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Old 21-04-2012, 12:19   #1
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Correct Voltage for Batteries.

My boat came with an 2KW Inverter and a monitor, as well as a Balmar.

The house batteries are 4 6V AGM's and a starting 12v battery. The battery switch is 1, off and all.

The owner replaced one 6v AGM battery and all the terminals before I took delivery, as the pole on one had melted/corroded off one terminal and it appeared the batteries were leaking. A mechanic apparently load tested the batteries and all were okay including the one replaced, but because of the terminal the system was not charging.

My monitor has a charge setting and an Inverter (Idle) setting. If I leave it in charge, it never seems to stop charging. Should this not intelligently stop charging to avoid overcharge?

Also, if I switch to Idle, the voltage on both banks goes down quickly and stops at 12.25-12.4v. Is that normal?

I'm thinking I should just replace all batteries immediately, and if I do that, I'm not sure if I should just add 3 more 6v AGMs or switch to 2 of the bigger AGM or Gel Cell batteries and then reset the monitoring system. Also, the inverter is quite far away and stored under the salon settee. I'm thinking it should be relocated to under the cockpit and the cables shortened as much as possible to avoid potential fire issues and open up some storage area that's wasted there in that mess of wires and connections. Advice?
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Old 23-04-2012, 09:26   #2
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AGM @ full charge with nothing attached should read 12.6v. That is with no cables attached to the terminals. So a reading of 12.25v-12.4v is acceptable. You will always have a minimal draw of voltage from the batterie any time it is connected to a circuit.
Just my 2 cents from exp.
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Old 23-04-2012, 09:56   #3
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Re: Correct Voltage for Batteries.

Is the "starting" battery a flooded unit?

Can you ever use the "all" setting in that case?
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Old 23-04-2012, 13:08   #4
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Re: Correct Voltage for Batteries.

I am not sure what you mean by "stop charging". Almost all (maybe all) inverter/chargers are three step chargers which means that they stay "charging" but maintain a float votage of about 13.5 V.

Your voltage readings could be lower than the theoretical 12.6 V for a couple of reasons: meter error, or a small DC load is pulling the voltage down. The only way to really check it to let the charger settle at its float voltage and then remove one or all batteries from the system. Let them rest, preferrably for 24 hours but no less than one hour and measure the votage. They should read 12.6 on an accurate voltmeter.

And FWIW there is only one real load test for a deep cycle battery bank: You probably have 440 amp hours of capacity at 12V. So charge the batteries fully to the float voltage, then disconnect shore power so the charger is inop. Then turn on lights or whatever to load the batteries to 1/20 of their amphour capacity or in your case 22 amps. You can use the inverter to power some 120 V appliance or AC light to get to 22 amps. Then see how long it takes for the voltage to drop to about 11 V which is considered fully discharged. If it takes 20 hours then you have all the capacity you can expect. Anything less and you have less.

David
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Old 23-04-2012, 15:36   #5
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Re: Correct Voltage for Batteries.

Quote:
Originally Posted by djmarchand View Post
I am not sure what you mean by "stop charging". Almost all (maybe all) inverter/chargers are three step chargers which means that they stay "charging" but maintain a float votage of about 13.5 V.

Your voltage readings could be lower than the theoretical 12.6 V for a couple of reasons: meter error, or a small DC load is pulling the voltage down. The only way to really check it to let the charger settle at its float voltage and then remove one or all batteries from the system. Let them rest, preferrably for 24 hours but no less than one hour and measure the votage. They should read 12.6 on an accurate voltmeter.

And FWIW there is only one real load test for a deep cycle battery bank: You probably have 440 amp hours of capacity at 12V. So charge the batteries fully to the float voltage, then disconnect shore power so the charger is inop. Then turn on lights or whatever to load the batteries to 1/20 of their amphour capacity or in your case 22 amps. You can use the inverter to power some 120 V appliance or AC light to get to 22 amps. Then see how long it takes for the voltage to drop to about 11 V which is considered fully discharged. If it takes 20 hours then you have all the capacity you can expect. Anything less and you have less.

David

I agree except for 2 things. Each battery should be checked individually - that way you find out if one is bad compared to the others. And 10.5 volts is considered a fully discharged battery.
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