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Old 03-03-2024, 11:24   #1
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Victron BMV-712 resetting SOC

Iíve recently changed my bank from AGMs to a larger lithium install and with that installed a CerboGX and wired my existing BMV-712 to this. However, the issue that Iím facing now is that on a couple occasions, the BMV-712 will reset the battery SOC randomly. For example, I disconnected at the dock but stayed around for a bit with the battery dropping to 85% from the loads. I take the boat out later and it shows the alternator charging and slowly going up but at some point shortly thereafter (5-10 minutes), if shoots up to 98% charged while still accepting a high load and with a 125 amp alternator, it couldnít charge that percentage in the short period of time. When back at the dock, it will still be accepting 100 amps saying itís 98-100% charged for a while in the bulk charging phase for quite some time. When itís done, Iíve reset the SOC again to see if that helps but itís now ďresetĒ itself a couple times like this. Any ideas?
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Old 03-03-2024, 11:42   #2
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Re: Victron BMV-712 resetting SOC

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Originally Posted by Letterkenny View Post
Iíve recently changed my bank from AGMs to a larger lithium install and with that installed a CerboGX and wired my existing BMV-712 to this. However, the issue that Iím facing now is that on a couple occasions, the BMV-712 will reset the battery SOC randomly. For example, I disconnected at the dock but stayed around for a bit with the battery dropping to 85% from the loads. I take the boat out later and it shows the alternator charging and slowly going up but at some point shortly thereafter (5-10 minutes), if shoots up to 98% charged while still accepting a high load and with a 125 amp alternator, it couldnít charge that percentage in the short period of time. When back at the dock, it will still be accepting 100 amps saying itís 98-100% charged for a while in the bulk charging phase for quite some time. When itís done, Iíve reset the SOC again to see if that helps but itís now ďresetĒ itself a couple times like this. Any ideas?
Did you study the manual?

First thing you need to get right is setting the absorption voltage and float voltage for all chargers you have, both MPPT, AC chargers etc.

After that you need to configure the BMS for lithium settings. Then comes the most important setting: charged voltage. This needs to be lower than the absorption voltage, I recommend a setting of 13.8V for absorption and 13.6V for charged voltage.

When the charger reaches 13.6V, the BMV will set itís reset trigger but only trips it when charging stops and current flows out of the battery instead of going in. When the charger reaches 13.8V it switches to absorption phase. Watch the SOC on the BMV: you want the absorption phase to last ling enough to fully charge the battery.

The tricky part: with a charged voltage setting of 13.6V the system needs the battery to get fully charged before starting discharge or the calibration will be off. If you can fully charge because of a lack of solar or you used too much energy, then it would be better if the BMV does not reset to 100% that day. For this you may have to increase the charged voltage to 13.7V but at some point you risk missing a reset when the charger switches to absorption because it sees 13.8V but the BMV thinks itís only 13.68V so you didnít reach itís charged voltage setting. Keep an eye on things, keep a log etc.

The BMV will not jump from 60% to 80%. It will jump to 100% when it resets, even when it didnít reach 100% yet during charging.
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Old 03-03-2024, 14:15   #3
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Re: Victron BMV-712 resetting SOC

the "charged voltage" setting causes a lot of issues. especially if you have solar. the default of 13.2v is totally wrong.

if you absorb is 14.2v set the bvm charged voltage to 14.0v (0.2v below absorb)

set the tail current to 2% as well.
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Old 03-03-2024, 15:42   #4
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Re: Victron BMV-712 resetting SOC

Quote:
Originally Posted by s/v Jedi View Post
Did you study the manual?

First thing you need to get right is setting the absorption voltage and float voltage for all chargers you have, both MPPT, AC chargers etc.

After that you need to configure the BMS for lithium settings. Then comes the most important setting: charged voltage. This needs to be lower than the absorption voltage, I recommend a setting of 13.8V for absorption and 13.6V for charged voltage.

When the charger reaches 13.6V, the BMV will set itís reset trigger but only trips it when charging stops and current flows out of the battery instead of going in. When the charger reaches 13.8V it switches to absorption phase. Watch the SOC on the BMV: you want the absorption phase to last ling enough to fully charge the battery.

The tricky part: with a charged voltage setting of 13.6V the system needs the battery to get fully charged before starting discharge or the calibration will be off. If you can fully charge because of a lack of solar or you used too much energy, then it would be better if the BMV does not reset to 100% that day. For this you may have to increase the charged voltage to 13.7V but at some point you risk missing a reset when the charger switches to absorption because it sees 13.8V but the BMV thinks itís only 13.68V so you didnít reach itís charged voltage setting. Keep an eye on things, keep a log etc.

The BMV will not jump from 60% to 80%. It will jump to 100% when it resets, even when it didnít reach 100% yet during charging.
Are these voltages battery brand agnostic and more chemistry? Just want to make sure I have these set correctly. It has an internal BMS so no setting in Victron for this.
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Old 03-03-2024, 15:50   #5
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Re: Victron BMV-712 resetting SOC

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Are these voltages battery brand agnostic and more chemistry? Just want to make sure I have these set correctly. It has an internal BMS so no setting in Victron for this.
Does the manufacturer give any guidance?
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Old 03-03-2024, 16:18   #6
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Re: Victron BMV-712 resetting SOC

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Does the manufacturer give any guidance?
Not a ton (the cheapo litimes). My mistake here was thinking the installer did the configuration correctly. Attached is the current settings (just updated from 13.2 to 13.6v). What else needs changing? Seems like the charge efficiency factor might need to be 99% based on the victron manual and Peukert exponent 1.05? Tail current 1.06%?
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Old 03-03-2024, 16:35   #7
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Re: Victron BMV-712 resetting SOC

Well I have a LiTime bank as well

Attached the BMV config as well as a MPPT controller. Note that I have 24V so you have to divide voltages by 2.
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Old 03-03-2024, 17:49   #8
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Re: Victron BMV-712 resetting SOC

Thanks for that. I matched mine to yours. Will have to do solar when I get down to the boat as my mppt isn’t hooked up to my CerboGX just yet. Can’t get the wire run down to connect it yet.
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Old 03-03-2024, 20:07   #9
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Re: Victron BMV-712 resetting SOC

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Originally Posted by s/v Jedi View Post
Well I have a LiTime bank as well

Attached the BMV config as well as a MPPT controller. Note that I have 24V so you have to divide voltages by 2.
Can you explain (once more!) why absorption set at 13.8 and not 14.2 which is the lower end of the Litime suggested range? The latter I use with good effect although I suppose there isn't so much more charging to do in the 13.8 to 14.2 range. Does the bms equalize the cells ok at 13.8?
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Old 04-03-2024, 05:52   #10
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Re: Victron BMV-712 resetting SOC

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Originally Posted by HeinSdL View Post
Can you explain (once more!) why absorption set at 13.8 and not 14.2 which is the lower end of the Litime suggested range? The latter I use with good effect although I suppose there isn't so much more charging to do in the 13.8 to 14.2 range. Does the bms equalize the cells ok at 13.8?
I have no insight to the balance of the cells because the batteries are too cheap to have Bluetooth communication with their internal BMS.

I have been running this setup for more than a year now and all is good, not a single hickup, no HVC, just clean power 100% of the time.

The reason is stop at 27.6V is that with a little extra absorption time, the batteries charge to 100%. Why would you want to charge beyond 100%?

Itís easy to find out, just get the BMV right, then fully charge the battery at the higher voltage 3.55V per cell, 14.2V for 12V or 28.4V for 24V and when the charger stops, the BMV resets itself to 100% and now you cycle down, change the charge voltage and see what SOC next charge cycle brings you. 100% is 100%.
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