Adding a third battery?

yes you can have third battery in parrallel wire it positive to positive and negative same as first two ie connect 3rd battery to second battery as if you were jump starting 2nd batt with 3rd batt.

It is best to have all three batteries the same type and age if possible but not absolutely necessary,note if one of the three batteries has a dead cell it will discharge all three if it is not isolated.

Hi Col, Yes you can safely add a third battery in parallel. Best that it is the same type and size. Adding a new battery to the older ones is not a problem. A small problem arises when eventually one of the batteries begins to fail. If it begins to self-discharge due to displaced plate material then it will also discharge the connected batteries. If this begins to happen you will observe depleted capacity from the bank and it is simply a matter of separating the batteries to test them individually. Then renew the faulty battery.

To connect the third battery in parallel it is simply connecting its positive to the others positive and negative to negative. Provided that the interconnecting cable is very short and carefully positioned to avoid damage there is no need for fuses in the interconnecting cable. However if the third battery is at all remote from the others then it is necessary to place fuses in the positive cable only. Two fuses, one close to each battery positive terminal. 30 Amp fuses should be OK.

Hello Col,

as has been said, no problem in wiring a new battery in parallel to the two older ones.
You can try to fuse the three batteries lightly, so that if one battery drops a cell, it isolates itself by blowing its fuse.
Start with 3x 15A, and if they blow (which I doubt they will) due to high alternator charging current, replace them with 20A ones.

If you want to keep an eye on the battery current distribution, you can wire a voltmeter between the batteries. As soon as a cell in one of the batteries starts to go down, one of the two voltmeters (or both, if it's the one battery in the middle) will start reading several tens or hundreds of milliVolts.
See the image for better illustration below - just add the 3rd battery with its own fuse, and another voltmeter if you prefer.

Image Could Not Be Found

cheers, Peter

Hi guy's

Thanks for that info, very much appreciated. Will the 220 watt of solar panels struggle to charge the 3 batteries or will it still be of some benefit to have the third battery with the set up I have?

Thanks from Col.

Col,

I've nothing to add to the earlier replies except to suggest that if you intend using the vehicle for most of your charging, a dc-dc charger near the batteries might be a better option than additional solar capacity. These chargers take the available voltage sent back to the van from the alternator, and increase it so as to increase the charging current going to the batteries. This can overcome losses in wiring and ensures that you batteries can in fact be fully charged by the vehicle. One side effect is that you may need heavier cable running from the engine bay to the van (suggest at least 6 B&S twin), but that may be the case anyway as you'll have more storage to charge.

Cheers

John

Hi all,

Thanks again for the additional info. I have no more space on the van's roof but do have the correct wiring from the car and will take on board all of your suggestions. We camp nearly always remote and after 2 or 3 days of overcast conditions I have to start the car which is no hassle really but another battery will give me peace of mind. But being from Vic the sun always shines after a day or two anyway Ha!
I'm one happy chappy for with this info I'll be able to put another battery beside the others and the better half won't have to be told to go easy on the power usage and I won't have to cop the earful of why things aren't coping.

Thanks again for your replies,

Col.