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Old 04-29-2011, 03:25 PM   #1
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Pulsating Alternator Gauge

During our last trip with the grandkids the fuse for the gauges blew in our Chevy powered Southwind . Luckily we made home without any problems. After I replaced the blown fuse and started the RV all the gauges worked fine for about 20-30 seconds and then teh fuse blew again. The only thing I had done before the trip was replace the battery isolator relay. So I unhokked the isolator relay and the fuse did not blow. I then charged the house batteries over night and then hooked up the relay again. The fuse did not blow but I did notice that the alternator gauge was pulsating from about 12 volts up to about 16 volts. After I shut off the RV I checked the connection at the solonoid coming from the isoloator relay and the wiring was real hot. Not sure is the solonoid is faulty or what else it could be.

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Old 04-30-2011, 03:32 AM   #2
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My alternator was doing that for some time - a GM type alternator, a 21si 160amp. It would waver between 13 to 18 fairly rapidly but consistent enough almost to act like a metronome regardless of engine rpm. Then one day it decided to peg the voltmeter all the way beyond the gauges 18v reading. A quick check with my handheld voltmeter confirmed 21volts at idle. I pulled the alternator and took it to a shop and they confirmed the voltage regulator inside had failed. Replaced the whole alternator since it was 15yrs old and voila, 14volts steady, no more oscillating voltage.

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Old 05-03-2011, 04:18 PM   #3
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I thought about the alternator but it seems to only acts up when the relay to charge the house batteries kicks in?
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Old 05-03-2011, 04:54 PM   #4
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Is the relay you installed to replace the bad one the same part number? Some relays are constant duty, some are intermittent duty. You said the wire was hot so something is drawing too much current. Could be the relay, a short in the wires, or a bad house battery.
You could have the house batteries tested to eleminate these as a problem.

You can get an in-line type amp gauge and install it in different positions in the wiring to check the draw.
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Old 05-04-2011, 08:14 AM   #5
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Humm. They put the relay on the guages line.

Sounds like the wrong isolator relay to me. or wired wrong... Or you got a bad one,, Which of these 3 I'm not sure.

The problem is the isolator relay looks a lot like a starter solenoid, in fact physically they are often identical.. Electrically they are NOT, a starter solenoid will overheat and burn out if left on too long, exactly the symptoms you have. (It is the coil that burns out, not the contacts) Oh, it can haul the current, no problem there. But the coil is not designed to be engaged for more than about 1 mniute or less.
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