12 v dc extension cord

[dutch6]

I need an extension cord for my portable macerator pump and 12 v air compressor. I installed a thru the hull 12 v marine receptical so I could do away with battery clamps. The equipment draws about 15 amps max each and the receptical connection to the battery will have a 20 amp fuse.

I have a supply of stranded 18/4 SO left from a previous project that I hope to use for the 12' ext. cord. If I split the 18/4 into 2 pairs will this give me sufficient capacity?

 

[JimB1]

Don't have the wire charts right in front of me but I know you'll be close to the limit.



Amperage wire capacities are written by firefighters and are based on resistive heating of wire under ambient conditions and insulation type cover.



Type SO outer cover is going to trap heat pretty good.



Also 12 volt loads are usually pretty sensitive to loosing even a volt or two re doing motor damage due to low voltage which resultingly then draws higher current.



20 amp fuse calls for #12 AWG size wire. I'd go one size better yet and do #10 AWG wire.



Give the supply battery and motor loads a break via high capacity wire.

 

[jelag]

30 amps = 10 gauge wire under a 20 ft run...
20 amps = 12 gauge wire under a 20 ft run...
15 amps = 14 gauge wire under 20 ft run
10 amps = 16 gauge wire under 20 ft run
8 amps = 18 gauge wire under 20 ft run

If over 20 ft run use the next large gauge wire.

 

[dutch6]

Thanks

That is the data I needed - thanks. I'll go with the 10 ga and save the 18/0 for still another project.

 

[jelag]

One other thought... . my 5er batteries never came up to a full charge... . and measuring the voltage at the batteries showed at least 1. 2 - 1. 4 volts lower than the voltage at the batteries in the truck.....

I ran an 8 gauge wire and 30 amp fuse from the back of the Alt to the trailer plug and dropped the factory wire... and than found that my trailer had a 14 gauge wire from the plug to the batteries and a 12 gauge ground... . these I changed to 8 gauge as well...

I'm now down about . 2 - . 5 of a volt below the truck batteries at the trailer... and we now get a full extra day without power with the trailer batteries fully charged... .

Just a thought...

 

[WestTN]

I second Jelag's suggestion. The batteries will also last longer when they receive the correct amperage to charge.

 

[R C Cola]

size wire

Cheap battery cables work pretty good and don't cost much. Ten and eight gauge are common in the cheap ones and they are way too small to use to start someones car.