winter battery performance

samuelsamuel Solar Expert Posts: 80 ✭✭✭✭
I have 14x golf cart batteries (6V; 220Ah) in a garage. The garage also houses the inverter and all the various temperature correction sensors for charging. I have observed the correct 1540Ah in summer when comparing Ah consumed to specific gravity. However, as of Dec 20, 2011 the same method gave an estimated 500Ah capacity. To sum it up:

Summer; 75°F; 1540Ah
Winter; 39°F; 500Ah

It's common knowledge that batteries loose a good deal of their functional capacity in the cold (try using alkaline batteries in a game camera when it is 15°F. When the camera quits working save the batteries until summer and you'll get another 50% of use from the batteries. So... back to the FLAs in question:

Can this be correct? - and where did all the capacity (1000 some Ah) go? Is it common for 'golf cart batteries' to appear to drop to 1/3 their warm weather capacity when winter sets in?

I still need to take a SG reading at full charge to rule out battery monitor error, but so far the data I've collected is compelling. I'll get to the bottom of this eventually (by collecting more data over time), but in the meantime I'm wondering if anyone else has had a similar experience.
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Comments

  • Volvo FarmerVolvo Farmer Solar Expert Posts: 209 ✭✭✭✭✭
    Re: winter battery performance

    What is your system voltage? Seems like you have a lot of parallel strings there.

    How are you measuring Ahr? What battery monitor?

    What is your charging source? Solar? Generator? Grid? How many amps can you charge with and for how long?

    Is this a grid tied, backup system or is it in daily use?

    What are your settings for bulk, absorb and float? What are your settings for equalize? How often do you equalize?
  • BB.BB. Super Moderators, Administrators Posts: 29,489 admin
    Re: winter battery performance

    At around 0C/32F, your battery should be at 75% of rated capacity... I am not sure why or how you know you only have 30% rated capacity.

    How do you know what the winter capacity is? Specific Gravity readings, Battery Monitor, or using power until the inverter input voltage faults?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • samuelsamuel Solar Expert Posts: 80 ✭✭✭✭
    Re: winter battery performance

    How I know what I know:

    I recorded today the following -

    1.210 SG (reproduced exactly on 5 cells)
    39°F (electrolyte temperature)
    11.91V (Victron BMV 600s) --- FIXED*
    11.9V (Xantrex MS control panel)
    380-400W load (Xantrex MS control panel)
    20.2 Amps load (Victron BMV 600s)
    22 Amps load (Xantrex MS control panel)
    198 Ah down from equalize charge (one week ago)


    There is a bit of disagreement between the Xantrex control panel and the Victron battery monitor.

    I have been fine tuning the battery monitor to accurately reflect charger efficiency, it also resets once the batteries receive a full charge - being winter with poor/little sun (L. Superior snow belt) this is why I want a SG reading when the system 'should' be at full charge to verify charger settings. Right now battery monitor, PV and generator batt. charger are all in agreement when the batteries are "fully charged" The dismal sunlight each day often only provides us with 5-15 amps to charge with - or sometimes the tiny 2 amp trickle when overcast.
  • VicVic Solar Expert Posts: 2,970 ✭✭✭✭
    Re: winter battery performance

    Looks like seven strings of two batts -- a 12 volt system. YES! Quite a number of parallel strings.

    It would be amazing to me if this could work well in the long term. There may well be other issues, but ... anyway, will stop picking. Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 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.
  • samuelsamuel Solar Expert Posts: 80 ✭✭✭✭
    Re: winter battery performance

    So far the batteries have remained very well-balanced (throughout various %SOC) in terms of specific gravity across all the cells. I have not found a better way to connect what I have in a 12V configuration and I would be very surprised if the 7-string parallel wiring ever lead to problems. My main concern is that the run-of-the-mill golf cart battery was never intended to function in the cold like purpose built off-grid batteries (this is purely speculation). I'm trying to determine where I should focus my attention - though it looks like I'll just have to wait for warmer weather to learn if the cold is solely responsible for lost capacity.
  • BB.BB. Super Moderators, Administrators Posts: 29,489 admin
    Re: winter battery performance
    samuel wrote: »
    typo fixed in original post

    --Question answered--

    Do you have a way to make sure the batteries are sharing the loads/charging current (my favorite, a DC Current Clamp meter)?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • samuelsamuel Solar Expert Posts: 80 ✭✭✭✭
    Re: winter battery performance

    My bad - 11.91V NOT 12.91V. I fixed the typo in the previous post as well.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: winter battery performance
    samuel wrote: »
    I would be very surprised if the 7-string parallel wiring ever lead to problems. <snip> it looks like I'll just have to wait for warmer weather to learn if the cold is solely responsible for lost capacity.
    I would be surprised if 7-string parallel wiring did not lead to problems. Also, as BB. wrote "At around 0C/32F, your battery should be at 75% of rated capacity". Your batteries should behave accordingly. No need to wait for warmer weather.
    samuel wrote:
    I recorded today the following -
    1.210 SG (reproduced exactly on 5 cells)
    You measured 5 of your 42 cells. That is a small sample size to assume all 42 cells are the same. Part of the problem with multiple parallel strings is that the cells begin to diverge in capacity. Also, you put too much faith in specific gravity. If all of your cells are uniformly undercharged, they will have uniform SG, but reduced capacity.

    I think the best thing to do now is hook up 1 string at a time to your charger and measure, charge, and measure again.

    By the way, I also keep my battery & electronics in a detached garage. I keep it above freezing with woodstove and my batteries (in insulated box) never get below 42° F. In the winter I set the trimetric battery monitor to derate the AH of the battery bank by 15%.
    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: winter battery performance

    one does need to be aware of the degradation in capacity when keeping a battery in a cold area. batteries are a chemical reaction and the cold slows that down which is also why a cold battery is said to last longer. for sunxtenders operating from 0 degrees c to 9 degrees c you will need to design for another 60% of listed capacity. i too am guilty of overlooking the temp factor as i thought being my batteries are indoors that it shouldn't be too bad. wrong!!!!!!!!

    in the dead of winter where my batteries are temps can get into the 50s f, but even at 77 degrees f (25c) they show a design factor of 1.25. yes, read into that as those of us who designed, or thought we did, with these agm batteries are underdesigned. they are still good batteries, but they are over rated for their ah capacity after one does the math.

    read into it for yourself,
    http://www.sunxtender.com/pdfs/Sun_Xtender_Battery_Technical_Manual.pdf
  • samuelsamuel Solar Expert Posts: 80 ✭✭✭✭
    Re: winter battery performance
    You measured 5 of your 42 cells. That is a small sample size to assume all 42 cells are the same. Part of the problem with multiple parallel strings is that the cells begin to diverge in capacity. Also, you put too much faith in specific gravity. If all of your cells are uniformly undercharged, they will have uniform SG, but reduced capacity.

    In the last month I measured the specific gravity of each cell on every battery. Having 42 cells to measure I only recently used just 5 cells to gauge the percent charge. Every 6 months to a year I got through every cells to check up on things - though I've only bean at this for about 3 years there are no odd trends between cells. SG stays very uniform. My impression that wiring config has more to do with keeping charge/discharge consistent amount individual batteries than my current decreased capacity issue.

    I may look into a DC clamp meter in the future.
    one does need to be aware of the degradation in capacity when keeping a battery in a cold area. batteries are a chemical reaction and the cold slows that down which is also why a cold battery is said to last longer. for sunxtenders operating from 0 degrees c to 9 degrees c you will need to design for another 60% of listed capacity. i too am guilty of overlooking the temp factor as i thought being my batteries are indoors that it shouldn't be too bad. wrong!!!!!!!!

    So it might simply be the cold. Wow. I read through the PDF on SunXtender a little while ago and noticed their diagram on temperature and capacity. My Dad, who spent 125 days at the cabin last year also observed that the batteries where appearing to require recharge more frequently than summer. Being the first winter with a battery monitor to back up his observations, this would appear to be the case. I'm really surprised to see a 60%+ decrease in rated capacity. Hopefully I get some of that back in summer.

    niel - would an appropriate course of action be to record the following data:

    spec. grav (calculate SOC from), Ah consumed from full charge, and voltage for 30, 40, 50, 60, 70, 80°F in order to determine the capacity of the batteries at each temperature? I would measure 5 of the 42 cells for this.
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: winter battery performance

    you could track the soc by specific gravity or even the voltages to make sure you don't go below the dod point you designed for, or get more batteries. you can do both and be sure. a battery monitor could help determine just what you can use over a course of time armed with the specific gravity or voltage points reached at the lowered temps.
    here is a graph showing for most batteries what the capacity actually will be for some temps,
    http://www.windsun.com/pictures/Batt_temperature1.gif
  • icarusicarus Solar Expert Posts: 5,228 ✭✭✭✭
    Re: winter battery performance

    If you really think it is the cold,, a simple short term solution would be to put the batteries on a styrofoam mat, and then build a simple styro foam Baxter around them. To some extent, the batteries will self heat due to charging and discharging, keeping them net/ net significantly above ambient.

    I have one set that lives in an unheard shed, and temps can easily reach -30 and the batteries perform as expected. My guess is that as has been suggested before, you have too many parallel strings.

    Tony
  • BB.BB. Super Moderators, Administrators Posts: 29,489 admin
    Re: winter battery performance

    Here are a couple of quick charts from Rolls/Surrette that give state of charge vs S.G. levels.
    % Charged         Specific Gravity
            
    100%         1.255 – 1.275
    75%         1.215 – 1.235
    50%         1.180 – 1.200
    25%         1.155 - 1.165
    0%         1.110 - 1.130
    
    [TABLE="class: spec"]
    [TR]
    [TD][CENTER]% Charged[/CENTER]
    [/TD]
    [TD] [CENTER]Single Cell[/CENTER]
    [/TD]
    [TD] [CENTER]12V
    [/CENTER]
    [/TD]
    [TD] [CENTER]24V[/CENTER]
    [/TD]
    [TD] [CENTER]32V[/CENTER]
    [/TD]
    [TD] [CENTER]48V[/CENTER]
    [/TD]
    [TD][/TD]
    [TD][/TD]
    [/TR]
    [TR]
    [TD] [CENTER]100%[/CENTER]
    [/TD]
    [TD] [CENTER]2.10[/CENTER]
    [/TD]
    [TD] [CENTER]12.60[/CENTER]
    [/TD]
    [TD] [CENTER]  25.20
    [/CENTER]
    [/TD]
    [TD] [CENTER]  33.60
    [/CENTER]
    [/TD]
    [TD] [CENTER]  50.40
    [/CENTER]
    [/TD]
    [TD] [CENTER]OPEN CELL[/CENTER]
    [/TD]
    [/TR]
    [TR]
    [TD] [CENTER]75%[/CENTER]
    [/TD]
    [TD] [CENTER]2.01[/CENTER]
    [/TD]
    [TD] [CENTER]12.06[/CENTER]
    [/TD]
    [TD] [CENTER]24.12[/CENTER]
    [/TD]
    [TD] [CENTER]32.16[/CENTER]
    [/TD]
    [TD] [CENTER]48.24[/CENTER]
    [/TD]
    [TD] [CENTER]UNDER LOAD[/CENTER]
    [/TD]
    [/TR]
    [TR]
    [TD] [CENTER]50%[/CENTER]
    [/TD]
    [TD] [CENTER]1.93[/CENTER]
    [/TD]
    [TD] [CENTER]11.58[/CENTER]
    [/TD]
    [TD] [CENTER]23.16[/CENTER]
    [/TD]
    [TD] [CENTER]30.88[/CENTER]
    [/TD]
    [TD] [CENTER]46.32[/CENTER]
    [/TD]
    [TD] [CENTER]UNDER LOAD[/CENTER]
    [/TD]
    [/TR]
    [TR]
    [TD] [CENTER]25%[/CENTER]
    [/TD]
    [TD] [CENTER]1.84[/CENTER]
    [/TD]
    [TD] [CENTER]11.04[/CENTER]
    [/TD]
    [TD] [CENTER]22.08[/CENTER]
    [/TD]
    [TD] [CENTER]29.44[/CENTER]
    [/TD]
    [TD] [CENTER]44.16[/CENTER]
    [/TD]
    [TD] [CENTER]UNDER LOAD[/CENTER]
    [/TD]
    [/TR]
    [TR]
    [TD] [CENTER]0%[/CENTER]
    [/TD]
    [TD] [CENTER]1.75[/CENTER]
    [/TD]
    [TD] [CENTER]10.50[/CENTER]
    [/TD]
    [TD] [CENTER]21.00[/CENTER]
    [/TD]
    [TD] [CENTER]28.00[/CENTER]
    [/TD]
    [TD] [CENTER]42.00[/CENTER]
    [/TD]
    [TD] [CENTER]UNDER LOAD[/CENTER]
    [/TD]
    [/TR]
    [/TABLE]
    

    You did not say if your readings are when you thought the batteries were fully charged, or after a night of loads and you would be recharging the bank.

    Also, where those temperature corrected s.g. readings or not?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • VicVic Solar Expert Posts: 2,970 ✭✭✭✭
    Re: winter battery performance

    Couple of things,

    Personally, think that the absolute max number of battery strings in parallel is TWO. I would only use single strings, myself.

    Often when we see many, many batteries in parallel strings, they seem to have been added serially, over time. Young and old batts in parallel = BAD! This may not be the case here.

    Smaller batts that seem inexpensive, individually, become expensive in time required to tend them well. ALL of those cells to monitor & water. ALL of those CONNECTIONS to retorque and keep clean and neat. ALL of those battery case surfaces to clean. And, then, just where does one place the BTS/RTS in the bank of many many batts. And so on and on ...

    Too many bees in my head dealing with all of this. Good Luck with the pride of batteries, or is it a clutch ... Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 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.
  • mike95490mike95490 Solar Expert Posts: 8,370 ✭✭✭✭✭
    Re: winter battery performance

    14 batteries, in 2 series, 7 parallel, strings, is trouble waiting to happen. Sorry.

    What is your charging source, has it been able to provide the needed 150A for charging in the summertime ?
    Can your genset provide that in the winter ?

    It's likely your batteries may be stratified from not being vigorusly charged to keep the electrolyte stirred up.

    ---

    Update, I see from your blog, in november, you discovered 500A missing from the batteries. I'd suspect slow, chronic undercharge got you there, and you likely incured sulfation damage at that time.

    I see you only have 45A from PV, to charge from, I think you need to get a "rolling cart" type of automotive battery charger, and run that at 100A from your genset, and charge those puppies up.
    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 ,

  • PhotowhitPhotowhit Solar Expert Posts: 4,994 ✭✭✭✭
    Re: winter battery performance

    As others have stated the multiple strings would worry me, and now is when you might find problems. In the begining they work fine, but as one cell/string becomes out of balance the others are drawn down to it's level, much as multiple panels in parralel can only reach the VMP of the lowest VMP in parrallel(this doesn't hurt the panels, just limits them)

    Golf Cart batteries are deep cycle batteries, I can't think of any other lead acid batteries that would work better, I have had mine in their outside battery box down to an outside temp of -10(though I place 2" blue board/insulating board around them.

    Are you manually equalizing? or just an automated equalizing? if it's been cloudy the automated equalizing might not have worked properly, CC can be pretty stupid devices, timed 2hr of higher voltage if the battery hasn't reached full capacity is just 2 more hours of charging. During short days even a sunny day may not have enough time to do your requested bulk and equalizing charges from a low battery in an automated setting.

    Your correct to want a SG reading, with diminished capacity small loads look bigger, as they are drawing down a higher % of the battery capacity so your voltage drops will be bigger. Even in winter I might be looking to diminish loads if I saw 11.9V with a 250-400Watt load.

    Your capacity will return with the warm temps, if you don't have bad cells or strings.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • samuelsamuel Solar Expert Posts: 80 ✭✭✭✭
    Re: winter battery performance

    Thanks for insights guys!

    This is a screen capture of the readings I recorded a few days ago on the batteries. The main row to look at is the "average" row and then the "standard" row which has the temperature corrected spec. gravity.

    Attachment not found.

    Equalization was done not too long ago (1-2 weeks) from a generator that can achieve the recommended charge current. I have to wonder though, if the batteries are suffering a loss in capacity from the cold does that mean my charger set points from the generator are no longer correct (1540 Ah versus ????-whatever it is in the cold-????) Would a summer charge/equalization rate from a generator hurt batteries in the winter?

    I also stirred the batteries with the specific gravity reader to a different degree in a battery and still got the same reading. While not a perfect test I would expect flushing the electrolyte in and out of the tube several times to result in a slight difference in SG compared to a single flush in a different battery IF acid stratification where happening.

    All batteries are the same age.

    I'm also wondering if series wiring is often preferred because there is really only one way to wire in series where there are many ways to wire in parallel. When deciding to wire my batteries I chose the configuration that I did after reading the accounts of others who wired parallel in ways that did not utilize buss bars (they chose cheaper ways... it took a bit of work and a lot of copper to achieve a 7 string buss bar config).

    If I could pose a question related to wiring instead of my initial question:
    If a cell fails in a series configuration what happens?
    If a cell fails in a parallel configuration what happens?
    How would one locate/identify a bad cell?
  • mike95490mike95490 Solar Expert Posts: 8,370 ✭✭✭✭✭
    Re: winter battery performance

    I think your batteries are suffering from the mid November incidient, when you discovered 500 missing Ah. That's a 30% loss, and well into sulfation territory, for who knows how long.

    Even with the buss bars, welding cable is problematic because of the fine strands working loose from the crimped lug.

    batteries in parallel can hide all sorts of ills, each string has to be disconnected and tested individually. Series strings, is much more easily diagnosed.

    Cold temps will affect the batteries, but they show at 39F, which is cool, not too cold.

    To test, get the entire bank into absorb, then you have to break the strings apart, and test (cycle up and down 20%) one at a time. Bad cells are the ones that are "different".
    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 ,

  • VicVic Solar Expert Posts: 2,970 ✭✭✭✭
    Re: winter battery performance

    samuel,

    Just re-read this thread. Few more questions;

    What are your charge settings and EQ setting. Is the EQ temperature compensated by the charger?

    Forget, ARE YOU USING RTS/BTSes (Battery Temp Sensors on all charge sources)?

    What brand are the batteries?

    If you could take the time to do a signature line, or profile with all of your hardware, it would make it much easier for you to get good advice in a timely fashion, without posters having to extract the data using questions. You do have the web pages, but it requires some sifting for data.

    It DOES sound to me that your batteries are simply not getting very well charged. THis could be the result of string imbalances, cells failing etc. Low temps have an impact, and believe that this is the judgment that you (or any other off-gridder) would like to hear ... but it seems quite possible that this is not the major cause of your problem.
    Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 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: 29,489 admin
    Re: winter battery performance
    samuel wrote: »
    I'm also wondering if series wiring is often preferred because there is really only one way to wire in series where there are many ways to wire in parallel. When deciding to wire my batteries I chose the configuration that I did after reading the accounts of others who wired parallel in ways that did not utilize buss bars (they chose cheaper ways... it took a bit of work and a lot of copper to achieve a 7 string buss bar config).

    If I could pose a question related to wiring instead of my initial question:
    If a cell fails in a series configuration what happens?
    If a cell fails in a parallel configuration what happens?
    How would one locate/identify a bad cell?
    Parallel has lots more cells to check (if flooded) and much more wiring to go wrong.

    In general, a single series string, if one cell (or cable) fails "open"--then the bank is dead until you fix the problem.

    If a cell fails shorted, your battery bank may appear near dead (10-11 volts on a 12 volt bank) or appear low (48 volts on a 48 volt bank instead of over 50 volts). Again, fairly easy to notice and diagnose.

    With a series/parallel string of batteries... You can have an open cell or wire and the bank voltage looks OK, but at reduced capacity.

    And with a series/parallel and shorted cell, you will may have OK voltage, high self discharge, and reduced capacity.

    In either case, if you have a DC Current Clamp Meter and check cell/battery voltage with a DMM (should log results), you can fairly quickly diagnose a problem.

    The big problem (in my humble opinion) are several.

    First, you have to actively monitor the bank for proper voltage/current. Weekly or monthly at least. If there is a open/shorted cell, can very likely kill the other series batteries or even the entire bank (no charging current, over charging in other batteries in string, draw down bank to dead when you are not there, etc.).

    There are more connections to make/monitor, as well as more cells to monitor/fill.

    And there is using fuses per each serial string to prevent a short circuit in one string from drawing so much current from the other batteries that you set the shorted string/wiring/batteries to smoking/on fire. Adding all of the heavy cable+fuses/breakers adds quite a bit to the costs.

    Lastly, there is the issue of current sharing... Batteries and wiring have very low resistance, and it make any slight variation of resistance (weak cell, dirty connection, corroded cable, mismatch in cable set lengths, etc.) more prone to "steering" current to the low resistance path (we are talking about 0.010 to 0.001 ohms here).

    And, from my experience in the computer field with parallel power cables and DC power supplies, it is usually the "best connection/path" that fails first. What happens is the lowest resistance path carries 50% of the current, and the heating effect is Power=I^2 * R... so 2x current is 4x the amount of heat... So, the lowest resistance path fails first (typically overheating a connection point), then the next path, and so on.

    My own rule of thumb... Try to design a series string of batteries (use large 6 volt, 4 volt, or even 2 volt cells) to make for larger AH battery banks. And I would suggest to not go over 2 or 3 strings in parallel. The number of cells to check, connections, and variability in resistance can make it a maintenance nightmare.

    Yes, there is the advantage of being able to "cut out a bad string" until you can get a replacement battery/fix the problem... But there is the issue of having more parts equals, on average, more chances of failure too (complexity seems to breed complex failures). (I used to design N+1 and fault resistant computer systems--on the "cheap" for commercial installations--It was always a problem to choose between fault tolerence and cost+complexity. In the end, having "different" backups--such as genset or two +fuel to run long enough to get parts/repairs made seemed to be a better solution than N+1 redundancy (unless you are supplying uninterrupted power for a computer server farm).

    And, not to say there are not people with >3 parallel strings of batteries that are very happy with their bank and get long battery life--Just my two cents worth of suggestion and what I would recommend.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • samuelsamuel Solar Expert Posts: 80 ✭✭✭✭
    Re: winter battery performance
    What are your charge settings and EQ setting. Is the EQ temperature compensated by the charger?

    I updated my signature to include some useful information. The PV charger, the Xantrex C60, is never used to equalize, but does make use of a temperature correction sensor. It is set for 14.5V bulk, 13.5V float (as best I can using the rotary dials inside the unit). The MS3000 Inverter/charger, also with a battery temp sensor, may not allow me to adjust those set points...let me dig a bit... OK, those are at default and called:

    absorption voltage 14.4V
    float voltage 13.5V
    float exit voltage 12.5V
    equalize voltage 15.5V
    In general, a single series string, if one cell (or cable) fails "open"--then the bank is dead until you fix the problem.

    My Dad uses the cabin 110-130 days/year. I only get there about 10x a year (for now). At this point redundancy is preferred since I maintain the system and my dad is the user. Battery bank 2.0 will likely be a series wire or a 2-string parallel since by that time I'll be transitioning to the primary user - or at least getting close to my Dad's presence at the cabin.

    There was a comment somewhere on here about sulfation. That just doesn't fit at this point. The batteries have always been kept at or near full - especially for the days the cabin is not in use. The November incident, as I suppose it will be known, while draining the batteries to almost 30% is still within normal use - especially considering the cold temperature and its effect on sulfation.

    Winter does suck. The cabin is in the Lake Superior snow belt so overcast is the norm and sunshine is the exception this time of year. We are pretty much reliant on the generator in winter - though in summer we never start the generator. This time of year the panels are pretty much just keeping the batteries topped off while we are away and replacing what the LED security/convenience lights are using. It's still looking like one of those "wait and see" sort of issues.

    I can't seem to pinpoint the cause.
    • Temperature? - could that really account for the 60% loss of Ah at this moment?
    • Sulfation? - just doesn't fit given how the batteries have been treated.
    • Battery monitor totally screwed up? - maybe, but a big drop in capacity was noted last winter by the ol' man. Speaking of which, he has been on my case lately more or less saying, "Ha! I told you that WE JUST DON'T HAVE the capacity in winter - the same thing happened last winter".
    • Charge settings messed up by the cold? - battery temp sensors are in play, though I could always double check SG when the battery charged light is on.
    • And of course the parallel wiring - but how then can the specific gravity be so well balanced between ALL of the cells (when all were measured in November and SOC was 33%)?
  • VicVic Solar Expert Posts: 2,970 ✭✭✭✭
    Re: winter battery performance

    Hi samuel,

    Thanks a lot for the additional info on charger settings, and in the sig line. THis should help all, and reduce the number of times you need to type that data (you know this).

    Cannot find any charging specs online for your batts. Guess that they are sold by Sam's Club (?). Are the Asorb, Float and EQ numbers directly from the manufacturer, or the seller? Your batteries are COLD, so the charger voltages will be considerably higher than those set in the inverter/charger menues. That would be a good check on the performance of the charger's temp compensation. There may be a hard limit that the charger hits -- perhaps cannot accommodate batts as cold as yours. Please check the actual charge voltage at the battery terminals when charging from the inverter/charger. THere may be a spec in the inverter's manual for the range of charger voltage, or the range of temperature comp for the RTS/BTS.

    The Asorb voltage seems OK, may be a bit low. EQ voltage may be a bit low, BUT if these values are from the mfg, then they must be OK.

    Batteries that get cycled to 75% SOC, or so, need hours of Asorb time. Forgot to ask about that.
    ..
    How do you determine the Asorb time? And, how long is your Asorb stage while on the generator?

    The Clamp On DC ammeter should be a magic bullet for multiple battery strings. Also, when your charger is in the later part of Asorb, you could remove EVERY cell cap, and try to note/compare the amount of bubbling. Similar number of bubbles in this stage can help you determing how well individual cells are accepting charge. This is a bit difficult to determine exactly, but until you get the Clamp meter, it might help your knowledge.

    Good Luck, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 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.
  • Volvo FarmerVolvo Farmer Solar Expert Posts: 209 ✭✭✭✭✭
    Re: winter battery performance

    I'm not an expert by any means, However, I have recently experienced the same reduction of capacity in my own bank and would recommend the following.. if I'm wrong, I'm sure someone more experienced than I will correct me.

    I would try and let the battery bank rest for as long as possible, an hour or two if you can manage and measure every single 6V battery to the tenth of a volt and record the settings. If you have large anomalies between batteries, that might be your problem.

    I think you might also measure SG on every single cell again, even though you just did it a month ago. maybe something has changed in the last month. If you have not stirred up the electrolyte within the last day with an equalization, you might be getting skewed numbers due to stratification too.

    My gut feeling is that you have one or more batteries way out of balance and this is affecting your observed capacity. But I have been known to be wrong before.
  • VicVic Solar Expert Posts: 2,970 ✭✭✭✭
    Re: winter battery performance

    Have not looked at the manual for the X MS3000, but, the Data Sheet specs batt voltage range to 15.5 Volts. THis is fairly LOW when EQing a COLD battery... More later, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 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.
  • DerikDerik Solar Expert Posts: 82 ✭✭✭✭
    Re: winter battery performance

    My batteries are on the cool (shaded) side of the house and never get above 40-45 degrees until spring. When I check SOC with the hydrometer the electrolyte is so thick it takes an good hard squeeze to get enough of it up the tube of hydrometer to get a reading.

    I adjusted the Absorb time on my system to 5 hours and my panels pump out extra watts this time of year so the batteries are getting a good charge but my feeling is that the electrolytes are not getting mixed as they would in the summer thus my SOC readings are a bit lower.

    I have just accepted this condition since for me it's very short term and in my area temps are only low for a few months. If I ever built another system I would put the batteries inside or at a minimum on the sunny side of the house. I have 12 Trojan L-16RE so I don't think your condition is unique to your batteries.
  • DerikDerik Solar Expert Posts: 82 ✭✭✭✭
    Re: winter battery performance

    The elecrolyte is noticbly thicker at 40 degrees then it is at 70-80 degrees and takes more of a squeeze to get it up the hydrometer; at 70-80 degrees I always get too much and have to squirt some of it out at 40 I have to fill it a few times to get it high enough to read/ float.

    To keep on topic temperature cetainly makes a difference in my batteries and I see lower SOC even though my panels are making more power and my absorb time has been increased.

    As mentioned I have Trojan L-16 RE batteries
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: winter battery performance
    If the liquid electrolyte in your batteries is thickening at temps of +40F, it's a brand new chemistry to me.
    I have often wondered about these trojan batteries... they advertise their "alpha plus paste electrolyte".
    Look at: http://www.trojanbattery.com/Tech-Support/TechologyLibrary/AlphaPlusTechnology.aspx
    --vtMaps

    edit: What I wonder most about is whether normal gassing is able to mix the electrolyte and prevent stratification.
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • DerikDerik Solar Expert Posts: 82 ✭✭✭✭
    Re: winter battery performance

    It's not slime or gel it's simply thicker. The thickening of the electrolyte and thinning as it warms is the reason for the temperature correction because it changes the specfic gravity.

    From what I have read and experienced this is not unique to Trojans or "golf cart batteries"

    I am a bass fisherman and have used numerous brands of deep cycle batteries and the cold affects all of them reguardless of them being fully charged or not.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: winter battery performance
    Derik wrote: »
    It's not slime or gel it's simply thicker. <snip> From what I have read and experienced this is not unique to Trojans or "golf cart batteries"
    Does not make sense at all. Not to me anyway, and I've been working around lead-acid batteries for well over 40 years, often in temperatures close to minus 30F.
    If the liquid electrolyte in your batteries is thickening at temps of +40F, it's a brand new chemistry to me. What would it be at minus 20F, a gel? Someone please enlighten me, as it would seem I have much to learn.
    I'm with waynefromnscanada. I've never seen a charged up flooded lead acid battery with thick electrolyte. The electrolyte does get slushy (or frozen) if the battery is discharged enough.

    Derik, How sure are you that your batteries are well charged?
    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • PhotowhitPhotowhit Solar Expert Posts: 4,994 ✭✭✭✭
    Re: winter battery performance

    I hope Vtmaps is on to something, my reaction to Deriks post was the same as Waynes, as far as I have experienced. Battery temps down to 0-10 degree range, inexpensive GC batteries.

    I haven't seen a change in SG either, though I switched from GC to a traction/forklift battery this year and have seen interesting voltage readings that I am associating to stratification, voltage of 26+ 5 hours after sunset dropping to mid 25's with a small load pretty quickly, also with a minimal load and 6-7 days of cloudy conditions a reading of 24.9 though no drop with a load added...(obviously a 24V system)

    I'm not 'big' on meters, not sure what a meter would make of this things, but I will learn to understand them and don't think I'm over charging in the first case or have a half dead battery in the secound... Shortly after the purchase I bought modular home and the array and battery have not been used much. Next year I will take the modular off line and learn a bit more...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
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