Thread: 12V caravan battery charging

Originally Posted by Pedro_The_Swift

wont all batts read the same if still connected?[/SIZE]

Yes but 12.2v is way to low.

You could have any number of problems from a failing battery to a faulty solar reg but a bad connection could also be a cause of your problem.

Also check all your appliances and make sure one of them is not using power when it’s not needed.

Unfortunately, you need to start at your batteries and see if they are getting a charger and then, see if they are holding that charge. This will probably mean disconnecting them.

Try all the above before disconnecting your batteries but if you do have to disconnect them, a faulty/failing battery will show itself pretty quickly in that it will very quickly drop it’s voltage while the other batteries may actually get a voltage rise.

Best of luck.

Presuming you have power from your solar panel coming to your controller, all loads connected to the controller and the batteries connecter directly to your controller. Nothing connected directly to the batteries. You could check things right at your controller. You just need to check current and where its going. Just make sure your multimeter will handle the current, many only do up to 10amp.

Pull one leg of the lead to your batteries. It wont matter, positive or negative. Then use the multimeter in between.

Disconnect the load and you will see exactly how many amp are going to your batteries from the solar panel.

Disconnect the solar panel and connect the load and you'll see how much is going to you load.

Without any figures, it's hard to calculate what it should be doing and if it's not performing right.

Happy Days.

Like this: (just put this together on the table)



With the light off so you can actually see the circuit.



Drawing 4.5amp/hr



7AH battery



7.0AH / 4.5amp = 1.5hrs.

That would be a start. Different batteries perform differently and loose some extra power in heat. The higher the current draw the less of the capacity you'll get. If you look at the spec sheet (link I provided earlier) for my 22AH battery, you'll see it should last for 20hrs at 1amp, 10hrs at 2amp but only 5hrs at 3.5(not 4).

Happy Days

I just checked the specs for the 7AH battery and it will only last 1hr not the 1.5hr calculated because they loose efficiency with the higher current draw.

Happy Days

When my house backup system had a similar problem recently it turned out that one of the two parallel batteries had a dead cell. You really need to separate the batteries and test them individually after a few hours of sitting time. 12.2 volts is equivalent to a fully charged battery at 14.4V with one shorted cell. It'll drop to around 10.5 volts when isolated.

As for amp-hours, the battery Ah rating is for a new battery under specified conditions and you'd be risking its life to draw all of it out. The 7Ah battery in joel0407's example can only supply around 4Ah at 4 amps load and then it would be quite flat.

Originally Posted by bee utey

As for amp-hours, the battery Ah rating is for a new battery under specified conditions and you'd be risking its life to draw all of it out. The 7Ah battery in joel0407's example can only supply around 4Ah at 4 amps load and then it would be quite flat.

Actually it will supply 14.2amp for 15 minutes.

And it's not so damaging to run AGM batteries down. This one will progressively drop capacity to 60% over 300 complete discharges.

Considering my next trip will be for a month (30 days) then I will have only used 10% of the life of the battery. It's more likely to deteriorate from age over 10 years than complete discharges.

A complete discharge is down to 10.5v. (9v for high current on the little 7AH battery in my pick). The voltage will jump straight back up to more than 11v as soon as the load is removed.

http://www.power-sonic.com/images/po...5_12_Oct_2.pdf

Happy Days

Edit: As for the AH being only for new batteries under specific conditions. I have had the little 7AH battery for over 4 years and it was replaced as standard replacement time for some Telstra equipment before then. It still has a capacity over 7AH. My charger will log AH discharge and AH charge. While it still has the capacity, it won't float. My charger expects to see charge load drop at peak charge before it goes into float mode but this battery still draws too much current for the charger to decide to disconnect. I don't mind sacraficing the odd charge cycle to check my batteries.

Happy Days

Originally Posted by joel0407

Actually it will supply 14.2amp for 15 minutes.

And I wrote 4Ah not 4A. At 14.2A load it would have a capacity of 3.55Ah.

Anyway, it's not the original poster's problem.

after disconnection--
Gel(still on regulator) is 13.56
ALSO immediately upon disconnect the Reg shows green flashing, indicates PWM charging.
2nd (AGM) shows 12.56
3rd (AGM) shows 12.56

both connectioms were good, clean and tight.

10 minutes later-- late edit,
after connecting the second bat the reg still shows green

late late edit,
gel isolated from everything shows 12.7, will leave for an hour and retest