My AGM starter battery is beginning to fail at about 3 years. Rather than do the sensible thing and replace with the stock lead acid, I've decided to replace with a small 40AH 6S Lithium Titanate Oxide (LTO) homebrew.
There isn't much out there on LTO batteries, particularly as starter batteries, and not much on this forum either. This thread will focus on the design, implementation, and success (or not) of this technology as a starter battery.
Goals:
Replace the starter battery. However, 40Ah (or 35 Ah as it may prove in use), is about the 1/2 capacity of a 27F Lead acid (full capacity is 80Ah, can only use 1/2), so I don't think I'm giving up much in key off capacity, and certainly gaining lots in C rate for discharge.
Save weight. It's lighter, by a lot. The full, finished pack should be 20lbs with the box and BMS and any other doodads.
Fits in the starter battery space.
Secondary goals:
to try out new stuff
it works - so then can add on six more cells and have a 80Ah starter AND accessory battery
A few basic details first:
LTO is not a 'new' chemistry. It's been around for at least 25 years. It is entering use in the general public over the last few years, as cells from transport buses are replaced and then sold into the secondary market.
LTO is not particularly cheap or space efficient or weight efficient.
Most LTO cells are '2.3v', with 1.8v discharged and 2.8v charged. ->>> 5s pack 9v to 14v ->>> 6s pack 10.8v to 16.8v. It's an awkward voltage for 12v. Works out really well for 24v and 48v though. Too bad we've got 12v systems here in the US.
LTO cells are incredibly safe. They don't really explode.
LTO cells can be flat for months, recharged, and pick up where they left off. It's really unbelievable.
'Yin Long' cells are made almost exclusively for buses in China. A few enter the market 'new' at 45Ah. Many enter the market after several years of use as 'new' at 40Ah. And more enter the market well used between 40Ah and 30Ah. Here's a link to the cycle curve for LTO, you can see why so many of these cells are sold as 40Ah. The toshiba SCIM cells can be purchased real new. BMW used LTO cells to create a starter battery already. These are also on the secondary market.
LTO cells are a lifetime investment. At 10,000 cycles that is 30 years of daily cycling. Think about it.
'Starter' kit
6 66160 Yin Long cells '40Ah' ($200 to $400, ymmv)
1 80A/80A/1000A 'start' BMS specific to LTO Cells (this may not be required) $50
3 ft of 3/8" by 1 1/4" aluminum bar $12
2 3/8" lead terminal studs (+ and -) $10
1 Group 27 Battery Box $15
1 300A coulomb and voltmeter $20
50 m12x1.75 nuts, Aluminum $35
1/2" aluminum washers $10
1 300A Class T fuse $25 (really this should be a 150A . . .)
1 250mm M5 allthread $5
1 18V1.5Kw50A TVS Diode $5
Optional:
1 Renogy 20A DC DC 12v $100 (or similar)
Patience and Time
Challenges:
Charging: I hope to use the alternator to charge. I am totally ok with the pack topping out around 14v. (2.33v per cell). Yes, that is around 35 Ah of capacity). Will it work? Audio guys on internet say yes . . .
Fusing/Breakers: Where? What capacity? How Many?
The unknown . . .?
There isn't much out there on LTO batteries, particularly as starter batteries, and not much on this forum either. This thread will focus on the design, implementation, and success (or not) of this technology as a starter battery.
Goals:
Replace the starter battery. However, 40Ah (or 35 Ah as it may prove in use), is about the 1/2 capacity of a 27F Lead acid (full capacity is 80Ah, can only use 1/2), so I don't think I'm giving up much in key off capacity, and certainly gaining lots in C rate for discharge.
Save weight. It's lighter, by a lot. The full, finished pack should be 20lbs with the box and BMS and any other doodads.
Fits in the starter battery space.
Secondary goals:
to try out new stuff
it works - so then can add on six more cells and have a 80Ah starter AND accessory battery
A few basic details first:
LTO is not a 'new' chemistry. It's been around for at least 25 years. It is entering use in the general public over the last few years, as cells from transport buses are replaced and then sold into the secondary market.
LTO is not particularly cheap or space efficient or weight efficient.
Most LTO cells are '2.3v', with 1.8v discharged and 2.8v charged. ->>> 5s pack 9v to 14v ->>> 6s pack 10.8v to 16.8v. It's an awkward voltage for 12v. Works out really well for 24v and 48v though. Too bad we've got 12v systems here in the US.
LTO cells are incredibly safe. They don't really explode.
LTO cells can be flat for months, recharged, and pick up where they left off. It's really unbelievable.
'Yin Long' cells are made almost exclusively for buses in China. A few enter the market 'new' at 45Ah. Many enter the market after several years of use as 'new' at 40Ah. And more enter the market well used between 40Ah and 30Ah. Here's a link to the cycle curve for LTO, you can see why so many of these cells are sold as 40Ah. The toshiba SCIM cells can be purchased real new. BMW used LTO cells to create a starter battery already. These are also on the secondary market.
LTO cells are a lifetime investment. At 10,000 cycles that is 30 years of daily cycling. Think about it.
'Starter' kit
6 66160 Yin Long cells '40Ah' ($200 to $400, ymmv)
1 80A/80A/1000A 'start' BMS specific to LTO Cells (this may not be required) $50
3 ft of 3/8" by 1 1/4" aluminum bar $12
2 3/8" lead terminal studs (+ and -) $10
1 Group 27 Battery Box $15
1 300A coulomb and voltmeter $20
50 m12x1.75 nuts, Aluminum $35
1/2" aluminum washers $10
1 300A Class T fuse $25 (really this should be a 150A . . .)
1 250mm M5 allthread $5
1 18V1.5Kw50A TVS Diode $5
Optional:
1 Renogy 20A DC DC 12v $100 (or similar)
Patience and Time
Challenges:
Charging: I hope to use the alternator to charge. I am totally ok with the pack topping out around 14v. (2.33v per cell). Yes, that is around 35 Ah of capacity). Will it work? Audio guys on internet say yes . . .
Fusing/Breakers: Where? What capacity? How Many?
The unknown . . .?
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