Multiple battery charge question

Submitted: Wednesday, Jun 10, 2009 at 21:59

ThreadID: 69700 Views:3174 Replies:2 FollowUps:2

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viz

This one might have been done before, if not specifically:

Want to add another battery to the aux circuit - at this moment it is a Waeco Thumper which is showing signs of dying after at least 6 years of stirling service. Thinking of replacing it with another AGM battery - they rock! Tried out the new aux AGM over the long weekend on the Autofridge and was impressed after two days (10 hours of running) voltage was down to 12.4 volts. Plenty left (eutectic fridges rock too :)

The question:

What is the best way to charge two aux batteries - simultaneously, or should I add a second isolator relay (using a Baintech one from Battery World at the moment) downstream from the first aux battery? (Sort of a cascade or waterfall effect I guess). The latter method seems to me the most logical and to give the most protection, and reduce the load on the alternator.

Gonna locate the second battery in the back, connecting using Anderson plugs. This battery will be able to to be used as required around the campsite and placed back in the car when required for charging or as a backup for the fridge...

viz

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Reply By: Sand Man (SA) - Wednesday, Jun 10, 2009 at 22:46

Wednesday, Jun 10, 2009 at 22:46

No real need to have a second isolator Viz.

An isolator is used to protect the starting battery from running flat when using accessories like fridges, etc.

You can have a third battery connected to the auxiliary with nothing more than a fuse to protect the circuit from a possible short circuit.

By the way, you can have the Thumper repacked with new battery cells from Blue Apple (Home of 12 volt) who are the manufacturers. Waeco no longer have any connection with the Thumper product.
If you do wish to have a second isolator/controller Blue Apple also have a couple of in-car charging kits. you may like to look at.
You simply attach one end to the auxiliary battery and the other end has an Anderson connector on the termination box to which you patch in the Thumper.

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AnswerID: 369436

Follow Up By: viz - Thursday, Jun 11, 2009 at 21:00

Thursday, Jun 11, 2009 at 21:00

Thanks Sand Man

I am thinking of getting new batteries in the Thumper, but I do *like* those AGM batteries. The Thumper in its time was the beezneez, but in terms of capacity in a given lump of lead (i.e. volume and weight in the car) I think the AGM would be better. When the Thumper dies, I'll revisit the issue - and this may take a while because I have semi-retired it - it just runs the camp lighting now and it has capacity for a week in this mode...

I also have in my parts bin a couple of those Blue Apple switches - something else to think about.

I also have a whole lot of 30 amp auto re-setting breakers in the bin as well - might make use of them too. I am however looking for a timer to turn the fridge off after a set run time (being eutectic it only needs 5 hours of running per day - 2 in the morning and 3 in the evening).

Before putting the 2 battery issue to bed, I have a couple of other concerns. If you have a dead flat (gel, say) battery hanging off a an AGM aux battery and connect the two, would it not cause a fuse to blow or melt some (if inadequate) wiring? Or is the an in-built resistance in the system?

Also - what thickness wiring should I be looking at from the front of the car to the rear, considering that I do not expect to exceed 15 amps continuous (that's everything on and includes a 25% reserve). I may have a start amperage of 30 amps for the fridge, but that is only momentary. Battery lead thickness, or can I go a little smaller without a voltage drop? I am using 50 amp Andersons, not the big ones.

Thanks again

viz

FollowupID: 636977