Renogy DC-DC Test Results-UPDATE 4 (Better!)

BFL13 wrote:

FWC wrote:
Something doesn't seem right with the DC-DC charger or the measurements. In all cases it calculates out to being about 65% efficient. That is terrible efficiency, and in that case it should have been getting hot as the charger would be dissipating about 135W of waste heat.

Agree on the watts in vs watts out which didn't come out as I expected. However, those were the numbers I got the way I got them. Measurements have some "internal consistency" so IMO they are ok. eg the way the engine battery voltage tapered with higher engine bay temps.

I carried on after the test and recharged the batts with the converter and the Tri was working right, and I compared Tri voltage with meter voltage and came out ok. Don't know what else could be skewing things.

Somebody else with a Renogy could try his numbers for a comparison. A guy in the other thread said his input amps draw was lower with fatter wire, but I did not see that at all. He has a clamp ammeter while I have an old time car dash type, but it showed 30 amps and wasn't stuck needled. Beats me.

I agree with FWC, something is wrong with your readings and/or your installation if your 20a Renogy dc to dc charger continues to draw 30a regardless what size cable you use. 30a is the absolute max current the input of a 20a Renogy dc to dc charger can pull---worst case. 30a tells me you have a very large voltage drop on the input to your 20a Renogy dc to dc charger. I'd guess-estimate you have at least a 1-2v voltage drop to force 30a. If you're willing to get that voltage drop down to less than .3v, you will see the input current to your dc to dc charger drop to less than 22-23a (with 20a on the output). Of course, if you're happy with 50% conversion efficiency you can certainly leave things the way they are.