Fridge wiring size help please!

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

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/111585926...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

[MDS69 Advanced Member Find all posts View Profile Close MDS69]

My opinion for what it is worth would be to run 6B&S to a distribution panel containing the gauges and sockets you want all appropriately fused. For an overall fuse 50A should be OK.

[Anth120playdo Banned Find all posts View Profile Close Anth120playdo]

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/111585926...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

Should I run 6 b&s or 8 b&s wire from my aux battery to the rear?
A. Either. All you need is 50amp dual core. The bigger stuff is more if you want to charge batteries in rear or camper etc.
Someone like Leigh can correct me if I'm wrong.

Can I run single core and find an earth on the body or do I need twin?
A. If it was for 8 b&s etc, single is fine. The great big chassis can conduct well. Eg; Anderson plug for trailer, earth to chassis.
If you decide to run 50amp dual it's done! That's all you need to run fridge etc.

And lastly what size fuse will I need? Less than your wire, 30 amp? Probably 10amp would be fine.

Hopefully you get some better replies, I'm no auto elec lol......

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

Should I run 6 b&s or 8 b&s wire from my aux battery to the rear?
A. Either. All you need is 50amp dual core. The bigger stuff is more if you want to charge batteries in rear or camper etc.
Someone like Leigh can correct me if I'm wrong.

Can I run single core and find an earth on the body or do I need twin?
A. If it was for 8 b&s etc, single is fine. The great big chassis can conduct well. Eg; Anderson plug for trailer, earth to chassis.
If you decide to run 50amp dual it's done! That's all you need to run fridge etc.

And lastly what size fuse will I need? Less than your wire, 30 amp? Probably 10amp would be fine.

Hopefully you get some better replies, I'm no auto elec lol......

In replying I personally recon its either best to stick to your area of great expertise and provide informed advice.... or.....to explain what has been done to your car...opinions are great, but you know what happens when people ask about wiring and dual batteries, and the like...it can go on for pages and pages, and sometimes some other people get upset...I'm just saying that's all. ...and so I say upfront I am not an expert, but i've done lots of research, lots of reading, listened to lots of opinions, and had a few set ups, including a current "temporary" set up which is working well while I do some short trips..but am planning some changes to my fridge power set up in the future.......but this is what I do know...and here are some of my personal opinions.

1. There are auto electricians, and there are auto electricians. Some folk know auto electrical wiring and do it very well, and some definitely don't know how to apply their knowledge very well....and you can very easily do or get the wrong thing that either wont do the right job, or will work but stuff your battery after just a year or so, or just cost you lots of money...honestly.
2. Your specific model Prado can make a difference to your fridge power set up, and aux battery charging choice etc...with newer model Prados having a voltage limited alternator (mine produces between 13.4 and 13.6 volts ..previous model could produce 14.4 volts with a voltage booster diode...which is not an option on the newer model.
3. 12v wires may not be what they seem to be...you can get say "50amp" auto cable, which will actually start to fry at 50 amps, and you can get "50 amp" wires that absolutely can carry 50 amps all day every day, and will fry at a much higher amperage...I wont try and explain as others can and have done a much better job elsewhere, but be very careful about the correct size and construction of cabling)
4. Fuses are placed in the positive cable for the purpose of protecting the actual circuit from burning your car to the ground if there is a short or an accident, so the correct fuse sizing depends on the capacity/rating of the wire and the anticipated current draw...but the fuse must be rated to blow well before the wires melt and catches on fire.
5. If you do the wrong thing you can easily cause a fire...very easily... a friends electronic rust protection device was "professionally" installed, without any fuse in the positive supply wire, it shorted with moisture during rain, melted, caught the engine bay on fire while the car was parked in the driveway, insurance was a hastle, and eventually the installer of the device payed....it could have been much worse, and if it was "self installed' incorrectly the cost could have been huge.
6. At this stage you might want to install cabling just for the fridge, but later on might want to use the same circuit for lights or for actually connecting a solar panel to charge your batteries etc...so I recon if you go to the trouble to install the cabling, make it bigger in the first instance than what you initially think....within reason...and bigger cable seems to ensure the fridge cools quicker etc. I'd also refer to some cable sizing guides, because it depends on what you want to do and how you want to charge the aux battery etc....here is one example of a wire sizing guide...https://www.redarc.com.au/images/upl..._worksheet.pdf

So, "should I run 6 or 8 B& S"...it depends on how far you are running cables, what load and what future loads you might have in mind etc. Bigger is generally better with 12v cables, but be careful what brand, and bigger is more expensive, and from a practical point of view, you may need to match the size of cable with the terminals or connectors you use..I try and minimise the number or terminals and connectors, I also try and solder connections and also use double walled self gluing shrink wrap over the solder...I have had professional crimp connections fail, and also cheap copy anderson plugs crack ad fail....and fixing them in the field can be a pain ...but others do different things, what I know is if connections are poor they break when you are travelling, they increase resistance in the circuit and cheap copy anderson plugs crack when you most need them, and so connections and terminals are equally important as cable size.

"Should I run single core and find an earth on the body"....you can do it that way, with just a single positive from the positive battery terminal, and I have got it set up that way (for now) despite specifically asking for both a positive and negative cables.....but if you run a positive AND a negative cable it just seems to be much easier to fault find if something goes wrong (especially if you want to travel remotely), and it can be much easier for others to understand whats going on if they ever work on or modify your car, and it avoids having to find a reliable earthing point that wont rust in the future or work loose etc etc...so its all worth thinking about, and seeking opinions indeed, but honestly, you can get as many opinions as there are individuals...and that's not even mentioning on DCDC chargers etc...
Also, if you use twin core cable (where both cables are within the one outer sheath) you actually have a lower capacity cable than if you had separate cables of the same conductor size...and remember, I am told that cable amperage capacity ratings are temperature dependent, the hotter the cable the lower the current carrying capacity....so I personally recon having a separate positive cable and a separate negative cable could prove to be the better way to go in the long run, and its potentially easier to fault find and or repair in the field should something go wrong...just my opinion based on experience with both set ups.


So...here are some questions which might help other folk provide some other opinions or advice or suggestions.

Whats your specific model Prado?
What and where are you planning on locating your aux battery?
How are you planning on charging an auxiliary battery?
Are you intending on using solar panels at all?
Are you intending on travelling remotely for long periods of time, or just shorter trips.

...and I'll make some popcorn and read others opinions/comments...

I've been busy travelling and camping etc, but I will post the details of my new Prado build with photos...my set up is currently working fantastically well, for as long as I tour with short 1 or 2 day stops only... which is what I have been doing ..but it wont be what I need for camping in one place for a few days at a time...so I will change, modify and improve the set up I have later on the year before I go for longer camping trips...I'm just doing one step at a time for now...details will be posted soon.

[Mattfunk 120 Advanced Member Find all posts View Profile Close Mattfunk 120]

Hi mate. I ran 6mm2 twin cable on a 30 amp breaker. Absolutely 0 voltage drop.
Cheers Matt

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[oceanracer Moderated member Find all posts View Profile Close oceanracer]

I used 8mm2, easy job to do , I ran power to a Baintech 6 way block then removed all the trim and followed the original cables to the jack position, ive got an Anderson plug on the end but plan to put some more points there








http://www.narva.com.au/products/browse/maxi

the fuse I used 40a

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

For the electricians,, To use 6 b&s or 8 b&s wire with a fuse at the battery seems pointless to me. To connect a say 6 b&s wire to the battery and then reduce the current flow through a "fuse" wire a thick as a hair then run the wire to the back of the car is nuts. Surely it must be better to use a circuit breaker near the battery and a separate fuse for the fridge or whatever is connected at the other end. I'm not a leccy just asking.

[Fred63 Advanced Member Find all posts View Profile Close Fred63]

For the electricians,, To use 6 b&s or 8 b&s wire with a fuse at the battery seems pointless to me. To connect a say 6 b&s wire to the battery and then reduce the current flow through a "fuse" wire a thick as a hair then run the wire to the back of the car is nuts. Surely it must be better to use a circuit breaker near the battery and a separate fuse for the fridge or whatever is connected at the other end. I'm not a leccy just asking.

The voltage drop across the fuse is minimal.
It you have a good meter try to measure the resistance it will read next to nothing.
In my install to the back cable is rated to 70 amp but i am only using a 20 amp fuse.

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

Hi mate. I ran 6mm2 twin cable on a 30 amp breaker. Absolutely 0 voltage drop.
Cheers Matt

Sent from my SM-J110F using Tapatalk

Was the fridge running when you measured the voltage drop?

S

[Mattfunk 120 Advanced Member Find all posts View Profile Close Mattfunk 120]

Was the fridge running when you measured the voltage drop?

S

No , just measuring voltage at battery versus voltage at fridge outlet

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[Mattfunk 120 Advanced Member Find all posts View Profile Close Mattfunk 120]

The voltage drop across the fuse is minimal.
It you have a good meter try to measure the resistance it will read next to nothing.
In my install to the back cable is rated to 70 amp but i am only using a 20 amp fuse.

Yeah the main cause of your voltage drop on a 12v circuit will be the length of cable, so the larger cable over say 8 metres will be to negate voltage drop rather than to accommodate a higher ampereage
Cheers Matt

Sent from my SM-J110F using Tapatalk

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

No , just measuring voltage at battery versus voltage at fridge outlet

That does not give you an accurate indication of voltage drop.
You'll need to measure it with the fridge running.

[RBJET Member Find all posts View Profile Close RBJET]

Excellent write up Brogers. I was the same as you and did a heap of research before I pit the bullet and did my wiring.

At the moment I only run a fridge and some lighting but decided to run 8 b&s twin core just in case any future plans arise.
I ran mine to a fuse box in the spare compartment in the rear and then just run whatever cable is necessary to the accessories I splice off it.

[Fred63 Advanced Member Find all posts View Profile Close Fred63]

That does not give you an accurate indication of voltage drop.
You'll need to measure it with the fridge running.

If you want to measure voltage drop and get an actual reading of the voltage drop in the wiring try this.
Get a length of wire only needs to be a light gauge wire.
Connect it to one of fuses at your battery.
Get your meter and connect it to the + on you fridge then connect the other lead to the wire from the battery.
When your fridge starts running you will see the voltage rise and this will be the actual voltage drop.
When the fridge is not running you will see very close to zero volts it may read Zero volts depending on how sensitive your meter is, as only the electronics in the fridge will be drawing and current.

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

For the electricians,, To use 6 b&s or 8 b&s wire with a fuse at the battery seems pointless to me. To connect a say 6 b&s wire to the battery and then reduce the current flow through a "fuse" wire a thick as a hair then run the wire to the back of the car is nuts. Surely it must be better to use a circuit breaker near the battery and a separate fuse for the fridge or whatever is connected at the other end. I'm not a leccy just asking.

I'm sorry I'm not an electrician, but from what I know its definitely not pointless having a good cable size and an appropriate fuse. Fuses are designed to be very very low resistance, and are designed to fail or blow at a certain current...having an adequate cable size, with an appropriate fuse is definitely the way to go, no doubt in my mind, from experience, from measurements I have taken. A couple of things to remember, the "rating" of a fuse (eg a 20 amp fuse) is usually not the current at which it will "Blow" ...they typically "blow" at a current up to twice the rated amperage from memory) ...(but please correct me if I am wrong)...If you use a thin conductor cable, and measure the voltage at the end of the cable run with a simple voltmeter, you will register very little voltage drop...the problem is that voltage drop is dependent on the actual current flowing in the cable s well as the resistance of the conductor. V=IR here V is the voltage drop , I is the current and R is the resistance. (and Resistance depends on the conductor properties such as cross sectional area, material, and temperature and length)...so, from what I see many people I know and others recommend that we use either 6 or 8 B&S type 12v cable for 4wd fit outs..some folk use a "tinned" copper cable to reduce issues with corrosion (especially if fitting out a boat or boat trailer). Some people use circuit breakers, but personally, I try to use"watertight" blade fuse holders mostly, simple, easy to replace, and less to go wrong...but that's just what I do, and it works for me. I have seen some folk use electronic circuit breakers, but they can be relatively costly, and they can fail or break done etc..Anyway...back on topic...a good conductor size will ensure very little voltage drop over the required length, a well fitted fuse will not contribute to a noticeable voltage drop when measured while the cable is under load (ie drawing a current)...and if done well your fridge will cool faster, and your batteries last longer...your car wont burn to the ground...and your beer will be at the right temperature
It seems most folk use either 6 or 8 B&S sized cable, and occasionally 4 B&S for much longer runs to a trailer, or if drawing currents higher than say 20-30 amps...BUT...it really depends on length of run, alternator output, if you are using a run from the battery to a DC charger or directly from the battery, etc etc...If not careful you can spend a small fortune and still not achieve what you need, or spend relatively little, and it may not be perfect, but its simple, easy to install, safe and effective for your specific setup....it all depends on your alternator output, what you are running, where you are running it, how long you want to run it for etc etc