Battery charger wiring

[concentrik]

I installed a 20A 3 stage charger for 2 x 110Ah bank. Batteries are new. I have sited the charger in the "electric" area, high up under the cockpit seats near the shorepower, MCB box etc. This means a run of about 25ft round trip for the charge cables to the battery bank. The charger doesn't have remote voltage sensing. I have been confounded by Ohms Law - 14.2v output from the charger ends up as 13.6v across the bank. It looks like I need very hefty charging cables to suffer only a 0,1v drop. This site:

http://circuitcalculator.com/wordpress/2007/09/20/wire-parameter-calculator/

makes the calcs easy and suggests a cable of 6mm cross sectional area - wow, cooker cable!

Any comments? Are my calcs about correct or am I missing something? I would prefer not to move the charger right next to the batteries.....

 

[prv]

suggests a cable of 6mm cross sectional area - wow, cooker cable!

6mm isn't particularly huge for 12v wiring. To be honest, I would have expected something bigger for this purpose.

Remember, at the lower voltage, you're running much bigger currents than for mains, and it's the amps that need the fat cable.

Pete

 

[VicS]

If you are to keep the volts drop to 0.1 volts in a 7.6 m (25 ft ) round trip you need wire about 6mm diameter, about 25mm² cross sectional area or AWG 3

That is very considerably heavier than 6mm² cooker/ shower cable.
6mm² is little more than the minimum safe cable size for 20amps!

It is a fairly heavy battery cable!

As Pete suspected!

Sensible solution may be to locate the charger closer to the batteries.



0.1 volt at 20 A is 0.005 ohms.

0.005 ohms in 7.6 m is 0.658 ohms per 1000 m

AWG 4 is 5.189mm diameter, 21.15 mm² cross sectional area and 0.8 ohms per 1000 m

AWG 2 is 6.543mm diameter, 33.6 mm² cross sectional area and 0.5 ohms per 1000 m

AWG 3 is 5.83 mm diameter and 26.65mm² crossectional area ... by interpolation that's 0.63 ohms per 1000 m

 

[elton]

Sensible solution may be to locate the charger closer to the batteries.

100% agree with that.

 

[Billjratt]

100% agree with that.

+1