Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
LTO Battery question
#41
Was quoted $26 last week.. in bulk. OSN. Wait for the US to go full tariff mad and the rest of the world pricing will be better.. I still think they will drop to well below $20 in the next recession.
If you can't quantify how much they cost, it's a deal, I'll buy 5 of them for 3 lumps of rocking horse ......
Reply
#42
I saw a youtube ( @DIY Solar Power with Will Prowse  "DIY 12v LTO (Lithium Titanate) Battery"  https://youtu.be/p1xildSl4Hk )  over the weekend that said LTOs have a 14% charge/discharge loss compared to 1% for Lithium-ion.  In other words, if you apply 100w charge you only get 86w out.     

Is this true?    If so, and you add this 14% and to inverter 10-15% loss you are getting in the neighborhood of 25-30% power loss overall which is pretty high.
Reply
#43
Comments from the video
1. Cells shown are re-wraps (damaged or less than re-labeled capacity, hence the re-wrap) - actual capacity, go figure
2. Build approach, WTF, where is the gaffer tape, lol.
3. Cells are rated up to 2.7V not 2.6V but actual renergy gain between 2.55V and 2.7V is near zero
4. The chart shown seems to be just some generic LTO type, not specific for these cells
5. Test discharge rate 633W at 12V = 52A per cell (see notes below)
6. Discharge efficiency might be true near 10C (try 10C with a 18650 and compare)
7. 22s for best compatibility with 12V lead acid systems voltage range
8. Stunned that the video got 498,000 views
9. Yes he was ripped of and sold 30Ah cells labeled as 40Ah

If you want to try and run old / used LTO's at 10C (400A in the case of the 40Ah cells) then yes the efficiency will be bad because even with a very low cell resistance when you have 400A it will generate a lot of heat even for very small resistances. The cells on the market generally have a higher than specification IR due to the previous heavy 10C charge regime.

For powerwall builds you should never even consider running them anywhere near this rate, unless desprate.

As an example even just 2 milli Ohm at 400A = 320 Watts and for a 90Wh cell... ouch, yes, around 10% losses discharging in 6 minutes

I have some test data showing a full cycle (charge/discharge) at 5A (0.125C) at 98.5% (including wire losses) and this was not the best case voltage range. Ramp it up to 0.5C and the higher cell resistance starts to impact and the efficiency drops to around 96% (including wire losses).

LTO cells have a very high coloumbic efficiency, higher than Li-ion.
If you can't quantify how much they cost, it's a deal, I'll buy 5 of them for 3 lumps of rocking horse ......
Reply
#44
(09-23-2019, 07:45 PM)completelycharged Wrote: If you want to try and run old / used LTO's at 10C (400A in the case of the 40Ah cells) then yes the efficiency will be bad because even with a very low cell resistance when you have 400A it will generate a lot of heat even for very small resistances. The cells on the market generally have a higher than specification IR due to the previous heavy 10C charge regime.

For powerwall builds you should never even consider running them anywhere near this rate, unless desprate.

As an example even just 2 milli Ohm at 400A = 320 Watts and for a 90Wh cell... ouch, yes, around 10% losses discharging in 6 minutes

I have some test data showing a full cycle (charge/discharge) at 5A (0.125C) at 98.5% (including wire losses) and this was not the best case voltage range. Ramp it up to 0.5C and the higher cell resistance starts to impact and the efficiency drops to around 96% (including wire losses).

LTO cells have a very high coloumbic efficiency, higher than Li-ion.

Thanks for this. As I said in my intro I'm looking for a replacement leisure battery for my narrowboat (12V nominally 460Ah) so I want something that will reliably provide 300A to run the inverter. My initial thought was 66160s as a 5S6P package since DoD for SLA is 50% max but reading this and other threads I'm starting to realise this isn't necessarily going to work as I'd be drawing 50A per cell.

Other issues I hadn't considered include the location of the battery (in an enclosed engine room which can get rather warm - though probably no hotter than a summers day in Florida) and whether the cells would be up to spec. Another question arises over how the inverter performs at 11V. Suppose I went for 6S10P; that would bring the current down to 30A which would be better all round apart from initial cost and would help to ensure the low voltage alarm (and eventual cut out) didn't happen.

I also need to think hard about the busbar/interconnects needed. IEE wiring regs suggest I'd want 150mm2 of copper.
Please excuse any errors introduced by autokorrekt.
All other errors are solely my own work.
Reply
#45
For 3kW inverter output I would start to consider moving to a 48V battery setup.
For getting 12V these might work quite well and few in parallel should provide enough for the starter motor.
https://secondlifestorage.com/showthread.php?tid=8065
The increase to 48V would make wiring a lot thinner and overall more efficient

LTO will be fine at higher temperatures, not ideal though as it is excess temperature which has just a large effect on cell degredation as sustained high charge voltage.

In terms of DoD I happily run around 85% use (95% to 10%), just to make balancing a non issue. The cells I have seem to have evened out on thier own and settled so that I have not needed to push or pull any individual cells in the pack (just under 400 cells in total). Draw / charge is less than 10A per cell (18p).

Big issue is buying LTO from China in small quantity the freight/shipping costs a lot per cell when factored back in. Pricing last time I had a quote was around $26 per cell for 40Ah. Shipping can be just as much as the cell in small numbers.

One option, which might work well for you are these cells, priced very reasonable if they are in ok condition, whcih they appear to be.
https://secondlifestorage.com/showthread.php?tid=8030
Downside might be the space to locate them due to the shape...
Not sure if the packs could be reduced down to 22-24s, the build is not that clear with the plastic cover over the busbars.
If you can't quantify how much they cost, it's a deal, I'll buy 5 of them for 3 lumps of rocking horse ......
Reply


Forum Jump:


Users browsing this thread: 1 Guest(s)