BMV Sync Problems Due to Very Short Absorption Times for LiFePO4

[orangeminnie]

I think I've found why the BMV 712's usually don't sync when LiFePo4 batteries are topped off. It appears to be due to very short absorption times needed by these batteries, at least the BB's. Absorption lasts just a couple of minutes (or less), when no loads are present.

Both Victron, Xantrex, and probably other chargers and controllers appear to unconditionally exit absorption and go to float, when the charge current drops to 2A. This overrides whatever fixed absorption time might be programmed. When the programmed surface voltage (typically 14.0 to 14.4) is present, along with a tail current less than the programmed level (typically 4%) for less than the programmed time on the BMV (default is 3 minutes), the BMV won't sync to 100% I have a workaround, but what is everyone else doing?

 

[Webbee]

I have a BMV 700 and mine won't sync either. I have two Battle Born batteries in parallel. I have my absorption time set for 50 minutes and mine isn't resetting. I have also the same settings as you, "charge voltage" set at 14.1 volts and the "tail" at 4% and default time at 3 minutes. I also changed the "Peukert Exponent" to 1.05 as in video I found on YouTube. Mine is still not syncing.

 

[jwu_cc]

I have a BMV 700 and mine won't sync either. I have two Battle Born batteries in parallel. I have my absorption time set for 50 minutes and mine isn't resetting. I have also the same settings as you, "charge voltage" set at 14.1 volts and the "tail" at 4% and default time at 3 minutes. I also changed the "Peukert Exponent" to 1.05 as in video I found on YouTube. Mine is still not syncing.

What's your absorption voltage is set at?

 

[Webbee]

I have the absorption set at 14.4 volts

 

[jwu_cc]

That should work fine if you are seeing battery voltage being hold at that level for the specified time. At least it works fine for my BMV712. You can try to lower the charged voltage in BMV to 13.9 and see if it syncs.

 

[Webbee]

Ok, I will try doing that. I was wondering if I should try that. Thanks!

 

[jwu_cc]

I think I've found why the BMV 712's usually don't sync when LiFePo4 batteries are topped off. It appears to be due to very short absorption times needed by these batteries, at least the BB's. Absorption lasts just a couple of minutes (or less), when no loads are present.

Interesting. I wonder if lowering the absorption voltage a bit would help holding the voltage long enough for BMV to properly sync the SOC ? I had mine set at 14.0V (28V with 24V system) as I have some imbalance in my prismatic cells and don't want to stress it too much. That seems to allow absorption voltage to hold long enough for the BMV to sync. Charged Voltage was set to 27.6V in the BMV by the way.

 

[orangeminnie]

My solution at the moment for the BMV:
--Set Charged Voltage to 0.3V below the Absorption Voltage of the charger(s) (eg: 14.1V for 14.4V Absorption). This is in line with what Victron recommends.
--Set Tail Current at 4% (pretty standard)
--Set Charged Detection Time to 2 min (instead of the standard 3 min).

 

[Webbee]

Mine is still not working so I will try the Charge Detection time @ 2 minutes and see if this work. I must admit I and not happy with this product. I really hope we can figure this out. However with this crappy weather I am only getting rain and no sunshine to test this.

 

[nebulight]

It's the most accurate for a reason, but you have to tweak it to get the settings right for your battery. Like others have said, lifepo4 doesn't really need an absorption phase of charge, so it drops off pretty quick. Set your charged detect time to as low as possible.

I consider my batteries full when it hits 14v regardless of tail current. The absorption phase is there to help balance any cell that may be out of balance.

 

[Webbee]

I think I might have figured it out. I am using a Victron charge controller (150/45) and the other day I was reading through all the settings and I noticed that the absorption time I set was 2 hrs, but here is what I changed. There is an option for fixed or adaptive. I change this setting to adaptive and now the absorption time is 2hrs maximum. Now the sync works because I just watched it change from 98.2 % to 100%. This is the only thing I changed and now it's work after two weeks or more of frustration.