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710K over-voltage

Posted: Mon Aug 27, 2018 5:55 pm
by edj710k
My 710K is going over-voltage at certain RPMs. I first noticed this when my 24>12 volt step down failed sending 26ish volts into my stereo which exploded. I also burned out a brand new headlight almost immediately. I see the 4500 indicator light flash when it goes over-voltage (as another thread discussed 4500 light flashing as a symptom of over-voltage). The volts are going to over 30 at some low rpms. I assumed the voltage regulator was bad and bought one from SAV. But I still get the same behavior after swapping them. What else could be the culprit?

Re: 710K over-voltage

Posted: Mon Aug 27, 2018 8:16 pm
by rmel
See schematic of a typical alternator-regulator circuit attached.
One possibility is a bad connection from the sensing terminal D+.
If this is low the regulator will drive a higher voltage to the field
winding then the output B+ will also be above nominal. 30V implies
something like that may be going on. Try getting a meter on that
terminal and see what that voltage is, if working properly it should
be close to the output voltage that connects to the battery. If
significantly lower that is a good clue. Could be a oxidized connection
or blown diodes in the alternator, there are 3 small diodes used for
sensing, one bad or more could lead to a problem, that could
although they typically don't fail as they are relatively low current.
boschschmgf-7ecomp-to-bosch-alternator-wiring-diagram.jpg
boschschmgf-7ecomp-to-bosch-alternator-wiring-diagram.jpg (21.98 KiB) Viewed 777 times

Re: 710K over-voltage

Posted: Tue Aug 28, 2018 11:11 am
by edj710k
Thanks for the reply. So in your diagram, the Voltage Regulator is integrated into the alternator and not the separate part I replaced that is mounted in front passenger corner of the engine compartment?

Re: 710K over-voltage

Posted: Tue Aug 28, 2018 11:21 am
by rmel
I lifted this schematic as a Google search as an example only.

The schematic is correct in the sense of the "how it works".
Indeed, the Pinz has the Regulator external, in some cases the
regulator is integrated into the Alternator housing. Just
ignore that. Find the D+ terminal on the connector near the fan
housing and get a meter on it. Let's see what that voltage is
when your output is over 30V.

Re: 710K over-voltage

Posted: Tue Aug 28, 2018 1:30 pm
by edj710k
Solved! The problem was the wiring from the alternator. For some reason a prior owner bypassed the molex connector and had the red wire wound in with a bunch of other wires and wire nut. That connection was the problem. Redid that and no more 4500 light and no more over-voltage.

Re: 710K over-voltage

Posted: Tue Aug 28, 2018 2:34 pm
by rmel
Bitten by a bad connection :?

Well RED should be the Alt output, BLU is the D+ signal to the regulator.
So a bad RED (B+) connection would not explain why a high over voltage,
that should lead to poor charging. Since someone was in there muck'n
around perhaps the wire positions got changed or wires replaced with
no care on the original schematic? I'm still betting on the BLU (D+) as
the problem -- which you may have actually taken care of at this point.

Re: 710K over-voltage

Posted: Wed Aug 29, 2018 12:03 pm
by edj710k
Ah yes, you are correct. It was the blue wire that was badly connected using a wire nut, not the red wire. The wire nut was red. Its so ugly what they did.

Re: 710K over-voltage

Posted: Thu Aug 30, 2018 11:22 am
by VinceAtReal4x4s
Anytime I see a wire-nut on a 4x4's electrical system I know I better check everything else carefully.