I don’t have a lower current charger handy, is there a way I can get my charger to output lower current? I’ve read that some have a pot inside I can adjust.
Just set it to balance off the charger (static balance) and leave it alone for a couple-few days.
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Wouldn’t cycling the battery a bit help it? Or no?
It will only start slowing down the charging current if the pack reaches the voltage set by the charger. This includes all voltage rises caused by cell and pack internal resistance, a “phantom voltage”, the opposite of voltage sag. This is the crossover point between the constant-current “bulk” charge stage and the constant-voltage “topping off” stage.
If the pack has not reached the charger voltage due to an overvoltage alert of some type (and the BMS stopping the charge) then the pack has never gotten to the point where it’s mostly charged and only needs to be topped off.
Raising your overvoltage settings (usually not good to do), and/or lowering your charger voltage, and/or lowering your charger current (less “phantom” voltage rise) can all help a charging setup get to the constant-voltage (CV) topping off stage before the BMS cuts things off.
As @bboybowzer mentioned you might also be able to balance when not charging, check the instruction manual for your BMS.
Something to consider…
Charging to a lower voltage, by skipping the CV topping-off stage, helps to extend cell life because it results in the cells dropping back down a bit more in voltage compared to letting them fully top off. Depending on the voltages you might lost a touch of range but if you don’t notice that then the lower voltage can help your pack last a bit longer. Adjust the balancing thresholds to take these lower voltages into account though.
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I think its been said but a 0.12 delta is very very high
That would technically be a full metric chonk. 12s3p a123 doesn’t exactly fit… @hummieee did you just use thick gaskets?
For once in my life(po4), I actually need a 12s lifepo bms instead of lithium ion. Any good sources where I don’t have to play lifepo/li-ion shenzen roulette?
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Ok, so I’m ready to close this beauty in a shrink wrap. I just need to solder the BMS (charge only) and I’m also waiting on some xt60ies for the charge port.
I’m also going to add an inline fuse on the charge positive line. What fuse should I use? I will be charging with a 4A charger.
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10A is what I use usually. Pack looks nice!
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How do you guys shrink wrap flexible packs? do you just shrink each individual section and have the series wires jumping between them?
I shrink them. The method depends on the spacing. For a Prototipo style battery, each segment gets its own wrap, and then I flatten the edges inward on the faces when the shrink is still warm.
For some packs where the whole thing has to be flec tolerant in a single compartment enclosure, I’ll wrap it and then carefully slice along the segment seams to allow the flex of things to happen.
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If you’re charging to a lower voltage won’t the BMS keep cutting on and off due to the “phantom” voltage? For example, if you want to stop charging at 4.1 V per cell, but the charger doesn’t do CV until 4.2 V per cell then won’t the BMS cut the charger off when you get to 4.1 V, the cells will drop back down some, the BMS will let it charge again until it hits 4.1 V per cell, and that will repeat many times until the cells stay at or near 4.1 V? Is that just how you’re supposed to charge in that case? Are there any issues with that cycling that will happen?
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this is exactly what seems like is happening with my battery, except with imbalanced cells.
my charger keeps going in CC until one cell reaches the cell overvoltage cutoff, then the phantom voltage leaves and the highest cell drops down to about 4.11V. it repeats this many times, adding 0.01V to each cell at best.
the only way I’ve found to deal with this in the LLT BMS app is to set the overvoltage release to about 4.05V, but keep the pack overvoltage release and overvoltage cutoff the same and set cell overvoltage to 4.25V-4.3V.
this way it charges slightly past 4.2V but then cuts off letting the phantom voltage release and the balancer kicks in bringing the cells closer. so far this has helped me cut my 0.12V delta of imbalance down to 0.06V in ~1.5 days.
My charger won’t go into CV until the pack is >50V at least. I have opened it up though and there are 3 potentiometers. if I knew which controlled the current I could tone it down for better, quicker, easier, safer, better balancing.
I may also just be completely misunderstanding phantom voltage and/or balancing, someone please tell me if I am.
This is a good reason to do your voltage adjustments on the charger end, rather than the BMS. If you lower the charger’s voltage, it will go into CV mode earlier.
Easily checked with a multimeter. A clamp-type meter that will measure DC is best (Uni-T UT210E for example), but any meter that can measure current and voltage will do.
Just hook up the charger to a suitable load (A partially charged battery will work) with the multimeter set up to measure current, then twiddle the pots till you find the one that controls the current. Label it, and put the other two back the way they were.
Then, without the charger attached to the battery and the meter measuring the output voltage, twiddle the other two pots until you find the one that controls the voltage. Label it, and put the other one back the way it was.
Et voila, you now know which pots control voltage and current.
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If you want to charge to a lower voltage, including a CV stage to top off the pack, then you need to set the charger to a lower voltage. Not the BMS.
The BMS will never allow the charger to go into CV mode if the BMS is set to cut off at below the charger’s voltage + the phantom voltage rise.
Yes, if the charger voltage + phantom rise is higher than the BMS cutoff then you can get lots of cycling on/off. This might not hurt anything, if it doesn’t happen very quickly, but it sure isn’t good.
Every time you stop current flow you get a voltage spike. At these relatively low current levels these spikes are small but they’re never going to increase the life of your BMS and could potentially shorten its life.
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Lower current certainly helps reduce phantom voltage rise but I think you should be able to help things by lowering your charging voltage or getting all settings up and away from the charger’s voltage (which might not be a good idea, depending on the charger voltage).
You have a very complex set of thresholds set up now, all trying to handle the symptoms you are seeing, but IMO never addressing the cause of all the symptoms…which hasn’t been discovered yet.
Try a lower charging voltage, even if you will never use it. This is just for testing to see if the charge finishes properly, going through a full CV stage down to the termination (charge stop) current setting level…if there is such a setting.
Keep your protection settings high and start balancing about 0.2V/cell below your charge voltage, e.g., 3.8V/cell balance start for a 4.0V/cell charge voltage.
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2018/19 everyone used Samsung 30Q
now Molicel P26A is the new norm it seems
i see that they have lots more A, but does it matter that much?
Also they’re 2.6Ah vs 3Ah which i don’t like… (if i’d have the space i’d go for 21700 cells)
In actual runtime the p26a ties or beats the 30q within our range. Rated capacity is generally not a factor we can look at for the high drain of esk8.
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can’t really see what you mean
Moochs e-Rating is about the same and the as expected 30Q last more Ah than the P26A
only thing i see is that P26A has less initial sag and is about 0.1V higher (does this make much of a difference?)
wait
in a 12S pack 0.1V adds up to 1.2V sag
But that just means i don’t have the same top speed?
sry, quite some time since i last looked into batteries
When draining at 10-15A, the P26A remains in a usable voltage longer than the 30Q. It also doesnt unbalance as badly.
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