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Author Topic: Battery help  (Read 723 times)


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Battery help
« on: March 17, 2020, 12:05:33 PM »
I have a Solar System installed in my van.  I have 525 Watts on the roof, a Morningstar TS45 Charge Controller, two Vmax 6V 225 Amp Deep Cycle AGM batteries.  I use a Magna 2000 Watt Pure Sinewave Inverter.  My system seemed to run perfectly for a year and a half, but now, when the sun goes down, and I pull about 5% off the batteries, my battery Volts drops from 14.4 to 11.2 and then the Inverter protects itself by shutting down (by design).  I need help to troubleshoot it.  Any ideas?



PJ Stough

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Re: Battery help
« Reply #1 on: March 17, 2020, 12:16:03 PM »
I would have the batteries checked.
PJ Stough   Iowa
2005 Winnebago Voyage 38J

“Those who can make you believe absurdities, can make you commit atrocities.”--- Voltaire

Lou Schneider

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Re: Battery help
« Reply #2 on: March 17, 2020, 12:25:54 PM »
Welcome to The RV Forum!

14.4 volts says the solar system is supplying charging voltage, the problem is either there's a dirty connection inhibiting current flow in and out of the batteries, or the batteries themselves aren't storing that power.

Make sure all of the connections are clean and tight, since these are AGM batteries there's no way to add water or check the individual cell voltages.  If you want you can use a DC voltmeter to see if one battery is weaker than the other or if both are equally degraded.  In any case, this is largely academic, if the batteries aren't storing power they need to be replaced - both of them as it's a bad idea to mix old and new batteries.


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  • 2005 Itasca Sunova
Re: Battery help
« Reply #3 on: March 17, 2020, 01:08:54 PM »
Yep, anything that dramatic will be a bad connection or batteries that are shot.   For a first pass test you can check the voltage right at the batteries when under load.  If it's dipping there then it's not the connections.  If it's OK at the batteries but the inverter is reporting low a quick way to check connections it to put healthy current through them (charge or discharge), say 25A then use a voltmeter on a low volts scale and go across each connection.  A good connection will be a few millivolts, bad ones maybe 100 millivolts or more.  As much power as that drop represents sometimes just feeling around for the warm ones gives them away.

Mark B.
Albuquerque, NM

Gary RV_Wizard

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Re: Battery help
« Reply #4 on: March 18, 2020, 11:03:13 AM »
Note that the battery voltage is always going to drop from 14.4 to 12.6 as soon as the charging stops (the sun gets low). 12.6v is the voltage for a new, fully charged, 12v lead-acid battery.   A 5% draw down probably knocks another tenth or so off that, so you are looking at an unexpected drop of an additional 1.2-1.3v.   12.2v is for all intents and purposes a "dead" battery bank.    Failed battery(s) is the likely answer, but bad connections is a possibility and ought to be checked first.  However, your twin 6v battery bank has a total of 6 x 2.1v cells in series and degradation in just one of them will knock the total available voltage down by 1-2 volts. Your symptoms match that perfectly.

How old are the batteries?  Have they been deeply discharged previously, i.e. below about 11.9v?  Lead acid batteries don't have long lives if routinely discharged much below abut 50% (roughly 12.0v). 
Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL