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Is my voltage meter broken?

Old 12-28-2015, 09:12 PM
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Default Is my voltage meter broken?

I have a 2007 Larson 254 escape with a 6.2 Mercruiser and a Bravo 3. I purchased the boat in July. I added a second battery with a selector switch. I usually run the batteries one at a time. One on the way out and the other on the way back. I have had no problem starting the engine, both batteries seem to have plenty of juice. But I don't think the voltage meter is working properly. When the boat sits for awhile the gauge is all the way to the left and rises slightly after I run for awhile. We took a trip over the weekend. We ran about three hours out on one battery and three hours back on the other. When I started the boat today this is what the gauge read.
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After about 10 min of running it dropped to 10
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Is it a broken gauge or maybe wired wrong. Any help would be very appreciated.
Old 12-28-2015, 11:08 PM
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Does the voltage work it's way back up over 14 after it runs a while ?
Old 12-28-2015, 11:38 PM
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What does a multimeter (20 volt scale ) read at the battery posts with engine off and running? The what does it read at the gauge terminals?
Did you connect the heavy gauge black negative to negative cable between the 2 batteries posts then one to the engine ground?

How old are the batteries and how corroded are the battery cables, engine ground connection and gauge wiring? You can take the batteries to any auto parts store to have them load tested and conductance analyzed for free to see what remaining CCA capacity they have compared to when they were new. .
Old 12-29-2015, 06:18 AM
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Check it with a digital multimeter where the wires attach to the gauge. I fully charged 12 volt battery should read like 12.6 and should go to about 14 when running. If voltage is lower I would check for corrosion in the wiring.
Old 12-29-2015, 07:02 AM
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Default Voltage meter

I would expect voltage to drop to about 11 volts when cranking to start cold but move back up to 12.6 at least in about 30 seconds t a minute. If the boat seems to start and run reliably I would check the gauge with a meter as recommended. If the voltage on thee circuit is really that low then you have to check wiring, charging system, etc.
Old 12-29-2015, 07:33 AM
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If the gage worked before you added the second battery I would assume something is hooked up wrong.
Old 12-29-2015, 07:39 AM
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All good info above. Another question is, "Do you switch batteries with the engine running?" Could damage the alternator.
Old 12-29-2015, 07:57 AM
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Car makers have figured that out. Voltmeters don't have numbers on them (at least on my cars).
Old 12-29-2015, 10:49 AM
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"Modern" being before most of the people here were born.
Any switch with "Both" being between 1 & 2 is "make before break". Just don't turn it "off".
The work boats I worked on in the 60s had that kind of switch.
The real question is if it ever recovers to 14+

A real slow recovery might indicate a weak charging system, a big load or bad batteries but if it never recovers with everything turned off the charging system may be bad.

Always start with cleaning all of the connections and checking the water in the batteries.
You might just get lucky.
Old 12-29-2015, 02:05 PM
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Originally Posted by Mud Runner View Post
All good info above. Another question is, "Do you switch batteries with the engine running?" Could damage the alternator.
Only if you switch through the OFF position, not just 1 through BOTH to 2 . Battery switches are all "make before break" these days.

Edit- didn't see the subsequent posts saying the same.
Old 12-29-2015, 02:13 PM
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Originally Posted by TTaxi View Post
Only if you switch through the OFF position, not just 1 through BOTH to 2 . Battery switches are all "make before break" these days.

Edit- didn't see the subsequent posts saying the same.
I failed to specify as you did. As a retired electrician, " I" know it but a lot of average boaters don't. Thank you for the correction.
Old 12-29-2015, 02:13 PM
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Originally Posted by SHAMROCK69 View Post
Check it with a digital multimeter where the wires attach to the gauge. I fully charged 12 volt battery should read like 12.6 and should go to about 14 when running. If voltage is lower I would check for corrosion in the wiring.
Correect.

At 11v - your battery is dead - so the picture showing the meter pegged at 10v = bad meter or bad wiring.

Def get 12v Doctor - a real bible for those doing their own boat wiring
Old 12-29-2015, 02:13 PM
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Get a multimeter and measure the voltage of the batteries themselves at the terminals. A good battery should read 12.8 - 13.2 volts.
Old 12-29-2015, 03:44 PM
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Thanks very much for all the good info. I'm heading there tomorrow with my multimeter. I do not switch batteries when the engine is running. Some of the replies said you can switch batteries or to both just as long as you don't rotate through off. Do I understand this correctly?
Old 12-29-2015, 04:46 PM
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Originally Posted by bigear1 View Post
Thanks very much for all the good info. I'm heading there tomorrow with my multimeter. I do not switch batteries when the engine is running. Some of the replies said you can switch batteries or to both just as long as you don't rotate through off. Do I understand this correctly?
Yes
Old 12-29-2015, 06:54 PM
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95% chance it's a wiring issue.
Old 12-29-2015, 09:22 PM
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Take a voltmeter to the battery when the engine is not running, then start the engine and wait 1 min then check again and report back. Should be 12.6 when off and 14.5 when on (about)
Old 12-30-2015, 04:55 AM
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Most electronics gps ff have voltage readings, easy way to double check, assuming their wiring isn't screwed up
Old 12-30-2015, 06:09 AM
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I had a similar issue. The problem was a loose ground wire.
Old 12-30-2015, 04:52 PM
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Alright, I had the chance to check the batteries today. Each one measured 12.6 without the engine running, 14.5 withe the engine running and 13.8 when both batteries were selected and the engine running. So it seems the batteries are ok and the charging system is ok. I didn't have the time to remove the dash so I was not able to check voltage at the meter. At least now I know its either the gauge or the wiring. I'm hoping its the gauge, that would be easier than trying to figure out the wiring.
Thank you to all that responded I appreciate the help.

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