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Welkman

Member Since: 02 Nov 2014
Location: Essex colchester
Posts: 332

Voltage drop and other rewire queries.

Apologies for the spate of posts !

Just adding a 12 volt/10 amp outlet at the rear of 110 towards the door. I have run the calculations and at 10 amps I would need 4mm^2 cable to keep voltage drop < 3%. Does this sound like overkill for a car? All my wiring previously has been on boats with much longer runs. This would also make the cable sizing for the 3 amp load work lights around the 1.5 - 2.0mm cable size allowing for 5m of cable.

Second question: I have a feed into the dash area from my aux fuse box that I want to use to power switches that will only run relays. If I had say 5 switches fed from this one feed and I popped a 3 amp fuse in to protect the cable do you think it would be adequate. Also Do you think that the earth feed from the same (1mm^2) cable would be sufficient to earth all the switches for illumination only? I have tapped into the large cable feeding power to the other standard switches for illumination as I felt this was large enough to take the load of another few LEDS.

Cheers James

9th Oct 2016 9:19am

LandRoverAnorak

Member Since: 17 Jul 2011
Location: Surrey
Posts: 11324

That does sound like overkill and can only think that there's something not quite right with your calculations. Standard automotive 28/.30 2mm cable is good for 17.5amps and the volt drop over the length of a Defender should be negligible. Darren

110 USW BUILD THREAD - EXPEDITION TRAILER - 200tdi 90 BUILD THREAD - SANKEY TRAILER - IG@landroveranorak

"You came in that thing? You're braver than I thought!" - Princess Leia

9th Oct 2016 9:44am

Welkman

Member Since: 02 Nov 2014
Location: Essex colchester
Posts: 332

Hi,

Im using this calculator and recommendation to keep below 4% drop.

http://www.12voltplanet.co.uk/cable-sizing-selection.html

9th Oct 2016 11:17am

custom90

Member Since: 21 Jan 2010
Location: South West, England.
Posts: 20583

I'd tend to agree with LRA above, I'd go for 2.5mm thinwall myself.

Earth should be the same dia, the earth loop is just as critical as the live feed in the circuit. KEEP CALM AND Drill ON
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9th Oct 2016 11:43am

Welkman

Member Since: 02 Nov 2014
Location: Essex colchester
Posts: 332

Well I just found a permanent live and earth in the rear drivers side behind the light panel so I may well just use that, looks like a 12 v feed for an aux socket. Will combine it with my new speaker panels.

9th Oct 2016 12:41pm

Cupboard

Member Since: 21 Mar 2014
Location: Suffolk
Posts: 2971

2011 Defender 110 Puma 2.4 HT Corris Grey

There's a thread about that. it's 20A fused and I'm pretty sure it's 2mm^2.
http://www.defender2.net/forum/topic20319.html

LED worklights will be much less sensitive to voltage drop than standard ones because they are regulated so constant brightness until they stop working.

9th Oct 2016 4:45pm

Welkman

Member Since: 02 Nov 2014
Location: Essex colchester
Posts: 332

Thanks for the help on this. I am going to use that feed in the back for a permanent 12 volt feed but might add a local illuminated switch so I do not leave it on.

I now have an issue wiring up my carling switches.They have three terminals that control the basic switch (on/off) and then two sets of terminals that control the large light and the small 'bar' light. I think I should have the bar light LED switching on with the vehicle lights (easy) but would like the bigger light to illuminate when on. The question is do I just jumper the switched live to the lamp live or is there a circuit inbuilt to do this like on other switches?

Thanks

James

15th Oct 2016 4:42pm

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