10-27-2022, 09:01 AM
Simon,
I've been busy with a project but I just logged-in with my wife's account to confirm that everything Jack wrote is what I had explained or alluded to in my Facebook discussion with you.
The Growatt inverters are exactly the type of "Chinese" transformer-less inverter that I recommended. While the Growatt is a more popular/marketed name, you can also buy a variety of identical hardware under lesser known names for even less. In addition, you would go with a split-phase unit and you'd be able to parallel for more wattage if required. Not only are the transformerless units smaller, lighter and less expensive -- they also run more efficient, which is crucial in your application / extending the kWh of the battery bank.
I've also had very good luck with the prismatic batteries that Jack uses. There have also been more recent / long-running studies on cycle-count where you'll far exceed 5000 cycles if applying the charge-curve Jack mentioned (not that you should ever need that many 80% DoD cycles). However, you can also buy nearly new, often no more than a dozen cycles, battery backup recovery cells, military/hospital recovery cells, EV cells that were never shipped, etc. Many of these can be the highest quality despite being a bit aged in years (largely irrelevant in this specific context/these high-end cells). I am also a big fan of buying Tesla packs from people that buy salvage Teslas and sell-off the parts. These are exceptionally well-built, energy-dense packs, and you'll be able to re-work the house battery compartment to accommodate.
Richard mentioned going with a higher voltage. In my humble opinion, Richard is spot-on and this is a no-brainer. Parallel a few DC-buck units to provide 12v from your bank, but ultimately go with a 48v or similar bank, strictly for your 110v (220v split-phase), if that's possible. The Growatt-style inverters have large voltage ranges; for example, the 48v will run anywhere from 38v to 60v (that's a very rough estimate based on memory; double-check the exact numbers before buying). What this means is that if you buy a Lithium pack that has a nominal of 52 volts (eg LiFePO4 15s bank) with a range of 58v to 45v across the charge-curve, you'll have no problem (lithium chemistries also have very flat discharge curves which further reduces this issue).
Speaking of paralleling batteries... You asked whether you can parallel more than 4. While it's true that many manufacturers (eg BattleBorn) recommend against paralleling too many batteries, this is not a concern when you design your bank properly. A big part of this is how you wire and whether you start by testing every cell's life. I mentioned this in the Facebook post; be sure you wire in a manner where the batteries are forced to discharge evenly. This form of wiring is a bit confusing at first; however, you only have to wire your batteries once; it's not something you have to commit to memory, etc.
I also do not feel that someone needs an excuse to go with Lithium chemistry battery banks. For example, even if someone doesn't do extensive boondocking, there remain hundreds of reasons that make modern-chemistry the far better choice at current prices. They're almost 3 times as energy-dense (aka 1/3 the weight) and technically more if you consider their DoD, which at a 15-95 curve (optimal lifetime/DoD curve) gives you 80% of their rated energy, versus an SLA at 50%.
Better yet, they have (essentially) no self-discharge, they are not permanently damaged by a situation where they run down, the required BMS provides a great deal more care/longevity than you'll get without, contrary to SLA or AGM batteries, they don't have limited "lifetimes" based on a number of years similar to SLA's (at least not for real-world RV purposes), etc.
In our class-B, we go so far as to run LiFePO4 as our chassis battery as well, simply because it's stored without power and we can go six months without using, without any issue whatsoever.
If you're considering LiFePO4 or Li-on solely as an alternative for standard battery use, without boondocking, they are absolutely the way to go at current pricing (anywhere from $120 to ~$440 per kWh all-inclusive with tax/shipping). NMC is also very easy to come by and in many ways that would work better in a Newell battery bank configuration, if you're doing a higher-voltage unit.
I could go on for pages on the benefits and reasons for going with modern chemistries over SLA or AGM; this is just the tip of the iceberg. I can provide far more detail on any of the areas where you're interested in digging deeper.
It's also worth reading the posts related to the battery isolator, which my wife posted along with some of my input, just a couple days back. This explains the benefits / trade-offs of the DC-DC charger that I had also recommended to you.
I've been busy with a project but I just logged-in with my wife's account to confirm that everything Jack wrote is what I had explained or alluded to in my Facebook discussion with you.
The Growatt inverters are exactly the type of "Chinese" transformer-less inverter that I recommended. While the Growatt is a more popular/marketed name, you can also buy a variety of identical hardware under lesser known names for even less. In addition, you would go with a split-phase unit and you'd be able to parallel for more wattage if required. Not only are the transformerless units smaller, lighter and less expensive -- they also run more efficient, which is crucial in your application / extending the kWh of the battery bank.
I've also had very good luck with the prismatic batteries that Jack uses. There have also been more recent / long-running studies on cycle-count where you'll far exceed 5000 cycles if applying the charge-curve Jack mentioned (not that you should ever need that many 80% DoD cycles). However, you can also buy nearly new, often no more than a dozen cycles, battery backup recovery cells, military/hospital recovery cells, EV cells that were never shipped, etc. Many of these can be the highest quality despite being a bit aged in years (largely irrelevant in this specific context/these high-end cells). I am also a big fan of buying Tesla packs from people that buy salvage Teslas and sell-off the parts. These are exceptionally well-built, energy-dense packs, and you'll be able to re-work the house battery compartment to accommodate.
Richard mentioned going with a higher voltage. In my humble opinion, Richard is spot-on and this is a no-brainer. Parallel a few DC-buck units to provide 12v from your bank, but ultimately go with a 48v or similar bank, strictly for your 110v (220v split-phase), if that's possible. The Growatt-style inverters have large voltage ranges; for example, the 48v will run anywhere from 38v to 60v (that's a very rough estimate based on memory; double-check the exact numbers before buying). What this means is that if you buy a Lithium pack that has a nominal of 52 volts (eg LiFePO4 15s bank) with a range of 58v to 45v across the charge-curve, you'll have no problem (lithium chemistries also have very flat discharge curves which further reduces this issue).
Speaking of paralleling batteries... You asked whether you can parallel more than 4. While it's true that many manufacturers (eg BattleBorn) recommend against paralleling too many batteries, this is not a concern when you design your bank properly. A big part of this is how you wire and whether you start by testing every cell's life. I mentioned this in the Facebook post; be sure you wire in a manner where the batteries are forced to discharge evenly. This form of wiring is a bit confusing at first; however, you only have to wire your batteries once; it's not something you have to commit to memory, etc.
I also do not feel that someone needs an excuse to go with Lithium chemistry battery banks. For example, even if someone doesn't do extensive boondocking, there remain hundreds of reasons that make modern-chemistry the far better choice at current prices. They're almost 3 times as energy-dense (aka 1/3 the weight) and technically more if you consider their DoD, which at a 15-95 curve (optimal lifetime/DoD curve) gives you 80% of their rated energy, versus an SLA at 50%.
Better yet, they have (essentially) no self-discharge, they are not permanently damaged by a situation where they run down, the required BMS provides a great deal more care/longevity than you'll get without, contrary to SLA or AGM batteries, they don't have limited "lifetimes" based on a number of years similar to SLA's (at least not for real-world RV purposes), etc.
In our class-B, we go so far as to run LiFePO4 as our chassis battery as well, simply because it's stored without power and we can go six months without using, without any issue whatsoever.
If you're considering LiFePO4 or Li-on solely as an alternative for standard battery use, without boondocking, they are absolutely the way to go at current pricing (anywhere from $120 to ~$440 per kWh all-inclusive with tax/shipping). NMC is also very easy to come by and in many ways that would work better in a Newell battery bank configuration, if you're doing a higher-voltage unit.
I could go on for pages on the benefits and reasons for going with modern chemistries over SLA or AGM; this is just the tip of the iceberg. I can provide far more detail on any of the areas where you're interested in digging deeper.
It's also worth reading the posts related to the battery isolator, which my wife posted along with some of my input, just a couple days back. This explains the benefits / trade-offs of the DC-DC charger that I had also recommended to you.