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Phil, Mechanical Engineer
Category: Home Improvement
Satisfied Customers: 8445
Experience:  Retired contractor, 51 years experience
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I have an off grid solar system for my cottage. My batterys

Customer Question

I have an off grid solar system for my cottage. My batterys are not charging fully. Do I

Submitted: 3 years ago.
Category: Home Improvement
Expert:  Rick Ridley replied 3 years ago.
difficult to say without some voltage readings, if you are having good sunshine then ether a panel or to are not producing their full output or indeed it could be your controller, poor connections are another possible cause, do you have a readout that tells you they are not charging fully,have they charged fully in the past? I have a similar system as I am also off grid, Rick
Customer: replied 3 years ago.

I have a digital remote meter that provides me with the state of charge of my battery bank. How do I test to see if the problem is with either the
solar panels or a connection from the panels to the controller?


Expert:  Rick Ridley replied 3 years ago.

You will need the data for the panels and compare this with what you are getting now, bear in mind the data will be off load, what would be use full is if you took on load data when they were installed then comparison is easier, can you give me more info like how many panels and the wattage of each as well as the open circuit voltage, also the battery voltage, Ah rating, what type of battery, Traction or leisure, etc, Rick

Customer: replied 3 years ago.

My system is small --I have 4 80watt Sharp panels (320WATTS).

Open circuit voltage 21.6

Maximum Power voltage 17.3

Maximum Power current 4.63A

Short circuit Current 5.16A


My battery bank consists of 8 - 6volt golf cart batterys totalling approx.

900 amp hours

Expert:  Rick Ridley replied 3 years ago.

OK depends on how the batteries are wired and type of battery if they are gell how long have they been in service and I guess in series giving 48 volts, I think your method of calculating AH is wrong seems more like 112.5 AH is better, 900 would make your bank around half a ton or more, Rick

Customer: replied 3 years ago.

Batterys are 3 months old . The battery bank is a 12 volt system
batterys are flooded

each 6 volt battery has 235 amp hours, they are hooked up in series and parrallel thus the 900 amp hrs


As for weight each battery is approx. 70 lbs., so thats close to 600 lbs. total


The problems I'm having only started 2 weeks ago ,everything was fine until then.

Expert:  Rick Ridley replied 3 years ago.
to put it in perspective, I do not know what you are running from these batteries, but an efficient fridge will run for around 4 days before they are fully discharged, assuming no charging in the mean time, if you are using an inverter to run a mains fridge it will be less due to inverter losses, I have been running off grid for ten years, have a very efficient home and have 800 Ah @ 24 volts, the bank is over half a ton of lead acid bats and this time of year, (summer) I use 5 ltrs of distilled water every 2 to 3 weeks, these are full traction batteries and have been in service now for 6 plus years with a life expectancy of 15 plus years but of course the Ah falls off over time, Rick
Expert:  Rick Ridley replied 3 years ago.
OK this is so open ended, what are you running and how, what is the weather like now? if it has been cloudy for a couple of days the panels will do very little, this is one of those questions that needs lots and lots of info, Rick
Customer: replied 3 years ago.

I only run lights, TV and Radio all my appliances are run off propane.

Until my problem started my system would be FULLY charged before noon daily.


What should I look at first to fix my problem.

Expert:  Rick Ridley replied 3 years ago.
you need to check the amps coming from your solar panels as a start point, this is where a reading at installation would help, but if fully charging it should be close to the short circuit amps specified if not then it could mean a panel is down to help indicate this the voltage should be x the number of panels in series, if it is low then yes a panel has failed, the power still gets through as there are diodes that bypass the faulty panel, if the voltage = the said max then the controller is probably at fault but this is very hard from here as during testing the sun may hide behind a cloud just as you test, Rick
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Customer: replied 3 years ago.

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Expert:  Phil replied 3 years ago.

Welcome to Just Answer!

Based on your discussion with Rick. it seems the problem boils down to bad wire connections or a bad controller.... if the wire connections are clean and tight and you are not draining the batteries faster than you can charge them, odds are in the 90% range that the controller is not working properly.

Those are not overly expensive, you can always use a spare in any case. I would buy a new controller, rated for 10 or 15 amps at the voltage you are charging the batteries with...... so it doesn't run near its peak capacity and overheat (that damages them)

If you want to do some tests you will need a DC volt meter, or a multi meter with DC voltage on it and a DC amp meter good for 0-10 amps DC.

We need to measure the draw on the batteries relative to the input.

We can go from there.