Aux batteries in parallel

[sam_d]

Question:

You have an auxiliary battery in your car connected to the main battery via a dual battery controller.

The existing auxiliary battery is an ordinary cranking battery (ie. not a deep cycle battery). You want to connect a deep cycle battery in parallel to the existing auxiliary battery. Is this:

a) Okay. This shouldn't be a problem.
b) Okay but maybe a little bit iffy.
c) It won't work very well.
d) No! No! No! No! People like you should not be allowed near electricity!

Note: this is just a thought I had earlier and I haven’t actually planned to do anything yet.

[Disco_owner]

G'day Sam;

your main Cranking battery and the 2nd battery which is also another Cranking battery can be hooked up in paralell, no issues there. but If you are running a Fridge at a camp site it will be drawing from both batteries,so be warned !

some fridges eg Engels have a Cut off switch to stop Drawing current from your parallel battery set up when total voltage drop reaches a Certain voltage ,think this may be about 10 volts so that if you are on a camp site
running camp lights / fridge etc you will be able to start your car next morning with some power left in both batteries , however not all fridges are fitted with this device , so be careful not to Drain your batteries if you're static at a camp site.

I heard someone from our 4wd club mention this a while back that this actually a Prefered installation for most people who set off out push for weeks on end,No voltage sensitive relays / Electronics to control the charge patterns , the alternator is charging both batteries all the time.

However as an alternative option you can install a Manual Switch which allows you switch between your Main/Aux/Both.

[BradM]

Hi Sam,
The people use use only a very heavy duty solenoid as the Aux battery isolator have the deEp cycle and ordinary battery hooked up in paralell all the time.

I had this setup in a 1996 GQ patrol when I lived in the NT.

BradM

[BradM]

Forgive my spelling - rush job

BradM

[streaky]

I would have thought that when connecting two batteries in parrallel they should both be of the same type,size, cca etc so as to avoid the stronger of the two betteries dragging off from the lesser one?

I don't know for sure but I had two batteries in parallel lnked up for winching on my series III lightweight this way & a another battery for engine duties.
This worked fine untill one of the winching batteries dropped a cell...then the remaining battery went down hill fast.

Regards.

S.

[PhilipA]

Pre electronic Engels do NOT have a cutout.
the compressor will work down to 10.5 volts, but it will just keep on trying, flattening the battery further.
AFAIK The Waeco has a low voltage cutout.
Regards Philip A

[Disco_owner]

yes that is correct , the Post Electronic models have the cutout circuitry built in, haven't had much experience with Waeco Fridges.

[Bulldog]

G'day Sam;

your main Cranking battery and the 2nd battery which is also another Cranking battery can be hooked up in paralell, no issues there. but If you are running a Fridge at a camp site it will be drawing from both batteries,so be warned !

some fridges eg Engels have a Cut off switch to stop Drawing current from your parallel battery set up when total voltage drop reaches a Certain voltage ,think this may be about 10 volts so that if you are on a camp site
running camp lights / fridge etc you will be able to start your car next morning with some power left in both batteries , however not all fridges are fitted with this device , so be careful not to Drain your batteries if you're static at a camp site.

I heard someone from our 4wd club mention this a while back that this actually a Prefered installation for most people who set off out push for weeks on end,No voltage sensitive relays / Electronics to control the charge patterns , the alternator is charging both batteries all the time.

However as an alternative option you can install a Manual Switch which allows you switch between your Main/Aux/Both.

Umm, have i missed something here?

If you're running camp lights and a fridge you WON'T be able to start the car the next morning. The fridge will cut out nicely at X voltage, and the camp lights will drain the remaining charge until (a) the lights go dim and you walk home, or (b) you don't notice the lights go dim, and you walk home. Correct me if i'm wrong.

Don't know about anyone else, but i'd prefer my fridge AND camp lights to cut out when the aux batt is flat/over flat/dead/etc and still be able to start the car the next morning, keeping in mind (being a LR ), it might need to be cranked for 30 seconds before it starts.

Alternator DOES charge both batteries all the time, except for the first minute or so of running... big deal on a X hour drive... Also, if the aux batt is overdrained and stuffed, the main is still as good as new. OK, the beer's a bit warm, but i can still DRIVE to the pub for a cold one .

The waeco fridges have a 3 position cut off selector: low, med, high. Doesn't stop your camp lights stuffing things up!

IMHO, the manual switch is useless (had one). As soon as you turn the ignition off, your main batt starts charging the flat one until you remember 3 hours later. Been there, done that.

[sam_d]

Thanks for all the responses everyone. I'm afraid none have actually answered my question (though streaky was close)...

What I was asking is this:

Is it okay to connect an ordinary cranking type battery (not the actual cranking battery) and a deep cell battery in parallel?

They will both be aux batteries connected to the main battery via a dual battery controller. Is it okay to do this?

[zwitter]

I would say d)
The ideal would be 2 identical batteries only should be connected in parallel. Infact often the cells are preferably from the same batch and even matched for performance.

But in the real world in a automotive environment things are far from ideal. I would still say do not mix types of batteries and in general the closer the batteries are in size / capacity / condition etc the better they would work.

The big solenoid system should just be wired to not connect the second battery until the car is running and preferable a few minutes later.

You could use the big solenoid charge method and just use 2 solenoids but would be better using a system to sequence the batteries into charge connection.

Or use voltage sensing relays and cascade them. or just ditch the existing second battery and purchase 2 deepcycles and use in parallel.

There are products advertised on this board that will do the trick either way. And discounts for batteries too. try a search fo some excellent past posts.

Any manual system is called an idiot switch as it relys on the idiot to switch them on and off and eventually you will forget.

Good luck
james