Outer Limits 4x4 Board

Ive installed an in cab dual cig plug direct from my aux battery. I had to run the power cables across the inside of the engine bay and through the firewall on the driver's side. They then run to the plug which is located in the center of the cab near the handbrake. The problem I'm having is that when I plug my fridge in, it fails to work properly. It will come on for a moment and then cut out like the battery doesn't have enough juice. The multi meter is reading the same from both the plug and battery. There is the standard fuse located close to the plug which has a 20amp fuse in it.

I connected the fridge direct to the battery and it works fine, which suggest something along the wiring is not setup properly. I used 4mm auto cable for both wires. Any help would be appreciated.

Is this a standard OEM socket? Some of them have a "fusible link" in the rear that can go high resistance, causing voltage drop. If you measure across the +ve & -ve on the outside of the socket it all seems OK, but under load, the middle contact inside the socket is at a lower voltage.

Try measuring resistance in the +ve terminal from outside the socket (where your wire connects) to inside. Alternatively, try to pick up 12V at the fridge when it's trying to start. Normally easier said than done.

Hi lowndsie, your problem is the cable size is way too thin.

4mm Auto is actually only 1.85mm2.

You need to run 6mm Auto, which is 4.5mm2.

Pull the ciggie lighter socket away from it's mount so you can measure the +12v voltage at the back of the socket with the fridge plugged in and let us know what you get. Measure the voltage of negative outer side of the socket and a decent body earth (under the dash/direct to firewall via bolt), this should be zero to less than 0.2v with the fridge connected/running. My guess is a dodgy earth.

People have OE lighter plugs in the back of their vehicles which have a longer run of marginal wire gauge that are able to take the 5 amps or so of a fridge (not an overly heavy current). Main issue with ciggie lighter plugs/sockets is mechanical (susceptible to vibration/falling out), they are after all able to take the current of a cigarette lighter (15amp)

http://www.rowand.net/shop/tech/wirecapacitychart.htm" onclick="window.open(this.href);return false;

Gauge 12V
22 5A
20 8A
18 10A
16 20A
14 40A
12 60A
10 100A
8 150A
6 ??A
4 ??A
2 ??A
1 ??A
0 ??A

http://www.tnt-audio.com/clinica/awg_e.html" onclick="window.open(this.href);return false;



So 1.8 mm2 ia about 15 AWG so should handle 30 amp for short runs and about 20 for decent runs (front to back of vehicle).

http://www.mwswire.com/barecu5.htm" onclick="window.open(this.href);return false;

Resistance of 3m (10 feet) of 15 AWG is 0.03 ohm. The maths at 5 amp drain would be 0.15V voltage drop over a one way trip = 0.3volts total for return. Add another 0.2 volts for plug losses and it's still within reason and overall nowhere near overloaded.

Practical upshot is the wire used is adequate for this purpose (not "best practice", but adequate nonetheless), and his problem lies somewhere other than with the gauge of wire used.

Thanx for the help guys. I'm pretty bloody hopeless with this sort of stuff so I ended up running a thicker gauge wire and the problem seems to be fixed!

Thanx again.

lowndsie wrote:Thanx for the help guys. I'm pretty bloody hopeless with this sort of stuff so I ended up running a thicker gauge wire and the problem seems to be fixed!

Thanx again.

I'd still piss the ciggie lighter plug off and used a dedicated plug for the fridge only using a 20A merit style plug and socket. Much better contact.