Navitron Renewable Energy and Sustainability Forum

Energy/Electricity Storage and Use/Grid Connection => Off-Grid, Batteries & Inverters => Topic started by: Pord on September 19, 2019, 09:46:59 AM



Title: Is it always necessary to EQ?
Post by: Pord on September 19, 2019, 09:46:59 AM
We've been running the following 24V set-up for just over a year:

4 x 250w 24v pv panels, each pair connected first in series then the pairs connected in parallel
Victron mppt 100/50 controller
Victron BMV700 monitor
Victron inverter
4 x 6v Crown CR220 FLAs

The system has operated flawlessly and our useage is very low. Consequently we never dip below 95% charge during summer (compared to down to around 65% in winter). Most recent SG readings had three batteries at 1.31 and one at 1.3 at 17degC.

With advice from the forum (and especially Scruff - thank you) I did some manual EQ charges at the start to bring the batteries up to consistent charge but haven't done so since Feb because the batteries have been largely consistent across all cells and our cycles are very shallow.

Should I still carry out an occasional EQ charge for battery health or is it unnecessary?


Title: Re: Is it always necessary to EQ?
Post by: Pord on September 26, 2019, 10:50:33 AM
Can anyone advise?


Title: Re: Is it always necessary to EQ?
Post by: oliver90owner on September 26, 2019, 12:02:56 PM
Would it hurt anything if you did?  Might it hurt if you donít?

Answering those two questions should allow you to answer your own question


Title: Re: Is it always necessary to EQ?
Post by: offthegridandy on September 26, 2019, 12:23:58 PM
Hi Pord,  I'd suggest that you'd be wise to run an Eq charge periodically. In your set up there is a chance that the batteries will stratify and begin to accumulate a hardening layer on the plates.  A good high charge is supposed to give the plates a "rattle" and dislodge the sulphate.

TBH I rarely bother once a year at most. But my cells are constantly being fully charged and discharged.  My peak charge Volt is 29.4 and I will allow them to discharge down to 22.9V. (24V nominal system).  My last set of cells were replaced after 12 years or so and I weighed them in for good money.

I suspect Scruff would insist on a monthly regime, but if you ask the manufacturers of traction batteries for fork lift usage they will wonder what you are talking about, as in a fork lift they get a full charge every night.  Really your usage pattern ultimatley dictates but as I say I suspect you may be wise to do so, now and again.

Andy


Title: Re: Is it always necessary to EQ?
Post by: Nickel2 on September 26, 2019, 03:27:45 PM
My MPPT charger operating program has a built-in equalisation function. This gets done every month, and I can vary the duration of the EQ from 0 minutes up to 120 minutes.
My batteries are old and tired, and I notice that when they are losing their charge retention capability, the EQ charge pokes a bit more punch into them.


Title: Re: Is it always necessary to EQ?
Post by: Scruff on September 26, 2019, 08:28:29 PM
I EQ once every blue moon. Usually as R&R after abusive treatment.
The purpose of EQ is to balance diverse cells or rattle soft sulphates.
If the SG is 1.275 or greater EQ is of no benefit (harmful..unnecessary heat).
If the disparity between cells is >0.03 then I would also EQ.

MorningStar and low discharge rates generally has all my lot tippy top so I d'nay have to.

1.3 is off the charts high. Are you sure your hydrometer float is floating Pord?


Title: Re: Is it always necessary to EQ?
Post by: Scruff on September 26, 2019, 08:44:30 PM
Is the water level correct?


Title: Re: Is it always necessary to EQ?
Post by: Pord on September 27, 2019, 08:55:50 AM
Thanks for the replies chaps.

Scruff, yes I was surprised at the SG reading but I repeated the process over all 12 cells and it was roughly consistent. It's the same hydrometer I've used since the start so I'm reasonably confident it's ok.

I've kept a close eye on water levels and haven't had to top up in over a year since installing the system. My understanding is that unnecessary watering can diminish battery performance, would that be right?



Title: Re: Is it always necessary to EQ?
Post by: offthegridandy on September 27, 2019, 12:02:03 PM
If you are not really cycling the battery i.e. neither fully charging or significantly discharging them you will use very little water on newish cells.

 You can only add water into the space available above the plates.  If you over fill the batteries and then charge them, the liquid can or will spill out through expansion vents in the caps.  This can lead to loss of acid which will eventually reduce the batteries charge capacity.  So follow the manufacturers instructions and maintain water level over the top of the  plates but not up to the top of the cell.

There used to be a web site called the battery university or sumat like, it had some sensible articles on chemistry and so on for FLA's'

Andy


Title: Re: Is it always necessary to EQ?
Post by: Scruff on September 27, 2019, 02:30:08 PM
The specified water level for crowns is tipping the bottom of the slot in the drop channels of the refilling aperture.
Electrolyte changes volume with SOC.
If air touches the plates they get scuppered.
High Concentration H2S04 will accelerate grid corrosion.

Fully charge (max electrolyte volume), water. Cycle for a week. Retest SG to establish a baseline.

They sound thirsty.


Title: Re: Is it always necessary to EQ?
Post by: V on October 03, 2019, 12:08:58 PM
I have an unusual configuration with SMA kit and FLA's. Because I have such a large battery bank the 'Full Charge' is never triggered. But I can manually run a EQ.

After talking to the manufacturer of my batteries, to SMA and to this list I found out that an SMA Full Charge is 2.45 volts per cell and so is the EQ charge. The Boost charge (every 5 - 7 days) is 2.25 volts per cell. My inverter charger should run a full charge every 14 days and get to app 95% capacity, but as I said, my capacity is so high that this never runs automatically. So I run an EQ charge once a month, 2.45 volts per cell. The battery manufacturer said this is good practice.

Good luck,

Vickie