91 alternator problems

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grawrant

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So I installed a larger alternator because I was going through batteries running my hydraulic pump for my plow.

The alternator had some wires melt inside, not sure what happened but I want to assume it was just a bad alternator.

Second alternator installed, not charging the battery. I went ahead and wired in a digital voltmeter, and a new plug for the exciter wire. I ran the new excite line on a switch, pulling power from the battery. I used a 330ohm 1/4watt resistor. I guess the resistor wasn't enough, pretty sure I fried the voltage regulator inside the new alternator because now it doesn't stop charging. I turned the truck off at 19.2 volts, took about 30seconds
New alternator is hotter than the exhaust manifold.

3rd alternator is on order. What size resistor should I be using? Is 1/4watt to small, I should go with like a 2waty 470ohm?

Any advice is appreciated. I already have the voltmeter and new exciter wire/plug ready to go. Just need to put on a better resistor so I don't fry another regulator.
 

grawrant

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I should know that the alternator now charges without the Exciter plugged in at all, so I know that the regulator inside the alternator is bad. I've disconnected the battery for an hour, came back and it still overcharges the battery.
 

kennythewelder

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I can't answer you question, but have you upgraded to a big 3 kit yet? Recharging the battery with a much larger wire, is a good idea when you are pulling a big load on the battery. The OE wiring is puny, to say the least.
 

Orpedcrow

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Why are you using a resistor and an external exciter wire? Is this an auxiliary alternator?
 

grawrant

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I can't answer you question, but have you upgraded to a big 3 kit yet? Recharging the battery with a much larger wire, is a good idea when you are pulling a big load on the battery. The OE wiring is puny, to say the least.
I upgraded all grounds, the entire harness for custom headlight and taillight housings/lights, and all new power leads. Much thicker wire for everything. Also running a big battery off a semi with a larger alternator.
 

grawrant

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Why are you using a resistor and an external exciter wire? Is this an auxiliary alternator?
the alternator wasn't exciting. Rather than trace the excite wire, rip the dash apart, and replace the battery light bulb... I chose to run a new plug and wire to excite the alternator. I put it on a switch to make life easy, and just need to run the correct resistor so I don't fry the alternators internal voltage regulator.
 
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