Behaviour of an old battery bank when EQ

[SolarMusher]

Hi Folks,
My 830Ah/48V bank which is 7 years old seems to be now almost impossible to EQ since a few monthes. Even if I only EQ when in float and 100% charged (1.265/1.275), batteries seem to still need a lot of power (2500W, no loads) to reach/hold a low 62V  EQ setpoint. After 2hrs, it also seems to ask for higher current to hold EQ and falls in EQ mppt. Battery temp seems to raise a bit faster than in the past (above 30°C after 2hrs).
All cells are still fine, lowest cells are 1.260/1.265 and highest are 1.275/1.280. This EQ was made with bright/sunny sky and minimum loads. I was hoping to keep this bank 2 more years but was maybe too optimistic...
Did someone ever seen such a behaviour with old battery bank?
Should I be ready for the next big bang?
Thanks for any input,
Erik

[Westbranch]

Hi Erik, are you getting lots of gassing during the ABSORB and EQ phases?  Thinking about the mixing effect while gassing. 

Have you increased the Absorb time or Voltage settings to see if that helps?

Eric

[Vic]

Hi Erik,

All of the battery banks in use here are 10 years old.

In the past 4 - 6 months,  it has been harder for me to accomplish an EQ  --  we use a Temperature-Compensated EQ voltage,  and have felt compelled to raise the Veq into the 62.7 V range on these Surrettes.   In using a somewhat higher Veq than in the past,  have noticed higher battery temperature at the point of running out of sunlight to maintain the Veq (and therefore,  giving up on EQ).

Some of the apparent need for more EQ current after about 2 hours might be from a non temp comped Veq,  and the battery warming (?).

Have been watching the WBjr current at the end of what has seemed to be a good EQ.  For these batteries,  with a 62 Veq at the battery terminals (not as read by the CC),  have felt good with a terminating current of about 2.7% of Nominal Capacity.

Are you running a single string of batteries for your 830 AH Capacity?

Seems to me,  that you need to do more EQing,  and perhaps at a bit higher Veq.  Although,  your SG range does not look too bad ...   are these Surrette batteries?  (I forget).

A battery that really needs an EQ needs a lot of current,  and  quite a bit of time to accomplish it.

One of the largest banks was  a bit abused initially  --  lightly cycled,  too warm environment in the summer,  and recharged on most days from an SOC in the mid ninety percent range.

This one bank,  here, may well not ever get much better.

Just some random thoughts.  Good Luck,  and please let us all know how this battery progresses.  Thanks,   Vic

[SolarMusher]

Hi Erik, are you getting lots of gassing during the ABSORB and EQ phases?  Thinking about the mixing effect while gassing. 

Have you increased the Absorb time or Voltage settings to see if that helps?

Eric

Allo Eric,
Yes, I get good gassing during Absorb (58.8V) but they take a bunch of water now (+/- 8L every month), I've had to decrease Vabs to 58.4V last summer but it didn't really change water needs. I'm using wbjr end amps for a while now and it did a great job since I get it installed. End current was around 9/10A when younger but now it has increased to 12/13A.
I just hope that I won't have to change the bank in winter!
Erik

[SolarMusher]

Hi Vic,

All of the battery banks in use here are 10 years old.

In the past 4 - 6 months,  it has been harder for me to accomplish an EQ  --  we use a Temperature-Compensated EQ voltage,  and have felt compelled to raise the Veq into the 62.7 V range on these Surrettes.

That's what I've noticed too, I've tried both EQ temp settings, and I gave up after 2hr30, was unable to reach 62V temp compensated (61.4V) with 2400/2500 watts out of the Classic, in fact it was hard to hold 60.5V with no loads.

In using a somewhat higher Veq than in the past,  have noticed higher battery temperature at the point of running out of sunlight to maintain the Veq (and therefore,  giving up on EQ).

That's exactly what I've seen but with a low 62V EQ voltage!

Some of the apparent need for more EQ current after about 2 hours might be from a non temp comped Veq,  and the battery warming (?).

Vic, it was compensated and batteries were above 30°C, that should have been easy to reach a lower voltage.

Have been watching the WBjr current at the end of what has seemed to be a good EQ.  For these batteries,  with a 62 Veq at the battery terminals (not as read by the CC),  have felt good with a terminating current of about 2.7% of Nominal Capacity.

I will check real current but the last time mine were closer to 40A (5%), I will try it longer next time.

Are you running a single string of batteries for your 830 AH Capacity?

No, they are 830Ah in two strings.

Seems to me,  that you need to do more EQing,  and perhaps at a bit higher Veq.  Although,  your SG range does not look too bad ...   are these Surrette batteries?  (I forget).

Well, that could have been my mistake, SG were so fine that I was thinking I didn't need to EQ that often.
They're interstate (yes I know...) 6V 415Ah 6V  . I've to say that I've been a bit lazy on EQ in the last year. There has always been good reasons..., washing, vacum, water heating for my wife (I'm looking for a responsible  ) and... for me, don't like to run EQ on gen.

A battery that really needs an EQ needs a lot of current,  and  quite a bit of time to accomplish it.

I'll give it another try with longer EQ time in the next days, it should be sunny.

One of the largest banks was  a bit abused initially  --  lightly cycled,  too warm environment in the summer,  and recharged on most days from an SOC in the mid ninety percent range.

Hey, that's mine 

This one bank,  here, may well not ever get much better.

Just some random thoughts.  Good Luck,  and please let us all know how this battery progresses.  Thanks,   Vic

Great thoughts.
Thanks Vic,
Erik

[Westbranch]

I'll give it another try with longer EQ time in the next days, it should be sunny.

I have to assume you are doing the BULK phase with the genny....?

[Vic]

Hi Erik,

Thanks for the replies.

If you are unable to reach EQ voltage,  and were stuck around 60.5 V,  with about 40 Amps into a 830 AH Nominal battery,  then  you really need an EQ.

The thing about parallel strings,  vs singles,  is that one string might well be the major laggard (you know if this is the case,  based on SGs for one string vs the other),  and possibly separating one string,  charging it,  then EQing it separately,  and then the same for the other ...   you know all of this.  And, separating strings can be a bit of a pain to do carefully and safely ...

Keep an eye on the current that is required to reach your compensated target Veq,  and then watch this current verses time.  The batteries here seem to be fairly EQed,  when the EQ current is below 3% of 20 Hr Capacity.

In this Hemisphere,  we all are now running a bit short on PV power (depends on the angle of the array,  and if fixed or not ..),  so it will be harder,  of course,  to get our EQs done with the available solar power  for a day.

Also,  with a bank in need of EQing,  doing the job over several days will obviously help increase the total EQ current into the battery,  and moderate,  to a certain extent,  the increase in battery temperature (all obvious).

As wb mentioned,  starting early in the AM with the genset,  getting into early Absorb,  and then trying to let the PV finish the job helps get more done in a day,  although,  if battery heating is a concern,  this is not a huge help,  as one might choose to end EQ,  when there is still a lot of solar power available.

IMO,  'all you need to do',  is EQ more.

Good Luck,   Thanks,   Vic

[SolarMusher]

I'll give it another try with longer EQ time in the next days, it should be sunny.

I have to assume you are doing the BULK phase with the genny....?

No, I don't think that I will need the gen, DOD for the evening/night is only 4 to 5% at this time (AC fridge), usually I reach absorb at 10h30 am. Battery temps would be a problem with a long EQ (batt temp is 30°C right now at 8hr pm) so I think that it would be better to equalize several times for 3 hours max on next days.
Erik

[Westbranch]

How much do they cool overnight?  Can you get some cooler outside air into them, it should help you ....  we are hovering around freezing these days

[mike90045]

Start your EQ after ABSORB.  Don't wait for float to happen.  You want to catch it right at the end of absorb while voltages are high.
Try extending your ABSORB for another 90 min or so, before starting the EQ (might need 2 days of this to pump up the batteries)
Run the genset in the morning to BULK the batteries, so the sun has a chance to finish the absorb and EQ

[SolarMusher]

How much do they cool overnight?  Can you get some cooler outside air into them, it should help you ....  we are hovering around freezing these days

Batts are 27.5°C and SOC is 95% this morning.
Eric, we did not have real summer here in Qc, but it seems that we're going to have it this fall. Forecasts are sunny for several days!

The thing about parallel strings,  vs singles,  is that one string might well be the major laggard (you know if this is the case,  based on SGs for one string vs the other),  and possibly separating one string,  charging it,  then EQing it separately,  and then the same for the other ...   you know all of this.  And, separating strings can be a bit of a pain to do carefully and safely ...

I think that I'm going to charge both strings to absorb and only EQ one string by day. My strings are easy to separate, just need to lower/limit current from the Classic. This way, I'll be sure to have enough power from the array and time to get it right even if weather is a bit hot with limited power.

Start your EQ after ABSORB.  Don't wait for float to happen.  You want to catch it right at the end of absorb while voltages are high.

Mike, I will follow your advice and start it just before float, thanks guys for the good advices.
Erik