I have two 16s battery packs running with WatchMonCORE and CellMate-K9. I start balancing at 3.45V (CV9). My charge voltage is 16 * 3.45V + 0.3V = 55.5V. Both packs are built equally and connected to the same busbar. Unfortunately, cell voltage measurement seems to be slightly different between both packs. In one pack, all cells get balanced all the time, while in the other pack all cells remain at 3.45V and don’t get balanced. I have to increase charge voltage by an additional 0.1V to get all cells into balancing and to reach 50mAh for every cell. Is it possible to fine tune the cell voltage measurement of CellMate-K9 to fix this issue?
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I don’t really understand.
You say the second pack is not balanced.
But on the other hand you say they all measure 3.45V ( so they are balanced).
And yes there is fine tunning for voltage measurement for CellMate-K9.
They might be balanced, yes. But please read on: They don’t reach necessary 50mAh Bypass Session (CA3) in one pack, while the second pack gets more and more increased bypassed amphours. Therefore, Batrium does not get into “Charging Full” state and that is the problem.
The wiki (CellMon Voltage Calibrator | Batrium Knowledge / Wiki) clearly states, that the CellMon Voltage Calibrator can not be used for CellMate-K9. I tried it and it does not work.
Hi Kleini, welcome back!
Sorry to hear you are having trouble! Which pack is electrically closer to the inverter? Sometimes if the cables between banks are too long or not thick enough, the closer pack gets all the charge current.
Yours seems not too bad considering that all cells do reach the balancing voltage, but you should definitely try to get to 50mAh of balancing to reset your SoC and prevent drift. Maybe you could raise your limited current a little? Your charge voltage is spot on, good job!
Here is some standard info we include with K9s that sort of illustrates what I mean.
Could you share some photos of your pack?
Hi James,
both cables are equally long to a common busbar with 240mm², which is between AWG450 and AWG500. I don’t see problematic resistances in my packs because cell voltages are very equal even with high current. The charge current limit does not matter in my system. I use Victron Energy with feed in from DC, so solar chargers always provide their maximum current.
If I raise charge voltage to 55.6V, I can get both packs quicker into reaching 50mAh balancing energy per cell. But I would like to reduce voltages as much as possible. And if charge voltage is just 0.1V less, I see balancing energies as shown in above picture. Second pack has much higher balancing energies than first pack. If there would be single cells in each pack with a very different balancing energy, than this cell needs more balancing that others. But all cells in a pack behave very similar and I see only this larger difference between the packs.
But we’re talking about 6.25mV difference per cell, which should normally not be an issue.
Will open the packs an provide pictures.
Thanks so much for your help and I am eager to implement and test dynamic voltage targets.
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