Battery Voltage

I have a 80AH Deep Cell Battery. I have found the following -

1. Checked battery voltage is 13.8V
2. Under load of fridge the battery drops to 10V
3. Then with 100W solar panel connect to battery as well it drops to as low as 7.5V

Solar panel connect to just battery is 12.6V

Can someone help me out with this issue. Is the problem the battery, fridge or solar panels

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Reply By: ABR - SIDEWINDER - Friday, Apr 30, 2010 at 16:49

Friday, Apr 30, 2010 at 16:49
Reg it sounds like the battery has a bad cell.

Do the same test on another battery and you will see.

AnswerID: 414868

Follow Up By: RegReagan - Friday, Apr 30, 2010 at 19:03

Friday, Apr 30, 2010 at 19:03
So would that be the reason it dropped from 13.8V to 10V when connected ???
FollowupID: 685074

Follow Up By: Battery Value Pty Ltd - Friday, Apr 30, 2010 at 20:12

Friday, Apr 30, 2010 at 20:12

it's a bit hard to tell what your battery problems are, could be a defective cell like ABR suggested.

You can do the following which should clear things up:

connect the battery to a mains powered charger and let it charge.

Because your charger mightn't be able to handle a defective battery without acting strangely (like blowing a fuse or going up in flames!), do this in an area which offers a safe distance from combustible materials.

Keep an eye on everything voltage and temperature, and don't go to bed, meaning don't do this overnight.

After several hours of charging, you can disconnect the charger from the battery and check the open circuit voltage.
It should read at least a touch over 12V. Let the battery rest for half an hour and recheck the voltage, it should still show around 12V.
Now you can confidently put it on charge again for 24 hours or so.

Stop charging, and check the voltage across the battery terminals in open circuit. You want to see between 12.6 and 13.2V.
Connect some light loads like 12V lights and check the voltage, connect it to the fridge and see what the voltmeter reads.

If the voltage holds above 12.2 to 12.6V under load, there is still hope.
If not, the battery's pretty much had it.
You can try another 24 hour charging session but chances are it won't come back any more.

Best regards, Peter
FollowupID: 685092

Reply By: obee1212 - Friday, Apr 30, 2010 at 20:10

Friday, Apr 30, 2010 at 20:10
The solar panels should be lifting the voltage unless maybe they are not wired correctly?

The voltage drop from 13.8 to 10 sounds severe to me though I am not a lot of experience though I run a battery/fridge/gennie/and or charge from engine. Couple of questions.

how old is the battery

has it been kept maintained when not in use

how many charge cycles has it done (has it done a lot of work)

Has it been run flat or below 10.5 volts

is the fridge a three way or at least run with a heater element as opposed to compressor motor (heater type will pull a hefty current)

All these things are factors in the performance of any battery. And just to let you know how dumb I am, I bought a battery that had been used to run stuff in a camper but the guy could not tell me if it ever run flat but it had been sitting a long time. It had 11.3 volts on it. Cheap enough to have a punt but when I got home I saw the walls had popped out on an end cell. I must make another appointment with my optomitrist dont you think.

AnswerID: 414898

Reply By: Member No 1- Monday, May 03, 2010 at 19:34

Monday, May 03, 2010 at 19:34
crook cell or cells in battery
get a good'n and try
AnswerID: 415250

Reply By: Maîneÿ . . .- Monday, May 03, 2010 at 20:02

Monday, May 03, 2010 at 20:02
1. ok
2. should be in vicinity of 12.2v - 12.4v
3. should be >13.6v

The battery should be showing a charging voltage of ~13.8v when tested with solar panel connected, under realistic conditions, without fridge connected/running.

There is not enough relevant information to give detailed explanation with-out some guesswork involved.

(a) What happens when you leave the solar panel connected for 24 hours with-out fridge connected ?

(b) What happens when you then connect fridge to battery, while still powered by the solar panel ?

(c) What brand/model solar regulator are you using ?

Maîneÿ . . .
AnswerID: 415255

Reply By: Steve and Viv - Tuesday, May 04, 2010 at 00:19

Tuesday, May 04, 2010 at 00:19
What type of battery is it out of interest. If it's lead acid you may be able to have a look at the cells to check for warped, dry, or collapsed plates.

The drop from a SOC of 13.8 to 10v to 7.2 with the panel would tell me your battery is dying, going, gone. The internal resistance will not allow it to charge properly if there is internal damage and the fridge could be taking more than the panel can put in anyway. Your load test is a good one and I for one would not be heading off to camp for the weekend with that battery.

I had one do the same thing although it was good for 2 hours but it then also failed quite quick after that. While I charged it up with a smart charger it still failed to quick for my liking in that your and family are counting on this to keep drinks and food cool.

Just my opinion

There are some very good threads on batteries and the way they work on here. Have a search and you'll get a ton of good info (and some so so)

AnswerID: 415286

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