Johncfii
Solar Enthusiast
- Joined
- Nov 24, 2020
- Messages
- 265
A few months ago I put a large DIY lithium battery pack in service. The pack is big enough to allow me to, under normal circumstances, easily use 15% to 20% SOC as a lower limit, and 80% to 85% as an upper limit. After contemplating/trying different ways to manage SOC, I installed a Victron BMV712 expressly for this purpose.
I chose the Victron BMV712 mostly because it is one of the few units that allows the user to calibrate/reset the indicated SOC to any level. It does not require 100% SOC to calibrate/adjust. I was hoping that it would not be necessary to fully regularly fully charge the pack to confirm SOC accuracy.
I’ve found that it is workable to, about once every two weeks, discharge my battery pack in the evening down to where the BMV712 indicates a SOC of exactly 50.0%. For my applications, that ends up being pretty easy to accomplish.
In the morning, after overnight rest, I then check the battery pack voltage. I’ve confirmed that 26.32 volts corresponds quite well, under this circumstance, to 50% SOC. If the pack voltage reads higher than 26.32 volts, I will reset the BMV712 SOC to read “somewhat” higher than 50.0% SOC. Converse if the voltage is less than 26.32 volts, I will reset the BMV712 to read “something“ less than 50.0% SIC. The only “problem”, though a happy one, is that the SOC has been so repeatable and consistent, that I haven’t needed to yet make enough adjustments to develop a “table” of adjustments to SOC that corresponds to the morning pack voltage.
I have found that, for my lithium batteries and my typical charge/discharge profiles, setting up the BMV712 with Peukert Exponent set to 1.00, and Charge Efficiency Factor set to 0.99, keeps the BMV712 indicated SOC in closest calibration.
I’ve found the BMV712 is a very nice unit.
My Outback Power MATE3 also reads SOC, but it is not user friendly, in my experience. It can only be reset to 100% SOC
I chose the Victron BMV712 mostly because it is one of the few units that allows the user to calibrate/reset the indicated SOC to any level. It does not require 100% SOC to calibrate/adjust. I was hoping that it would not be necessary to fully regularly fully charge the pack to confirm SOC accuracy.
I’ve found that it is workable to, about once every two weeks, discharge my battery pack in the evening down to where the BMV712 indicates a SOC of exactly 50.0%. For my applications, that ends up being pretty easy to accomplish.
In the morning, after overnight rest, I then check the battery pack voltage. I’ve confirmed that 26.32 volts corresponds quite well, under this circumstance, to 50% SOC. If the pack voltage reads higher than 26.32 volts, I will reset the BMV712 SOC to read “somewhat” higher than 50.0% SOC. Converse if the voltage is less than 26.32 volts, I will reset the BMV712 to read “something“ less than 50.0% SIC. The only “problem”, though a happy one, is that the SOC has been so repeatable and consistent, that I haven’t needed to yet make enough adjustments to develop a “table” of adjustments to SOC that corresponds to the morning pack voltage.
I have found that, for my lithium batteries and my typical charge/discharge profiles, setting up the BMV712 with Peukert Exponent set to 1.00, and Charge Efficiency Factor set to 0.99, keeps the BMV712 indicated SOC in closest calibration.
I’ve found the BMV712 is a very nice unit.
My Outback Power MATE3 also reads SOC, but it is not user friendly, in my experience. It can only be reset to 100% SOC
