Equalize

[Diesel Pro]

OK that got your attention. What idiot would try to equalize a Lithium battery. Hear me out for a bit here With all the discussion of where to start active balance, and battery life I got to thinking about this as a way to periodically top balance. Maybe the term EQ could be replaced with BAL for the purposes of this discussion.

My setup:

8S (24v) EVE LF280K (new not yet installed)
BMS: JK B2A8S20P active balance @ 2amps
4) 320w Solarworld panels
Midnite 150 Classic Charge controller
Magnum 4024 Inverter

Cabin is off grid and unoccupied 350-360 days a year. In reality I probably should just switch off the batteries when not there. Could not really do that with my lead acids and I roached them in about 4 years. I do have a small fan up high in partition wall to move air from room to room so it's nice to have on. Just phantom loads from microwave and TV plus inverter idle current. All quite low

My new battery capacity should be far and beyond what I need so my thought is to stop the charge short with a more moderate Absorb voltage say 27v since I don't need near my capacity. Then I would set my equalize voltage to say 28 volts. Balance could start at 3.45 +/-. I think the Classic will allow a scheduled EQ every 30 days.

 

[chrisski]

Since your batteries spend most of the time at the charged state, would adding some form of active balancer set for a lower voltage be better? Either that or balance the batteries both while charging and not charging?

I see why you’d want to balance the batteries.

Have not had my lithiums but a couple of weeks and with balance set to 3.4 per cell only while charging only and a charge of 3.475 per cell (totaling 27.8 for a 24 volt system) so little time is spent where the battery is charging so if balancing takes place, it does not last very long.

Whatever you do like using the equalize phase to increase the voltage to a safe point to balance these batteries, at 1 to 2 amps, just not sure how much balancing would be done if this balancer is only set to balance when charging.

I also noticed when I increased my voltage from 27.6 absorption to 27.8 absorption, only took my cells a few minutes to get the extra .2 volts. The charging profile for lithium is so steep because of the knee. I guess the time spent at the higher voltage could help, but my charge controllers would equalize for an hour or two depending on the model.

 

[sunshine_eggo]

IMHO, the battery is in "storage" most of the time and presumably for long periods of time. "Storage" according to most data sheets indicates storing at a reduced SoC - maybe 30-70%.

Sounds like your system should just float at a lower voltage most of the time. Balance-schmalance.

 

[Supervstech]

IMHO, the battery is in "storage" most of the time and presumably for long periods of time. "Storage" according to most data sheets indicates storing at a reduced SoC - maybe 30-70%.

Sounds like your system should just float at a lower voltage most of the time. Balance-schmalance.

This.

If your cells need balancing frequently, there is something wrong.

 

[Diesel Pro]

I just finished a discharge test and am in the process of charging back up on the bench. I'm thinking that I will charge to maybe 50% or so and build out the case and get ready to put into service. With a bluetooth BMS I can watch things unlike the LA battery setup. Most often the parasitic is so low that the Magnum sees load at 0 amps due to the scale being so coarse. I have to turn on my old Halogen outside lights or a group of CFLs to get it to read anything. Part of my reason for switching to Lithium was that they could tolerate and actually like standing at 50% charge or less if necessary. Going to contemplate my settings. May still opt to use EQ as an option to top and balance in the event that I may have a high demand upcoming.

There is one activity (maple syrup season) that I may choose to exercise the battery with an approx 1600w load that I can run for hours. Be nice to leave and not worry that the battery SOC is low. Let it come back up over a matter of days.

 

[sunshine_eggo]

The magnum has to pull around 15-30W idle that the BMS should see, but the Magnum won't.

No harm at all in using an EQ function to manually drive to higher voltage; however, make sure you configure the EQ period. It should be limited to 1h. 30 minutes is even better.

What you're likely to find is that in your application, since it's not cycled regularly, a teeny weeny difference in the self-discharge rates of your cells will result in an imbalance - even a 0.1% variation in SoC between cells can cause runners at peak voltage.

You can mitigate the above simply by charging to 3.45V/cell absorption (need 4+ hours absorption) and enabling balancing during charge only and only above 3.38V.

8S 3.2V 280Ah should run 1600W for 4 hours from a full charge.

 

[100 Proof]

I do this, but for a different reason. Once or twice a year I MANUALLY initiate my Equalize function to drive my pack to 14.0V to calibrate my Trimetric. Normally I bounce my pack between 13.0V and 13.3V.