I change my DC-DC 20A to 40A

[King76]

Hello,

I am in the process of replacing the connection from my car battery to my DC-DC. I am going from a 20A DC-DC to 40A and changing my cable to a 4 gauge instead of 8. The required length is approximately 13 feet.

I ran a new cable under the cad to connect the positive terminal.

My question is simple: can I use the two 8 gauge wires in place for the negative terminal?

THANKS

 

[eDJ_]

Welcome to the Van Living Forum King.

The 8 gauge would probably do what you are wanting to do but it's up to you. Many here would use a fuse at either end of that 13 ft run on the positive just for safety.


Like these:

 

[King76]

Hello,

Thank you for your answer.

I have a blue sea 60A before my DCDC, it's correct ?

Thanks

 

[bullfrog !]

Most estimates I have seen state two 8 gauge wires will conduct about 75% of what one 4 gauge wire will.

 

[King76]

Hello,

This is what I saw happen too, but given that it is on the neutral wire, can it work?

 

[bullfrog !]

In a DC circuit the current is the same throughout the entire circuit. 13’ is a fairly long distance for DC current and any resistance will be felt throughout the circuit so if you feel one wire is to be best to be 4 gauge I would use 4 gauge for the other for best efficiency as well. This is just my personal opinion.

 

[King76]

Hello,

Finally, I ordered a new cable, 4 AWG.

Thanks

 

[DLTooley]

Do you mind if I ask what brand/model of DC-DC chargers you are using?

 

[King76]

I use Renogy 40A

 

[INTJohn]

Most estimates I have seen state two 8 gauge wires will conduct about 75% of what one 4 gauge wire will.

This is correct. 4 ga wire has about a 21mm cross sectional area for current to flow thru; where 8 ga is about 8.3 mm. So 2 8 ga will give about 16.6 mm cross section.
16.6/21 yields approximately 79% and taking an increase in current resistance into account, 75% would be an accurate approximation.

INTJohn