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19-10-2018, 16:53
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#1
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Registered User
Join Date: Apr 2018
Posts: 25
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Battery voltage with Inverter on.
I have a battery bank with approximately 1300 amp hours. Charger keeps them at 100% SOC. When I go out on the boat and have the inverter on, the voltage drops in a few hours to 12.4 or so. I am drawing about 40 amps 12 volt.
Is this OK, normal?
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19-10-2018, 16:59
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#2
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Registered User
Join Date: Oct 2015
Posts: 2,007
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Re: Battery voltage with Inverter on.
If the battery voltage reads 12.4 WHILE you are drawing 40 Amps, and after you have been for a "few" hours, yes that is normal.
After 4 hours drawing 40 amps, you have pulled 160 Amp-hours out of the battery, so they are down about 15%.
If that is the voltage after a significant amount of time "resting" without putting out any power, that would be lower than I'd expect.
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19-10-2018, 17:02
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#3
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Registered User
Join Date: Apr 2018
Posts: 25
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Re: Battery voltage with Inverter on.
I understand your point. This is not a resting voltage, this is a reading when inverter is on supporting a load of 30-40 amps. It has gone as low as 12.0 volts when under a relatively high load.
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19-10-2018, 18:12
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#4
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cruiser
Join Date: Jan 2017
Boat: Retired from CF
Posts: 13,317
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Re: Battery voltage with Inverter on.
It is normal, but can be a problem. Gets worse as batts age, lose capacity.
Bigger bank will help, also some AGM batts are better than most.
LFP much better at this than lead.
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19-10-2018, 21:23
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#5
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Registered User
Join Date: Jun 2013
Location: canada
Posts: 4,634
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Re: Battery voltage with Inverter on.
Seems a bit low for such a big bank.
I would do a 20 hour discharge test on it. Google it
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20-10-2018, 09:40
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#6
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Registered User
Join Date: Feb 2015
Location: Rappahanock River, Va
Boat: Caliber 47
Posts: 186
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Re: Battery voltage with Inverter on.
What's drawing 40 Amps?....that's a pretty big draw....what size boat do you have?
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20-10-2018, 09:44
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#7
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Registered User
Join Date: Aug 2013
Location: Laboe - Germany
Posts: 528
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Re: Battery voltage with Inverter on.
Quote:
What's drawing 40 Amps?....that's a pretty big draw....
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@ 1300Ah it's a pretty big bank too ;-)
Carsten
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20-10-2018, 09:51
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#8
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Registered User
Join Date: Sep 2013
Location: Alert Bay, Vancouver Island
Boat: 35ft classic ketch/yawl.
Posts: 1,980
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Re: Battery voltage with Inverter on.
You don't say what size charger you have. I would expect a bank that size to have at least a 40a charger. If the voltage is dropping while the charger is on it should still maintain full charge so voltage should not drop. If the charger cant keep the batteries at full charge you have a charger fault. If not all seams OK.
But as others say, what draws 40a continuously? That is in the realm of always having to be hooked up to shore power or a generator, its 1000a/h day. Only system that will handle that is a large lithium bank with genset and large solar array costing sever $K
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20-10-2018, 10:32
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#9
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Commercial Member
Join Date: Dec 2008
Location: St. Petersburg, FL
Boat: Gulfstar Long Range Trawler; 53'; BearBoat
Posts: 1,524
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Re: Battery voltage with Inverter on.
Seems high for a 1300Ahr bank as the 20 hr rate is 65A so you are not pushing too hard with a 40A load. The age and subsequent state of health (SOH) of your bank is coming into play here. How old are your batteries? Do you always charge to 100% after a discharge cycle? Do you discharge to <50% often? Do you leave them in a partial state of charge (PSOC) condition?
__________________
Charlie Johnson
ABYC Master Technician
JTB Marine Corporation
"The Devil is in the details and so is salvation."
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20-10-2018, 15:46
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#10
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Registered User
Join Date: Aug 2015
Location: SW Florida
Boat: Grand Banks 49
Posts: 572
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Re: Battery voltage with Inverter on.
Quote:
Originally Posted by spudsdailey
I have a battery bank with approximately 1300 amp hours. Charger keeps them at 100% SOC. When I go out on the boat and have the inverter on, the voltage drops in a few hours to 12.4 or so. I am drawing about 40 amps 12 volt.
Is this OK, normal?
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===
It sounds normal to me. We have about 1,000 amp-hours and draw 30 to 40 amps more or less continuously. Voltage will be down to 12.4 or so after a few hours, and down to 12.2 over night. It takes an hour or more of bulk charging at about 110 amps, and another hour of absorb charging starting at 110 amps, tapering down to 40 amps to get them back to nearly a full charge.
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20-10-2018, 16:14
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#11
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cruiser
Join Date: Jan 2017
Boat: Retired from CF
Posts: 13,317
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Re: Battery voltage with Inverter on.
Those numbers don't add up.
What model batteries?
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20-10-2018, 21:19
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#12
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Registered User
Join Date: Aug 2015
Location: SW Florida
Boat: Grand Banks 49
Posts: 572
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Re: Battery voltage with Inverter on.
Quote:
Originally Posted by john61ct
Those numbers don't add up.
What model batteries?
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===
Eight Trojan T-145s in series/parallel (lead acid, 12 volt bank).
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20-10-2018, 22:45
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#13
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Registered User
Join Date: Feb 2015
Boat: Land bound, previously Morgan 462
Posts: 1,991
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Re: Battery voltage with Inverter on.
Quote:
Originally Posted by spudsdailey
I have a battery bank with approximately 1300 amp hours. Charger keeps them at 100% SOC. When I go out on the boat and have the inverter on, the voltage drops in a few hours to 12.4 or so. I am drawing about 40 amps 12 volt.
Is this OK, normal?
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What is "a few hours"? If you can find out more precisely how many hours it takes to drop to 12.4 volts at 40A, then you will get better answers about the health of your battery bank.
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21-10-2018, 05:43
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#14
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Registered User
Join Date: Dec 2009
Location: Australia
Boat: BUILT!!! Roberts Mauritius 43ft
Posts: 3,563
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Re: Battery voltage with Inverter on.
[QUOTE=spudsdailey;2744967]I have a battery bank with approximately 1300 amp hours. .
QUOTE]
Do you mean 1300 Cold Cranking Amps (CCA) or have you missed a decimal point? A 4WD battery would typically have 700 CCA
I have two quite large AGM batteries in my 43 ft yacht and each are 135 Amp Hours (AH)
Clive
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21-10-2018, 05:53
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#15
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Registered User
Join Date: Dec 2009
Location: Australia
Boat: BUILT!!! Roberts Mauritius 43ft
Posts: 3,563
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Re: Battery voltage with Inverter on.
Quote:
Originally Posted by wayne.b
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Eight Trojan T-145s in series/parallel (lead acid, 12 volt bank).
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According to my research each T-145 weighs 28kg so you have app 250kg of batteries?
WOW!
Clive
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