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#11567936 - 04/26/16 09:30 PM Volt Meter Question
Duke 59 Offline

Registered: 01/02/12
Posts: 171
This is probably a dumb question....I should know the answer but I don't.

What is the volt meter on my boat dashboard measuring? Does it measure the voltage output of the boat going to the battery....or is it measuring the current voltage of the battery?

#11568070 - 04/26/16 10:06 PM Re: Volt Meter Question [Re: Duke 59]
Flippin-Out Offline
Extreme Angler

Registered: 02/25/15
Posts: 1564
Loc: Magnolia, TX
It is measuring both - they are one in the same.

The engine's charging system is connected to the battery, as is the voltmeter. If you turn the key on (but do not start the engine), the only source of power is the battery. If you look at the voltmeter then, you should see it around 12-13 volts for a good battery. These voltmeters aren't precision instruments, so it's an "indicator" as much as anything. This shows that you have good battery voltage. The engine isn't charging the battery yet....

Once you crank the engine, you may see an increase in voltage. Whether or not you do depends on how your charging system works. Some need to be above "x" RPM to generate output. For sure, once you get up to 2000 RPM, you should notice the voltmeter has moved to a higher indicated voltage. Again, exactly what voltage depends on your particular charging system. What you're looking for is that it increases vs. before the engine was running.

So, learn what the gauge reads when it's all working, and then in the future, make sure that's what it's doing. If you see a different reading, that tells you something may be less than ideal, or about to fail, or has failed.

#11568133 - 04/26/16 10:22 PM Re: Volt Meter Question [Re: Duke 59]
bronco71 Offline
Extreme Angler

Registered: 02/05/06
Posts: 1049
Loc: Farmers Branch/Sulphur Bluff
Technically it is measuring the charge voltage when running, not the current.....current is measured in amps by an ammeter, very different from voltage.

#11568351 - 04/27/16 07:15 AM Re: Volt Meter Question [Re: Duke 59]
SteezMacQueen Offline
TFF Team Angler

Registered: 11/02/14
Posts: 3022
Loc: Red Oak, Galveston, and Pagosa...
Both answers are correct.

The problem with a voltage meter is it usually only shows the result of a part failure for most folks that do not understand what is a correct reading. A voltage swing from 12.6-13.8+ is normal. A 12 volt battery has 6 cells at 2.1 volts perm cell. So 12.6 is considered a charged state for a battery. In order the charge a discharged battery, the charging system must show a potential of higher voltage than 12.6. Most charge voltages are around 13.8-14.4'volts, but not all of them. As long as the voltage readings do not get lower that these ranges on average, you are probably "ok". However, voltage reading do not show the state of health of a charging system. It only shows potential. An amp gauge would be more accurate in showing a charging system status. But, it requires more wiring and it also causes voltage drop across its terminals. Haha.
I have read time and again Flippingout posts on this stuff. He is pretty straight forward and knowledgeable on the subject.

#11570249 - 04/27/16 09:51 PM Re: Volt Meter Question [Re: Duke 59]
Flippin-Out Offline
Extreme Angler

Registered: 02/25/15
Posts: 1564
Loc: Magnolia, TX
I ignored the reference to "current". I go too far overboard on the tech side sometimes, and I just let that one slide in an attempt to have my post still readable by my fellow fish-heads. You're correct to note where the needle normally sits when things are good. It should go up when you get the RPMs going, and will drop when you shut down. If it starts showing something different, look into why and fix it before you get stranded.

I learned the same thing about gauges such as water pressure and cylinder head temperature. (I almost always added that gauge to the panel in a boat.) If that needle didn't sit where it was supposed to, I knew to check for what was wrong. That habit saved me many times - I've never blown a motor in 35 years of running outboards. Man, I bet I was stupid for saying that.....hope it doesn't jinx me!


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