down-converting from 24V to 12V isn't very efficient. The same issue would be there for a 48V system.
I was worried about this at first but after more calculations and now plenty of real world tests, it's clear that converting from 48V to 13.8V for house DC loads is a non-issue because the real power draw is the a/c. Having a 20.5kWh 48V LFP battery bank, a 48V inverter, and a 240V a/c saves so much that it makes the DC load conversion loss look like a rounding error.
Good point about the solar array. I'm about to install mine and plan for a ballpark 135 Voc. That kind of DC voltage obviously has risks associated with it, but it's also very efficient. For most users targeting 60-80V would be safer.
The real issue with 48V rotating power is the risk of a load dump. Victron batteries do have a way to signal an impending dump to the WS,500, but that's not the only way you can suddenly disconnect an alternator, as plenty of people have learned the hard way, with tears and significant loss of money.
I recently had a forum user message me about a breaker in his alternator path which tripped, costing him a few grand to replace the inverter. Granted the breaker was undersized and shouldn't have been there at all in my opinion, but it goes to show 48V alternators with no available Sterling OVPD device are risky business.
I'm still debating whether I'll even need the 48V alternator with a 1110W solar array and the most efficient a/c system I could possibly source. 24V has none of those issues, and is probably better for 95% of users, even if it's a tad less efficient when inverting for a/c or some other very high power device (ambulances, crane operators, etc).
Cabling doesn't really save you much by going 48V because breakers, fuses, switches, and other components rated for 60V+ (ballpark max charging voltage) are much more expensive and more difficult to source. I also tend to oversize my cables, so I'm using 2/0 for 48V even though I could probably have gone 1/0. The cost difference between 4/0 and 1/0 is significant, but after you add up all those pricey 60V+ breakers, switches, fuses, and other gear, I doubt there's any savings, and possibly even a loss.
That Victron Smart Battery Protect is a POS. I returned two after discovering (even InvertersRUS blew 2 proving this to themselves) that it can't even work with a basic DC converter. It's well publicized about not using it with inverters, but nothing about it's inability to function even with a simple DC converter. Apparently even the basic smoothing caps in a DC converter will brick it. It really only helps to protect against power draw from purely resistive 48V+ loads, of which there are very few.
Plus, most good inverters let you program a low voltage cutoff, and they are by far the largest draw, so the SBP is redundant in that regard, and at least in my case the largest house DC loads (heat pads, heat trace) are all controlled by timers and temp relays, so there's just not enough continuous drain to worry about. My battery bank is also 20.5kWh so it would take a very long time for the remaining small DC loads to drain it down to the BMV's alarm voltage, and then another long period of time with the alarm going off non-stop before it would finally reach the battery's BMS cutoff voltage, at which point the BMS will do its job. There's next to no chance the battery will disconnect from a low-voltage cutoff while the alternator is charging, so really what use is the SBP? I ditched my broken units, got a refund from InvertersRUS, and found myself again wondering what all the hype is about Victron.
Some of their products are worthwhile, like the BMV-712, and maybe the overpriced Cerbo GX, which I'm really only using to push BMV-712 data to the cloud. But as far as I can tell the rest is way overpriced (batteries about 200-300% above standard kWh LFP prices), full of caveats like "this only works when this doesn't," plenty of users complaining about inverter noise, devices like the SBP that are largely useless, and a terrible customer service process that often ends up going in circles with a distributor who knows less than you.
Why Victron can't just support its own products like every other company is beyond me. It sounds like a cheap-skate way of saving a few bucks. "I know, we'll make the distributors do tech support so we don't have to!" Gee thanks. They had a glaring error on a product data sheet, and it took me dozens of emails, including some to senior management just to get them to even look into it, at which point they finally apologized and corrected the error.
I know they're popular with many users, so I'll probably take slack for saying all of that, but I kept expecting good things and kept discovering it was a bit like buying an Apple product. You pay ten times as much for the same features that were offered a year ago on a Samsung or Google product, plus you keep finding proprietary hidden costs (sensors, cables, etc), and little annoying issues like the pricey Cerbo being unable to just push the exact wattage the BMV-712 is reporting to the cloud. The BMV shows a consistent -8W (small parasitic loads), which tells me everything is normal when the RV isn't being used, but the portal (yes, its in real-time mode) flips between -5W or -10W, presumably unable to display 1W granularity. At first it made me think some small device was malfunctioning, but nope, all is well, so now I just accept it as yet another annoying bug. Maybe some Victron aficionados know how to fix it, but I sure couldn't find any easy answer.
Cheers.
