Short EQ to balance SG

[dapago]

Hello,

Can someone please advice. Every 3 days I take a state gravity reading. About half of my cells reaches  90% SOC, the other half 100% SOC. I perform a mini EQ (5mn to 10mn  time) and then all cells balance again (100%).
Is it a normal process to perform?

Can it be the quality of the hydrometer I use (see pic)?

I have 8 batts wired in serie.

Thanks

[Vic]

Hi dapago,

Here is a good Article from Surrette Battery on measuring SG:
http://support.rollsbattery.com/support/solutions/articles/4347-measuring-specific-gravity

It is very,  very important that the Hydrometer be completely rinsed with Distilled Water,   when you are finished using the Hydrometer  --  rinse three or four times.

EDIT:   Would not let a Hydrometer sit,  unrinsed for more than about two hours.   Incomplete/improper rinsing,  or allowing a Hydro to sit unrinsed   will cause a sticky residue to accumulate on the glass float and inside the outer tube.   This residue  will allow air bubbles to stick to the tube and float,   causing erroneous readings  --  usually false high SG readings.   Once  this residue is in place it is almost impossible to remove.

When you say that you are doing an EQ for 5 - 10 minutes,  do you mean,  that the Absorb has been completed,  you start the EQ,   and then you wait for 5 - 10 minutes  AFTER the set EQ voltage has been reached ?

Also,   are you using the Trojan-recommended Absorb voltage,   and the correct Temperature Compensation value for your batteries?

Believe that you have extended the Absorb time to about 150 minutes per charge? <

More later,   Vic

[dapago]

Vic. I admit that the for the first readings I did not rinse the hydrometer. Since then I do it but it did stay a few weeks without being rinsed. Maybe a residue problem then?
I do a short eq in float after noticing some cells are not balanced. 5/10 min eq total time (from the moment I hit the eq function).

Trojan doesn't specify absorb voltage so I use the Bulk voltage recommended by Trojan  (59.28V) as absorb voltage setting. Yes I use the correct temp comp (0,005v/cel). Absorb time at 150 min when 120 is the recommended time.

[Westbranch]

dapago, what is the result of a 3 hr Absorb? 

You have already depleted part of your batteries and IMO you need to do longer Absorbs for more than 1 or 2 days to recover the depleted portion,
then you lower either the time, voltage or both depending on how high you went and the result......

hth

[dapago]

3 hours absorb and I get 100% SOC. Will lower it to 2 hours, wait 2 days and see what happens. I don't think I  can raise the absorv voltage above Trojan bulk voltage recommendation which is already the one I entered last week.
What about doing short EQ (5/10min) to get 100% SOC if when entering float batts are not totally full?

[Westbranch]

dapago,  this is good  3 hours absorb and I get 100% SOC. 
How much time did it take to get to 100%? and How much more time was the sun shinning and able to hold the charge in Float?
You previously had 7 minutes... Float is the finishing stage and is a long slow phase.

Rather than go back to 2 hrs , try 150 minutes and observe the time to reach 100% SOC and amount of Float you get with a few days of normal usage., the equinox is still about 9 weeks away... lots of time for foul weather ... and fine tuning.

enjoy     

[Vic]

3 hours absorb and I get 100% SOC. Will lower it to 2 hours, wait 2 days and see what happens. I don't think I  can raise the absorv voltage above Trojan bulk voltage recommendation which is already the one I entered last week.
What about doing short EQ (5/10min) to get 100% SOC if when entering float batts are not totally full?

Hi dapago,

In Reply #2 above,  you said,  "I do a short eq in float after noticing some cells are not balanced. 5/10 min eq total time (from the moment I hit the eq function)".

So,   assuming that the Hydrometer readings are repeatable  (ie,  if you continue taking SG readings on  a single cell,   that you get the same reading,  within a few SG points),   then  this mini-EQ seems to just be increasing the Absorb time.  It is possible that when you initiate this mini-EQ,  that the EQ voltage might not be met after those 5 to 10 minutes,  and the Classic would display EQ-MPPT (meaning that the EQ voltage has not been reached  --  you could confirm this by looking at the MNGP display,  or on the Local App.

Forget if you have done a full EQ recently,  and what the variation of SG readings is between all cells in the bank,   when it is fully-charged?  Perhaps this battery could use an EQ,  if there is more than about 20 or 25 SG points variation between the cells.

As an aside,   for Flooded batteries,   Float is NOT a charge stage.  On a fully-charged battery,  Vflt is selected so that  a full charge is just barely maintained while in Float.   To the extent that the battery cools while in Float,  the SGs could appear to rise during the later part of Float due to cooling.

There are some things that happen during Float.   One of these,  is that plate material that has been previously shed,   that was stirred into circulation within the cells during Absorb,  or EQ  will settle out of suspension.  This could possibly  change apparent SG readings somewhat.

And,  dapago,  based upon SG readings before morning charging takes place,   what is the approximate State Of Charge of the battery?  What are those average readings before recharge?

AND,  are the cells that indicate they are not fully-charged when Absorb has ended,  the same cells that had the lowest SG readings before charging started for that day?

How long has this battery bank been in service?   What number of charge cycles do you believe that this battery bank has had since new?

Thanks,   Vic