Advice on changing circuit breaker

[Piratepete Member Find all posts View Profile Close Piratepete]

I have a dual battery set up with Redarc SBI 12 and Optima D34. Goes to panel at back near Jack with dual usb, , cig & engel. Have an Anderson plug that runs down chassis next to tow bar.

In the set up the auto electrician did, he has installed a 20 amp circuit breaker. (I know, not the favourite approach by a lot of people on Pradopoint). I connect a Dr Air Pro compressor at back via the Andersen plug rather than by clips to battery (have leads configured so I can do it both ways).

Anyway, under load after a while, the circuit breaker cuts out. Checked with the auto electrician and he reckons that the circuit breaker is too small, says he only installed it for a caravan load, not for a compressor. (By the way, no problems with compressor when connected direct to battery).

It's only $12 for a 30 or 40 amp circuit breaker from Supercheap so I was gonna have a go at changing it myself.

Always nervous with auto electrics, any advice for changing it over appreciated ie do I need to disconnect from battery, any issues with SBI 12, can I just leave everything connected and just swap over

[pradosteve97 Junior Member Find all posts View Profile Close pradosteve97]

undo and lift the negative battery terminal first that way if the spanner shorts to the body it doesn't matter.
undo the nuts on the c/b undo swap the c/b do up nuts .
Put the negative batter terminal back on .

[AussieAndy Find all posts View Profile Close AussieAndy]

undo and lift the negative battery terminal first that way if the spanner shorts to the body it doesn't matter.
undo the nuts on the c/b undo swap the c/b do up nuts .
Put the negative batter terminal back on .

Remove BOTH negative battery terminals

[drivesafe Senior Member Find all posts View Profile Close drivesafe]

Hi Pete, and sorry mate but DO NOT CHANGE THE CIRCUIT BREAKER before you replace the cable, read WIRE, going to the back.

That circuit breaker is the highest current rating you can safely use with that size WIRE.

Another example of an auto electrician who has no idea of how to setup a dual battery system properly and safely.

[pradosteve97 Junior Member Find all posts View Profile Close pradosteve97]

drivesafe's just pointed out why i never make any money all ways redoing things for nothing.
Maybe run a complete new feed to the comp In my real job I can't over rate circuit breakers to cables so I 'd best not be telling people to do it on their cars .

[Piratepete Member Find all posts View Profile Close Piratepete]

Thanks guys... Auto electrician said I'd have to leave car for a day, that's why I thought I might do it myself.

He did say something about doing a load test. I guess that's what drivesafe might be hinting at, might need to upgrade cable to rear before upgrading circuit breaker.

You reckon I'm p&$:?d off about having to pay for the changes. Auto electrician is RAA approved and been around for 30 years. Proper cable and circuit breaker might have cost an extra $30. Grrrrrrrrr

[brogers Advanced Member Find all posts View Profile Close brogers]

I have a dual battery set up with Redarc SBI 12 and Optima D34. Goes to panel at back near Jack with dual usb, , cig & engel. Have an Anderson plug that runs down chassis next to tow bar.

In the set up the auto electrician did, he has installed a 20 amp circuit breaker. (I know, not the favourite approach by a lot of people on Pradopoint). I connect a Dr Air Pro compressor at back via the Andersen plug rather than by clips to battery (have leads configured so I can do it both ways).

Anyway, under load after a while, the circuit breaker cuts out. Checked with the auto electrician and he reckons that the circuit breaker is too small, says he only installed it for a caravan load, not for a compressor. (By the way, no problems with compressor when connected direct to battery).

It's only $12 for a 30 or 40 amp circuit breaker from Supercheap so I was gonna have a go at changing it myself.

Always nervous with auto electrics, any advice for changing it over appreciated ie do I need to disconnect from battery, any issues with SBI 12, can I just leave everything connected and just swap over

Hello piratePete,

I hope I'm not mentioning something that you already know, but fuses and circuit breakers in the positive wire in your installation are not there primarily to protect your compressor or accessories, they are in the circuit primarily to protect your car from burning to the ground...ie to protect the actual wiring from overheating, failing or burning out. The circuit breaker is typically chosen on size according to the cable, which is typically (or should be ) chosen for the planned or possible loads and voltage drops etc...soooo... just to swap out the circuit breaker for one of higher capacity may be problematic unless your wiring is capable of taking the increased load...so the answer is...it all depends on how its been wired pirateP and what wire was used. It sounds like the circuit breaker is actually doing what it designed to do, ie trip out to prevent the wire from heating up and burning when you use the compressor and draw more current than what the circuit was designed to handle. You may indeed need new wiring, or a dedicated circuit for your compressor, or just connect your compressor directly to you battery with battery clips..perhaps

[Guest Close Guest]

What is the wire gauge and the length of the run? That will tell you the maximum current carrying capacity and circuit breaker needed.

[Piratepete Member Find all posts View Profile Close Piratepete]

Ok, let's try lan B. Don't think it will be worth upgrading wring to the back. I'm still keen to access an Andersen plug for ease of connecting the compressor.

I've seen on some mine spec' prados an Andersen type plug at the front of the vehicle. Found out that this is for jump starting on mine sites to eliminate any sparking compared to jumper lads with clips on the battery. Apparently this is a high amperage set up for jump starting.

I would appreciate advice on setting one up at the front, probably poking through the lower plastic grill in front of the radiator. I would take the feed off my auxiliary battery to drive my Dr Air Pro compressor.

What size wire should I use, do I need a fuse ( obviously isn't in place when compressor is connected via leads ) will standard 50 amp Anderson plugs be sufficient?
Anything else I should consider?

[drivesafe Senior Member Find all posts View Profile Close drivesafe]

Hi again Pete, fit a length of 6B&S twin cable to your cranking battery, not your auxiliary battery.

Fit a 50 amp auto resetting circuit breaker to the Red cable of the 6B&S, as close as practical, to the positive ( + ) terminal of your cranking battery.

While you can get dust covers and safety boots for the Anderson plug, these are more a personal preference than an absolute need.

With this setup, you can run your compressor, which should only be done while the motor is running.

Or you can use the setup to jump start your vehicle or to jump start someone else’s vehicle from yours.

You also give yourself a good place to connect a battery charger or voltage regulated solar panels.

[peter_mcc Senior Member Find all posts View Profile Close peter_mcc]

How long does it take to trip the circuit breaker? You said "a while" - can you time it?

Are you pumping the tyres up with the engine bay hot or cold? If hot, try it again cold and see what happens.

If you take a look at the datasheet for the Cooper Busmann circuit breaker that looks like yours (see here) you'll see two things:
- the breaker needs to be derated as the temperature goes up. If your engine bay is at 65C then it could be derated by to around 75% (making your 20A breaker a 15A one)
- the trip time is a function of current. As you get closer to the rated current (20A) it takes longer to trip. So a 20A breaker won't ever trip at 21A and may never trip at 30A (as I read the graph). But if you draw 100A it will trip very quickly

You might find a 25A breaker doesn't trip. I'd be surprised if the extra 5A would cause the cable to heat up to a dangerous point but I'd need to know more about the cable used before we could do any calculations on that.

[Bushbasher Out of control poster! Find all posts View Profile Close Bushbasher]

I have a ARB compressor under the bull bar at the front connected direct to cranking battery. I also have an anderson plug in front of the grill with a 50 amp fuze connected to the aux battery which used to drive my portable ARB compressor. Running the compressor from the front just means having 2 x hoses if I need to pump up the trailer tyres. I can also hook up my 200w solar panels via the anderson plug up front. The plug runs battery cable. If you're intent on running the compressor from the rear then you'd be wise to run separate cabling as others have advised.

[Piratepete Member Find all posts View Profile Close Piratepete]

Thanks for all the feedback guys. Looks like a cable and fuse off the cranking battery with Andersen plug for connecting to the compressor will be the way to go. Saves running the separate cable to the rear. I like the idea of a connection at the front of the Prado.

[drivesafe Senior Member Find all posts View Profile Close drivesafe]

Hi Pete, if you use a fuse, just make sure you have spares and you can go to a 60 amp fuse with 6B&S cabling.

If you think you may need to do some jump starring, then you may blow a fuse.

Where as, if you use an auto resetting circuit breaker, it will not matter if it trips while jump starting.

The largest commonly available auto resetting circuit breaker is 50 amps but this is still large enough to allow jump starting.

[sweetpea Senior Member Find all posts View Profile Close sweetpea]

The largest commonly available auto resetting circuit breaker is 50 amps but this is still large enough to allow jump starting.

Narva have a higher range which may not be commonly available

http://www.narva.com.au/products/bro...-amp-automatic

About $55 on ebay or $59 at https://automotivesuperstore.com.au/...-breaker-55954

S.