Recharging Lithium Titanate cells: Toshiba SCiB BMS: Help?

[Syonyk]

I'm working on a pack from a Schwinn Tailwind. It's the most absurdly overbuilt pack I've ever met in my life, but the total voltage across it is 7v. Rather low for a 24v pack (10S LTO).

Cells range from 0.65v to 0.8v.

I'm seeing, in general, cutoff voltages around 1v for this chemistry. So I'm not *that* far below it. It also looks like it's capable of taking a charge from a deep discharge, as the chemistry claims to be dimensionally stable at a deep discharge.

Is this a reasonably safe chemistry to attempt to charge manually from a low voltage like this? It shouldn't take much to get it back above 10-12v, at which point I think the BMS will allow for charging.

Thoughts?

 

[jaunty]

i'm not expert by any means...

but for my severely low voltage lithiums i start them charging at a very low amperage, then once in the healthy range, can support more amps. I use a lab power supply.

i'm sure more experienced peeps will chime in.

 

[nutnspecial]

Ditto jaunty. http://endless-sphere.com/forums/viewtopic.php?f=14&t=69512

'peaceful' discharged lipo pack back up safely from close to 2v with .5 to 1% charge on a gophert ps.

IDK wth titanate is, but it's prob more friendly than lipo, so you have my vote of confidence

 

[liveforphysics]

Titanate doesn't seem to be bothered by extreme low discharge. They will likely function like new when charged.

 

[blisspacket]

Been there, done that.
As a shadetree wrench, I couldn't handle all the circuitry in the battery itself. I sliced out all the diodes and gizmos and reassembled the battery with leads directly from the ten cells to the terminals that match the controller power in buttons.
I drilled small holes in the terminals so I could put a charge to the 10 cells. That hi-dollar charger that's part of the package is likewise beyond my shadetree abilities. I've scavenged a couple 24 volt, .5 and 1.5 amp chargers (computer power supplies?) and provided them with plugs that slide into the terminals on the battery.
No heat from charging, batteries behave while pedalling, and so far we've logged maybe 35 miles, three charges, on the batteries. Titanate is supposedly very safe. I'm impressed that these created in 2008 will light up and work. Our initial run was 14 miles, and the indicator went from 4 lights to 3, sometimes 2, but back to three in the end. I was even thinking that there might be a regeneration component in the Tailwind, but I doubt that's the case.

 

[Syonyk]

Titanate doesn't seem to be bothered by extreme low discharge. They will likely function like new when charged.

Great, thank you! That's what it looked like when I dug into the chemistry a bit - and they're not even totally flat.

Been there, done that.
As a shadetree wrench, I couldn't handle all the circuitry in the battery itself. I sliced out all the diodes and gizmos and reassembled the battery with leads directly from the ten cells to the terminals that match the controller power in buttons.
I drilled small holes in the terminals so I could put a charge to the 10 cells. That hi-dollar charger that's part of the package is likewise beyond my shadetree abilities. I've scavenged a couple 24 volt, .5 and 1.5 amp chargers (computer power supplies?) and provided them with plugs that slide into the terminals on the battery.
No heat from charging, batteries behave while pedalling, and so far we've logged maybe 35 miles, three charges, on the batteries. Titanate is supposedly very safe. I'm impressed that these created in 2008 will light up and work. Our initial run was 14 miles, and the indicator went from 4 lights to 3, sometimes 2, but back to three in the end. I was even thinking that there might be a regeneration component in the Tailwind, but I doubt that's the case.

What were the issues you found that caused you to eliminate the BMS circuitry? I'm generally hesitant to bypass safety systems, even with "safe" cells. I'm hoping that once the batteries are balanced properly, the BMS will let the charger finish the charge, as intended. There's definitely balance issues right now (0.65-0.8v range on cells) that might show up when charged in bulk. It's an option I'm considering, but I'm hoping not to need it.

 

[blisspacket]

I just don't have the technical knowhow. The battery comes with two separate charging points, as well as the third discharge terminals. No way would the included charger cooperate even after I'd nursed 10 cells up to 2.4 volts. Yes, a BMS would be great. If you're able to make it work, 3 cheers, and hopefully you can post the solutions!

 

[Syonyk]

Hm. Well, that's been my plan (except not 2.4v, something much lower). Did you disconnect the BMS while charging, or run the current through the high amperage plugs?

Hopefully I can find a way to make it cooperate.

 

[blisspacket]

I'm pretty sure I had the battery fully assembled and the systems allowed me to charge through the gold female terminals. BUT!!! then when I asked for emf from the discharge terminals, there was nothing there. All KINDS of failsafes, for one reason or another.

Isolating the cells from the failsafes and the bms is readily done from within. The cells are packed within a plastic grid, nothing heavy duty, they don't swell or warm up while being charged, so I'm content to just charge and ride, no bms.

Surely there's wizardry that can be performed to make it perform as engineered--but I don't have the knowhow. Good luck.

 

[Syonyk]

Yes, I'm aware it can be bypassed.

I believe the gold terminals are always live - they seem to have pack voltage at all points, and are likely wired straight to the pack, with some monitoring. They're designed for high amperage charging, near as I can tell.

I'm hoping that by charging the battery with the BMS disconnected, it won't sense anything weird, and will let me charge properly. The one problem could be if it has some state stored that "knows" the battery has been drained - this isn't something that will be easy to work around.

 

[Syonyk]

Well, as predicted. the BMS is not happy with the charged cells, even though they're nicely balanced.

Does anyone have any documentation on this BMS laying around? Or has anyone ever actually made it live after being drained? I suspect the BMS is latching the state or something, but a week+ of being disconnected hasn't reset it.