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Old 05-02-2010, 18:16   #1
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Too Much Voltage from Alternator

Hi all,
I've tried to search for this problem, as I'm sure I'm not the first, but its a tricky one to find, so perhaps someone has seen it before.
My alternator died, so I had it 'fixed'. Some mumblings about the stator having failed. It seemed to operate OK for a few weeks, and then it died again. I sent it back and the voltage regulator was replaced. This time I plugged it back in and the voltage began to rise after a short time, heading beyond 16v when I stopped it and removed it. Back again. New regulator again (I didn't pay..) started off well, 13.5V then after about 1/2 hour I checked - 15.2V.
My understanding is that the regulator is meant to output max about 14.8V, but twice in a row seems to suggest that there's something else wrong with my setup. Any ideas?
thanks
JMB
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Old 05-02-2010, 18:52   #2
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Further info

I found one previous post, but no real solution there. My setup is wired directly to 4 x 6v Golf Cart wet cell batteries (two groups of 12v). A hygrometer test shows them to be varying a little in terms of the specific gravity. Some show good, where others show the low end of fair. I can see that if the batteries are asking for more charge that the current flow would remain high, but my understanding of the regulator's function is that it would cap the maximum output voltage.
Argggh. Too much to know.
thanks
JMB
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Old 05-02-2010, 19:06   #3
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Does your regulator use a separate volt sense wire? If so maybe this is a source of trouble. i have seen where this wire had a fuse that went out and it did the same thing you are talking about. Might be something to look for.

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Old 05-02-2010, 19:11   #4
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Check the resistance on your voltage sense wire. There is supposed to be virtually no resistance. If that is not it then your regulator is toast.
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Old 05-02-2010, 19:14   #5
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Quote:
Originally Posted by sailvayu View Post
Does your regulator use a separate volt sense wire? If so maybe this is a source of trouble.
OK, that sounds like a reasonable suggestion, but I don't think so. Its got a wire that comes out of the regulator and piggy-backs onto the main + terminal, I'd assumed this is the exciter circuit. Otherwise it has the tachometer output, the warning light output (the light works), and the negative, which is strapped to the block, and a smaller wire to the -ve side of the control relays, which I assume really just goes straight to the block via the strap.
Could it be a dodgy earth?
JMB
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Old 05-02-2010, 19:42   #6
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That wire may be your voltage sensor and not your field wire. Disconnect it just for a second or two and see if the voltage jumps through the roof. Of course, power down all your electronics and shut off all your 12VDC breakers before doing this.

Check the resistance through your ground primary wires.
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Old 05-02-2010, 20:24   #7
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Keep in mind that, if this is an alternator with an "internal" regulator, it may not have an external battery sense lead (many don't).
A voltage output of 15.2v would leave me a bit uncomfortable too. May also be worth cross checking you multimeter just before you spend time on more involved things.
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