Fridge wiring size help please!

bigdan91

Member
I know it's probably been asked before but I've been reading mixed opinions everywhere
I've got my dual batteries mounted in the bonnet of my 90 series prado

Now it's time to run power to my ironman 50L fridge
I also want to put in a voltmeter and cig socket to go with the merit plug
(like this)
http://www.ebay.com.au/itm/111585926655?_trksid=p2055119.m1438.l2649&ssPageName=STRK:MEBIDX:IT

Should I run 6 b&s or 8 b&s wire from my aux battery to the rear?

Can I run single core and find an earth on the body or do I need twin?

And lastly what size fuse will I need?

Cheers
 

sharkcaver

Well-Known Member
There is not a lot of difference between 6 and 8 b+S. If you went with the lower cost unit (most likely 8BS if you shop around) I doubt with the power usage and length of run you intend that you would notice any difference. I ran 8BS in the old unit and it was no drama at all, even supplying a portable compressor that drew 48A.

I don't know your vehicle nor its characteristics to determine if you should run twin or body earth. Mine is monocoque and I could measure no discernible difference using a body earth.

The fuse will be dictated by the wire size. You will find online all manner of ratings for the same sized wire. I reckon you could safely run 8BS @ 80A, but if you have no need for such a huge draw, limit it to 50 or 60 or so. I doubt you will ever short a 50A fuse unless you short it to earth.
 

Tink

Well-Known Member
If you are just running a fridge in the back, 8 B&S. If you want to charge caravan/camper batteries, then 6 B&S.

Twin core is always the better option. The majority of 12 volt faults can be traced to faulty earths.

Fuses are there to protect the cable. For twin core 8B&S, suggest a 50 amp fuse as the maximum.

Tink
 

bigdan91

Member
If you are just running a fridge in the back, 8 B&S. If you want to charge caravan/camper batteries, then 6 B&S.

Twin core is always the better option. The majority of 12 volt faults can be traced to faulty earths.

Fuses are there to protect the cable. For twin core 8B&S, suggest a 50 amp fuse as the maximum.

Tink
Thanks mate. Not charging batteries. Just fridge, voltmeter and led light strip or usb phone charger run off the cig lighter

What's the best way to split the power between the 3 sockets?
 

bigdan91

Member
There is not a lot of difference between 6 and 8 b+S. If you went with the lower cost unit (most likely 8BS if you shop around) I doubt with the power usage and length of run you intend that you would notice any difference. I ran 8BS in the old unit and it was no drama at all, even supplying a portable compressor that drew 48A.

I don't know your vehicle nor its characteristics to determine if you should run twin or body earth. Mine is monocoque and I could measure no discernible difference using a body earth.

The fuse will be dictated by the wire size. You will find online all manner of ratings for the same sized wire. I reckon you could safely run 8BS @ 80A, but if you have no need for such a huge draw, limit it to 50 or 60 or so. I doubt you will ever short a 50A fuse unless you short it to earth.
It's a 90
Depends on what's on the back of the panel you are going to use. Maybe the blade terminals shown in figure 7, 8 or 9
http://www.narva.com.au/products/browse/blade-2
Tink
http://www.ebay.com.au/itm/111585926655?_trksid=p2055119.m1438.l2649&ssPageName=STRK:MEBIDX:IT
ive bought this one

those terminals wont fit 8 b&s cable though?
 

Jaye

Well-Known Member
That will be alot of power for a fridge and ciggy socket. Most fridges draw less than 10 amps and your std narva ciggy socket is only rated at 20amps which is more than enough for most 12v applications. You can run wiring that is overkill and can handle 100 plus amps bit for what? Your ciggy socket can only handle 20 amps. Fuses always rated for the weakest link, may it be wiring, ciggy socket or load. If your only running a fridge and charging a few accessories you don't really need to worry about voltage drop over the long distance (not really that long) as it won't really have a noticeable effect. 5mm wiring is more than likely required. Often I will run a thick cable down the back with 50 amps to a fuse box down the back. That way I can add more sockets or whatnot without the need to run more cable through the vehicle.
Body earth's are fine. All vehicle manufacturers use them these days. Remember all earth's should be rated the same as the power supply.
 
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Batts88

Well-Known Member
Twin core 6mm is usually the size recommended for fridges that's what I have also used in passed vehicles without any problems. I would usually use a 15amp fuse so I didn't overload either socket if you need more which you won't then you would have to run a separate fuse to each socket so you can get the most out of them but still supply protection and not going above their individual recommended current draw but that gets a bit more involved which is usually not required.
 

Swaggie

Moderator
6mm squared will be fine, what I did is run two, one for the fridge only and one for my gauges, fused at the battery's, then if there's an issue with the fridge its easily diagnosed...
 

Yogi6

New Member
Just bought a 45L fridge freezer (Dometec )
4WD factory lighter socket worked great (dropped 10degC in about 10 min).
Fitted cable (looks like 50 Amp, 6mm) with a new lighter socket to auxiliary battery... would only maintain temperature. The wires in the new socket were only about 1mm so probably low amps.
SOLUTION: bought a “heavy duty” Narva socket rated at 20 Amp. WORKS GREAT. Dropped from 20 degC to zero in 20 minutes.
 

Yogi6

New Member
I would recommend using anderson plugs for the fridge these days. They never come loose losing your fridge temp.
Thanks Rick
I decided to stick with cig lighter because of versatility. Can plug into another car easily. And can use cig socket for various gadgets (spotlight, air compressor, mattress blower etc). Will see how it goes. Oh, also, I later realised I could unscrew the fridge cig male fitting to reveal an Engel fitting (2 flat pins). That would have been useful.
 

Albynsw

Well-Known Member
Thanks Rick
I decided to stick with cig lighter because of versatility. Can plug into another car easily. And can use cig socket for various gadgets (spotlight, air compressor, mattress blower etc). Will see how it goes. Oh, also, I later realised I could unscrew the fridge cig male fitting to reveal an Engel fitting (2 flat pins). That would have been useful.
Cut the plug off leaving a short length of lead and put an Anderson plug on it to use as an adapter when you do need to plug into a cigarette plug on the odd occasion but agree with Ric about using the Anderson plug for your usual setup, the ciggy plugs are rubbish for the power a fridge draws plus they rattle loose
I always cut them off and use an Anderson plug on my fridges
 

Swaggie

Moderator
Thanks Rick
I decided to stick with cig lighter because of versatility. Can plug into another car easily. And can use cig socket for various gadgets (spotlight, air compressor, mattress blower etc). Will see how it goes. Oh, also, I later realised I could unscrew the fridge cig male fitting to reveal an Engel fitting (2 flat pins). That would have been useful.
There's one guarantee that a cigarette lighter connection will give you... IT WILL LET YOU DOWN, sooner rather than later, something you don't need with a 12 volt fridge... Especially on hot days
 

red99td5

Active Member
I am not sure what a narva socket is, but with most weaco and arb fridges, you can unscrew the cigarette lighter tip and you have a engel posifit plug, which is a screw in plug and will never come out. This way you can put the lighter tip back on when needing to use a cigarette socket
 

Yogi6

New Member
I am not sure what a narva socket is, but with most weaco and arb fridges, you can unscrew the cigarette lighter tip and you have a engel posifit plug, which is a screw in plug and will never come out. This way you can put the lighter tip back on when needing to use a cigarette socket
Narva is just the brand name (photo). High amp rating fixed the cooling speed (20 amp). Will see how I go with it coming lose. Will get the Anderson or Engel connector if needed.
 

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Bronto

New Member
Just for the record, using a decent gauge wire is sort of important, somewhat more so in 12 volt systems than 24 volt ones as the voltage dropped even if the same, is a higher percentage of total voltage in the 12 volt system given the same cable is used in both cases.
The more voltage drop the more power you lose. You had it but lost it through insufficient cable size.
For a fridge expect it to use less than 10 Amps so the below numbers are higher at 15 Amps (used in the calcs). Still, I maintain it is better to use higher current rated/lower voltage drop cable where needed and when funds allow. I buy locally as it is cheaper than online and that is to be expected when postage is included with copper being heavy and AP being greedy.

A summary of what you can may lose at the socket in the rear of your 4wd on a 4M (twin) cable run compared with what the battery is outputting.
6mm cable lose 0.44 of a volt (aka auto cable) Good for fridge to nearby socket, eg: the supplied fridge cable. R=29A
6mm2 cable lose 0.34 of a volt Note: its mm squared. Good for in-vehicle runs - battery to rear socket for example R = 37 A
8B&S cable lose 0.26 of a volt Good for between tug & tow or multiple circuits within van, camper trailer & car topper. R = 74A
6B&S cable lose 0.15 volts. Good for battery to battery and longer runs. R= 103A
 

Rusty Panels

Active Member
Hi, I would personally go with the heavier wire option. As the previous replies said most electrical problems are faulty connections and in particular bad earths so unless you can ensure that your earths are spot on run twin cable.
The main reason for the heavier cable is that you may want to use that power source for other accessories at some point so, go bigger.
As far as fuses go the fuse is there to protect your equipment and wiring. If your fridge has a starting current of 10 amps then a 15 amp fuse will suffice. Check the manufacturers recommendation for the fuse. DON'T put too heavy a fuse in the line or you will cause catastrophic damage somewhere if a fault develops.
I'm sorry Gents if I sound like a Smart Alec but the mentions of 50 amp fuses in a few of the replies scare me a bit. You can't run fuses of that size safely in a vehicles accessory circuits. Things like winches and starter motors draw a lot of current which can be in the hundreds of amps depending on what it is but, generally the other gear like headlights, ignition systems, demisters etc might pull up to 20 amps for the initial start up but then drop back to around 10 amps or less once they're running. You won't normally find anything much larger than about a 20 or 30 amp fuse protecting those circuits. Like I said the fuse is there for protection of the circuit putting in a larger one just defeats the purpose and can be dangerous. Cheers.
 

Batts88

Well-Known Member
Hi, I would personally go with the heavier wire option. As the previous replies said most electrical problems are faulty connections and in particular bad earths so unless you can ensure that your earths are spot on run twin cable.
The main reason for the heavier cable is that you may want to use that power source for other accessories at some point so, go bigger.
As far as fuses go the fuse is there to protect your equipment and wiring. If your fridge has a starting current of 10 amps then a 15 amp fuse will suffice. Check the manufacturers recommendation for the fuse. DON'T put too heavy a fuse in the line or you will cause catastrophic damage somewhere if a fault develops.
I'm sorry Gents if I sound like a Smart Alec but the mentions of 50 amp fuses in a few of the replies scare me a bit. You can't run fuses of that size safely in a vehicles accessory circuits. Things like winches and starter motors draw a lot of current which can be in the hundreds of amps depending on what it is but, generally the other gear like headlights, ignition systems, demisters etc might pull up to 20 amps for the initial start up but then drop back to around 10 amps or less once they're running. You won't normally find anything much larger than about a 20 or 30 amp fuse protecting those circuits. Like I said the fuse is there for protection of the circuit putting in a larger one just defeats the purpose and can be dangerous. Cheers.
Some of the reasons for 50amp fuses is for the main power supply from the starter battery to the aux battery which may be located under the bonnet or in the rear of the vehicle. Then all additional accessories will have their own fuses to suit.

Or from an aux battery which is mounted under the bonnet a heavy cable is run to a fuse box at the rear of the vehicle it has a larger fuse to protect that cable if damaged or overloaded you can put a fuse at either end if you desire but not necessary. Then each item run off the fuse box has it's own fuse to suit. Nothing wrong or unsafe with either set ups you may have missunderstood what some people were saying none of them are just using a single 50amp fuse to protect one item for eg their fridge.
 
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