DV to DC charging question

navillus

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Feb 11, 2021
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I hope this is a good spot to post this question. I am looking at using the renogy 40A DC-to-DC battery charger and I am getting some conflicting information on wire size. I have a run of approx 12 to 15ft from vehicle battery to the charger. According to my wire guide chart, I would need to use 6awg wire. I have read that some people are using 2awg and even 0awg for this connection. Do I need to double the distance accounting for positive and negative wires? Will the renogy accept 2awg wires on its terminals? I appreciate any information.

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HRTKD

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Round trip distance is what you have to take into account. 15' of physical distance becomes 30' of wire.

Renogy's reputation has suffered greatly lately. Quality and customer service just don't seem to be there. Keep that in mind when you purchase a Renogy product.
 

navillus

New Member
Joined
Feb 11, 2021
Messages
60
Round trip distance is what you have to take into account. 15' of physical distance becomes 30' of wire.

Renogy's reputation has suffered greatly lately. Quality and customer service just don't seem to be there. Keep that in mind when you purchase a Renogy product.
Thanks for the reply. The wires are only running from point a to point b. They are not completing a circuit. So 15ft red and 15ft black. Am I looking at this wrong?
 

HRTKD

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Thanks for the reply. The wires are only running from point a to point b. They are not completing a circuit. So 15ft red and 15ft black. Am I looking at this wrong?

That's still 30' of wire length that you have to plug into the calculator, if the calculator is expecting round trip distance. Some calculators assume the number you're inputting is a one-way length and automatically doubles it.

40 amp is the output of the charger. It will likely draw more amps on the input side. To be on the safe side, I'm assuming 50 amps max on the input side, with a round trip distance of 30'. Using my favorite wire gauge calculator (used by a lot of forum members), I come up with a recommendation to use 2 awg, with 4 awg being marginal. Note that the calculator is assuming 105° C wire. If you use cheaper 90° C wire you may need a heavier gauge.

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We could fudge the voltage number up to 13v, with the expectation that the source is capable of producing a solid 13v+. In that case, 4 awg is acceptably under the 3% voltage drop. Would I rely on that? Probably not, unless I had a bunch of 4 awg sitting around waiting to be used and my DC-DC charger was going to be used to top off a LiFePO4 battery, not charge it from a very low state of charge. But we're quibbling here and my preference is to design/implement for the worst case scenario, so I would go 2 awg.
 
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