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Old 13-12-2012, 12:31   #16
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Re: Runaway Alternators

Thinking how an ACR will figure into this imbalance act.
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Old 13-12-2012, 13:13   #17
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Re: Runaway Alternators

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Originally Posted by poboy View Post
Thanks for all of the replies. I have a good handle on what I need to looking for now.
Some comments have been made regarding battery switches, so I need to add some more info on my battery setup. I used two Blue Seas Add A Battery kits to isolate the house and start banks at all times except when charging with the alternators. Each bank has its own Off-On-Combine switch and ACR. Via these switches, I can combine the start batts with each other and combine the house bank with the start bank if needed. No switching is needed for charging, though. The ACR's create a one way gate that let's voltage pass from the house to the start bank when charging, but isolates the banks from each other at all times.
I'm thinking that I need to have the sense wire tied to the house bank (I don't know what it hooked into at present).
I have this uneasy feeling that the switches might be part of the problem. At what place in your electrical system are you getting the high amps and voltage? For trouble shooting, it would be a good idea to make a wiring diagram showing switches, all three wires for both alternators, and batteries. For that matter, you should do a wiring diagram for the whole boat and in the process, discover what the condition of the wiring is for the boat because it is evident there already is a wiring problem and who knows what else there might be. It's a good idea to keep the electricity under control on a boat and many systems are "custom" where the installation is not that well thought out and installed.
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Old 16-12-2012, 09:17   #18
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Update -

Reinstalled port alternator (brand new, bench tests perfect) and attached the sense wire (white) to the BAT terminal at the back of the alternator so that it would sense the house bank. Warmed up the engine, turned on the alternator, same result - upwards of 17 volts and 100 amps. Measured with a Victron battery monitor and a hand held meter at the batteries. I pretty stumped. The only thing different in the system are the two new GC2s I installed a month ago. But, the day I put them in, the charging system worked as it should. It put out about 14 volts at 65 amps. After charging for an hour or so, it down to about 13.5 volts at 11 amps. Three weeks later, with no changes, I get this. Further thoughts are welcome!!!!!
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Old 16-12-2012, 10:24   #19
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Re: Runaway Alternators

On forther thought

How is the wire from the B terminal to the batteries. Does it run to the batteries direct or to the start solenoid or battery switch.??

Are you 100% sure the wire you moved to the B+ wire was the sense wire and not the field wire. The sense wire should have prevented the alternator from going to 17 volts. But if the field wire was moved then nothing was really changed... Some alternators have different Field / sense connections, even with the same brand alternator.

So I'm wondering if the field and sense wires are reversed??

Something in the wiring is wonky for sure.

One other thing, are you sure the wiring for the Victron battery monitor is correct and that its measuring the amps correctly. same goes for the multi-meter. Double checking voltage with a second multi meter or volt meter would be good..
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Old 16-12-2012, 10:48   #20
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Re: Runaway Alternators

You'd better get your alternator shop to tell you which terminal is the sensing one.
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Old 16-12-2012, 11:12   #21
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Re: Runaway Alternators

Actually just switch the field and sense wires and try it. It will not hurt the alternator.

The field wire generally runs through the engine ignition switch with a idiot light in circuit. The "alt" light will put a resistance on the field wire and drops the voltage just a little. SO, Try swapping the field and sense wires.

It would also explain why the alternator works at the shop but not on the boat.
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Old 16-12-2012, 11:25   #22
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Re: Runaway Alternators

What voltage are you getting on the sense wire? Run a temporary test wire from the sense wire to the each battery and see what happens. Be sure to run the sense wire to the starting battery since that is the one that will control the alternator on first startup. This battery connection would also be good even after the relays drop and connect the house battery because the voltage would be the same with both house and engine batteries connected by the relays
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Old 16-12-2012, 12:23   #23
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Re: Runaway Alternators

poboy, if the bench tests on the new alternator say it is perfect, then the alternator is very likely to be perfect, and the problem in your wiring.

I'm not sure what contacts are on your alternator but connecting a "sense" wire to a "b+" terminal may be part of the problem. B+ could mean that is the primary charging output, which connects to the battery positive. In which case, you'd still be having NO sense wire connected, which would cause runaway output as you have.

I think if you post the exact make and model of alternator and how you've got things wired up, the real problem will be easy to find. Something is getting lost in the translation.
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Old 16-12-2012, 12:24   #24
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Re: Runaway Alternators

Quote:
Originally Posted by poboy View Post
Update -

Reinstalled port alternator (brand new, bench tests perfect) and attached the sense wire (white) to the BAT terminal at the back of the alternator so that it would sense the house bank. Warmed up the engine, turned on the alternator, same result - upwards of 17 volts and 100 amps. Measured with a Victron battery monitor and a hand held meter at the batteries. I pretty stumped. The only thing different in the system are the two new GC2s I installed a month ago. But, the day I put them in, the charging system worked as it should. It put out about 14 volts at 65 amps. After charging for an hour or so, it down to about 13.5 volts at 11 amps. Three weeks later, with no changes, I get this. Further thoughts are welcome!!!!!
On your first post you said the GC's were in parallel. The GC's are 6 volt batteries, which should be in series.

The 13.5 and 11 amps tells me something is wrong as after being at 14 volts and dropping to 13.5 Volts. The batteries should be at float and have a very low amp charge rate.

So did you have 12V batteries first and then swapped two 6 volt or did you have 6 volt all along. If you swapped in 6 volt batterys is the sense wire still reading 6 volts.

Please verify that you have two 6 volt batteries in SERIES making 12V. IF they were in parallel you would only have 6V's and the alternators would run wild...

If the GC2's were in parallel, then your most likely going to need two new GC2's also...
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Old 16-12-2012, 12:30   #25
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Re: Runaway Alternators

s'chic you might have also coincidentally hit a nail on the head. If he has two 6v batteries replacing two twelves, and the sense lead goes to the "middle" now somehow...it would only see about 6 when the alternator was putting out normal voltage, wouldn't it? Once again telling the alternator to give it more juice, with a runaway output resulting.
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Old 16-12-2012, 12:33   #26
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Yes, I have two 6 volt batteries in series. They replaced two other 6 volt batteries in series that were a little over 5 years old.
Just for grins, I took the GC2s out and put in a known good group 27. The alternator did its job - charged it at 14 volts. So, I am in the process of putting two new (by one month!) GC2s in. Will report results.
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Old 16-12-2012, 12:47   #27
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Re: Runaway Alternators

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Yes, I have two 6 volt batteries in series. They replaced two other 6 volt batteries in series that were a little over 5 years old.
Just for grins, I took the GC2s out and put in a known good group 27. The alternator did its job - charged it at 14 volts. So, I am in the process of putting two new (by one month!) GC2s in. Will report results.
Cool!.. sounds like one of the old new GC's was bad.

Once I thought about it, after you connected the sense to the B+ and still had a problem, it had to be battery related.. Probably happened from the beginning too.
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Old 16-12-2012, 13:30   #28
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Sailorchic - I hope that's the problem. Will be sometime next week before I know, though. Out of time for this weekend and have to head home.

All - thanks for everyone's help. I'll post an update as soon as I know something new!
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Old 17-12-2012, 03:35   #29
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Re: Runaway Alternators

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Originally Posted by poboy View Post
Yes, I have two 6 volt batteries in series. They replaced two other 6 volt batteries in series that were a little over 5 years old.
Just for grins, I took the GC2s out and put in a known good group 27. The alternator did its job - charged it at 14 volts. So, I am in the process of putting two new (by one month!) GC2s in. Will report results.
Shorted cell in one of the batteries. If the batteries have caps on the cells, pull them and see if the electrolite (fluid in the cells) is way down on one of them.
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Old 17-12-2012, 06:27   #30
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Re: Runaway Alternators

My guess is that the sense wire is connected incorrectly or the battery connection is to 6V not 12V.. I have seen folks wire 6V banks before trying to tap off the "series" connections. Any connections to a series wired bank for 12V MUST be to the 12V side....
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