BiGH wrote:maybe in the USA ...
in australia the charger is $239AUD! its stupid.
its cheaper to buy a us charger and voltage converter.
From my experience the Dewalt chargers are even worse than that.GGoodrum wrote:I'm not a big fan of the DeWalt chargers. I have four of them that I used to charge 8 packs. I recently re-did these into two 10s4p packs, as described earlier in this thread. Before I took the 8 packs apart, I put all on on the DeWalt chargers, and left them on for half-an-hour after the 3 lights first came on, just to make sure they were well-balanced. When I got the packs apart, and I was able to check the voltage of each cell, I was quite surprised at how out-of-balance they were. Almost every pack had cells that ranged from about 3.40 to 3.70V. In one pack, one cell was at 3.36V and another at 3.78V. They were so out-of-whack that I thought maybe some of the cells were stressed, and had lost capacity. They weren't, though, as I was able to balance the pack using a TP-210V balancer and then charge these back up using a TP-1010C charger and the cells are all very close now.
Maybe I just have four bad chargers, but I think that's highly unlikely. Anyway, I'm done with the DeWalts.
Doctorbass wrote:Just by combinating that to the LVC made by Bob and the PBC realized by GGoodrum would finally close that debate about the best way to charge and protect LI-ion !!
lawsonuw wrote:How about adding cell balancing to the BMS boards you've made GGoodrum? Recently poking around the web I found the attached circuit. It's a cell by cell shunt regulator that clamps the maximum cell voltage, and uses an opto-isolator to signal it's status.
brandonh wrote:lawsonuw, you want to check out Jeff's "BMS package for A123 cells" thread here: http://endless-sphere.com/forums/viewtopic.php?t=2387
It features an improved version of the MetricMind BMS schematic, with SMT components sized just right for the A123 cells.
GGoodrum wrote:I'm still trying to decide if it is better to have balancing logic in the pack, or if this should be external. For one thing, I know the LVC circuit draws about what the cells will loose just sitting on the shelf, but can the same be said for a more complex clamp circuit? Can you leave this connected all the time?
Jozzer wrote:Makes for a much simpler charger circuit, just plug in a PSU and away you go. Means we would be able to sell the pack to average customers...
GGoodrum wrote:what if we just used one of these clamping circuits to simply limit the voltage that each cell can reach to 3.7V. Then we can use any one of many existing SLA chargers, that also have the CC/CV charging profile, but at a pack voltage level.
Malcolm wrote:Couldn't have put it better. There are so many decent SLA chargers available that can do most of the job (and do it cheaply) that it seems overkill to start messing about with lab power sources and replicating stuff that's readily available. But how do you shut off the charging circuit if one cell takes too long to reach the cutoff voltage?
brandonh wrote:Some RCers already use CC/CV supplies to charge their A123s, and there's even a YouTube video showing how it's done with a Mastech 5020E supply.
I think there's an issue with your overvoltage-threshold-in-series idea. I'll assume that a CC/CV charge is being used, with voltage set to (#batteries*3.6v). In an out-of-balance pack, one cell will need longer to reach full voltage. That lagging cell might be at 3.4v, while the other cells are at the 3.6v target. Since the charger starts in CC mode (not at Vlimit yet), the other cells rise in voltage until the total of their voltages plus the lagging cell voltage equals the charger limit (#batteries*3.6v). At Vlimit, the charger switches to CC mode, with current through the string dropping quickly - many cells won't accept as much current. The cycle stops when all cells have reached at least the 3.6v threshold. But while the lagging cell voltage is rising, the other cells are all being overcharged! The cycle does nothing to balance the pack.
This is the whole reason for the shunt regulator "voltage clamp" design; it enables each cell to rise in voltage to exactly 3.6v, then accept no more current. The pack comes out of every charge cycle balanced.
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