Puzzled about new batteries SG

Desert Rat

A neighbor asked me about his one-month-old Trojan T-105 batteries; seems the battery bank voltage has not been as expected when he is checking them first thing in the morning. I have told him that 24.2 V or 50% DOD is about as low as you want to see. He reported that the batteries were reaching Float every day, but that the early morning voltage was in the high 23s a couple of times, and even 22.8 one day. I went over with my hydrometer, expecting to see a weak battery or a dead cell. At the time I checked them it was late afternoon on a sunny day and the batteries were in Float. All cells were in the 1.160 range; nothing as high as 1.200. He says there has been no change in his loads. This never occurred with the previous battery bank. What do you think?
The system:
735W array
4--Trojan T-105 batteries
Schneider MPPT-60 CC
Schneider SW 2524 inverter

Aguarancher

Sounds like the new batteries were never commissioned. He need to first charge the batteries to a full charge then do a serious EQ. There is more to it but this will get you started..

mvas

All of the acid is locked up in sulfate crystals.
What are the amps during Bulk Charge?
What is the voltage during Absorb Charge?
What is the Float Voltage?

When was the last time the batteries were equalized?

Have the batteries been in a state of Partial Charge for too long?

westbranch

You need to look at the charge  parameter settings too and check all of the connections, there may be a loose one or 2, as the battery connections would all have been disturbed, use a clamp on DC Amp meter...

mvas

Stratification?

Estragon

Personally, I'd get them on a known to be working charger pronto and see how they do.  If the voltage comes up really fast, it might already be too late.

Vic

mvas said:

All of the acid is locked up in sulfate crystals.
What are the amps during Bulk Charge?
What is the voltage during Absorb Charge?
What is the Float Voltage?

When was the last time the batteries were equalized?

Have the batteries been in a state of Partial Charge for too long?

The above are good questions,
AND,  on the CC,  what is the Absorb time setting?
If End Amps (Exit current on the SCC)   is used to end Abosrb,  What is the setting for battery AH?
Does this system also have  a genset available?
If there is a genset,   is there an SCP or a Combox (or both) on the system,  in order to set good Charge parameters for Flooded batteries?
Is there a Temperature Sensor installed a battery?

Here is a Link to the MPPT CC Manual:
https://www.solar-electric.com/lib/wind-sun/XW-MPPT60-manual.pdf

YES,  these batteries really DO need to be recharged ASAP.

Vic

Desert Rat

Absorb 29.6V
Absorb time 1 hr.
Float 26.2V
There is no generator available.
I've asked him to EQ the batteries . I'll go over this week and check things out again.

westbranch

He needs to go to 3 - 4 hrs now and once the batteries revive, if they do, then back down to 2 hrs or more,  /winter is a bad time to have low Absorb times and 1 hr is too low...

Estragon

I would tell him to up the absorb time to 4 hours and watch amps going in to the batteries at half hour intervals. When amps in gets to about 4-5a (without loads hogging available solar) start the eq. Stop eq when lowest sg readings stop rising (or sun goes down, in which case repeat tomorrow).

I would also highly recommend an alternate charging source.

Vic

Hi D R,  thanks for the info.

YES,  the Absorb time is certainly too short,  for the present SOC of the batteries.   It is good to use a high quality Hydrometer for the SG readings,  as you know.

The recommended EQ voltage,  is 31 V for Trojan RE batteries,  and this should be Temperature Compensated.

Is there a Temperature Sensor mounted on a battery in this bank ??

It will probably require several days of concerted effort to charge the batteries to the point where the EQ should be attempted.   It would probably be OK to increase the Absorb voltage to about 30 V,  Temperature Compensated,   until the batteries become fully-charged,  or as close as possible to being fully charged.

If the CC allows the Temperature Coefficient for Temperature Compensation (believe that it does),  check that this set to  --4mV/Cell/degree C.  Believe that Schneider requires the user to calculate that this is -- 48 mV/C for a 24 V battery.

The Target SG for full charge is 1.277.  Some battery manufacturers recommend to continue an EQ for 30-60 minutes after the SG of the lowest cell/s stop rising.

As you know,  if the charge and EQ process requires a number of hours (as it probably will),  the SG readings should be temperature compensated,  as the battery temperature will probably have risen significantly.   Compensate SGs by adding four points of SG for every 10 degrees F,  above 80 F electrolyte temperature (and subtract for every 10 F below 80 F).  The Hydrovolt docs says that it automatically compensates the reading.

With no genset,  it is unlikely that the battery will become hot,  with full charging and EQing,  but discontinue charge/EQ,  if the battery temperatures approach 115 F (or even somewhat before),  and continue the following day.

If this apparent low SOC situation has been ongoing for a number of days/weeks,  it might be difficult to recover this battery bank completely,  but certainly worth a try.

Good Luck,   Vic

Desert Rat

Thanks for the helpful answers. I increased the absorption time to 4 hours and will continue to check on things every couple of days.