Lithium MS2812 Conversion from Lead Acid

[WinePress]

I have successfully converted from lead to lithium. I used information from this forum (Thanks Richpatty) and others to arrive at the settings for the non existent lithium profile of the Magnum MS2812. I am trying to now fine tune the settings. I have no issues with bringing the batteries to 100%, My issue is trying to maintain the resting levels at less than 100%. When set up on shore power I would like to have the batteries set at about 80%. My understanding is that will allow the batteries to have a longer life. This seems to be elusive with my current settings. Once the bank is fully charged I bring down the voltage and the bank will begin to discharge down to about 80%, then a couple of hours later it back will be back at 100% then slowly begin to discharge down. So it is this constant back and forth that I can’t figure out.
I am unfamiliar with the Magnum feature CC/CV and was wondering if anyone has used this setting to manage their Li bank. It seems like this may be a possibility but I’m not sure what the settings should be.
The Chinese manufacturer, Chin is of no help. They only offer to say charge to 100% and don’t worry about it as the internal BM will keep the cells from overcharging.

Here is my settings currently-
Batteries- Two 12 v 280 amp LiFePO4 batteries Mfg. Chin
Charge profile for Full Charge-
Absorb- 14.2
Float- 13.6
EQ- 14.2
EQ Time- .1
Absorb done- 5.0 hrs
Charge rate- 100%
Max charge time- 8.0 hrs
Final Charge- Silent
Re-bulk Voltage- 13.2

Charge profile for 70- 80 %Charge- (Will not stay at 80, creeps back and forth from 70 to 100)
Absorb- 13.0
Float- 12.9
EQ- 13.0
EQ Time- .1
Absorb done- 5.0 hrs
Charge rate- 100%
Max charge time- 8.0 hrs
Final Charge- Silent
Re-bulk Voltage- 13.0

Any help and experience is greatly appreciated.

 

[Richpatty]

This is a great point... I believe there is a way to do this... This is from page 13 from the ME-ARC remote (which is an upgrade from the one that comes with the MH.).
I have NOT tested this.

SOC Connect – Incoming AC only connects when the battery bank State of Charge (SOC) falls below the Connect SOC setting in the SETUP menu’s 02E AC In - SOC menu item. Disconnects from incoming AC when the battery bank SOC rises above the Disconnect SOC setting, also from the 02E AC In - SOC menu. This feature requires the optional ME-BMK (battery monitor) to be installed. See SETUP menu 02E for more information on the Set Connect SOC menu settings.

You do need to make sure you get to 100% at least monthly to ensure all the cells in the batteries get balanced.

Also there is some good videos on this topic from Will Prowse.




I don't travel as much right now and my RV is covered when stored, so I shut down as much as I can and let the batteries drift down in charge, They take a full month to get low...and by then it is time for either a trip or the RV's 30 day "exercise" where I get the batteries back to 100%.

I hope this helps ...

 

[WinePress]

Thanks Rich,
I will make these changes and see how the system reacts.

 

[newmarokie]

Wine,
You might consider adjusting the rebulk voltage and let the batteries cycle up and down

 

[WinePress]

I’ve done quite a bit of testing to get the Magnum to respond correctly to the Lithium’s. My aim is to be able to be on shore power and have the batteries holding at about 80% charge. I’ve learned that trying to vary the charging voltage isn’t the way to go as Lithium’s hold the voltage throughout the discharge curve. I made changes setting 2E. This setting is suppose to limit charging based on SOC of the the batteries. I found this did not work. I was hoping that the SOC connect % would be the answer.
Newmaroakie suggested above to look into the rebulk voltage. This is working. By going to the silent charge setting you can vary the voltage to when it will bring the batteries back up. For my application 12.9 to 13.0 works. Not perfect, but they are not sitting at 100% charge 24/7.

That said, my perfect scenario would be for the inverter / charger to bring the batteries up to 80 or 90% and then disconnect them until needed. Instead what happens is that even on shore power the batteries are in a constant state of flux, sometimes charging, sometimes discharging, never just idle.
Current settings:
Absorb- 14.2
Float- 13.8
EQ- 14.2
EQ Time- .1
Absorb done- 90% SOC
Charge rate- 70%
Max charge time- 8.0 hrs
Final Charge- Silent
Re-bulkVoltage- 13.0



The answer is of course to replace the Magnum with a more up to date replacement.



Any suggestions welcome.

 

[Richpatty]

Interesting. I am glad you got the rebuke option to work…at least mostly. And I agree that the magnum interface and functionality sometimes leaves me wanting more. If mine ever dies, I will be happy to get a Victron.

Keep us posted.