Battery equalizing / rotating?

Volvo Farmer
Volvo Farmer Solar Expert Posts: 209 ✭✭✭✭✭
Bank: 8x Surrette S530, two series strings, two parallel strings wired for 24V. Connectors 2/0 crimped and equal length.

Been seeing unusually low voltage in the AM, like 24.4V with only 100AH out overnight. On sunny days like today, I'm out of a 2 hour absorb (29.2V) by 1-2PM or so and float (26.6V)for 3-4 more hours. I'm charging at about 40A right now with various and sundry normal household loads.

I checked battery voltage while charging this morning. "At rest" aint gonna happen with the wife and kids home.

Series string (1) 6.57 6.62 6.60 6.61
Series string (2) 6.64 6.64 6.69 6.46

I've been doing regular equalizations at least quarterly, sometimes more often. These batteries are about 4 years old.

I'm going to equalize each string separately this PM. My question is.. Should I rotate the high or low voltage battery out of one string and into the other? I'm concerned that the high and low battery in the same string will be hard on the high one while trying to bring up the low one.

Probably have some SG numbers later this afternoon. Thanks.
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Comments

  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Battery equalizing / rotating?

    'normalizing' (rearranging) the batteries would not hurt, before the EQ, 6.46 for the 6.62 would be my choice, then one string is all above 6.61
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • Volvo Farmer
    Volvo Farmer Solar Expert Posts: 209 ✭✭✭✭✭
    Re: Battery equalizing / rotating?

    Uh oh. Middle cell in that low battery is off-the-scale low on the hydrometer, I can't even get the float to float. I split the bank and am running off the good half now.

    Anyone got an opinion on that? There's no bringing this thing back is there? I've got shorted plates or something huh?

    Oh boy, I know I'm not supposed to mix old and new batteries but what are my options, other than throw away $3000 worth of batteries after 4 years and start over?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Battery equalizing / rotating?

    You might call Surrette and see what they say/suggest. Presumably, you have some warranty left on the battery (prorated or even flat rate for first few years).

    The big issue is to ensure that the string that was sharing that cell is still OK. A shorted cell can overcharge the rest in the string.

    Another reason to plug (for the 15th time this week :roll:) the very reasonably priced starter DC Current Clamp Meter + DVM ($60 from Sears).

    Use the meter once a month or once a week to check current sharing between strings (under charging and discharging). That plus watching/logging bank/battery/cell voltage and S.G. and looking for something that does "match" the rest of the strings.

    A string that is taking too much current may have a shorted cell; Or the other string may have an open cell/poor connection/etc....

    But, yes, I would replace the one battery (assuming all the others look OK). It is not going to shorten the life of the rest of the string/bank of batteries.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Volvo Farmer
    Volvo Farmer Solar Expert Posts: 209 ✭✭✭✭✭
    Re: Battery equalizing / rotating?

    Thanks for all the help. I don't know what's going on here, I just measured the battery after 4 hours of rest and it was at 6.6 V. So I don't know why I get abysmal SOG readings on one cell but the voltage at rest seems ok, or even high.
    Maybe I'll start a new thread after getting some more measurements. I really appreciate the feedback.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Battery equalizing / rotating?

    I have to point out that if you can't take an "at rest" battery Voltage reading due to constant use then you won't be able to do a proper Equalization either as the batteries are not supposed to be connected to any loads during that process.

    Further to that it would be ideal to be able to equalize batteries independent of one another, as applying continued high Voltage to those that don't need it can actually damage them. It's a pity, but there it is.
  • Volvo Farmer
    Volvo Farmer Solar Expert Posts: 209 ✭✭✭✭✭
    Re: Battery equalizing / rotating?
    I have to point out that if you can't take an "at rest" battery Voltage reading due to constant use then you won't be able to do a proper Equalization either as the batteries are not supposed to be connected to any loads during that process.
    I separated my parallel strings for almost 4 hours and measured the battery in the string that had had no charging or discharging for that time. Voltage seemed higher than I would have expected.

    So If I have 100A available for charging and 10A out of the batteries through the inverter , you say that I can not get a good equalization charge as I have loads applied to the batteries at this time? This statement does not make sense to me, could you explain further?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Battery equalizing / rotating?

    The issues (as I see it):
    • 100 AH battery bank, 10 Amp load. Usually, 5% recommended for equalization current, so you need 15 Amp total current from the charging source.
    • For a 12 volt bank (example), equalization is around 15 to 15.5 volts. And even higher if the bank is cold (near freezing or lower). Many 12 volt devices/inverters start to have issue at 15+ volts (and inverters will sometimes over-voltage shutdown).
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Volvo Farmer
    Volvo Farmer Solar Expert Posts: 209 ✭✭✭✭✭
    Re: Battery equalizing / rotating?

    Wow, it's getting more confusing by the minute. I do not have a 100Ahr battery bank, I have a 1060 Ahr battery bank @24V. Sometimes there is a 10ADC load on my system while I attempt to equalize them with 50A@ 24V nominal solar + whatever I can get out of a VFX3524 on a 7500W generator. I guess once I turn on the generator, the 10ADC load switches to the generator and becomes a 2.x VAC load, but the net effect seems to be the same to me.

    I equalize my batteries at 32V and they are in an insulated box which was at 64F here today and has never been below 45F in the last four years. I completely understand the voltage limitations of cheap 12V inverters and the effects of cold temperatures on batteries.

    I fail to understand how these issues pertain to me and my concern that I have a three cell six volt battery which reads 6.6V after four hours rest yet one of the cells is extremely low when I test it with a hydrometer. I will gather more data and attempt to post a more concise summary of my problem in the next few days. Thanks for the replies.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Battery equalizing / rotating?

    voltages on batteries can show high even when a cell is bad. it would be an extreme overcharge to the good cells of that battery and that voltage stays there for a bit of time. are you noticing any abnormal water usage from the cells of that battery? maybe try a small load for a minute or so to get the battery to see closer to the at rest voltage quicker by bleeding off a bit off the temporary higher voltage due to charging. do this also to a battery you know is good and use the same load for the same amount of time and compare the 2 for how far the voltage drops. a bad cell will drop the overall voltage of the questionable battery farther down than on the good battery. it may be necessary to isolate any low batteries and bring them up individually or at least in a small group to minimize the overcharge to the better batteries while bringing the lower ones up assuming it is just a low cell and not a bad one.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Battery equalizing / rotating?
    you say that I can not get a good equalization charge as I have loads applied to the batteries at this time? This statement does not make sense to me, could you explain further?
    As I understand it, equalization is at a constant (fairly high) voltage. As long as your generator/charger combo can hold that voltage (despite your other loads), your other loads are irrelevant.
    BB. wrote:
    Usually, 5% recommended for equalization current
    Bill, When I do equalization of my L-16 bank, I just set the voltage according to the manufacturers instruction. I have not paid attention to the current. Do you recommend that I should adjust my equalization voltage to make the current equal to 5% of my battery's AH rating?
    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Battery equalizing / rotating?

    If I remember correctly, it was Surrette that recommended a 5% equalization current. And that was one of the reasons for sizing the minimum charging current/pv array/etc. to 5% minimum current.

    I am not a battery expert--So, I would start with the instructions from your manufacturer. But I would not exceed the recommended charging current force the 5% current.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Ralph Day
    Ralph Day Solar Expert Posts: 1,019 ✭✭✭✭
    Re: Battery equalizing / rotating?

    Hi VF
    This thread (we all thank you) illuminates the need to check battery SOC with hydrometer and not rely on voltage readings to determine SOC. If you can, hydrometer readings give you a truer SOC indication and you don'tneed to shut down everything for hours.

    As to bad cells...I had 2 bad cells in my 48v Surrette bank. I tracked them for months and their sg readings went lower and lower regardless of eq charging or how much the sun shone. Their water consumption was nil while the remainder would use 250mls per month. The voltage of the 2 batteries they lived in didn't reflect their ill health (voltages were on par with the other 4 batteries...6 x 8v). They were replaced pro-rated under warranty, a bit of a pain, but not the whole bank was bad. The new cells are working well and their sg's are 1.280-1.290 when fully charged. I don't see them being "dragged down" by the rest of the bank, or maybe I can't see how that would be reflected.

    Double check all the other cells and make sure there's not any others on the downslope. Shipping 1 or 3 cells is probably the same cost at any rate. And if you replace with an entire battery you will have 2 cells to hold in reserve...providing you keep them charged. I kept one bad cell and use it as a dummy load as I build my 2v charger (for charging just one cell as needed).

    I found Surrette customer service good to work with, but it took a while to make them see that the cells concerned were trash. Good luck.

    Ralph
  • Volvo Farmer
    Volvo Farmer Solar Expert Posts: 209 ✭✭✭✭✭
    Re: Battery equalizing / rotating?

    Okay. Here are my SG readings. These were taken in the morning after some recharging with the generator before dawn. Battery temp 58F Voltage 26.9V while charging 29A from solar.

    Series string 1
    1250 1280 1255 1275
    1250 1270 1250 1235
    1255 1250 1255 1260

    Series string 2
    1245 1260 1265 1265
    1250 1090 1250 1250
    1270 1225 1260 1270

    The battery with the bad cell was at 5.95V this morning after about 100Ahr out of the bank overnight and no recharging. I find it hard to believe that the other 2 cells could hold that voltage if the bad cell is really 100% bad

    My plan is to disconnect series string 1 and attempt to equalize series string 2 for two to three hours at 32.5V today. I have approximately 50A available on solar to do this, which I think should be enough for a 530AHr battery bank.

    Thanks for all the help so far. I think I'm going to need to replace this battery though.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Battery equalizing / rotating?

    Yes, that 1.090 SG is a problem all right. Probably indicates a shorted cell. Don't be surprised that the over-all Voltage of the battery is close to normal; the good cells can go high in Voltage when one fails. As in: instead of have 2-2-2 Volts you have 2.5-1-2.5. If you think that's bad for the other two cells, you're right.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Battery equalizing / rotating?

    "I find it hard to believe that the other 2 cells could hold that voltage if the bad cell is really 100% bad"

    they can and do. i have seen this first hand on fla batteries i had long ago where there was a high surface charge that fooled me initially into thinking all was fine until i had put a load on it and it fell like a rock. it may very well be at a different point of being defective, but it is still defective.

    it may even be advisable to take the batteries with the worst specific gravities, except that one with 1.09 sg, and then charge this bank by itself to see if it brings some of these cells more inline.
  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    Re: Battery equalizing / rotating?

    $03:

    Personally, I see no prob having nominal Inverter loads while EQing from PV, or AC, when using high quality inverters. If one has a 12 V system, and has DC loads on the batts, then EQing with loads can be bad.
    Some inexpensive inverters shut off at 15 or so volts, which is quite a bit too low.
    Most good inverters have the High Batt Disconnect V settings that exceed any reasonable E! voltage.

    BB Bill, in the past, recall that you mentioned te 5% EQ current as the MAX suggested, by Surrette -- not to exceed current.

    A good indication of the health of a battery/cell can be determined quickly by measuring voltages of individual cells/batteries with substantial charge currents flowing. Quick/easy measurment. Altho, parallel strings could lead to false readings. Would guess that this technique would hold for reasonable discharge currents as well.

    S-530s are not really 530 AH. THis number comes from the 100-hr rate, not the 20 hr rate. An S-530 with 1.280 SG Electrolyte is rated at 400 AH. With 1.265 SG (as probably shipped), it is perhaps 380 AH. FWIW. Not that this makes a huge difference.

    The Internet if FLAKEY again today ... more later Good Luck, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Battery equalizing / rotating?

    Vic makes a good point; EQ is about holding the Voltage at higher than normal charge point, not maintaining a fixed current level. Any current mention by a battery manufacturer in reference to equalization is bound to be a max; if the battery draws more than that then it is not fully recharged and you shouldn't be trying to do the EQ. High Voltage and 'high' current is a sure recipe for premature battery failure.

    This of course brings up the conundrum of trying to charge a battery that's too far out of spec. It usually just plain doesn't work. Making up a difference of 0.020 on the SG is one thing; making up a difference of 0.200 is quite another. It's not likely that one cell will recover, and the others have significant variations in SG.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Battery equalizing / rotating?

    "Any current mention by a battery manufacturer in reference to equalization is bound to be a max; if the battery draws more than that then it is not fully recharged and you shouldn't be trying to do the EQ."

    i don't know about that being true as a modest voltage increase to a charged battery can cause a huge current increase to go along with it.
  • Volvo Farmer
    Volvo Farmer Solar Expert Posts: 209 ✭✭✭✭✭
    Re: Battery equalizing / rotating?

    I set the solar to EQ, and then we left for 6 hours. I forgot to split the bank though. Upon return, the bad cell has risen to 1150 and the batteries were at 85F. I failed to reach 32V for 2 hours as it was still trying to EQ when I got home.

    I fired up the generator, increased the EQ voltage to 33V and split the bank. More info as it rolls in. I feel somewhat hopeful that I was able to get the SG to rise at all in that cell. Maybe I can bring it back after all! Thanks again for all the comments. I'm soaking them all in.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Battery equalizing / rotating?

    Monitor all of the cells, and if you have parallel strings, it may make sense to disconnect the strings that are fully equalized already (their SG is not increasing).

    Equalizing is hard on batteries/cells and you do not want to over equalize other strings if you can (safely) avoid it.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Battery equalizing / rotating?

    You may have a low battery, that got out of balance, and while EQ'ing the rest of the cells will bring up the low one, you may want to pull it out, and charge it on it's own, with a generic 6/12V charger. Or cook the rest of the bank... For a small imbalance, EQ is fine, but I think you are beyond small, but may have already gotten 70% there.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • Volvo Farmer
    Volvo Farmer Solar Expert Posts: 209 ✭✭✭✭✭
    Re: Battery equalizing / rotating?

    Yeah, I would love to try and charge this battery for a good long time by itself. I'm going to work on that, but I think I need a good 24-48 hrs on grid power, I don't know if my 6V charger is beefy enough and these things are heavy! :)

    Final result for the day was the bad cell came up to 1175 with 120F battery temperature. This seems to be OK according to Surette document 605. I took the string off line to let it cool down and will measure SG again in the morning.

    I learned a lot in the last 24 hrs! Thanks again to everyone who commented!
  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,728 ✭✭✭✭✭✭
    Re: Battery equalizing / rotating?

    For the future, and not sure if you are doing this but Surrette has always reccomended preventative EQ's as a way of preventing corrective EQ's (where you are now). They use 2 hours every six months or a 1 hour EQ every quarter.
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • Volvo Farmer
    Volvo Farmer Solar Expert Posts: 209 ✭✭✭✭✭
    Re: Battery equalizing / rotating?

    Just an update here. I have managed to bring the bad cell up to 1235 SG today. It has taken three or four cycles of coming through an absorb cycle and trying to push voltage up to 32V with the generator alone. I can only put 55 or so amps into these at 31.x volts through a VFX3524. We have not seen the sun for two days :(

    Anyone reading here with parallel strings, be advised to check them from time to time. I had a little chat with Tom Duffy, who sold me these and he had a funny analogy. He said that battery cells in parallel strings are like children set loose on the playground. They're going to run off in all directions and you have to round them up from time to time.

    So if anyone reading this in the future thinks they have a bad battery cell, I suggest the "corrective equalization" procedure, but you have to do it one series string at a time, and you might have to do it several times. What really sucks is having to do this during the shortest days of the year with a persistent cold front. I think I've burned through 20+ gallons of gasoline in the last 3 days. :cry:
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Battery equalizing / rotating?

    120F is awfully hot. I would try to stay below that by 10-20F.

    Also disconnecting the good strings and using less current just charge/equalize the one string.

    Or, I would use a six volt charger driven by your ac inverter. Using all that fuel for one cell/battery is a killer. Probably disconnect the one string you are charging that battery on.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Volvo Farmer
    Volvo Farmer Solar Expert Posts: 209 ✭✭✭✭✭
    Re: Battery equalizing / rotating?
    BB. wrote: »
    120F is awfully hot. I would try to stay below that by 10-20F.

    I'm going by what Surrette, the manufacturer of my batteries recommend. I would be interested in hearing why you disagree with them.
    Also disconnecting the good strings and using less current just got the one string.

    I read this three times, and I still don't understand it. Do you disagree that it is important to equalize one series string at a time? Or are you trying to warn me that I need to equalize the other string as well?
    Or, I would use a six volt charger driven by your ac inverter. Using all that fuel for one cell/battery is a killer. Probably disconnect the one string you are charging that battery on.

    To equalize a single 6V L16 I need a battery charger that can deliver 8V at approximately 20A and will limit the current at 8V. I would be very interested in learning about an affordable battery charger that meets these specifications.

    Also, are you really recommending I correctively equalize a battery on an off grid solar system in the dead of winter, when I haven't seen the sun in two days with the OTHER BATTERIES? to save gasoline? ... REALLY?
  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    Re: Battery equalizing / rotating?

    Hi VF,

    120 F is the LIMIT of Surrette's guidance for Tmax during EQ. This IS very warm.

    A fairly simple battery charger can be constructed with a Variable Autotransformer (Variac), a stepdown transformer, bridge rectifier, filter capacitors, and Auto type jumper cables. You would also need an in-line ammeter, and a DMM. Wired correctly, this allows one to set the DC charge current, and measure the charge V using the DMM. If you had a small genset this single battery charger would sure need a lot less fuel.

    IIRC, you WERE EQing one string. If the "only 55 Amp" number you mentioned is the current to a single string, this is a bit excessive, based upon the 5A max per 100 AH of 20-Hr capacity (IMHO).

    Are you using a temperature compensating Hydrometer when taking your SG readings at the end of the EQ? And you prob checked the water level, and added water near the end of EQ to make-up for any water loss.

    At times like these, it is very convenient to have 2-volt cells, or batteries with accessible terminals for each cell -- you know this.

    Do not mean to be preachy. EQing is always a trade-off. Good Luck, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Battery equalizing / rotating?
    I'm going by what Surrette, the manufacturer of my batteries recommend. I would be interested in hearing why you disagree with them.

    Batteries age about 2x faster for every 10C/18F over 25C/77F... 120F-77F=43F; 43F/18F=2.4 aging factor. 2^2.4~5.3x faster aging at elevated temperatures. I know that is only a few hours to a day at elevated temperatures (i.e., 1 day at 120F is around 5.3 days at 77F), but for the long term, keeping batteries cooler will help prolong their life.
    using less current just by just charging the one string.
    I read this three times, and I still don't understand it. Do you disagree that it is important to equalize one series string at a time? Or are you trying to warn me that I need to equalize the other string as well?
    Sorry, typed that on my phone and it got messed up (new VBB software is confusing my phone browser)

    I was trying to say that if only one string/cell needs equalizing, disconnecting the other strings that don't need equalization will be a bit easier on those strings and use less current from your charging system.
    To equalize a single 6V L16 I need a battery charger that can deliver 8V at approximately 20A and will limit the current at 8V. I would be very interested in learning about an affordable battery charger that meets these specifications.

    Here are a couple of battery chargers--Don't know if they will do 7.5+ volts on a 6 volt bank or not--But they will give you between 10/20/40/80 amps dependign on which one you may choose:

    www.amazon.com/Schumacher-SE-4020-200-AMP-Wheel-Style-Charger/dp/B0002YR8H2
    www.amazon.com/Schumacher-SE-3000-Manual-Battery-Charger/dp/B00030BFNS

    You might need to call the factory or find somebody locally that has them and see how they perform on a 6 volt battery...
    Also, are you really recommending I correctively equalize a battery on an off grid solar system in the dead of winter, when I haven't seen the sun in two days with the OTHER BATTERIES? to save gasoline? ... REALLY?

    I am trying to offer options... Running your 6 volt battery charger from a your AC inverter (probably disconnect the bank string that needs equalization) or use a smaller genset (like a Honda eu1000i or eu2000i) to run the smaller 6 volt battery charger (a eu2000i may use as little as 1/10 gallon per hour to charge a single 6 volt cell).

    You are in a tough spot... Either equalize the cell using any method you can (probably out in the middle of nowhere) or call the vendor and try to get them to replace it (or find a used one). I do not know what would be best for you...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Battery equalizing / rotating?

    VF, I was told by the SAFT rep (wet NiCd's, totally different chemistry) that to convert a constant voltage charger to a constant current (Amps) charger, to split a 12 v battery into to 2 - 6 volt parallel strings. You might want to talk to battery rep to see if this is a possible way to 'recover ' your low cells.

    PS the SAFT manual protocol is to 'treat' them for 15 hours ( they boil like crazy) and then do a discharge test and compare against the discharge tables, 5 hour test at C5 rate.

    hth
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • Volvo Farmer
    Volvo Farmer Solar Expert Posts: 209 ✭✭✭✭✭
    Re: Battery equalizing / rotating?

    I apologize if I got a little snarky there. I think I was unclear. To equalize this out of spec battery, I would have to haul it to a grid tied location and do it there, while surviving off half my capacity in the dead of winter. I've been a little stressed out lately if it is an excuse, sorry.

    I get your point Vic. I know that SG is dependent on temperature, some of my measurements were taken 20-30 degrees off 70F, but I do understand the correlation. I should have mentioned temperature while reporting that. I also realize that SG is dependent on water added to the cell, and this is where things get tricky. I haven't been religious about making sure that the level between cells is exactly the same when I water the cells over the last few years.

    Maybe someone can explain this to me. I have four 6V L16 batteries (800AHR @20 hr rate) hooked to my system @24V ( I split the parallel batteries out). They are maybe 20-40% discharged according to SG. I try and absorb charge them with the generator and the VFX3524. I can easily reach 29.2 V within a half hour and charge amps drop to 15A or so within 30 minutes.

    I let them charge another 30 min at 29.2V. Amps in are still 15 or so . Batteries might be 80F or so but no higher at this point. I assume I now have fully charged batteries and might try to EQ now. I push the voltage to 32V, but the generator ( through the 20AAC limited VFX3524) cant keep the voltage that high more than 10 minutes. Voltage drops to 31.8, then 31.6 over the next hour.

    Do I need to be more patient in my absorb cycle? It is usually programmed into the charge controller for 2 hours, and we hit it and go into float almost every single sunny day of the year. My reported numbers are my observations trying to correctively equalize this bank with a generator over the last week or so.

    I thought it was important to hit the 2.66v/cell for a good hour or two to do a proper equalization. My experience has been that I either push the battery temperature way high or that I can't muster enough current to keep the voltage up for that length of time, which confuses me.

    Hehe, I should have posted this in the beginners forum, because the more I learn, the more I realize I don't know!