Voltage drop

[Vicdicdoc]

What size wire should I use between alternator to 12v fridge which is 6foot away ? The installation booklet isn’t much good except to say the energy consumption is 1.3Kwh in 24hour period; the factory fitted wire seems to get warm to the touch & I’ve found there’s a 0.40 volt drop - would I be better off replacing it with equivalent of 2.5mm household cable ?

 

[Wissel]

Might be worth using this calculator:
https://www.12voltplanet.co.uk/cable-sizing-selection.html

If your fridge uses 1.3kw in 24 hours that's about 4.5Ah draw per hour - except it won't be drawing 4.5Ah as it won't be on all the time, so if it's on say 1/3 of the time it's pulling 13.5Ah. If you have 2.5mm cable, a 2m length should drop 0.37v @13.5Ah.

I'm guessing a lot of above as without knowing the actual draw and the actual cable size it's all I can do. But if I'm close and you are using 2.5mm cable, swapping to 6mm would change the voltage drop to about 0.15v and should stop the cable getting warm.

If it were me I'd test the actual draw with a multimeter, then size the cable.

Hope this helps.

 

[Millie Master]

When I installed the WAECO 12V fridge into 'Millie', I followed the WAECO supplied instructions and used 6mm cable.

Phil

 

[Vicdicdoc]

Again you guys have given excellent advice & I’ll swap out to 6mm.
On this particular model of fridge, when on 12v (when engine running) there is no thermostat control so I’m guessing when it’s on it’s on all the time.
Actually I’ve tapped into the cigarette lighter circuit & inserted a 10Amp fuse which was easier & more convenient rather than direct to the alternator

 

[wildebus]

One of the most common mistakes made when installing 12V Compressor Fridges is to read the consumption figures and size the cable based on that.
6mm is really the minimum size and sometimes 10mm is the cable run is fairly long.

Reason why you need the thicker cable is to avoid the voltage drop on the inrush when the compressor kicks on - that will draw a current way higher than the numbers quoted in the manual. And if the cable is too thin, the voltage drop will be so great the fridge will see a "Low Battery" situation and not start, even though the battery itself could well be perfectly fine.

This is an example of the inrush power for my setup when the Fridge kicks on...
Fridge pulls 74W from the system (Fridge+Inverter) when running, but that momentary inrush is way higher as you can see.

 

[Vicdicdoc]

My friendly electrician has given me a length of 10mm (multi strand electric shower cable) so over the distance I ‘shouldn’t suffer as much voltage drop- only a trial will show

 

[wildebus]

10mm is good - as long as it is properly multistrand . Most of the domestic mains cable are not suitable for vehicle use even if it is rated at sufficient amperage and has multiple solid core
This is the kind of multistrand needed:

This 10mm Cable with the twisted solid cores is not really that ideal:

 

[Vicdicdoc]

Yep that looks like it

 

[GEOFF]

The reason that the domestic cable is unsuitable is because it is not flexible enough and is liable to fracture with vibration. The more strands the better for automotive and marine use. Geoff.