Outer Limits 4x4 Board

Sorry if this has been covered but I want to know asap. The jaycar guy just sold me a 20amp circuit breaker for my dual battery setup. My maximum draw should only be around 15amps ( with a couple of lights and a fridge ). I was about to put this between the isolator and the aux battery, but I see that the isolator is 140amp. Will a 20amp circuit breaker be big enough to allow the aux battery to charge ? Won't my alternator's charge be too much for it and trip it constantly ? He told me to put it as close as possible to the isolator also. I think that part is right.

Cheers for any info. Turbz.

The current it will carry is more a function of your charging system, the battery and the setup.

Although your isolator is rated for 140A it cannot carry more than the alternator can generate.

Your alternator may be rated for a large current, but it is unlikely to deliver that to your second battery.

A 20A breaker is rated to carry 20A indefinitely - 21A may take an hour to make it trip, it may carry higher current for a minute or two.

Personally, I would've selected higher rating (I have a 60A fuse) - but, as you've now got it, run with it and see how it goes.

Cheers,

Scott

Hi Turbz, what type and size of an auxiliary battery are you going to be charging.

I find a 30 amp circuit is about right fo 90% of single auxiliary battery set-ups.

Your 20 amp circuit breaker will handle around 30 amps for about an hour and a 30 amp will handle about 45 for an hour.

There’s a lot more to it but let us know your battery details and I’ll give you some ideas.

As for the circuit breaker needing to be close to the isolator, not so, it should, for safety reasons, be as close as practical to the battery.

Cheers.

Interesting. My aux battery is a 75 amp hr. Total amps going to be used from that aux bat is no more than 15amps/hr ( that is including an initial 5-10amp spike from the fridge starting up, and 2 spotties that get turned on every now and then. )
As long as the 20amp breaker can handle the charging system ( 55amp alt ) it should be ok. Fridge uses like 2.5 max and 2 50watt spotties would use ( 110/12=9.2amps ) 9.2 amps ?

I guess I can just try it. Whats the easiest way to check amp draw ? Can you buy gauges that show current draw from a battery?

Cheers. Turbz.

Hi Turbz, with that small a load, you shouldn’t have any problems but if the loads do go higher, the circuit breaker will simply trip and no harm done.

As for measuring amps, for currents up to 10 amps, a $10 multi meter will do the job but for anything over 10 amps probably the cheapest way to go would be a simple automotive amp meter, like what you can get at places like Supercheap Autos.

Cheers

Cheers bro. I will fit this 20amp breaker tmr. As you said, if it trips I can just reset it and buy a bigger one. This one only cost me $6 from jaycar.