12v conversion wiring help!

I recently converted my 300u to a 12 volt system. It seems to be wired correctly, it starts, everything works, but to date i have fried two alternators! everything is fine for about 4 to 5 starts/runs- charging kicks in about 1500rpms. Then i start up the tractor, and suddenly it won't charge the battery(warning light stays on, no matter what the rpms).

electrical system components:
original 6v delco starter with new 12v solenoid
delco 4 pole ignition switch(came on the tractor when i got it) with poles for ACC, BAT, SOL, and IGN
delco 12v coil
delco 3 wire alternator
new repro IH ammeter

wiring:
(8ga)BAT post on alternator to (L) post on ammeter
(8ga)wire from B post on ammeter to large post on solenoid
(4ga)wire from same large post on solenoid to +battery terminal
(1ga) wire grom -battery terminal to body
(12ga)terminal 1 on alternator to ACC on ignition switch thru warning light- tho wires into and out of the warning light are 16ga
(12ga)terminal 2 on alternator to BAT on alternator
(14ga) SOL on ignition switch to small post on solenoid
(12ga) BAT on ignition switch to (L) post on ammeter
(12ga) IGN to + post on coil
(12ga)light switch to (L) post on ammeter
(12ga)cigar lighter to power out(always hot) on light switch

One thing i noticed when the alternator charges- the ammeter needle sits all the way at the top of the gauge at first, then drops down to about 2/3 up the gauge.

anyone have any insight into what the prob cold be? thanks alot.

from what i read you have it wired correct,only thing i can think of to try, next time it fails take a test light an check #1 terminal at alt. for voltage,it may not be your alt. rather the ind. light or ign. switch may not be making connection. as for amp guage sounds like you have a 30 amp guage and a 60 amp alt. i have 2 like that, all i do is not rev the engine to fast for a couple seconds until reg. starts to cut back works o.k.

Read this. It worked very well for my IH 240 Utility. Four years and no problems. David.....................

http://www.ytmag.com/articles/artint131.htm

Your wiring sounds right.

Do you know what failed in the 2 alternators that quit? (Diode bridge, regulator, stator winding?) Does the alternator case get hot after running a few minutes?

i don't know what failed in either one. they are both used, first one was tested at parts store to confirm bad, traded in at the junkyard for an identical alt. put that one on, which worked for a day, fired up the tractor a coupla days later and it wouldnt charge. havent actually tested the second one yet. symptoms same as first on tho. how do you tell what part of the alternator failed?

just wondering, when you say it won't charge did you put a voltmeter across the batt terminals, while running, and when you did do you measure a minimum of 13.5 v because if you do the your alt is charging and something else is making the light come on...

Seems like that is a high rpm for an alt to be kicking in.
Make sure all connections are "Bright and Tight"
Dell

I suppose you can have TWO "good" junkyard alternators both suddenly fail though it seems kinda unlikely. For the price for a fresh rebuilt alternator ($40 or so) you might be ahead to get one instead of another junkyard unit.

However a healthy alternator will be ruined if the charge circuit (alternator BAT to ammeter to battery positive) goes open while it's charging - if even for an instant. Also if the sensing circuit (wiring to the #2 terminal) goes open while running. So I'd suggest double checking all wiring for good tight connections - including the battery cable terminals

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As for determining exactly what's failed on a dead alternator here's a couple things to check:

1 - With the engine running at 1/2 throttle bypass the regulator by grounding shorting tab inside the back of the alternator. If it now charges hard the regulator has failed.

2 - If you have a VOM or DMM set the meter on the lowest ohms range. Now disconnect all wiring from the alternator and take a resistance reading between the BAT terminal and the case. Note the reading then reverse the meter probes and measure again.

A "good" reading is infinite resistance with the probes one way and very low resistance with the probes reversed.

Infinite ohms in both directions means an open circuit in either the stator or diode bridge. Low ohms in both directions is a shorted bridge. Only fix for either is to replace with new.

thanks for the good info bob.
i had thought that the first alternator fried due to a bolt on the clutch assembly grounding out on the starter/solenoid strap when the clutch was pushed in during start. i fixed that problem before i installed the new alt. the plug that fits on the 1 and 2 terminals on the alt fits quite loosely, is old and seems pretty worn out. possible engine vibration causes open circuit there? also, there does not appear to be a tab visible on the back of the alt to short out the regulator. is it under the back of the case? do you think a faulty ammeter can cause an open circuit? also, what do you think about installing an inline fusible link/circuit breaker? the guy at the shop where i had the first alt tested said it would be a waste of time to do that.

mike,
i did not test it with a voltmeter, but since the first alt was tested and confirmed bad, and the same symptoms happened with the second alt, i am assuming the alternator fried again. i will voltmeter the battery to confirm tho.

I always run a #14 wire back to the battery for the #2 terminal, so it senses battery voltage as opposed to reading alternator voltage at the Bat. terminal of the alternator. Also if your plug for the 2 terminals on the alternator is questionable, crimp/solder on a couple of 1/4 inch spade lug ends on the individual wires--much more solid connections.
I always use a 10 ohm 25 watt resistor in the line to the "turn-on" terminal from the switch. Delco specified 11 ohms originally [resistance wire].

thanks brownie,
regarding the resistor in the turn-on wire, do you mean the acc wire going to terminal 1 on alternator? if so, do you use the resistor in addition to the warning light, or instead of? i was told that you could use a resistor OR a warning light to prevent backflow when you shut off the rig.

the plug that fits on the 1 and 2 terminals on the alt fits quite loosely, is old and seems pretty worn out. possible engine vibration causes open circuit there?

Click to expand...

A momentary open circuit in a loose-fitting plug could definitely cause problems! I'd get a new plug in there before you do anything else.

also, there does not appear to be a tab visible on the back of the alt to short out the regulator. is it under the back of the case?

Click to expand...

Punch here for a photo of the regulator test tab: http://i101.photobucket.com/albums/...ges 2/IMG_635612SIalternatorbackside-crop.jpg

do you think a faulty ammeter can cause an open circuit?

Click to expand...

Very unlikely. The current path inside the ammeter is a solid copper strap. Unless the terminals somehow are loose it's almost impossible for even a faulty ammeter to go open circuit.

what do you think about installing an inline fusible link/circuit breaker?

Click to expand...

I agree with the guy at the shop. A fusible link won't really protect anything. And should the link itself fail it could fry ANOTHER alternator on you. Better to wire it up solid.

Yes, I put the resistor inline to the #1 terminal from the ignition switch. I only use the resistor by itself. Lots of guys use the light or diode & get by.
Your alternator problems could be caused by the brushes being worn or maybe the diode trio being bad. Our 1460 alternator had 2 of the 3 feed strips melted when we were getting it ready for the field last fall---no obvious reasons for it to happen.
You can take the alternator apart & see what is going on inside. Test the diode trio using an analog meter on Rx1 scale. Should read ~ 30 to 40 ohms in one direction & infinity with the leads reversed checked at all 3 terminals to the single lead going to the regulator. This is done with the diode trio removed.
If brushes/ brush holder is bad, it will be evident. Hope this helps--these alternators are pretty reliable as a general rule--you just have a small problem somewhere.