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Old 06-17-2012, 09:10 PM   #1
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Low volt reading

Hi Folks-
My voltmeter has gone from reading around 14v to just above 12v.
Batteries charged off of shore power charger are at 13+ volts.
I can get a reading of 14.25 volts off the alternator when boat is running.
Voltmeter reads below zero when key is off. It reads high 12v's when key is turned on and then drops to just above 12v when running.
What should I be looking at?
Thanks-
Eeber
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Old 06-17-2012, 09:31 PM   #2
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Originally Posted by Eeber View Post
Hi Folks-
My voltmeter has gone from reading around 14v to just above 12v.
Batteries charged off of shore power charger are at 13+ volts.
I can get a reading of 14.25 volts off the alternator when boat is running.
Voltmeter reads below zero when key is off. It reads high 12v's when key is turned on and then drops to just above 12v when running.
What should I be looking at?
Thanks-
Eeber
Check the circuit breaker between the alternator and the batteries. Also, check your ground connections.
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Old 06-17-2012, 10:54 PM   #3
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Read the voltage on the terminals right on the back of the voltmeter.

If that voltage is actually low, trace the wires back towards the battery untill you get the same voltage as your battery.
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Old 06-18-2012, 06:28 AM   #4
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Read the voltage on the terminals right on the back of the voltmeter.

If that voltage is actually low, trace the wires back towards the battery untill you get the same voltage as your battery.
good troubleshooting proceedure..
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Old 06-18-2012, 07:15 AM   #5
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Thanks.
I'm looking at the schematic and power runs from the alternator, through the battery isolator, to the batteries, then to the battery switch and the voltmeter.
Looks like I should be reading 14.25 at the batteries when running?
I'm not.
I ran the water pressure pump and then with the engine running, I watched one battery slowly come up; 12.74, 12.75, 12.76, etc..
Thanks-
Eeber
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Old 06-18-2012, 08:26 AM   #6
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Read the voltage on the terminals right on the back of the voltmeter..
That is the obvious first test, especially if the boat's volt meter reads "below zero" with the key switch turned off.

If a "known good" meter reads one voltage when attached to the terminals on the back of the boat's volt meter and the boat's meter shows something else, the boat's volt meter is inaccurate. Boat (and car) volt meters are usually not very accurate to start with.
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Old 06-18-2012, 10:27 AM   #7
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It still sounds to me as if the problem is between the alternator and the batteries. If the alternator is putting out 14.25 volts, and the gauge is reading battery voltage, the alternator voltage is not getting to the batteries. Check for a tripped circuit breaker or blown fuse between the alternator and batteries. If that is not it, it could be a broken wire or connection. Rig a temporary wire from the alternator to the batteries, and check the gauge reading.

If there is a fuse in the circuit from the alternator to the batteries, (and it is not blown) pull the fuse and clean all contacts with emery cloth or wire brush. You may have to disassemble the fuse holder to do this. Then replace and check. It only takes a small amount of oxidation to break a circuit or reduce the voltage going through.

In the past, I have also had some bad ground connections behind the instrument panel that have caused some bad readings.
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Old 06-18-2012, 11:57 AM   #8
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Originally Posted by Eeber View Post
Thanks.
I'm looking at the schematic and power runs from the alternator, through the battery isolator, to the batteries, then to the battery switch and the voltmeter.
Looks like I should be reading 14.25 at the batteries when running?
I'm not.
I ran the water pressure pump and then with the engine running, I watched one battery slowly come up; 12.74, 12.75, 12.76, etc..
Thanks-
Eeber
If you have a battery isolator (not a combiner), you can expect a voltage drop through the isolator of about .7 volt because of the loss through the diode(s).
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Old 06-18-2012, 09:11 PM   #9
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Issue resolved.

I cleaned up the connectors on the alternator and that did the trick.
Thanks for the ideas. It helps me get my head around what I'm dealing with.

Does anyone use any gunk to keep connectors more healthy?

Thanks Everyone -
Eeber
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Old 06-18-2012, 09:27 PM   #10
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Greetings,
How about something like:
Crc Chemicals 06026 Coating No Corrode 12 Oz
There was another product and I can't remember the name (it might easily have been the same stuff) that was in non aerosol form. Ah, just remembered this:
Corrosion Block - Corrosion Control and Inhibitor products Seems I got a small sample bottle at one of the boat shows....
Hope this helps...
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Old 06-18-2012, 09:55 PM   #11
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That CRC stuff looks perfect. Great reviews.
Thanks a bunch RT.

Sincerely-
Eeber
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Old 06-18-2012, 10:34 PM   #12
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Electricityy confounds/bewilders me.
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Old 06-19-2012, 06:02 AM   #13
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Greetings,
Hold on now Mr. Eeber. Maybe I was too fast in suggesting. The CRC stuff says not for use on plastics or rubber AND it's an aerosol which sprays everywhere. Maybe not the best stuff for electrical use. Sorry about that. Next time I'll read the labels first. Suggest you go through the Corrosion block site to see if there is the same disclaimer.....Again, mea culpa
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Old 06-19-2012, 06:34 AM   #14
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Greetings,
Hold on now Mr. Eeber. Maybe I was too fast in suggesting. The CRC stuff says not for use on plastics or rubber AND it's an aerosol which sprays everywhere. Maybe not the best stuff for electrical use. Sorry about that. Next time I'll read the labels first. Suggest you go through the Corrosion block site to see if there is the same disclaimer.....Again, mea culpa
Can't remember if that's the waxy brown stuff...if it is ...it's great stuff for connentions in the bilge. Some boat manufacturers spray it on everything...like the new Sea Rays. It may not be ok for natural rubber and some plastics...but never saw it affect anything around normal electrical terminations...my have to use it sparingly around fuse/cb blocks.

When in doubt...spray it into the cap and use a q-tip to cover terminals in sensitive areas...it is a very good terminal/general sealer.
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