Battery Banks not balanced

Belize1 · September 2023

I have two sets of eight batteries, side by side. 235 AH each side. All wiring is exactly identical to positive and negative bus bars connecting out to system.
Charger operating today showing 25 amps going to batteries at 57.1 volts. Left bank batteries are warm, right bank are not. Check with multimeter, left bank shows 20 amps going through battery interconnect cables. Right bank shows 4+ amps through cables. Am I correct that something is wrong with the right bank (low amps flowing)?? Possible causes??

BB. · September 2023

Can you take a volt meter and measure/log the voltage across each battery in your bank?

It is possible that you have a battery with a shorted / failing cell (or several cells) that have low voltage. The string with the low cell voltage will draw more current that the other string and "over charge" the rest of the batteries in the string.

Are these flooded cell batteries that you can measure the specific gravity of? That will also help identify any weak / problematic cells too.

You have 16 "identical" batteries in your bank--You are looking for "differences" in the batteries here. And differences potentially means possible problems in that battery (or wiring to that battery--Such as loose or dirty connections).

-Bill

Belize1 · September 2023

Bill, thank you for responding. SG and voltages are consistent across all batteries in each bank, although slightly different in each bank. I.e., Left side SG is 1.255 in all cells, right side is 1.260 in all cells. All of the batteries read between 6.29 and 6.32 volts at rest.

Those readings are taken after 8 hours of charging at 57.2 volts/25 amps. Absorb setting on the charge controller is 57.2 volts /120 minutes although it did not time out after 120 minutes as I expected. I have attempted to equalize which the manufacturer would say is 59 volts, but my controller won't rise above 57.6. Seems to be a battery limitation prohibiting the controller from moving beyond???

Out of curiosity I checked amps draw under load this morning. Total draw of 8 amps, left bank is drawing six amps the right bank is providing 2 amps of the load...... Similar imbalance as the charging

BB. · September 2023

What are the battery voltages under load (and/or under charge)?

One thing you can try, when current is flowing (charging or discharging), set your volt meter to 2 volt (or lower scale) and check each jumper cable voltage drop (one meter lead on battery A + post, other lead on battery B - post, etc.). Looking to see if you have higher voltage drop on one cable vs the others.

You could try disconnecting 1 battery string and EQing the other. Ideally, you are aiming for 5% (down to 2.5%) of battery AH capacity (235 AH * 5% = 11.75 Amps EQ charging current per string). The batteries will bubble and get hot over a few hours of EQ charging.

So far, it sounds like there are no obvious battery issues.

-Bill

Marc Kurth · September 2023

BB. said:

What are the battery voltages under load (and/or under charge)?

One thing you can try, when current is flowing (charging or discharging), set your volt meter to 2 volt (or lower scale) and check each jumper cable voltage drop (one meter lead on battery A + post, other lead on battery B - post, etc.). Looking to see if you have higher voltage drop on one cable vs the others.

You could try disconnecting 1 battery string and EQing the other. Ideally, you are aiming for 5% (down to 2.5%) of battery AH capacity (235 AH * 5% = 11.75 Amps EQ charging current per string). The batteries will bubble and get hot over a few hours of EQ charging.

So far, it sounds like there are no obvious battery issues.

-Bill

This is good trouble shooting advice that is often overlooked.

Marc

softdown · September 2023

Sounds like it could be a connection or wiring issue somewhere?

Belize1 · September 2023

Two days of solid charging. Batteries held at 57.1 volts/20 amps charge for four hours. At sundown disconnect all loads. After an hour of rest, Left bank is 50.2 volts at rest Individual batteries measure 6.31 6.32 6.33 6.33 6.30 6.31 6.33 6.31 Right bank is 51.2 at rest. 6.37 6.37 6.35 6.38 6.40 6.37 6.37 6,38

I have very intentionally cycled and observed the operation last two days.. Sunday night into Monday morning Trimetric showed use of 142 AH overnight. All AH restored plus 20% by end of day. Monday night into Tuesday morning Trimetric shows 88Ah drawn down. Replaced 150% by end of day. Then the measurements above were taken.

The anomaly the started this search is that the Midnite Solar charge controller is set for Absorb at 57.2 volts to be held for 90 minutes. Each day it gets to 57.1 and then won't go beyond. Just sits there .1 below Absorb voltage and won't proceed. Won't time out and go to float.

During charging I tried measuring individual cables A+ to B-, I get readings of .001 Is that correct? One cable had green corrosion on one end that I had cleaned off four days ago and today green corrosion is back. Sign of anything? I removed that cable and put in a new cable.

Dave Angelini · September 2023

Old batteries ? Were you doing EQ's before? I would look at SG after full charge but you can't So system never goes to float?? How much solar?
The corrosion may be from the terminal plating that has worn off.
Belize humidity, getting ventilated well?

If you do not have enough solar, you will need to get a genset to do a proper EQ and save this bank.

Belize1 · September 2023

Belize is an old user name. This system is in Georgia. Grid power is included in system and avail for charging. Batteries were all purchased together fifteen months ago. Batteries have been in a basement room at 74 degrees with excellent ventilation entire life. Have not equalized in past six months due to the charging issues. Charge controller can't seem to get the voltage high enough to accomplish EQ with either solar or grid. PV system is 2600 watt. Controller MPPT. One cable that had corrosion did have plating missing. Cable removed and replaced with new today.

BB. · September 2023

When you are at 57.x volts, what is the charging current to the battery bank (20 amps for both strings)? You are looking for 5% charging current to EQ (2.5% suggested minimum). Per battery string current...

5% * 235 AH per string = 11.75 amps per string "target" EQ current and probably somewhere around 60=61 volts EQ bank voltage charging.

Also, when high current (charging and/or discharging, what is the per battery string current)--How are the batteries performing with current flow. What are the battery voltages then? Again, looking for differences here.

Some of the industrial type FLA batteries can really be helped by cycling to 75% SoC at least (i.e., turn off charging for a day if needed to get the bank to cycle deeper).

Battery resting voltage and SG per cell is a good start... But knowing the per battery voltage when current is flowing (discharging/charging) tells us a lot more about the "condition" of each battery.

The fact that you are seeing around 57.1 volts @ 20 amps charging (10 amps per string)--That usually shows that more time on EQ is needed to bring the voltage above 57.1 volts... (i.e., 1% of 235 AH = 2.35 Amps per string "full charging" termination current suggested). The fact that you are still seeing 20 amps flowing into 470 AH battery bank after 4 hours of not that high of charging voltage (14.275 volts for a 12 volt reference) is not that high of voltage.

What brand/model of FLA batteries do you have? What charging (and EQ) voltage do they recommend... A "typical" FLA battery would be around 14.75 volts charging or ~59.0 volts for charging (charge to 59 volts, hold for 2 hours for a partially discharged bank, and 6+ hours for a deeply discharged bank are typical numbers).

Ideally, you should be seeing the battery charging current dropping to 1% or so of bank capacity at 57.1 to 59.0 volts

Again, different battery brands/models can have different specifications for charging. Need to know yours.

I am certainly no battery expert (there are others where with much more knowledge and experience than I), but it would appear to me that that your battery bank is not getting fully charged (suggest fully charge at least once per week... Don't need to fully charge every day or EQ at high voltage--That is hard on FLA battery banks too--The gassing erodes plates, and the Oxygen can corrode plates and plate grids).

Note that EQ charging can cause banks to overheat--Watch cell temperatures. It is not unusual for an extended (multiple hours) EQ charging cycle to cause bank to reach max operating temperature--And having to shutdown charging and restart the next day when that happens.

-Bill

Belize1 · September 2023

Per the post from Dave A, the one terminal that was showing a small amount of green corrosion was cleaned yesterday. That cable connection was missing a small amount of the nickel plating and had some copper visible. Replaced that cable and immediately the two banks began registering almost identical amp flows under small load. The system pullled down 90 AH overnight, today it is charging and both banks have nearly equal amp flow during charge. Will watch over the day to see if charger can get up to EQ voltage.

Dave Angelini · September 2023

Turn off all battery loads tonight if you do not get to EQ voltage today. Use the grid for loads for now. Georgia peaches! We have some here in Northern Nevada😊 Picking time this week!

Belize1 · September 2023

BB
Batteries are Crown CR235. All new in June 2022. It is likely that they have never been EQ and have been cycling down to 68% SOC and back up to ?? most days since. I have in the past seen the charger go to Absorb at 57.2 and then switch to float. But I never saw it reach an EQ of 60 volts.
My understanding of charging has been limited.
I have struggled to find good explanation of charging logic. I.e., Charger holds at 57.1 until Amperage drops (?) to 5% of Bank AH? THEN the voltage climbs?? Until......?

Crown recommends transition to constant voltage charging at 2.37 volts per cell (56.88 volts). Then hold 5 amps until 118% of AH returned.

According to my Trimetric, I often have returned far greater total AH but never reach the voltage......... ?

Belize1 · September 2023

Dave
Turn off loads and use grid overnight. OK. Then what...... Try again next day to continue charging?

Vic · September 2023

Belize1 said:

BB
Batteries are Crown CR235. All new in June 2022. It is likely that they have never been EQ and have been cycling down to 68% SOC and back up to ?? most days since. I have in the past seen the charger go to Absorb at 57.2 and then switch to float. But I never saw it reach an EQ of 60 volts.
My understanding of charging has been limited.
I have struggled to find good explanation of charging logic. I.e., Charger holds at 57.1 until Amperage drops (?) to 5% of Bank AH? THEN the voltage climbs?? Until......?

Crown recommends transition to constant voltage charging at 2.37 volts per cell (56.88 volts). Then hold 5 amps until 118% of AH returned.

According to my Trimetric, I often have returned far greater total AH but never reach the voltage......... ?

Your batteries appear to not have been fully charged, for some time. So, the return current (battery charge current) of a single charge attempt matters little, as the batteries appear to need quite a bit more total charge current, than if the previous charge had really been a full charge.

As BB Bill noted, you should try to increase the Absorb voltage to at least 59 volts, or so (check electrolyte levels, first).

It may take hours and hours to bring the batteries up to target SGs. Then some EQ may be necessary, especially, if the SGs vary by 20-ish points, between the highest and lowest SG cells.

What IS this target SG, from Crown? ... It is often about 1.275-ish, for many Flooded LA batteries.
What is the Hydrometer that you are using?

Use the Battery Temp Sensor, for your CC/grid charger.

Often, Off-Grid systems need higher Absorb voltages, you do appear to have grid power, but think this is in the off grid Topic ...

Good Luck, Vic

Belize1 · September 2023

Crown says fully charged SG is 1.275. I am using a glass tube hydrometer from auto parts store. Some cells at end of charge day show 1.255 best cells show 1.265 or, maybe at best, 1.270.
Crown says "Timeout for charging phases 1-3 16 hours." I get nervous at about eight hours of charging based on batteries feel hot to touch and are smelly. Charge Controller does not have a temp sensor so I lack a good way to measure battery temp. Is there an alternate method to accurately measure battery temp? What would be a maximum temp acceptable during Absorb or EQ charging?

Vic · September 2023

The glass tube Auto Store Hydros can be fine, one wonders about the accuracy of them ...

You might be able to still find a glass tube Candy Thermometer to measure electrolyte temps, BUT, then that makes you the Chief Charge Voltage Controller. Each charge source should really have its own Temp sensor -- are these available? What brand/model are the grid charger/inverter/s, and what CC are you using?

As you know, charge voltages on LA batts must really, be compensasted for the nominal battery temps.

What is this Compensation % for your batts -- in a quick search, could only find that mind-numbing Chart of ALL the CR batts.

If you smell that Sulphide aroma, during Absorb and EQ, that, to me means that a FLA bank needs more charge.

Please be very careful breathing this air, as, can be TOXIC gasses liberated, under certain charging conditions. Good that you note that ventilation is good, but Arsine, and Stibine are VERY TOXIC. Try to stay out of the battery cellar while in Absorb, and during EQ.

Heavy charging and EQs, can be spread out over a few days, to try to limit battery overheating.

AND, BB Bill, thank you for deleting my erronious Quoted Post that I was unable to delete, yesterday !!

Winter's comin', back to work, here, Later, thanks, Vic

Vic · September 2023

Will add, that Hydrometers that we use with our FLA batts, MUST be fully rinsed with fresh Distilled Water, at least three times, after every SG measuring session. Otherwise, a sticky residue can build up on the innards of the Hydro. This often causes air bubbles to stick floating glass vial inside the Hydro. This can cause serious errors in readings, and, at times huge variability in readings on a single battery cell.

FWIW, IMO, etc, Vic

softdown · September 2023

It could be useful if you could do resistance testing in the wiring and in the batteries. That is just a semi wild guess by me. And DA has informed us that my opinions are to be avoided and should not be expressed.

I like to check resistance of batteries to help determine health. I suspect it is more common to sell inferior batteries due to labor and supply issues etc.

Dave Angelini · September 2023

softdown said:

It could be useful if you could do resistance testing in the wiring and in the batteries. That is just a semi wild guess by me. And DA has informed us that my opinions are to be avoided and should not be expressed.

I like to check resistance of batteries to help determine health. I suspect it is more common to sell inferior batteries due to labor and supply issues etc.

BS here ! I needed an answer for a very sick person and your over the rainbow post was not helpful. Lucky that Bill was here and posted what I needed. Point here is if you do not have an answer, it may be best to let someone else post.

I did not mean to hurt your feelings and when I posted, I was not thinking about anyone but my client who has now passed.

Really sorry also to derail your thread here Belize1. Hope you are making progress😊

Belize1 · September 2023

Update. Right bank of 8 batteries was disconnected from system and allowed to rest for two full days and nights. Bank at rest measures 51.2 volts. Individual batteries are within 2/hundreths of each other. 6.39 to 6.41. Seems like that bank is fine and fully charged.

Have been focusing on the left bank this week with daily charging. Charge Controller reaches Absorb voltage of 57.6 and stays there all day. Amps hover around 16 amps and don't seem to significantly change. After two days of that, disconnected the bank and let it rest overnight. In the morning measures 50.6. Individual batteries are all very close from 6.29 to 6.32 volts. Does not appear any single battery is worse than any other (?)
Third day of charging underway. Have been at 57.6 volts and 16 - 18 amps for seven hours. (great sunshine).

Should I be seeing a decline in the amps when the volts stays in Absorb for so long??

Thank You all for your help

Dave Angelini · September 2023

You should see a decline in amps. Sounds like if all the wiring is good you should perform EQ. SG measurments after EQ or before if you have time.

Vic · September 2023

Belize1 said:

Update. Right bank of 8 batteries was disconnected from system and allowed to rest for two full days and nights. Bank at rest measures 51.2 volts. Individual batteries are within 2/hundreths of each other. 6.39 to 6.41. Seems like that bank is fine and fully charged.

Have been focusing on the left bank this week with daily charging. Charge Controller reaches Absorb voltage of 57.6 and stays there all day. Amps hover around 16 amps and don't seem to significantly change. After two days of that, disconnected the bank and let it rest overnight. In the morning measures 50.6. Individual batteries are all very close from 6.29 to 6.32 volts. Does not appear any single battery is worse than any other (?)
Third day of charging underway. Have been at 57.6 volts and 16 - 18 amps for seven hours. (great sunshine).

Should I be seeing a decline in the amps when the volts stays in Absorb for so long??

Thank You all for your help

With 1.275 SG electrolyte, you need a significantly higher Abosrb setting, than 57.6-ish volts (this seems to be your Abs voltage, as it seems to be fixed for many hours, and you seem to be without temp compensated Abosrb V).

Try Absorb at about 59.5 V, or so.
Too bad that you do not appear to have a BTS/RTS, to compensate charge voltages.

There are a number of pending questions:
What is the suggested Temperature Compensation value, recommended by Crown for your batts (this can imply the Metallurgy of the battery plates, and therefore some guidance on the best Charge Voltages)?

What CC are you using -- brand & model?
What inverter/charger are you using " ?
How much PV do you have @ STC ratings?

It would help if you would take the time to make a Signature, which lists the above questions, plus info on your CR batts, etc.

Thanks! Vic

Belize1 · October 2023

Inverter/Charger is Midnite Solar MN5048. Does not have input for battery temp. CC has ability to charge from grid, from PV or combined. With full sun CC max output (grid and solar combined) is 60 amps. Grid only (night) charging is max 40 amps.

PV is 8 panels 350 watt. Current at MPP 9.97 amps Voltage at MPP 33.62

Crown spec sheet says: Transition to Phase 2 Constant Voltage at 2.37 VPC U2=2.37VPC Which is 56.88 MN5048 has choices in settings of 57.2 or 57.6. Have tried 57.6 setting previously. Currently using 57.6 setting which is higher than Crown specs.
Transition to Phase 3 at 5amps approx.

Crown says Phase 3 charging 5 amps to 2.7 VPC (64.8 ) The MN5048 won't go beyond 60 volts.

Crown suggests temp compensation at +/- 3mV / C

I let the system operate overnite on only the questionable battery bank. (left the good bank disconnected). Trimetric says 109 AH drawn overnight. Individual batteries meter check before starting charge, 6.03 on four batteries. 6.02 on three batteries. 6.04 on one battery.
Started combined grid/PV.

JRHill · October 2023

I don't do lead batteries anymore for anything but starting equipment but when I was in the days of monitoring SGs I bought two brand new glass squeeze bulb testers at the same time just so I could verify that they were reading similarly - or at least wrong similarly. But they are inexpensive at least.

Vic · October 2023

Belize1 said:

Update. Right bank of 8 batteries was disconnected from system and allowed to rest for two full days and nights. Bank at rest measures 51.2 volts. Individual batteries are within 2/hundreths of each other. 6.39 to 6.41. Seems like that bank is fine and fully charged.

Have been focusing on the left bank this week with daily charging. Charge Controller reaches Absorb voltage of 57.6 and stays there all day. Amps hover around 16 amps and don't seem to significantly change. After two days of that, disconnected the bank and let it rest overnight. In the morning measures 50.6. Individual batteries are all very close from 6.29 to 6.32 volts. Does not appear any single battery is worse than any other (?)
Third day of charging underway. Have been at 57.6 volts and 16 - 18 amps for seven hours. (great sunshine).

Should I be seeing a decline in the amps when the volts stays in Absorb for so long??

Thank You all for your help

Hi Belize, thanks for the added info on your system.

First, those CR batteries appear to want somewhat lower charge voltages than Lead Antimony batteries.. I assume that they are some form of Lead Calcium-ish batts. This is primarily based on the suggested Temp Comp value.

Also, many times the battery manufacturers spec charge voltages and times that are based on charging from the Grid, where the Bulk phase can be at a constant current. Our offgrid, or systems primarily charged from Solar, we cannot do constant current Bulk stage in a Solar Day -- where the Bulk phase begins at very low current, builds fairly constaly, until constant voltage (Asorb).

Too bad thay your inverter/SCC/Grid charger does not do Temp Comp, or EQ voltages that match the voltage needs of FLAs.
Think that these AIOs are really designed for Li batts. But, I DO like MN gear ...

Seems that you could really could use about twice as much PV as you now have, for your two strings of batts.

Probably, my suggested Absorb voltage is a bit high, BUT, getting FLAs fully charged, at least several times per week, for offgrid-ish systems is what they need, so, we often need fairly high Vabs to do this in one solar day. This can mean fairly Vabs settings, especially in Winter, or, as needed.

It may be difficult for your present PVs to produce enough current to allow the Absorb or EQ voltage to rise enough to finish Absorb or EQ. This causes these stages to appear to stall at a too-low voltage.

Later, Good Luck, Vic

Belize1 · October 2023

Vic
Thank you for helping out. I appreciate your support.
MY PV may be too small to achieve full charge in a single day, I understand. But,
If I don't use batteries overnight, and then restart charge again the next day, am I building on to each day and over a few days should accomplish the same result??? Given enough total hours of charging, should I expect the batteries to get back to full charge and then I can rethink and reset my approach??

RC

Vic · October 2023

Hi RC, thanks for the reply, AND, your Signature!

Thanks, too, for the info on how your system is typically used, this is good info. This discussion was in the Off-Grid Topic, so, I assumed, a bit too much, though, you did mention that you did have a grid connection ...

So, yes, nibbling away on any charge deficit, daily should work. And, you can probably get by with a smaller PV array, given your typical use of the system.

When your batteries are cold, you might want to increase the Absorb voltage a bit, and when the batts are warm-ish, you might want to reduce the Vabs, and Veq, a bit. Realizing, that your inverter/charger/CC has a limit on how high these settings can go.

Thanks, Vic

Saggys · October 2023

I am pretty sure the maximum charge voltage on your MN5048 is only 58.2 vdc, that is all I can get out of my SRNE clone, which is what the MN5048 is.

Belize1 · December 2023

Followup. Have been charging batteries and checking SG. One half (eight batteries) come up to full charge and all is well. Other half (eight batteries) charge to 90% and then charger just gets stuck. Goal for Absorb is 57.2 volts. On the functioning bank, when charger sees 57.2 volts and less than 5 amps, it goes to float. I assume this is the logic Midnite Solar wrote in to the charger controller. the other bank of batteries goes to 57.1 volts and 5.5 amps and then just sits there refusing to move any further. Manufacturer says SG on full charge is 1.275. The battery bank hat won't go through Absorb and into float they all charge up to 1.260 or even 1.265 and then stay there.

BB. · December 2023

Check the per cell (or per battery) voltage.

If there one cell or battery with a different voltage? A shorted cell will bring the bank voltage down, but should "over voltage/over charge" the other series cells.

Bill

Battery Banks not balanced

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