Hi all,
Looking at installing a dual battery set up in the next month or two.
Is it better to wire up my accessories (UHF, Stereo, Spot lights, etc) to the main battery or to the second. The fridge would be running off the second.
Cheers
Paul
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Dual Battery and accessories
Moderator: -Scott-
You really only need to connect anything that will be running while the engine is off to the second battery. The idea is that if the second battery is run flat from fridge etc. you can still start the vehicle from the main battery. If you use the UHF with the car off then you can connect that to second battery.
I recommend you read this - http://neuralfibre.com/paul/?p=37
and check out the attached spreadsheet.
Cost varience is huge. The most common system is the least cost effective.
PM me if you need more info or want to see mine.
Paul
and check out the attached spreadsheet.
Cost varience is huge. The most common system is the least cost effective.
PM me if you need more info or want to see mine.
Paul
Lexus LX470 - hrrm Winter Tyres
Gone - Cruiser HZJ105 Turbo'd Locked & Lifted
Gone - 3L Surf
Gone - Cruiser HZJ105 Turbo'd Locked & Lifted
Gone - 3L Surf
The isolator starts to apply charge to the second battery at a preset charge, so long as the alternator is good and charging at more than 14v it shouldn't matter what accessories are on the main battery. If the voltage in the main battery drops below that preset voltage the isolator will just stop charge going to second battery so the alternator can charge the main battery only.
I never installed fuses in any of the systems i have fitted. You can if you really want to but it shouldn't need it. If you do, make sure it is the right size fuse for the intended load/cable used.
Last edited by ScrawnC on Tue Jan 22, 2008 2:10 pm, edited 1 time in total.
The fuse protects the wires from going up in flames and burning down your car.barbz wrote:thats what I thought, never seen one that requires one, it reccomends it in the instructions, worst case it blows the isolator?
Paul
You call.....
Paul
Lexus LX470 - hrrm Winter Tyres
Gone - Cruiser HZJ105 Turbo'd Locked & Lifted
Gone - 3L Surf
Gone - Cruiser HZJ105 Turbo'd Locked & Lifted
Gone - 3L Surf
The fuse is not so much to match the load it's to match the cable... although of course the cable should match the load.
What I am getting at is that I have seen people use fuses to allow for their expected "load", when the fuses are actually too big for the cable they're using. So just be careful with that. It sometimes seems like people think they are protecting their electrical bits and pieces with the fuse, but that's not really it. The purpose is to prevent a dead short from starting a fire, basically. Car batteries can pump out a lot of power through a dead short, it can be pretty catastrophic. Hence, a fuse or circuit breaker as close to the battery as possible is the go.
I'd use an appropriate amperage resettable circuit breaker from Jaycar. In fact that is what I used in my vehicle.
What I am getting at is that I have seen people use fuses to allow for their expected "load", when the fuses are actually too big for the cable they're using. So just be careful with that. It sometimes seems like people think they are protecting their electrical bits and pieces with the fuse, but that's not really it. The purpose is to prevent a dead short from starting a fire, basically. Car batteries can pump out a lot of power through a dead short, it can be pretty catastrophic. Hence, a fuse or circuit breaker as close to the battery as possible is the go.
I'd use an appropriate amperage resettable circuit breaker from Jaycar. In fact that is what I used in my vehicle.
This is not legal advice.
I have a 70A one of these:
http://www.jaycar.com.au/productView.asp?ID=SF2266
Costs about $20. I would not know whether you're better off with the 70A or the 100A with that cable.
http://www.jaycar.com.au/productView.asp?ID=SF2266
Costs about $20. I would not know whether you're better off with the 70A or the 100A with that cable.
This is not legal advice.
Hi barbz, 8B&S cable is only rated at 100 amps when used in a 50% cycle situation, such as powering something like a fridge that cycles on and off.
In a 100% cycle situation, such as that that exists in a dual battery set up where the high currents can be constant, 8B&S is only rated at about 60 amps.
Be very careful when buying cable by it’s marked amp rate, it usually has little to do with what it’s going to be used for, EG., 8B&S cable is rated at around 145 amps when being used in a 20% cycle situation like as starter motor cable.
Next, never use fuses in a high current circuit, anything over 30 amps and circuit breaker are faster acting so are safer.
In your case, with 8B&S cable, a 40 amp AUTOMOTIVE type circuit breaker would be ideal and contrary to the size of your DBS, you are very unlikely to ever require more than 25 to 35 amps max in a single auxiliary battery set up, no matter what type of battery you use or how big your alternator is.
Hi chimpboy, sorry mate but that type of circuit breaker is probably the worst kind to use in a DBS set up and is actually something better suited to a sound system.
Because of the way they work, you need to fit a much high current rated device than would normally be necessary and in doing so, this reduces the safety fact of the circuit. You would be far better of fitting a fuse.
Cheers
In a 100% cycle situation, such as that that exists in a dual battery set up where the high currents can be constant, 8B&S is only rated at about 60 amps.
Be very careful when buying cable by it’s marked amp rate, it usually has little to do with what it’s going to be used for, EG., 8B&S cable is rated at around 145 amps when being used in a 20% cycle situation like as starter motor cable.
Next, never use fuses in a high current circuit, anything over 30 amps and circuit breaker are faster acting so are safer.
In your case, with 8B&S cable, a 40 amp AUTOMOTIVE type circuit breaker would be ideal and contrary to the size of your DBS, you are very unlikely to ever require more than 25 to 35 amps max in a single auxiliary battery set up, no matter what type of battery you use or how big your alternator is.
Hi chimpboy, sorry mate but that type of circuit breaker is probably the worst kind to use in a DBS set up and is actually something better suited to a sound system.
Because of the way they work, you need to fit a much high current rated device than would normally be necessary and in doing so, this reduces the safety fact of the circuit. You would be far better of fitting a fuse.
Cheers
2007 TDV8 Range Rover Lux
2009 2.7 Discovery 4
2009 2.7 Discovery 4
No need to apologise but can you explain a bit?drivesafe wrote:Hi chimpboy, sorry mate but that type of circuit breaker is probably the worst kind to use in a DBS set up and is actually something better suited to a sound system.
Because of the way they work, you need to fit a much high current rated device than would normally be necessary and in doing so, this reduces the safety fact of the circuit. You would be far better of fitting a fuse.
I have used this type of circuit breaker in my vehicle. It's not between the two batteries (which is what I thought we were talking about but I could be wrong)... it's between the aux battery and the things that run off it, ie the 12V-240V inverter, and a couple of other accessories. Have I used the wrong thing?
This is not legal advice.
Hi mate, for protecting an inverter it would be fine.
Now to the differences between these and automotive type circuit breakers and this is going to be long winded but there is no short cuts.
The type of circuit breaker you have ( this is from memory so the figures wont be spot on but you will get the drift ) has been designed to have a low tolerance to current spikes or surges and only allows as little 10% greater current than their rated maximum, to pass through them for a few minutes before they trip and currents of more than 15% greater than their rated maximum will cause them to trip in a few second while automotive type circuit breakers have a high tolerance to current spikes or surges and will allow 40 to 50% more current than their marker rate, to flow through them for up to an hour before they trip ( which is about the same action of a standard automotive fuse ).
Now, armed with the info above, you can get an idea of what circuit breaker to use in which circuit.
If you are protecting a circuit that is going to power a sound system or an inverter and virtually anything that has a known maximum operating current, the circuit breaker you have there is fine.
The problem arises when there is an unknown maximum current requirement for a circuit and this is exactly the case with Dual Battery Wiring Systems.
Most battery to battery systems will require no more than about 25 to 35 amps depending on the size of the batteries, MOST OF THE TIME.
This is only one of many similar situations but you will get the idea. If occasionally you run your battery down to a fairly low state of charge, when you first start to recharge it, some batteries, particularly some AGM batteries, can pull every amp available and most AGMs, contrary to common belief, should not be charged with anything like these high current for anything but a few minutes.
If you want to cater few the few minutes of high current when you start charging, you have to fit a 70 or 100 amp circuit breaker like the one you have but the problem is that if the AGM keeps pulling this high current, there is nothing to stop it.
If you use a 30 amp automotive circuit breaker, you will allow high current surges, like those required when first starting but if the battery keeps pulling high currents, the circuit breaker will trip and even though the circuit breaker will reset, it gives the battery some respite from the high charging currents.
There are other benefits such as battery failures where the battery doesn't go into a short circuit situation but has a cell collapsed. This can cause a high current constant drain on the rest of the electrical system and if the current drain is up around 70, 80 or 90 amps, your circuit breaker is not going to give you any protection and your hole electrical system is going to be overloaded, a low current automotive CB will give you protection.
There’s a hell of a lot more to it but this will give you some idea of the differences between CBs and in short, you can use a much smaller automotive type circuit breaker which will give you much safer protection but still allow your dual battery system to work as designed.
Now to the differences between these and automotive type circuit breakers and this is going to be long winded but there is no short cuts.
The type of circuit breaker you have ( this is from memory so the figures wont be spot on but you will get the drift ) has been designed to have a low tolerance to current spikes or surges and only allows as little 10% greater current than their rated maximum, to pass through them for a few minutes before they trip and currents of more than 15% greater than their rated maximum will cause them to trip in a few second while automotive type circuit breakers have a high tolerance to current spikes or surges and will allow 40 to 50% more current than their marker rate, to flow through them for up to an hour before they trip ( which is about the same action of a standard automotive fuse ).
Now, armed with the info above, you can get an idea of what circuit breaker to use in which circuit.
If you are protecting a circuit that is going to power a sound system or an inverter and virtually anything that has a known maximum operating current, the circuit breaker you have there is fine.
The problem arises when there is an unknown maximum current requirement for a circuit and this is exactly the case with Dual Battery Wiring Systems.
Most battery to battery systems will require no more than about 25 to 35 amps depending on the size of the batteries, MOST OF THE TIME.
This is only one of many similar situations but you will get the idea. If occasionally you run your battery down to a fairly low state of charge, when you first start to recharge it, some batteries, particularly some AGM batteries, can pull every amp available and most AGMs, contrary to common belief, should not be charged with anything like these high current for anything but a few minutes.
If you want to cater few the few minutes of high current when you start charging, you have to fit a 70 or 100 amp circuit breaker like the one you have but the problem is that if the AGM keeps pulling this high current, there is nothing to stop it.
If you use a 30 amp automotive circuit breaker, you will allow high current surges, like those required when first starting but if the battery keeps pulling high currents, the circuit breaker will trip and even though the circuit breaker will reset, it gives the battery some respite from the high charging currents.
There are other benefits such as battery failures where the battery doesn't go into a short circuit situation but has a cell collapsed. This can cause a high current constant drain on the rest of the electrical system and if the current drain is up around 70, 80 or 90 amps, your circuit breaker is not going to give you any protection and your hole electrical system is going to be overloaded, a low current automotive CB will give you protection.
There’s a hell of a lot more to it but this will give you some idea of the differences between CBs and in short, you can use a much smaller automotive type circuit breaker which will give you much safer protection but still allow your dual battery system to work as designed.
2007 TDV8 Range Rover Lux
2009 2.7 Discovery 4
2009 2.7 Discovery 4
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