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Old 28-12-2014, 09:43   #1
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Batteries not charging

Hello,
We are having a problem with our batteries charging and holding a charge. We have three Outback batteries, with 300 AH. We have five solar panels which gives us 350 W total. The batteries are a few months old and have been performing well. We recently had the boat hauled and had to remove our outboard engine from the boat. After disconnecting the engine from the batteries, we have been having trouble with the batteries holding a charge or gaining more than 12.6 volts. We have checked all connections several times. We had the controller checked and it is fine. Does anyone have any suggestions?
Thank You!
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Old 28-12-2014, 10:02   #2
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Re: Batteries not charging

One thing I can suggest is after charging the batteries overnight, check and see if one of them is hot. if it is, that battery has a shorted cell and is drawing the others down. I have had that happen a couple times with fairly new batteries. You can confirm this by taking the hot battery out of the bank ( I mean disconnecting it) and charging again.. the remaining good batteries should stay up to proper charge.


Hmmm... I just re read your post... Last year I replaced both batteries with new. I found they never stayed above 12.6 after charging. These are in a small powerboat, so if I'm out for 8 hours, they are being charged for 8 hours. The next day they will be at 12.5-12.6 volts with no load on them. Apparently that is the resting voltage.
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Old 28-12-2014, 11:43   #3
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Quote:
Originally Posted by JoeBradley View Post
Hello,
We are having a problem with our batteries charging and holding a charge. We have three Outback batteries, with 300 AH. We have five solar panels which gives us 350 W total. The batteries are a few months old and have been performing well. We recently had the boat hauled and had to remove our outboard engine from the boat. After disconnecting the engine from the batteries, we have been having trouble with the batteries holding a charge or gaining more than 12.6 volts. We have checked all connections several times. We had the controller checked and it is fine. Does anyone have any suggestions?
Thank You!
Assuming you disconnected the wires to the motor and wrapped them with electrical tape, the solar panels are probably doing what they can this time of year, which isn't much. The biggest problem is there just isn't much usable sunlight.

You have 350W of solar panels, which if you divide by 12 gives a maximum output of 29 amps. But my 300W of solar panels gave less than 50% of the rated output at noon in august in San Diego; so the rated output is just theoretical. A 50% "reality reduction" is probably generous, and gets you down to 14.5A. In August you only get about 8 hrs of usable sunlight, which cuts the max amps x hours to about 116 Amp Hrs/day. But there are lots of rainy and cloudy days, and you don't wash the panels every day, so 75 AH is probably more realistic.

But it's Jan, not August, which means the sun isn't as bright. And your (presumably) flat mounted panels are much less efficient when the sun isn't directly overhead. If you look at the Daily average insolation tables for flat panels here, http://rredc.nrel.gov/solar/old_data...tlas/serve.cgi, and assuming you are in say South Carolina, the average daily insolation for a flat panel in Aug is 5-6 KWh/sq meter/day, and drops to 2-3 in Jan. So you can cut that 75 AH by 60%; you are now down to 30 AH output per day.

Then the question is, what can you do with 30 AH? Boat refrigeration systems are the biggest energy hogs. Mine uses 5A and runs about 50% of the time in summer, using 60AH/day! A 10W halogen bulb uses about 1 A, burn 3 of them for 6 hrs of winter darkness and you use up 18 AH. There are many websites that help you calculate your loads, and I'd bet it is at least 30Ah.

This is all approximation, and sticklers may argue about my math. If you want to calculate for yourself, you can find a good summary of loss factors here. http://www.csudh.edu/oliver/smt310-h...n/solarpan.htm
Vtrdfftesux

As for voltage, you have to look at the controller. An MPPT controller is more efficient than a PWM, but by how much is debatable. But both charge in stages; Amps going in decrease as the batteries get closer to full charge. Even with summer sun in San Diego and no load on the batteries for several days, , I rarely got above a charging voltage of 13V, only the shore charger or running the engine for many hours could get a full charge. (charging voltage for a full battery is about 13.5V; take the charger off and put a small load on, and a fully charged wet cell will show 12.7V.)

For about $150 you can cut through all this confusion by using a battery monitor. There are many out there; I love my TriMetric. It measures electrons in and out of your battery 24/7, and has detailed data outputs. The simplest is %charge. Start with fully charged batteries, tell it how many AH your bank holds, and at a glance anytime you can see how much usable power is left. You can also measure amps in and out. Turn off all loads and you can see how many A your panels put in; turn loads on one at a time and you can see how many amps each one draws.
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