Couple of questions about DC-Dc charging

NRALIFR wrote:
Actually, Renogy recommends 4-2 awg wire on the input side for that length of run. Since your friend’s circuit length is at the outer end of the range, I’d probably have chosen the 2 gauge wire as well. The data in the box I circled is formatted a little hokey because the font is too large, but that’s what it’s trying to convey.

otrfun wrote:
If you feel the case of a 40a Renogy while it's converting such a low voltage you'll be firm believer it is using 10-20a of current to pull off this conversion. The case gets *very* hot while both fans run full-on. Also, let's not forget the current consumed by the 1.3v voltage drop created by the cable, terminals, and fuses. It all adds up.

These DC chargers aren’t all created equal. My Redarc doesn’t run that hot at all. Not even close. Warm is the hottest it ever gets. And, it doesn’t even have fans. It’s rated to run in environments exposed to high heat (over 50° higher than the Renogy) and open weather. I could have installed it on the frame rail of the truck if that’s where it would work best. Maybe there’s a reason why the Redarc products all cost so much more than the Renogy products.

otrfun wrote:
Folks have no choice but to use the proper gauge cables with their inverters. Use too small of cable with your inverter it simply shuts down. Not the case with a dc to dc chargers. They will silently ramp up current draw until either your fuse or alternator gives up the ghost.

That’s not quite true, they all have upper and lower voltage limits. I don’t know about Renogy or Victron chargers, but the closer you get to the lower voltage limit with the Redarc, the less amount of time it will stay engaged. It will drop offline on its own.

I’d at least consider that there may be something wrong with your friend’s charger contributing to the “wasted current”. You’ll never convince me that using 2 awg wire on MY install would result in anything more that an insignificant amount of gain. Had Redarc recommended 2 gauge wire, of course I would have used it. But they didn’t, and I see no reason to use your friend’s install as the yardstick for what I should have done with mine.

:):)

You're correct. I miss-spoke slightly on the Renogy cable requirement for the 40a. My apologies.

By the way, did you see the "Notice" at the bottom of the Renogy pic you posted?

When charging converter is sending full charge, the amperage consumption will be 50% greater on the input side.

I believe this confirms what I've been saying about the Renogy dc to dc charger all along---that it *wastes* current. Contrary to your claim it doesn't. 50% greater than 40a is 60a. This concurs with the current measurements I observed with my friend's 40a Renogy dc to dc charger install.

I never suggested, implied, or tried to convince you in any way that you should use 2 gauge cable with your Redarc. My focus has ONLY been the Renogy's lack of conversion efficiency ("wasted" current)---nothing more, nothing less. You said the Renogy did not waste current, I said it did.

In any case, by your own admission you don't know what amperage your dc to dc charger is pulling, and don't care. I do care and regularly make current measurements to make sure all my various loads remain within tolerance. As such, my comments and observations are based on realworld measurements that I've personally made.

With all due respect, sometimes it's difficult to appreciate something unless you see it with your own eyes. For what it's worth, I've personally found a clamp-on ammeter to be a very useful and enlightening tool.