Couple of questions about DC-Dc charging
I've been thinking about adding a DC-DC charger now that I've added 400 amp hours of AGM batteries. There are lots of useful posts but I haven't run into a couple of things I'm curious about. One ...
Forum Discussion
StirCrazy wrote:Both. Based on my 2 gauge install vs. two folks I know that installed 40a Renogy's using 4 gauge in their 5th wheels. Current was measured on all (clamp-on ammeter), but each installation had a different run length (20-30 ft.). Not an ideal comparison, but it did give me a rough idea.
did you measure that reduction in amprage or is that a calculated value? I have been going back and forth between the 20 amp and 40 amp renogy, so I am curious about the effect of cable size to the load
Steve
Renogy's input cable recommendations (specifically those at/near the maximum recommended run length of 30 ft.) seem to result in the input load being at or near 150% of the output current (i.e, 20a charger output, 30a input; 40a output, 60a input; 60a output, 90a input). I have not confirmed this with the cable gauges specified for the 10 and 20 ft. runs. If you're at all concerned about loading your alternator too much, I would highly recommend going at least one gauge larger (physically) than what Renogy recommends. This should drop the input load down to <125% (based on max 30 ft. run length). At the top of the Renogy page, you'll notice the Renogy manual recommends this in a roundabout way ("larger wire sizes generally improve performance"). BTW, I downloaded this screenshot from the Renogy website today (version 1.4). Some of the cable gauge recommendations are different from the version NRALIFR uploaded (I can only assume he uploaded an older version).
We were going back and forth between the 40a and 60a Renogy (we have a 220a alternator). Knowing what I know now, I probably would have gone with the 60a Renogy vs. the 40a. If we had used 2 gauge, or even 1 gauge, cable (20-25 ft run) with a 60a Renogy, I believe we could have reduced the input load to less than 70a. Our input load with our 40a Renogy using 2 gauge (20-25 ft. run) is 43.5a.
Lastly, if you're loading your alternator on the edge of its capability, don't count on a fuse to be some kind of current regulator. I've witnessed a number of fuses support 125-150% of their rated current before opening. I would only count on a fuse to protect your TV and Renogy in the event of a catastrophic short.
