Hi Itinerant1,
As you know, my personal experience with Magnum has been poor. Perhaps I was expecting too much, or I did not research well enough. The design flaw of not having cooling fans independent of the inverter on/off switch is a potential fire hazard. DAMHIK
It is true that watts are watts. But I do believe that 12 dc to 120 ac is harder to do than 48 dc to 120 ac. The efficiency numbers I found bear that out and the higher the load the worse the efficiency is--based on Magnum's own published numbers.
It is also true that lead acid will droop voltage far more than LI. If one never plans to run the roof air then most heavy loads may be of short duration--so again, in that case 12 or 48 makes little difference--except for the 5% better efficiency. The puekert numbers for LI are immensely lower than for lead acid. But I have heated mostly electrically--so I need long duration high amperage loads to be addressed.
I believe you took a great deal of care in designing your system. I did with mine, too. But mine was designed for at most week long trips. For the first five years, I did not have a generator at all.
Once I moved to full time, (which I had not planned to do) I didn't have enough solar to meet my needs and I ended up, as Mex so wonderfully said, as a "power pole princess". The Load support feature made that possible on a 15 amp shore power from April to the middle of October, except for the GFCI problem that made me tear my hair out. I know that Victron doesn't have any issues with GFCI outlets. And at least two folks I respect on Rvnet have spoken of Outback as being "bullet proof".
The rest of the year I had to have 50 amp shore power, or go south. Faced with redoing my system or spending money on a generator, due to my beer budget, I caved in. However in 2018 I only filled the generator tank up 3 times.
It is my understanding that LI have "cliff" like treatment requirements. Exceed them once, and you may be replacing them. Further they have a definite limit for long term loads as far as amperage goes. It would be quite an "ouch" to find out the hard way. I'd love to have a set of the ones that can be charged at well below freezing--but have never seen them with the number of watt-hours that an RV would need.
In short 48 volts means less money spent on cables, more effective solar, with a less expensive charge controller, more efficiency from the inverter. The down sides are the loss of alternator charging (an inverter could remedy that), and the extra cost of a dc to dc converter for the small 12 volt loads in the RV. The bottom line may be much the same price--but 48 volts may work better.
As I'm now back to not being full time, there will be no more upgrades to my RV, except for minor items, such as a trik-l-start for the generator, so I can leave the remote control active for any trips I take.
I've learned a lot following the folks such as yourself who are trail blazing the way for LI technologies, so thank you for doing so.
I am extremely glad your system meets your needs. Well Done!
Itinerant1 wrote:
Not being argumentative just trying to understand better.
Lately it seems more suggestions are to go with higher voltage always by people who don't use the higher voltage but always claim the next time they'll do it. If it's so great why not do it now using the same wiring you have now (should be little to no V drop seeing it's bigger wire). The only thing that seem your changing is the battery configuration and a couple components.
What exactly will it do in an RV that I'm doing now and have been for years? I know run the AC unit but in order to do that for a long period of time won't you need a larger battery bank so it's not depleted even at 24v or 48v? 12v @ 400ah, 24v @ 200ah 48v @ 100ah all equals 4,800wh it's the same capacity isn't it? Or does this benefit more a lead base battery compared to lfp battery?
