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Old 23-07-2019, 14:08   #1
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Solar - Unusual low battery voltage

My solar system consists of an array of 4 panels totaling 290W connected to a dumb 30A controller which only shows current status, no history. The battery bank consists of 3 12V probably deep cell batteries, which have been meeting my power needs for the past year since I acquired the boat. The batteries are 9 years old so they don't really owe me anything, I understand they were meticulously maintained by the previous owner. Last night before I went to bed, I just happened to glance at the controller and it showed 10.4V, and there was nothing creating a large draw at the time. I shut off everything else with the exception of the anchor light and it bounced between 10.4 and 10.5V. I decided to turn the fridge back on for the remainder of the night. When I arose just before sunrise, the battery level was at 11V. Normally the bank is at its lowest of about 12.3 to 12.5 first thing in the morning. I decided to try starting the engine, with little hope of there being enough juice in the batteries, however was happily surprised when it managed to start, a little sluggish compared to normal but good enough.. I ran it for about 5 to 10 minutes then shut it down. The batteries then showed about 12.6V, dropped a little bit then picked up again as the solar panels started contributing power to them. I later ran the motor for an hour and in mid afternoon, they are showing about 13.5, as it typically is this time of day. Last fall I tested the SG of all 3 batteries and there were a couple of cells a little below the ideal level but not anywhere near dead. I realize the batteries will need replacing soon, and I'm waiting for delivery of a new Victron SmartSolar 100/20 to replace the old one which will help me decide what to do for replacement batteries when the time comes. Just wondered if anyone has thoughts about my experience.
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Old 23-07-2019, 14:12   #2
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Re: Solar - Unusual low battery voltage

Your batteries are toast. The rapid drop and rise in voltage indicates that they no longer have a useable capacity. Sure they can sort of maintain a voltage, for a while, but thatís about it.
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Old 27-07-2019, 05:54   #3
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Re: Solar - Unusual low battery voltage

Sounds like one of your batteries has a shorted cell - is the electrolyte level significantly different in a single cell? After charging a while, is one battery hotter than the others, is one cell fizzing a lot less (or a lot more) than the others? If so, remove that battery and the other two might give you a few more weeks.

But you do need new ones.
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Old 27-07-2019, 06:29   #4
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Re: Solar - Unusual low battery voltage

Quote:
Originally Posted by sunluvr View Post
I realize the batteries will need replacing soon, and I'm waiting for delivery of a new Victron SmartSolar 100/20 to replace the old one which will help me decide what to do for replacement batteries when the time comes. Just wondered if anyone has thoughts about my experience.
your 9 year old batteries have passed "need replacing soon"
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Old 27-07-2019, 09:30   #5
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Re: Solar - Unusual low battery voltage

SB call's it correctly. The time to replace your batteries was many months ago. A new solar charge controller will not "FIX" that. The Victron controller is very sweet, but can't fix DEAD cells.
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Old 27-07-2019, 09:33   #6
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Re: Solar - Unusual low battery voltage

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SB call's it correctly. The time to replace your batteries was many months ago. A new solar charge controller will not "FIX" that. The Victron controller is very sweet, but can't fix DEAD cells.

Edit: make that 2 years ago.
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Old 27-07-2019, 09:43   #7
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Re: Solar - Unusual low battery voltage

Old batteries are worth 50p a kg in the UK, so if you have a scrap yard near by it could be worth making the trip. There is some hope they will be re-cycled so good for the environment and your Karma. Managed to earn £25 for my last lot.

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Old 27-07-2019, 12:17   #8
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Re: Solar - Unusual low battery voltage

First off. BArteries should not be dropped below 12v.

When you saw them at 10.4v. You certainly should not have gone to bed. You should have been sh*tting yourself and spent the night trying to charge them

2nd the engine should be in its own battery. A dead house battery should never effect starting a motor.

Running an engine for 5 mins won’t do anything.
Three 12v battery’s (guess group 27 at 80ah each?) at 10.4v would probably take ~6 hours (at high rpm) to charge back up with a ~60a alt.

Buy new batteries. And buy a victron 712 as well.
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