MPPT Blue Solar leaving equalize too early

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thomassolar asked Oct 20, '19

MPPT Blue Solar leaving equalize too early

Before the MPPT regulators from Victron had a problem with switching too early from BULK to absorption, causing the "count down timer" to start and never bring large lithium ion packages to the set absorption voltage before switching further to FLOAT.

This however was fixed in the firmware 1.42 and later firware releases. Nice!!

But I experience some of the same problem with the automatic EQUALIZE setting.

To periodicly balance my lithium ion batteries correctly, I have programmed my MPPT to do an automatic equalize to 28,70V every 7 days. I have chocen these obtions:

Equalization current percentage : 100%

Automatic equalization: every 7 days

Equalization stop mode: Automatic, on voltage

Maximum equalization duration: 7 hours

When I check the history page of the MPPT, I realize that the regulator has charged up to 28,60V instead of 28,70V in equalization mode, and than left the EQ mode. It should charge to 28,70V. (The maximum eq duration had not expired, so that is not the reason)

EDIT: To make sure nobody misunderstand:

I am NOT overcharging my Lion/batteries!!! The recomended charge voltage for these used electric car battery cells is 4,1V/cell, that means 28,70V for the whole 7 cells in serie package.

So my set Equalize voltage is actually the recomended absorption voltage. But I do not want to charge up to this voltage every day, that is why I use EQ. I am not using it like it is used in Lead Acid batteries. And of course I have a BMS that balance my cells and keeps the battery safe and prevent overcharge or to high cell voltage.

Of course I could use the "Fixed equalize time" mode instead, but the fixed time does only provide a fixed time in EQ mode, not a fixed time at the set eq voltage.

Victron, I kindly ask you to do one of two:

Either:

Create an equalization obtion where one can choose a fixed time for staying in EQ after reaching the set EQ voltage (like the absorption works today)

or:

Make an adjustment so that the MPPT actually equalize charges all the way up to the set EQ voltage (and maybe keep the voltage there for a few minutes) before switching to float when in the "automatic, on voltage" stop mode.

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thomassolar commented · Oct 24, 2019 at 12:23 PM

Could someone confirm my experience, that automatic equalize with "automatic, on voltage" stop/mode, in fact stops about 100mV BEFORE reaching the set equalize voltage?

And if so is true, it should be possible for Victron to fix this in a software update, just like they fixed the similar "bug" when switching from bulk to absorption, which in previous software versions (before 1.42) happened to early.

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Answer 1 · 2019-11-01T23:59:07Z

Justin Cook answered · Nov 01, 2019 at 11:59 PM

@ThomasSolar, the equalization settings should never, ever be used on an LFP bank. "Equalize" is not the same thing as "balance"!!! You can seriously destroy your LFP bank by doing what you describe yourself doing... An equalization cycle is a deliberate overcharge of a battery to desulphate lead batteries. Your LFP doesn't have lead, and doesn't have sulphation, and should never, ever be overcharged like this. Please, please for the sake of your batteries, stop doing this immediately; if you want to balance your LFP bank, you should get a battery balancer like this https://www.victronenergy.com/batteries/battery-balancer

Once again, these are two entirely separate concepts, and to avoid severe battery damage and a high risk of collateral property damage and/or loss of life or limb, STOP running equalization cycles on your LFP bank!

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thomassolar commented · Nov 02, 2019 at 02:48 PM

No, no. You completely misunderstand here!

Of course I know what I am doing! I have lithium-ion cells with a nominal voltage of 3,75V and should by standard be charged to 4,10V/cell

However I normally just charge them to 4,05V/cell. And I use the equalize to ocacionally charge them to the recomended 4,1V/cell. So my Equalize charge setting is NOT a overcharge or over voltage charge like the EQ is used in a Lead Acid battery. My set EQ voltage is actually the recomende absorption voltage!

And of course I have a BMS system that shut of the charging if the cell voltage for some reason should rise above the set value.

My BMS starts balancing the cell when they reach 4,1V/cell. But to extend battery life I only charge to 4,05V in daily use, and I have to charge up to 4,1V/cell every now and then in order for the BMS to do a proper balance job.

These Li-on cells can not be compared to the «normal» LFP batteries you are talking about.

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