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Hi Brock. Any efficiency gains are really at the highly academic end of the choice difference. It will be so minimal to the point of being 'undetectable'.

Wonder more about your choice. I can't speak for that 'sizing calculator', nor the data you've fed it, but that panel suggests a 75/15 (or 100/15), and for 400W a 100/30. A /20 would in theory be 'adequate' for those batts, but daily-cycling tends to need a little extra 'push', and the 30A suits 400W and loads at the same time too.

The issue you may strike if you add to that Kyocera is matching it to the added one. It's specs are a little odd, and it may be difficult to match. Ideally an added one would be of similar W and Vmp. A little tolerance to be had there, but the further away your efficiency concerns will come into play. Not the cc's fault, just panel mismatch.

Thanks JohnC. I may or may not keep that panel it is 10 years old and intended more for a grid tie system one with the PV array running at a few hundred volts. The gist is this is the system I have, and I am wanting to swap out my Morningstar MPPT controller for something that doesn't have an annoying whine since this system is residing in my van and I need to turn off the controller when I'm sleeping in it for when the sun comes out it will start making a whining noise unless there is a bit of a load being drawn, which there usually isn't.

I guess a better question would be if I was to buy the 100/30 and put it in my system now would there be any issue? If I'm replacing my charge controller I would like to future proof it some to be able to handle a larger system.

Yeh Brock, that would be a good choice. Not to say that's your only choice, as additional units can always be paralleled in. But it's the simplest way to go.

The Victrons are quiet, and if a glowing led annoys you just cover it with a button of Blue Tack. :)

Under-utilization of capacity is what they're designed to do, following that daily solar bell-curve.