LiFePO4 balancing question …

[kingofcary]

Dear Holders of Knowledge … I have a 12v system with a 4 cell LiFePO4 house battery. The battery was in my Catalina 350 when I bought it 4 years ago. I ‘believe’ it was installed 2-3 years before that. I also have a MagnaSine Hybrid pure sine wave inverter/charger. Charging comes from shore, alternator and 2x285 watt pv panels which use a MidNite Classic 150 mppt controller. Overall this system has been providing excellent capability for me without issue. On the cells as you can see in the pic below I have 4 EV Power cell balancing and monitoring modules. My question is about an imbalance I measured in the cells. In cells 1, 2, 4 I measure 3.32v. On cell 3 I get 3.29 or 3.3v. Am new into this … is that much of a difference significant ? Is it an indication that the cell is bad or going bad. This is the first time I tried to measure so I have no history here. Note the yellow lite on each module is yellow indicating I believe all is ok. Thx .. Dennis

[SV Confianza]

That does sound like a decent difference. Make sure you’re testing the battery at rest as well with no draw or charging on it. If you still have problems it could be that you need a new BMS. Go check out Will Prowse videos for a good bms to swap it out with if needed.

[wholybee]

2 things.
First, some older installations did not use a BMS, only cell balancers. You should upgrade and install a BMS. Second, you can't determine cell balance at such a low voltage. You need to charge the battery to about 3.55vpc and check the voltage difference there. However, without a BMS, this can be dangerous if the cells are out of balance, as an out of balance cell can very quickly run up to over 3.65v.(overcharged)

It would be a lot of work, but it would be worth taking all of that apart, and performing a "top balance" as if it were a new installation, then re-installing them with a modern BMS.

[kingofcary]

FYI I do have an EV Power Battery Control Unit (Bcu-ppak) that. Interfaces with the cell balancing modules.
Pic below. Thx

[wholybee]

Originally Posted by kingofcary

FYI I do have an EV Power Battery Control Unit (Bcu-ppak) that. Interfaces with the cell balancing modules.
Pic below. Thx

Very good then. I should not have assumed.

Charge the battery until the cells are ~3.55V. Then check the voltage difference. If it is still off, then let the batteries sit for a while at that voltage and see if the balancers can take care of it. If not, then take it apart and do a top balance.

Given the age, it is not surprising if the balance is a bit off, especially if you don't frequently charge to 3.55vpc.

The manual for your BMS is here:
https://www.ev-power.com.au/evpower/...lus-manual.pdf

[LeighC]

Hi Dennis,
I have an EV power system similar to yours installed in 2013 & still going strong.
Every couple of years or so I just drop my charge back to minimum about 5 amps & raise the voltage to about 14.4v & when the cell voltages reach about 3.65vpc the small green LED on the high cells will go red & bleed off allowing the low cell to come up, this balances the cells, while watching the process with a voltmeter. The BMS will monitor the process & warn of any trouble & switch off the solenoid if things get out of control, but mine never has had to do that. Mine usually come within a couple of millivolts.
Hope this helps - Leigh

[kingofcary]

Hi Leigh … thanks very much this is very helpful. Dennis

[kingofcary]

Leigh … when you say drop the charge to 5 amps what do you mean by this ? Tx

[LeighC]

I have an Outback MX 60 solar charge control & I just go into the settings & dial the amps back from 60 or whatever to the lowest setting which is 5 amps to do the top balance.
The EV power balance boards are only rated at 2 amps each, so it gives them a good chance of working correctly.
Your Midnight Classic 150 is even more modern & would do the same. Get the operators manual it will tell you how to do it, they are a nice piece of gear.
Cheers - Leigh

[LeighC]

Current Limit
The Classic has a current limit component which interacts with the temperature of the charge controller.
If the Classic is exposed to extremely hot ambient conditions the output current will be reduced
automatically to keep the charge controller safe. If the orange LED comes on the MNGP, it means that the
Classic is in current limit mode. If you believe the Classic is not hot and the orange LED is on, most likely
the current limit set point is too low. To check this, follow steps below.
 Press Main Menu
 Highlight the CHARGE menu and press the Enter Button
 Scroll to LIMITS and press the Enter Button
 Press the right arrow key to highlight ―Out Amps‖ or ―In Amps‖ column
 Use the up and down arrow keys to change the current limit then press the Enter Button to save
this data

[kingofcary]

On my Magna ME ARC remote I have a charger setup parm 03A AC Input amps = 5A. This is what it was set at when I purchased the boat. This seems lower that you were thinking in previous post. What is the implication of a number this low ? Thanks gain for all this useful info .. Dennis

[LeighC]

I do my top balance with solar & its DC amps you want to back off to 5 amps on the Midnight Classic. I think what you state is mains charging (AC) on the Magna & I don't think that will reduce the DC charge, but there may be DC on that also.
Others may be able to help here because the rest of my set up is Victron.
Cheers - Leigh

[kingofcary]

Good point … rechecking if I can do same via magna. Could do from MN as you suggest … tx

[kingofcary]

Folks ... just figured I would close this out. Appreciate all the feedback. I went thru a charging phase via shore power. When it automatically cut off due to reaching max I tested voltage and each cell was the same. Also, when it rested for a while I retested and it seemed to settle at exactly 3.36 for each of the four cells. 3.36 x 4 = 13.44 which is basically around where it normally resides. In net, once charged up and then settling, the bms and associated bmk balanced properly doing a fine job. At least that is how it seems to me. Thanks again for the knowledge/input here ... Dennis

[smac999]

Originally Posted by kingofcary

On my Magna ME ARC remote I have a charger setup parm 03A AC Input amps = 5A. This is what it was set at when I purchased the boat. This seems lower that you were thinking in previous post. What is the implication of a number this low ? Thanks gain for all this useful info .. Dennis

that is how many amps the inverter charger will allow to use and pass through.

it means if you plug a 5a load into the outlet. the charger will never charge because it's already at it's 5a limit. and if no loads are plugged in it will use a max of 5ac to charge. so you will have a very slow charge.

generally that number is set to the shore power size IE 30a. or a bit less if large loads bypass the inverter.