Renogy 20A dc to DC report
Hi All, Regarding the Renogy 20A DC to DC Battery Charger 12V, the unit puts out 20 amps, but draws 30 amps when doing so. This is the result of bench testing.
Forum Discussion
pianotuna wrote:Yes, input and output voltage delta of a typical dc to dc charger is a factor. However, the delta is not enough to substantially change the final calculation based on current alone. For general discussion it's more than accurate.
otrfun,
The bench testing used #4 wire input and the length was inches.
30 amps in and 20 out is not a measurement of efficiency--because we are dealing with mppt boosting the voltage, i.e. swapping amps for volts.
I've set the unit to 14.7 volts output to maximize charging.
In the RV the wire length is about 12 feet due to the dc to DC having to be located under the passenger's seat. It is #8 wire which is more than adequate for 30 amps input (about 6 feet on input side).
I have seen 16 amps going to the house bank at idle. The highest reading noted was 19.6 amps, when driving. I don't have an easy way to measure input amps to the unit.
I'm more than satisfied with these results and I'd recommend dc to DC charging.
On a disappointing note, Victron, who make excellent equipment, in general, chose to not have a cooling fan on their dc to DC charger. Some reports say it gets too hot to touch after operating for an hour.
The renogy does have a cooling fan.
The typical dc to dc charger install will have less than a 10% voltage delta. If it's a quality install, it will be significantly lower.
In our case, our 40a dc to dc charger had an input voltage from the alternator of 14.2v with the output charge voltage set to 14.4v (voltage increased from 13.6v to 14.4v during the charge process). Max input current was 44a, max output current 40a. ~90% efficiency even with the voltage delta taken into consideration.
