as well. I didn't at first. I added a sealed red marker light on the under side edge of the hood, just inline with the oil filter. It dosen't come on until the alternator gets excited, but once it does, I know I'll be pulling the coil wire. I'll be getting a new 3 to 5 amp diode today to wire in, I'll let you guys know what happens.
 
Update: I installed a 6 AMP, 1000 PIV diode and it seems to be working fine. It starts right up and begins to charge (on the amp gauge) right soon after, and then it shuts down with the key as advertised. I couldn't find a 3 or 5 AMP diode in the PIV range you guys wrote about, so I went with the 6/1000 option. I hope this will be fine down the road as my 8N is semi retired. I take the kids on rides and it goes to local shows and cruise nights. I'll be posting a pic on this sight this weekend. Thanks for all the tech info. God Bless America and God Blessed Texas!!
 
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