Thread: Dual Batteries and Fuses...

Hi sam, anything like a dual battery system’s cabling should have circuit breakers not fuses and you should not fit anything bigger than a 50 amp circuit breaker other wise anything other than a short circuit will, like just a current overload can actually melt the cable before a 100 amp circuit breaker ( or fuse ) goes open circuit.

Cheers.

Originally Posted by drivesafe

Hi sam, anything like a dual battery system’s cabling should have circuit breakers not fuses and you should not fit anything bigger than a 50 amp circuit breaker other wise anything other than a short circuit will, like just a current overload can actually melt the cable before a 100 amp circuit breaker ( or fuse ) goes open circuit.

Cheers.

Cheers for that.

I had just found this post http://www.aulro.com/afvb/showthread...ight=100a+fuse from Feb last year.

I am installing this: http://www.projecta.com.au/documents/item/303 controller, the instructions for which are not clear about the fuse rating which should be used.

So, a 30A circuit breaker should be adequate for day to day operation, but what about the 75/100A direct charging should the main battery become flat?

Oh, and another question, why a circuit breaker and not a fuse?

Originally Posted by sam_d

So, a 30A circuit breaker should be adequate for day to day operation, but what about the 75/100A direct charging should the main battery become flat?

Not quite sure what you mean?

In high current circuits, circuit breakers react quicker than fuses plus as dual battery systems operate within specific current range like most circuits BUT unlike other circuits, dual battery system currents will occasionally have high current requirements, like when charging a low auxiliary battery, that can last for long periods of time but then go back to normal current operations, like for powering a fridge or the likes.

By using an automatic resetting type circuit breaker you can pick the correct rated circuit breaker that will handle the regular current requirements and the occasional higher charging current for short periods of time, 50% higher current than the circuit breaker’s rate, for about an hour but if the current goes higher or lasts longer, the circuit breaker will go open circuit and act as a current overload regulator.

There’s a lot more to it but that’s the basics.

Cheers

Originally Posted by drivesafe

Not quite sure what you mean?

Cheers

As I understand it from the instructions (here: http://www.projecta.com.au/documents/item/303) the control unit allows a 500mA current to recharge the aux battery.

However, should the starting battery become flat, the unit can be manually overridden to allow the aux battery and starting battery to beconnected in parallel. I'm guessing this is the 75A/100A peak mentioned in the specification?

They also list a 150A fuse in the 'items needed' section.

Hi sam_d,
I think that you'll find on, re-reading, that the unit draws (consumes) 500mA when in use & 30mA in standby mode.

Originally Posted by sam_d

As I understand it from the instructions (here: http://www.projecta.com.au/documents/item/303) the control unit allows a 500mA current to recharge the aux battery.

However, should the starting battery become flat, the unit can be manually overridden to allow the aux battery and starting battery to beconnected in parallel. I'm guessing this is the 75A/100A peak mentioned in the specification?

They also list a 150A fuse in the 'items needed' section.

Originally Posted by sam_d

As I understand it from the instructions (here: http://www.projecta.com.au/documents/item/303) the control unit allows a 500mA current to recharge the aux battery.

I'd hope not. That would mean 160 hours to recharge a 80Ah battery.

I'd guess this is the current it consumes.

However, should the starting battery become flat, the unit can be manually overridden to allow the aux battery and starting battery to beconnected in parallel. I'm guessing this is the 75A/100A peak mentioned in the specification?

I wouldn't want to use the device itself to parallel the batteries for jump starting. I think I'd carry a very short jumper lead to bridge the positives for that. (Especially if you have a 150A fuse inline somewhere)

They also list a 150A fuse in the 'items needed' section.

Use a circuit breaker - apart from the operating speed advantage, you won't be replacing fuses if you do get a momentary short somewhere.

In my setup, I have a circuit breaker between the output of the SC80 DBC and the aux battery, plus a very short run to an extra fusebox from the aux battery, then all accessories fused from that. For paralleling the batteries I'm going to use a battery switch mounted on the seat box which will common the positives when needed.

Okey then, final question:

Where does one get a 150AMP fuse/circuit breaker from? I asked at Repco the other day for a 100A fuse and they looked at me as if I was mad and that 100A can only be generated by God

Dick Smith only do blade fuses up to 35A and a circuit breakers up to 8A.

Originally Posted by sam_d

Okey then, final question:

Where does one get a 150AMP fuse/circuit breaker from? I asked at Repco the other day for a 100A fuse and they looked at me as if I was mad and that 100A can only be generated by God

Dick Smith only do blade fuses up to 35A and a circuit breakers up to 8A.

A good but expensive source for high amperage rated fuses and CB's is an aviation parts supplier such as Aviall. Go have a poke around your nearest larger general aviation airport.