Odd LFP/LTO configuration idea / question

[pvnick]

Hi. I have an off-grid cabin which is currently running off of 1800W of solar and am using 4 of the BattleBorn 100ah and find that this is more than ample for my needs up there and gives me a couple days of autonomy with one or two critical loads. Normally I would winterize the place and disconnect the BattleBorn batteries (for obvious reasons) in the winter as it can reach -30c up there. I would like to be able to have some remote monitoring up there, or at least the ability to quickly get the place up and running when I go up in the winter though.

I notice that the LTO cells are coming down in price and can be charged far below 0 degrees so I figured I would build a smaller battery pack with LTO cells and leave those connected in the winter time. I'm wondering however, though, given that LTO cells have such a spectacularly large cycle life, if it wouldn't make sense to somehow interconnect the smaller LTO pack with the battleborn's somehow to put them in use in the summer too. I'm thinking that since in a normal scenario when it's sunny I barely dip into the total capacity of the LFP bank, cycling the LTO cells more often would give me better longevity on the LFP bank, and give me a little extra capacity anyway?

I realize that LTO cells are a different voltage, and I would have a smaller capacity pack but there must be some way to interconnect these two systems? Perhaps a programmable BMS + SSR to flip the bank over to LFP when the LTO are fully discharged? Or maybe buck/boost converter? It seems like in 6s / 12s configuration for the LTO would capture most of the discharge curve WRT the LFP cells . I don't even know if this is possible.... Any ideas?

 

[Craig]

yes you can do it it will just be a little wanky with the differential voltages. Quickly thinking here since the LTO cells charge higher than the LFP maybe you could cut off the charge of the LFP cells and top off the LTO hen as you use power once the LTO get to the voltage of the LFP turn them all on and use all your batteries. This way the LTO will get the bulk of the daily usage. They would kind of work like Super Capacitors for your daily needs.

 

[Craig]

I have been contemplating this as well for the same cold weather charging and the desire to have cameras etc during the winter. You already have your Battle born cells but you can actually create the same size LTO bank for less than a BB if you play your cards right.

My LFP batteries would be the 280AH EVE cells since they are so much cheaper than anything.

 

[pvnick]

I have been contemplating this as well for the same cold weather charging and the desire to have cameras etc during the winter. You already have your Battle born cells but you can actually create the same size LTO bank for less than a BB if you play your cards right.

My LFP batteries would be the 280AH EVE cells since they are so much cheaper than anything.

>> you can actually create the same size LTO bank for less than a BB if you play your cards right.

yes, something I have quite recently discovered myself...

>> My LFP batteries would be the 280AH EVE cells since they are so much cheaper than anything.

Yeah. Full disclosure when I started construction on the cabin project I knew it was going to be off-grid but hadn't done all the research yet / didn't realize that you could put together a battery system with raw cells that would be just as good / perhaps even better than the "drop in" ones at pretty much half the cost... Hindsight is 20/20 I guess...

Ok well thanks for the suggestion here, actually quite a good idea. I think I will put together a small LTO battery and run some tests, see how it is, and perhaps report back.

Thanks again!

 

[Sparky]

I'm watching because, while i have a lot of lifepo battery, they're the shunbin type, so i feel like i'm on borrowed time. I want a 24v lto battery in front of them to handle as much of the 'daily cycling' as possible.