Is this not usually the case? About 2 months ago, which was after 6 months of near-daily use of the LTO setup in my 2000 Insight, I checked all 72 cells and the highest cell voltage was only about 0.02 volts above the lowest cell voltage.That is of course assuming all your cells are very well balanced.
Lithium batteries are usually charged with a combination. Typically it's constant current charged up to a threshold and then switched to constant voltage. Generally speaking this is so you actually store the desired energy in the battery because it tends to "rebound" like a rubber band a bit. If your desired voltage was 180V and you CC charged it to 180V and let it sit for a day when you came back to it the next day you'd find the voltage of the batteries would be under 180V. Same is true for discharge, many EV owners especially in the beginning when range was limited would run out of juice not far from home (because they screwed up) and instead of calling a tow truck come back the next day and it had that little bit of juice to get home. Basically it rebounded on the downswing as well. To actually get the batteries up to the voltage you want you generally CC charge to the threshold and then CV charge until the amps drops to almost nothing. Basically, it holds the voltage steady through that rebound phase so that when you take it off the charger it'll stay at that voltage.I recently read that lithium batteries should be grid-charged using a constant voltage (CV) supply, not the constant current (CC) supply since grid charges were designed for NiMH batteries. Can someone comment please. Also can a single two-pack of LTO's (24-cells) be grid-charged with the normal CC charges set to 180V? Thanks
As Jime has said you don't want to charge up to 2.7V/cell he recommends 2.5V/cell (60V for 1 24 pack or 180V for 3 24-packs) because there is no BMS in play. Most true CC chargers either use dV/dt to shutoff or are just purely time based. To know if your charger would work and what it would do depends on what make/model it is (how many amps it does, what it shuts off at, what it's voltage range is, etc.).I assume you are saying that the open circuit voltage of the charger is 180V. If that is the case and it is a true CC charger, then the voltage will fall immediately when it is loaded with the battery. Is this a common Insight grid charger? What is brand?
You will recall that many of us use the common Insight CC chargers for cycling of the OEM batteries. In that case, their output voltage can be quite low when the OEM battery is empty.
BUT, you do not want to charge 24 cells in series to 64.8V That is 2.7V/cell, the full cell spec, and would be the maximum IF your had perfect cell balance between the cells OR if you had a BMS controlling the charger. Neither is the case. The non-BMS operating range for these packs has been discussed many times and the consensus has been that about 2.5-2.0V is the most judicious range, without benefit of BMS. That would give you a 24 cell maximum charge of 60V. Nothing above that is likely safe for the packs in a non-BMS mode.
For sure, basically if you don't have a BMS or something actively balancing the cells in series you should not get close to 2.7V (stay at 2.5V as "fully charged). I think the confusion came into play when talking about the power supply being 180V before we started talking about Constant current chargers. 180V is 2.5V per cell on 72 cells which for a 24 pack is 60V which is your recommendation not to exceed without balancing.No it isn't OK. I added the word "well" to say "well short of maximum" which is precisely what I meant., as an improved wording. The short and easy message is, "Don't charge a 24 cell pack above 60V until you somehow know better." Enough said??
How are these holding up for you? I just bought two to try out. If any of them have failed for you, this would be a Bad Thing for the rest of us with higher ambient temperatures and higher altitudes.I've just bought 5 x 125A l50S fuses as they were very cheap on flea bay. $10 each.
One cell at a time? 😅😂🤣😙john asked...
What is the best way to balance a complete 72 cell LTO pack?
because the premise with grid charging a NiMH pack is that the cells that reach full charge first don't accept more charge; they stop charging and start burning the additional energy off as heat while the lesser charged cells continue to charge.john postulated...
...just charge while monitoring and hopefully the low cells will charge up to the others? Doesn't sound like the best idea.