battery dead cell question; Rolls

soloronesolorone Solar Expert Posts: 254 ✭✭✭
I am almost embarrassed to ask this.

How can I tell which cell is dead with in two 12v batteries of a 24V set?

This 24V battery, when isolated, is not taking a charged, no amps flowing. Per Fluke meter.

I thought I had it sorted out. I keep spare cells, so I made a connection up last night and popped the tops just awhile ago. SP is from 11.00 to 11.50. V are from 1.6 to 2.1. No clear cell that says replace me.

I have not had the best service out of my Rolls. Great batteries, but they were turned over in transit, acid has been replaced, but performance has never been what it might have been. The company has been of help, warranted a couple of cells, guided me in two acid replacements.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,706 admin
    Re: battery dead cell question; Rolls

    I am a little confused... Which Model Battery do you have (sounds like a series 4000 HT or T model).

    Anyway, can you get to the bus bars for each cell, or only measure battery voltage at the +/= 12 volt terminals?

    No current sounds like an Open Cell (cracked/failed structure from roll-over?).

    If you had a shorted cell, you would get lots of charging current or even some load current out of the bank.

    If you place a charger on the 24 volt battery bank--one 12 volt battery will probably read less than 13 volts (the "good battery") and one will read over 13 volts (the bad or open battery)--assuming that the battery charger output reads 24-30 volts or so...

    If you have a load (light bulb or other resistive load), then the good battery will read over 12 volts, and the bad battery would read less than 12 volts (possibly near zero volts).

    I am a bit confused--where these batteries service/repaired/1 cell replaced? would seem to be a different battery construction (one usually cannot replace one cell in a modern 12 volt battery with sealed top case).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • soloronesolorone Solar Expert Posts: 254 ✭✭✭
    Re: battery dead cell question; Rolls

    These are Rolls batteries, they come apart, easy to replace a cell, I have done so a couple of times, this is one reason I really like Rolls.

    The voltage readings I gave are per cell, varies from 1.6 to 2.1 volts.

    I am wondering now if I can tell by shorting out the individual cells, this not something I would recommend others do, but with a large fan to remove any stray gas it should be safe.
  • BB.BB. Super Moderators, Administrators Posts: 29,706 admin
    Re: battery dead cell question; Rolls

    That is a huge variation in cell voltage... From dead to pretty much fully charged (at least by voltage.

    Place your battery charger on the bank and then measure cell voltage and charging current. In theory, you should be putting 5% of the AH capacity through the battery to equalize the cells.

    If you cannot get any current through the battery--then something is open (cell should read very high voltage) or most of the cells are fully charged and you need >15 volts to get enough current through the battery. Typically for equalization that would be 5 amps per 100 AH of cell capacity (5%).

    Something does not sound right for the battery cell voltages to be so far off from each other...

    Also check the connections between cells and to the charger and make sure that there is no large voltage drop (open/loose/corroded) connections anywhere.

    For the cells with 1.6 volts--they will not supply much current at all (because they are below 1.75 volts--which is usually considered dead). But you could try placing a load on the other cells--those above 2 volts--and see if you get any useful current out of them (if you have any loads that will pass significant current at 2 volts).

    I wonder if you have some cells with partial internal shorts (or simply "aged") that are causing them to self discharge... That could cause those cells to discharge with respect to the other cells...

    If you have several parallel strings of batteries--it is possible that an open cell/bus connections was open and the battery sat for a period of weeks/months without ever really getting a charge--and the weak cells self discharged.

    You really need to get some current flowing through the cells/batteries to see if you can recharge the weak cells and that everything else (electrical connections) are OK.

    By the way, how old are the batteries? It sounds like your's may be collapsing and replacing any one/two cells is just postponing the eventual entire bank replacement (and hopefully, you avoid the shipping damage next time).

    -Bill :confused:
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • soloronesolorone Solar Expert Posts: 254 ✭✭✭
    Re: battery dead cell question; Rolls

    Thanks Bill.
    The bank is 8 YO, they have all been in service the entire time.

    I sensed some trouble a couple years ago, let me explain, my wife and I both had cancer over the past 3 years, it was all I could do to keep water in them. I had noticed some PG and voltage problems, so I am just the the past few weeks really digging into th state of things, but I knew the problem was with in this 24V set.

    Age and the other problems already mentioned are surely a part of the problem, but I was hoping a cell swap would buy some time.

    I will wait till tomorrow and put the 24V battery under charge again, with the tops off and see what readings I can get like that.

    Shorting individual cells, if there were a break inside, it seems there would be no spark?? Worth a try, before charging?? I can not think of anything to load a 2.2 V cell, other than a 12V bulb, of which I am sure I still have one or two:D
  • BB.BB. Super Moderators, Administrators Posts: 29,706 admin
    Re: battery dead cell question; Rolls

    Be really careful about sparks around the battery bank... If you wanted to hook a jumper cable to the 2 volt cell and then spark those free ends 6-10 feet away (something like a plate of metal and a welding rod/chunk of metal)--You don't want to spot weld your cables to the posts. But I am not sure that even this is really "safe" (you could pop a weak connection in the cell and cause an explosion inside the cell).

    If you have a 12 volt car battery charger--you could try charging 5-6 cells at a time and see if you can get current going through them. Would be a good way to try and charge the low voltage cells without overcharging the high voltage cells (equalization/overcharging good cells is not healthy for them).

    I hesitate to make too many suggestions here... Batteries can output a huge amount of current (1,000's of amps into a dead short). That plus hydrogen gas and acid--I would hate to hear about anything happening to you from trying to debug the battery bank (although, I am sure the cancer was not a walk in the park for either of you either--I hope that everything is going better for you guys now).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • soloronesolorone Solar Expert Posts: 254 ✭✭✭
    Re: battery dead cell question; Rolls

    Thanks, I will sleep on it, and believe me, I know about the amperage potential, LOL won't discuss that in depth here, but it involved two 2000 amp banks of telephone batteries and and a 800 amp double pole throw switch and some 600 MCM wire.:D

    Telephone batteries were the suggested do all end all from the late 70s, little did we know that they would not support the inverters that were soon to be available.
  • soloronesolorone Solar Expert Posts: 254 ✭✭✭
    Re: battery dead cell question; Rolls
    BB. wrote: »
    That is a huge variation in cell voltage... From dead to pretty much fully charged (at least by voltage.


    Also check the connections between cells and to the charger and make sure that there is no large voltage drop (open/loose/corroded) connections anywhere.

    By the way, how old are the batteries? It sounds like your's may be collapsing and replacing any one/two cells is just postponing the eventual entire bank replacement (and hopefully, you avoid the shipping damage next time). Bill:

    The batteries are 10 years old.

    After cutting out the problem battery, the rest of the bank performed very well, as the sick battery had of course, been dragging down the whole bank, so I was not pressed to deal with the problem, right away.

    I did forget/fail to check the internal battery connections. These being factory setup and having worked for so long, did not seem like a likely trouble spot, BUT.:roll:

    I borrowed a battery charger and isolated the 12 battery at fault. I could not get any amperage to flow. Then, using the 6 V mode, I checked the cells within the battery.

    I was surprised and delighted to see sparks fly out of a factory connection. I later found all of the internal connection's a bit loose, I don't know the torque spec, but they were a good 1 to 1& 1/2 turns loose.

    Looking back at the battery performance over the last three years of our illness, I suspect this problem has existed for at least that long.

    The batteries are 10 years old, not 8, but we will try and squeeze a bit more out of them.

    I will be curious to see how the bank performs as a whole.

    I did a load test on the problem battery, and would like an opinion on these numbers.

    This 24 V battery is 375 AH at 20 Hour.

    I put a 25 AC Amp load it. The 24 V DC amp rate was about 140 to 155 A
    The Voltage fell to 22 and 21.8 .

    Thanks for all the advice.

    I should have checked the interconnections sooner, but knowing how Rolls makes their interlocking connection it just did not seem likely, guess everyone that has the Rolls should have a look inside.
  • Ralph DayRalph Day Solar Expert Posts: 892 ✭✭✭✭
    Re: battery dead cell question; Rolls

    I have Rolls batteries, one cell in one 8v unit will not get up to full SOC as measured by SG. It also uses much less water per month so appears to not charge completely, although you still see bubbling action when charging. Customer service says it's just a lazy cell. The voltage is still ok, but I've wondered about pulling the gang top and checking the interconnections. Sounds like it might be a plan for the future if things decline further.

    SG on suspect cell 1.245, another random/pilot cell 1.265 or higher (even after eq charging). It might get to 1.250 after several full absorb cycles. I worry too much.

    RALPH
  • soloronesolorone Solar Expert Posts: 254 ✭✭✭
    Re: battery dead cell question; Rolls

    If it is not using as much water as others one would think it is not charging properly.

    If you pop the top of you can get a V reading of the cells, preferably after they have been at rest for awhile. If the one battery as whole, is not showing any voltage fall off, is there really a problem ?? In my case the lower voltage pulled the whole bank down.

    I am still evaluating my bank, but it is surely operating a lot better than 2 /3 years ago, but it took a near 5 hour bulk charge today. That was a very long run, not sure what that means, other than old age.:D I would love to see 12.60 again.

    You can just pull the plugs that hold the top on, in my case, I can not get to the back, so a sharp chisel cuts off the plastic head. The caps hold the top on without the plastic pins.

    Tom.
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,840 ✭✭✭✭✭
    Re: battery dead cell question; Rolls

    Tom,
    How does it look compared to it's neighbors in EQ? I would guess it is not boiling as much. You need to move into the realm of corrective EQ from preventative EQ.
    I just don't have the time and would have to bill for it "with my people" , but you might check Surrettes bulletins on corrective EQ. The voltage is about as high as you can get and then 3 hours longer while keeping the temperature under control.

    Good Luck! 10 years isn't bad, they will do longer with tlc
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • soloronesolorone Solar Expert Posts: 254 ✭✭✭
    Re: battery dead cell question; Rolls
    Tom,
    How does it look compared to it's neighbors in EQ? I would guess it is not boiling as much. You need to move into the realm of corrective EQ from preventative EQ.
    I just don't have the time and would have to bill for it "with my people" , but you might check Surrettes bulletins on corrective EQ. The voltage is about as high as you can get and then 3 hours longer while keeping the temperature under control.

    Good Luck! 10 years isn't bad, they will do longer with tlc

    Thanks Dave, I am still feeling out the "new battery bank" . I think 12.40/45 may be my new "good". Trying one hour charge per day now, just see how they perform.

    When I get a sense of how the bank is working I will call the techs, I have one young mans name in my file, hope he is still there. I ran a equalizing charge the other day, the first time, it rolled hard for 2 hours. A lot of cells SG are all over the place, but they have fresh water, so may take awhile to get good reading.

    The bank acts/performs/charges totally different with the repaired battery back in the loop. This requires a total change in my prior battery 6Th sense:D In other words I am not comfortable with what I THINK i know.
    Tom
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