Hi all. The title of this post may not be the most descriptive but it's late/early and I can't think of a better way to describe my problem.
I have (2) 12v 125Ah VMAXTANKS AGM batteries connected in series to form a 24v 125Ah battery bank. It's connected to the KID. I thought the batteries would charge up in synch but I have noticed that when the batteries are nearing the end of the absorb stage, their voltage start to diverge. That is to say, battery A will get very high in voltage (15.1v or even 15.2v) while battery B backs down in voltage (e.g. 12.9 or 13.1); then in a little while, battery A will decrease in voltage and battery B will increase in voltage. Eventually both batteries will decrease to around 13.5v individually and they will enter FLOAT. I am able to see these voltage difference because I individually measure voltage on each battery with separate Fluke DMs. (They are calibrated and measure/read the same.) If I measured the battery bank as a 24v battery, then the combined voltage of the two 12v batteries are inline with the ABSORB and FLOAT voltage. That is to say that one would only notice this divergence of individual 12v battery voltage if one were actually checking them individually. One would not notice anything wrong with the 24v series battery bank if one were solely monitoring the 24v bank itself.
Is this normal? I didn't see this behavior when I had the battery connected up in parallel. When connected in parallel, both batteries basically measured the same voltage all throughout all the charge stages. I switched between a parallel and series battery setup to see if this divergence in voltage showed up in a parallel setup. It did not, only in my series setup.
What I am most concerned about is the spike in voltage at the latter stages of absorb. Each of the batteries -- when connected in series -- are going up to 15V+. It's not for a very long time -- probably 20 to 30 minutes -- before gradually coming down in voltage. I have my ABSORB set to 28.8v (normally it's set to 29v) so as to try to reduce the HIGH voltage each of the battery reaches at the end of ABSORB.
Is this normal? If it's not normal, what might be causing this behavior? The KID? Or the batteries?
Batteries were purchased brand new (Sept 2014).
Thanks in advance for any helpful insights!
NKOTB
What this means is that the batterys are not the same. No suprise there. To be precise they are either at a different SOC or possess differnent internal resistance. Most often youd see something like this is you took two random batterys and combined them for the first time. To mitigate this you would usually precharge both cells individually, prior to connecting them. Also theres a rule of thumb around here that batterys should only be combined that are identical in terms of brand, rated capacity and whose difference in age is "insignificant".
On one hand youre right enough to watch out for this, because one battery could overcharge. If your cells are otherwise identical in both capacity and history, then one cell may be deteriating faster than the other. How old are these batterys? Of course your average multi cell battery endures this everyday. Offsetting this is the fact that lead acid batterys are fairly tolerant to overcharge. And the fact that the cells have always operated together and were tightly binned to start with.
In general terms if the bank gets properly absorbed, then the pack becomes more or less top balanced so capacity differences show up at lower SOC. In that case you should notice this less as time goes on. If it gets worse then it may be a sign that one of the cells is dieing.
Quote from: zoneblue on October 29, 2014, 02:31:47 PM
What this means is that the batterys are not the same. No suprise there. To be precise they are either at a different SOC or possess differnent internal resistance. Most often youd see something like this is you took two random batterys and combined them for the first time. To mitigate this you would usually precharge both cells individually, prior to connecting them. Also theres a rule of thumb around here that batterys should only be combined that are identical in terms of brand, rated capacity and whose difference in age is "insignificant".
On one hand youre right enough to watch out for this, because one battery could overcharge. If your cells are otherwise identical in both capacity and history, then one cell may be deteriating faster than the other. How old are these batterys? Of course your average multi cell battery endures this everyday. Offsetting this is the fact that lead acid batterys are fairly tolerant to overcharge. And the fact that the cells have always operated together and were tightly binned to start with.
In general terms if the bank gets properly absorbed, then the pack becomes more or less top balanced so capacity differences show up at lower SOC. In that case you should notice this less as time goes on. If it gets worse then it may be a sign that one of the cells is dieing.
hi
zoneblue. Thanks for replying.
These batteries were brand new when I purchased them (mid Sept 2014). They were purchased within 2 weeks of each other in Sept. They have a manufacturing date of June 2014. They are the same make/model. (Vtank Vmax 125Ah Solar batteries) ( http://www.vmaxtanks.com/servlet/the-43/vmax-tanks-AGM-battery/Detail ) It's possible (but I suspect highly unlikely) one of the batteries is prematurely dying. These are very robust AGM batteries ($250/each) and they were brand new when purchased. They came precharged at ~13.04 to 13.09v -- I measured as soon as I got them.
What I don't understand is why this out of synch voltage happens only when connected in series. It does NOT happen when connected in parallel. I've monitored the batteries as they are charged when connected in parallel and they both go up in voltage in synch as they undergo ABSORB and FLOAT. It's only when I connect these same batteries in series that they go out of 'whack' during the ABSORB stage.
There is ONLY one cable that connects the series changed batteries together. I've tried re-wiring my setup so that the one cable connects to the other two terminals but that doesn't change anything. Same thing happens.
If one of the battery were truly bad, wouldn't this out of synch phenomenon happen when the batteries are hooked up in parallel? It does not happen in parallel.
Because it doesn't happen in parallel hookup, I was thinking perhaps it might be the KID malfunctioning?
One thing that is kind of frustrating is the fact that I can't seem to 'equalize' these batteries as they are AGM and completely sealed. If I were able to equalize them, I think I could probably help this situation a bit.
Would it be very bad to try 'equalizing' these AGM batteries at a lower voltage than normal equalization voltage of 15.4v? say 15.0v or 15.1v for an hour or so? I now wish I went with the Trojans lead acid batteries so I could equalize, but the AGMs have a lot of positive qualities in their own right. When these batteries are connected in parallel, they work great. No problems. The only thing that really prevents me from changing to a 12v parallel battery bank is that my nice 1500w pure sine wave inverter is 24v and I don't want to get another 12v pure sine wave inverter. Otherwise I'd just connect the batteries in parallel and be done with it.
This out of synch voltage at end of ABSORB really caused a lot of anxiety for me. Everyday I feel like my batteries are prematurely being overcharged to death when it gets to 14.9v or 15v at the end of the ABSORB stage.
I've ordered (2) more 100w mono panels to my existing (4) 100w mono panels for a total of 600w.
I plan to order (2) more of these 125Ah batteries for a total of 250Ah (24v) series/parallel connected battery bank. But I really wanted to work out this out of synch phenomenon before I ordered the additional batteries.
I understand it's not ideal to have batteries that are not matched up perfectly/exactly but I think a two month difference should be acceptable given that these batteries are designed for 8-10 years of lifetime use.
Dc circuits 101:
ANY 2 batteries (or other circuit components) in parallel will always read the same voltage when connected together in parallel .
The nature of parallel connections is that they all see the same voltage. Period.
So that begs the question how do you know they only get out of whack in series?
In a perfect world matching batteries should be very close on voltage in series. In the real world connection imperfections could easily skew readings, especially under charge or load.
Just from here.
Tom
Quote from: New KID On The Block on October 29, 2014, 05:47:55 PM
Because it doesn't happen in parallel hookup, I was thinking perhaps it might be the KID malfunctioning?
...
This out of synch voltage at end of ABSORB really caused a lot of anxiety for me. Everyday I feel like my batteries are prematurely being overcharged to death when it gets to 14.9v or 15v at the end of the ABSORB stage.
This is definitely an issue with battery cell internal resistance.
The KID cannot see each battery separately but just one nominal 24volt bank so it cannot adjust charging to account for the SOC of individual cells in the bank. Therefore its very unlikely the KID is malfunctioning.
There is probably nothing you can do about this without changing to different batteries.
In parallel then each battery is probably charging at different rate but the parallel connection to the controller means voltage will appear identical on both batteries. Hence your comparison will be meaningless.
I would suggest ignoring this and if battery fails within warranty period then replace it (them)
dgd
Quote from: TomW on October 29, 2014, 06:04:57 PM
Dc circuits 101:
ANY 2 batteries (or other circuit components) in parallel will always read the same voltage when connected together in parallel .
The nature of parallel connections is that they all see the same voltage. Period.
So that begs the question how do you know they only get out of whack in series?
In a perfect world matching batteries should be very close on voltage in series. In the real world connection imperfections could easily skew readings, especially under charge or load.
Just from here.
Tom
Tom, thanks for your comments.
I fully admit I'm a neophyte when it comes to electricity. I don't have a EE degree. I studied Philosophy and Economics. :-)
I measure/monitor each battery individually -- when connected in series or parallel -- with separate Fluke DMs. I was under the impression that is how I could tell if each battery was charging at appropriate voltages. I stand corrected if my impression was incorrect.
Are you saying that even when each battery is reading, for example 13.15v, during charge that they may actually be charging at a different voltage? That doesn't sound right to me. I thought a voltage reading at the battery terminals would reveal the actual, instantaneous charging voltage to the battery. That is why I assume the batteries were properly charging at the same voltage when in parallel because I can see the voltage from each battery from separate Fluke meters.
Quote from: dgd on October 29, 2014, 06:08:26 PM
This is definitely an issue with battery cell internal resistance.
The KID cannot see each battery separately but just one nominal 24volt bank so it cannot adjust charging to account for the SOC of individual cells in the bank. Therefore its very unlikely the KID is malfunctioning.
There is probably nothing you can do about this without changing to different batteries.
In parallel then each battery is probably charging at different rate but the parallel connection to the controller means voltage will appear identical on both batteries. Hence your comparison will be meaningless.
I would suggest ignoring this and if battery fails within warranty period then replace it (them)
dgd
Thanks
dgd for your comments.
I monitor each battery in parallel with separate DMMs. They show very similar voltage. I'm confused about this issue. Am I to understand that even though a battery shows a certain voltage when connected in parallel that they actually may be charging at a different voltage than what my DMMs read? That just doesn't seem right given my understanding -- albeit, I am a neophyte to all this stuff.
Regarding your last sentence of ignoring this, I am starting to accept that I may have to. :'(
Quote from: New KID On The Block on October 29, 2014, 06:58:36 PM
I monitor each battery in parallel with separate DMMs. They show very similar voltage. I'm confused about this issue. Am I to understand that even though a battery shows a certain voltage when connected in parallel that they actually may be charging at a different voltage than what mhttp://midniteforum.com/index.php?action=post;quote=20202;topic=2153.0;last_msg=20202#y DMMs read? That just doesn't seem right given my understanding -- albeit, I am a neophyte to all this stuff.
The voltage over each battery when parallel connected will be identical, its the charging current to each battery that will be different, the lower resistance cells taking the higher currents.
Keep the 24volt configuration. When you connect the next two batteries in series to each other then in parallel to the exiting series pair remember to take +ve from one pair and -ve from other pair -
see the link Vic posted previously:
http://www.smartguage.co.uk/batt_con.html (http://www.smartgauge.co.uk/batt_con.html)
dgd
Quote from: dgd on October 29, 2014, 07:17:56 PM
Quote from: New KID On The Block on October 29, 2014, 06:58:36 PM
I monitor each battery in parallel with separate DMMs. They show very similar voltage. I'm confused about this issue. Am I to understand that even though a battery shows a certain voltage when connected in parallel that they actually may be charging at a different voltage than what mhttp://midniteforum.com/index.php?action=post;quote=20202;topic=2153.0;last_msg=20202#y DMMs read? That just doesn't seem right given my understanding -- albeit, I am a neophyte to all this stuff.
The voltage over each battery when parallel connected will be identical, its the charging current to each battery that will be different, the lower resistance cells taking the higher currents.
Keep the 24volt configuration. When you connect the next two batteries in series to each other then in parallel to the exiting series pair remember to take +ve from one pair and -ve from other pair -
see the link Vic posted previously:
http://www.smartguage.co.uk/batt_con.html (http://www.smartgauge.co.uk/batt_con.html)
dgd
THANKS
dgd! Current: that's what I was missing! You're right. Obviously it's not only voltage that matters but the current as well when charging. I totally forgot about current into each battery! ???
Yes, I am aware of smartguage's diagrams. I will be sure to follow their suggestion.
So in sum, this "phenomenon" of seeing different voltage in series connected batteries is actually normal. It may be the case that my batteries are getting out of whack to a greater degree than other batteries connected in series -- due to internal resistance of each battery -- but any batteries connected in series would show some divergence in voltage as they accept different charging current. Is that correct? I think I'm seeing the bigger picture now.
You can try manual balance on them, by charging the lower voltage battery a bit with a standard charger, say 5 or 10 AH at a time. Since AGM are sealed, it's hard to equalize them safely. So charging the lower battery a bit on it's own should help even them out.
Quote from: mike90045 on October 29, 2014, 09:42:09 PM
You can try manual balance on them, by charging the lower voltage battery a bit with a standard charger, say 5 or 10 AH at a time. Since AGM are sealed, it's hard to equalize them safely. So charging the lower battery a bit on it's own should help even them out.
Thanks
mike90045. I have been doing just that to the one battery that is lower by ~0.05 volts.
I will admit that I may have initially made the situation worse -- when I first noticed the batteries going out of whack -- by connecting a 12v DC fan directly to the 12v battery I saw going above 15v during ABSORB. I kept the fan running on that battery to lower the charging voltage. It did lower the charging voltage but it probably added to the problem of the two batteries now being out of balance.
I figured that this would be resolved (balancing out) whenever the batteries are fully charged and floats. But that has not been the case.
Quote from: New KID On The Block on October 29, 2014, 08:15:46 PM
So in sum, this "phenomenon" of seeing different voltage in series connected batteries is actually normal. It may be the case that my batteries are getting out of whack to a greater degree than other batteries connected in series -- due to internal resistance of each battery -- but any batteries connected in series would show some divergence in voltage as they accept different charging current. Is that correct? I think I'm seeing the bigger picture now.
Not correct. In series they have the same current.
The problem you are having is probably a bad cell in one battery. Realize that you have 12 batteries in series.... but because 6 batteries are in one block (12 volts) with only one set of terminals, you can't see what is happening at the level of one battery cell.
If you had a 24 volt system made up of individual 2 volt batteries, you would find that one of the 12 cells was the outlier.
One of the dirty little secrets of battery charging is that the manufacturer's recommend charging protocols are designed to routinely overcharge almost all their cells... explanation:
No two cells are ever exactly the same... and about half of them are below average :(
Suppose a manufacturer produces cells and finds that 99.90% of them will fully charge up at 2.4 VPC (volts per cell -- that's 14.4 volts for a 12 volt battery). If they recommend 2.4 VPC and sell only 2 volt batteries, they will have warranty issues with 0.10% of their batteries.
Now, what if they sell 12 volt batteries? Their warranty claims will be almost 0.60% (six times as many chances to get one of those outlier cells in the battery).
The battery manufacturer also knows that if they recommend 2.45 VPC (14.7 volts on a 12 volt battery), then 99.99% of their cells will fully charge up. That means their warranty claims on a 12 volt battery will be 0.06% (rather than 0.6% with 2.4 VPC).
Naturally, battery manufacturers recommend the higher voltage... and that's why the vast majority of battery cells are routinely overcharged. Fortunately, lead acid batteries are fairly tolerant of overcharging (unlike some lithium batteries which need BMS (battery management systems) to prevent overcharging the first cells that reach full charge.
In your circumstance, I suspect you have an outlier cell in one battery.... possibly far enough out that it should be a warranty issue.
--vtMaps
Also be aware that a new battery takes a while for the plates to 'form'. I would put a couple dozen cycles through them and review the situation. If you find the high battery going over 15 or 16V then start to worry. Thats about where thermal runaway will commence, but even that will take hours. Thermal runaway is more acute problem with AGMs and something to watch out for. And certainly if the battery gets hot, (feel all around it), then turn it off. AGMs dont get hot in normal use.
vtmaps and zoneblue, thanks for your input.
lol. So in parallel they have the same voltage but potentially different current, whereas in series they have the same current but potentially different voltage. haha. Confusing, but I'm starting to get it. Thanks vtmaps.
I think once I get the additional two batteries of the same make/model, it will clarify a few things. I'll test out all four batteries and see which one behaves the most differently.
BTW, if it is the case that one of the battery has a bad cell and the has higher internal resistance, is there a way for me to test the internal resistance of each battery?
If I were to hook up each battery individually to the solar or AC charger to charge, would I be able to detect a bad cell?
Thanks all for your input/comments/feedback. It's much appreciated.
Where I work we have AGM batteries in the fire alarm system that floats them pretty much all the time. They are 24v with two 12v in series. One of the systems gets new batteries every year because the annual inspector says capacity is bad. After only one year . I can never figure that out , the charger always seems to be working but it just floats them all the time .
I would never get AGM batteries for my system just because of the problems you are experiencing. At least with flooded lead acid you can take the specific gravity of each cell and figure out what is going on and check for imbalances.
At work the testers use a capacity tester on the AGM . I don't really understand how they work or if they are truly accurate . Not sure they figure out the internal resistance of the battery or if they do some kind of load test . Usually no AGM battery ever shows their rated capacity even when new.
Quote from: New KID On The Block on October 30, 2014, 03:53:49 PM
BTW, if it is the case that one of the battery has a bad cell and the has higher internal resistance, is there a way for me to test the internal resistance of each battery?
If I were to hook up each battery individually to the solar or AC charger to charge, would I be able to detect a bad cell?
Unfortunately you cannot get to the individual cells to check their voltages. You can do capacity tests and impedance tests that can tell you something.
You ask about detecting a 'bad cell'. As I mentioned earlier, cells are not all the same... they can vary in their capacity, charging voltage, charging time, lifespans, etc.
It is normal that you should overcharge most cells in order to fully charge the weakest member of the bank. The question is do you have a truly bad cell (warranty issue) or do you just have a weak cell. Sometimes a cell is clearly defective (either open or shorted), but there is also a range of weak cells, some of which may be so weak as to be a warranty issue.
If you can charge the batteries individually, that is best... for two reasons:
1) since you have to overcharge some cells in order to charge the others, you might as well limit the stress to one battery at a time.... one of the batteries probably does not need to be stressed as hard as the other.
2) You can compare the the two battery's electrical behavior, both under charge and under load.
Regarding that last point:
It would be good if you had a shunt based ammeter... can you get a whizbangjr and shunt? If so, you can watch the current into each battery as it charges. Normally, during absorb the current tapers off to an 'end amps' value. It would be good to compare the end amps of the two batteries.
Another thing you can do is watch how the batteries perform under load. Get them as charged up as you can (long, long absorb). Then put a constant load on them (maybe run 200 watts of incandescent bulbs). See how the voltage holds up for an hour or two.
Another load test that can give you some useful information is to watch how the voltage sags under a larger load. Let the battery rest for a couple of hours, then with the voltmeter on the battery, connect a large load and immediately record the voltage. If you know the voltage drop and current, you can estimate the battery's internal resistance. example: you know that your large load draws 40 amps DC from the battery. You observe that the voltage drops from 12.50 volts resting to 12.38 volts under the large load.
0.12 voltage drop ÷ 40 amps = 0.0033 ohms
If you can do this sort of testing on both batteries, you will have something concrete to discuss with us on the forum, and with the battery manufacturer if you want to submit a warranty claim.
--vtMaps
Quote from: vtmaps on November 02, 2014, 01:14:04 AM
Quote from: New KID On The Block on October 30, 2014, 03:53:49 PM
BTW, if it is the case that one of the battery has a bad cell and the has higher internal resistance, is there a way for me to test the internal resistance of each battery?
If I were to hook up each battery individually to the solar or AC charger to charge, would I be able to detect a bad cell?
Unfortunately you cannot get to the individual cells to check their voltages. You can do capacity tests and impedance tests that can tell you something.
You ask about detecting a 'bad cell'. As I mentioned earlier, cells are not all the same... they can vary in their capacity, charging voltage, charging time, lifespans, etc.
It is normal that you should overcharge most cells in order to fully charge the weakest member of the bank. The question is do you have a truly bad cell (warranty issue) or do you just have a weak cell. Sometimes a cell is clearly defective (either open or shorted), but there is also a range of weak cells, some of which may be so weak as to be a warranty issue.
If you can charge the batteries individually, that is best... for two reasons:
1) since you have to overcharge some cells in order to charge the others, you might as well limit the stress to one battery at a time.... one of the batteries probably does not need to be stressed as hard as the other.
2) You can compare the the two battery's electrical behavior, both under charge and under load.
Regarding that last point:
It would be good if you had a shunt based ammeter... can you get a whizbangjr and shunt? If so, you can watch the current into each battery as it charges. Normally, during absorb the current tapers off to an 'end amps' value. It would be good to compare the end amps of the two batteries.
Another thing you can do is watch how the batteries perform under load. Get them as charged up as you can (long, long absorb). Then put a constant load on them (maybe run 200 watts of incandescent bulbs). See how the voltage holds up for an hour or two.
Another load test that can give you some useful information is to watch how the voltage sags under a larger load. Let the battery rest for a couple of hours, then with the voltmeter on the battery, connect a large load and immediately record the voltage. If you know the voltage drop and current, you can estimate the battery's internal resistance. example: you know that your large load draws 40 amps DC from the battery. You observe that the voltage drops from 12.50 volts resting to 12.38 volts under the large load.
0.12 voltage drop ÷ 40 amps = 0.0033 ohms
If you can do this sort of testing on both batteries, you will have something concrete to discuss with us on the forum, and with the battery manufacturer if you want to submit a warranty claim.
--vtMaps
vtMaps, thanks! Some great info there I'm sure -- not all of which I fully understand but I'll slowly try to digest it all.
I
do have a Whiz Bang Jr with shunt. I purchased it with the KID. Your suggestion above is to monitor each battery individually with the WBJ, correct? I already monitor the battery bank with the WBJ. Then I monitor each battery with individual Fluke meters.
I will try out some of your load testing suggestions. The only minor problem is that each passing day the sun is giving me less and less total Ahr as winter is coming. I have less leeway to test and play around but I'll try to do some testing.
Quote from: ClassicCrazy on November 01, 2014, 09:34:48 PM
I would never get AGM batteries for my system just because of the problems you are experiencing. At least with flooded lead acid you can take the specific gravity of each cell and figure out what is going on and check for imbalances.
At work the testers use a capacity tester on the AGM . I don't really understand how they work or if they are truly accurate . Not sure they figure out the internal resistance of the battery or if they do some kind of load test . Usually no AGM battery ever shows their rated capacity even when new. [/size][/font]
ClassicCrazy, yes, I agree somewhat with what you're saying. I now have my own beef with AGM batteries in general but there are pros with AGM batteries. While I like the ability to equalize flood batteries, my batteries are placed/stored in an environment that would NOT be suitable for much gas to be released.
At any rate, I don't want to this thread to get into a wet vs dry battery war. There are pros and cons to each type of battery. Thanks for your comments.
I have added two new 100w panels for a total of 600 potential watts. :D
What I find interesting is that I'm able to ABSORB and FLOAT much earlier in the day. ;D
What I dislike is that I have 6 of these panels in series and it's getting knocked out very early into the afternoon @ ~ 3:05 pm. There is a tree to the side of the house and its shade is hitting the panels starting as early as 3 pm. :'(
during the summer, it didn't hit until much, much later, but now it's hitting it around 3pm, especially with the two new added panels.
I may be forced to separate the 6 panels into two strings of 3 parallel. :(
Quote from: New KID On The Block on November 05, 2014, 09:26:57 PM
I may be forced to separate the 6 panels into two strings of 3 parallel. :(
Huh? That doesn't make any sense. If you have two strings, each string would be three panels in series. The two strings would be parallel to each other.
If you have three strings, then each string would be two panels in series, and the three strings would be parallel to each other.
Putting all six panels in series is the worst of your options, unless the panels are very far from the controller. The controller will be more efficient if the string voltage is lower.
I believe (correct me if I'm wrong) that your panels are "12 volt panels" with a Vmp about 17 or 18 volts. If so, your optimum string length for a 24 volt system is three panels in series (two strings).
It will probably work OK with a string length of two panels, but there is not much headroom for the controller to work with. If your batteries need higher voltage absorb or EQ, and the panels are hot, two panels in series may not have high enough voltage.
When you reconfigure your panels, try to make sure that all the panels that get shading are in the same string.
--vtMaps
Quote from: vtmaps on November 05, 2014, 10:51:12 PM
Quote from: New KID On The Block on November 05, 2014, 09:26:57 PM
I may be forced to separate the 6 panels into two strings of 3 parallel. :(
Huh? That doesn't make any sense. If you have two strings, each string would be three panels in series. The two strings would be parallel to each other.
If you have three strings, then each string would be two panels in series, and the three strings would be parallel to each other.
Putting all six panels in series is the worst of your options, unless the panels are very far from the controller. The controller will be more efficient if the string voltage is lower.
I believe (correct me if I'm wrong) that your panels are "12 volt panels" with a Vmp about 17 or 18 volts. If so, your optimum string length for a 24 volt system is three panels in series (two strings).
It will probably work OK with a string length of two panels, but there is not much headroom for the controller to work with. If your batteries need higher voltage absorb or EQ, and the panels are hot, two panels in series may not have high enough voltage.
When you reconfigure your panels, try to make sure that all the panels that get shading are in the same string.
--vtMaps
Hi
vtMaps. Still being new to this, my terminology/phrasing my not be correct. My next configuration will be 2 strings in parallel, each consisting of 3 x 100w panels in series. However you want to phrase it, that's my next config if I change my current setup.
I understand about the theoretical efficiency loss with 6 panel in one string. I want to see some empirical numbers of my current 6 panel in one string before potentially changing my config to compare the results of the two configurations.
All 6 of my panels are Renogy RNG-100D. They are advertised to work optimally for 12v systems.
Vmp: 18.9V
Imp: 5.29A
Voc: 22.5V
Isc: 5.75A
RE: Grouping 3 panels into shade region. Yes, I definitely thought of that. Will be doing just that if/when I reconfigure. Thanks!
Next thing up is probably ordering two additional 125Ah batteries. I'm still conflicted, trying to figure out the exact problem with my current batteries. If I get two more batteries, I'll have more data points to see which battery is behaving anomalously. But I'm concerned about buying two additional batteries before having my current, possibly bad, battery replaced under warranty.
Quote from: New KID On The Block on November 06, 2014, 12:23:08 AM
I understand about the theoretical efficiency loss with 6 panel in one string.
to be clear, if you have a shading problem, you have trouble and if you stick with a single string of 6, you risk the entire strings output when the shade comes into play, depending on the amount of shade on how many (?) panels...
you need a layout that allows for thee 'normal max output' from some of the strings ie 2p X 3sor possibly 3p x 2s as Vtmaps has said. Your choice as you are the one that can evaluate the amount of shade and number of panels affected.
FYI the shade of a single branch on a leafless Aspen can (did) cut the production of panels by > 50% at mid day for me... that tree did not last long...
hth
Quote from: Westbranch on November 06, 2014, 12:54:55 AM
Quote from: New KID On The Block on November 06, 2014, 12:23:08 AM
I understand about the theoretical efficiency loss with 6 panel in one string.
to be clear, if you have a shading problem, you have trouble and if you stick with a single string of 6, you risk the entire strings output when the shade comes into play, depending on the amount of shade on how many (?) panels...
you need a layout that allows for thee 'normal max output' from some of the strings ie 2p X 3sor possibly 3p x 2s as Vtmaps has said. Your choice as you are the one that can evaluate the amount of shade and number of panels affected.
FYI the shade of a single branch on a leafless Aspen can (did) cut the production of panels by > 50% at mid day for me... that tree did not last long...
hth
I did not like what I had to do today, but I did it. I cut off a lot of branches from the lemon tree next to the house. :'( I am a big time tree lover/hugger. I do not like cutting down trees. I try to comfort myself by saying it was just some minor trimming but honestly it was some major branch cutting. It was quite a bit of work but I got all the branches that was immediately affecting my panels.
That gave me about another hour of 100% sun in the later afternoon -- albeit, that 100% sun is at quite an angle.
I also just contacted via email the seller of my batteries. I am still going to purchase two more 125Ah batteries from them but told them I wanted to work on getting one of my current two batteries replaced at the same time. The email was quite long. We'll see how they respond. I guess it's a good thing that I get to test out their warranty process before forking over another $500 for two more batteries.
I'm a forester.
One of the problems with shading trees is that they grow each year... this might be an ongoing process, look into how to prune that tree to keep it in check... for at least a few years.
I use a bit more draconian method, a chain saw, end of problem.
Quote from: zoneblue on October 30, 2014, 03:02:15 PM
Also be aware that a new battery takes a while for the plates to 'form'. I would put a couple dozen cycles through them and review the situation. If you find the high battery going over 15 or 16V then start to worry. Thats about where thermal runaway will commence, but even that will take hours. Thermal runaway is more acute problem with AGMs and something to watch out for. And certainly if the battery gets hot, (feel all around it), then turn it off. AGMs dont get hot in normal use.
Hi
zoneblue, it's been over a dozen, closer to two dozen, cycles. It's still the same. :-\ At the end of absorb, I see one battery at 13.8v and the other one at 14.9v. I have my ABSORB set at 28.8v. When I've set absorb to 29v, the bad battery will be closer to 15.1v at the end -- that is with a load; if there's no load at all, it'll get above 15.1v. I've seen it go to 15.2v at which point I added a HIGH load to bring down the voltage. Now a days I set ABSORB at 28.8v and constantly keep at least a light load so the bad battery doesn't go above 14.9v.
Thermal runaway is of course worse than the battery boiling/gasing itself. Even at 14.9v, I can start to hear bubbling sound inside the battery. At 15.1v, it's definitely bubbling inside.
I purchased a infrared thermometer. I do monitor the temperature of the batteries, among other equipment of this entire solar setup. As you allude to, the batteries are not generally hot at all, even when it's bubbling inside. I've never seen the batteries above 80F. Most of the time they're exactly room temperature. I also have a Midnite Solar temperature probe connected to my KID that monitors the batteries. (Hmm.. wonder if Midnite can program the KID to fire off a blinking LED if the temperature probe detects temps above a certain threshold. That would be a helpful.) The temp of the batteries doesn't deviate too much from 25C.
Quote from: Westbranch on November 06, 2014, 11:56:12 PM
I'm a forester.
One of the problems with shading trees is that they grow each year... this might be an ongoing process, look into how to prune that tree to keep it in check... for at least a few years.
I use a bit more draconian method, a chain saw, end of problem.
A forester for the US Forest Service I hope. :-\
I'm headed off to camp @ Stanislaus National Forest tomorrow through Sunday. Won't be able to tinker with/monitor my setup for the weekend.
The shade has previously been great at shading the sun from the house so it gets less hot during summers. Now it's going to be more sun hitting the roof during summer. :( But I guess it can't be helped. I need sun for the panels.
It's kind of sad. I live in CA. We desperately need rain. We're in EXTREME drought conditions -- probably worse than what the Aussies were enduring several years back -- but I hate the rain now because any clouds, let alone rain, drastically reduces the output of my panels. I was monitoring the KID one day when it did rain all day here and I was probably getting 5% --if that-- of the max output of my panels. :'(
Quote from: New KID On The Block on November 07, 2014, 12:28:37 AM
A forester for the US Forest Service I hope. :-\
Nope, I am in BC Canada
One may not like to do it but it is a choice of what takes precedence, shade or solar power... chioces choices...
Quote from: vtmaps on November 02, 2014, 01:14:04 AM
Another thing you can do is watch how the batteries perform under load. Get them as charged up as you can (long, long absorb). Then put a constant load on them (maybe run 200 watts of incandescent bulbs). See how the voltage holds up for an hour or two.
If you can do this sort of testing on both batteries, you will have something concrete to discuss with us on the forum, and with the battery manufacturer if you want to submit a warranty claim.
--vtMaps
Hello vtMaps.
I am working with the seller of the batteries -- who in turn is supposedly working with the manufacturer -- on a warranty replacement. They're having me do some testing on my end.
Last Friday late afternoon, after finally going into FLOAT, I disconnected the KID from my batteries and let the batteries rest for 3 hours -- as instructed by manufacturer to see what the voltage would be after resting.
---------------------------------------
At 4:41 pm PST Friday I disconnected.
At 7:43 pm I went and checked voltage for the two batteries. They both read 13.04V.
I then proceeded to test using my desktop computer setup connected to the inverter and the load was around 150 - 200 watts. I subsequently checked the voltage thereafter each hour for the next 5 hours.
At 8:44 pm, the two batteries showed A) 12.64v and B) 12.61v.
At 9:44 pm , the two batteries showed A) 12.54v and B) 12.51v.
At 10:44 pm, the two batteries showed A) 12.43v and B) 12.39v.
At 12:33 am, the two batteries showed A) 12.21v and B) 12.18v.
At 1:44 am, the two batteries showed A) 12.07v and B) 12.03v.
----------------------------------------
That is part of what I sent them. They were suppose to call me today but did not. I'll see if they call me tomorrow.
On another related matter, I have reconfigured my PV panels. Just now, as the sun was about to set, I split my 6 x 100w single series connected panels string into TWO parallel strings, each consisting of 3 x 100w series connected panels.
That should be most efficient into the KID for my 24v battery bank, yes?
Tomorrow I'll see how this new config performs. The best I achieved out of the previous config was about 435W out of a total theoretical 600W.
Also, with further testing, I've been able to determine that if I set ABSORB to 28.5V, then the highest voltage the 'bad' battery will reach is about ~14.75v. So I've decided to leave ABSORB to 28.5V so as not to 'equalize' my AGM batteries daily. But in doing that, the 'good' battery is charging at only 13.7v or 13.8v during ABSORB. :-(
The interesting thing is -- as can be seen in my results above -- even with lower voltage during ABSORB, the 'good' battery holds voltage better than the 'bad' battery under load.
Quote from: New KID On The Block on November 10, 2014, 08:15:52 PM
I am working with the seller of the batteries -- who in turn is supposedly working with the manufacturer -- on a warranty replacement. They're having me do some testing on my end.
At 8:44 pm, the two batteries showed A) 12.64v and B) 12.61v.
At 9:44 pm , the two batteries showed A) 12.54v and B) 12.51v.
At 10:44 pm, the two batteries showed A) 12.43v and B) 12.39v.
At 12:33 am, the two batteries showed A) 12.21v and B) 12.18v.
At 1:44 am, the two batteries showed A) 12.07v and B) 12.03v.
That is part of what I sent them. They were suppose to call me today but did not. I'll see if they call me tomorrow.....
The interesting thing is -- as can be seen in my results above -- even with lower voltage during ABSORB, the 'good' battery holds voltage better than the 'bad' battery under load.
Two batteries within 0.3volt of each other after several hours loading :o
I think you will be darn lucky if the battery supplier entertains a warranty replacement as both these batteries look good to me.
If you are expecting dead on identical performance from two same model batteries from the same manufacturer (and even from the same manufactured batch) then I fear you are always going to be disappointed.
I recommend you forget this issue and only make a warranty claim if one of the batteries fails
dgd
Quote from: dgd on November 10, 2014, 09:02:03 PM
Quote from: New KID On The Block on November 10, 2014, 08:15:52 PM
I am working with the seller of the batteries -- who in turn is supposedly working with the manufacturer -- on a warranty replacement. They're having me do some testing on my end.
At 8:44 pm, the two batteries showed A) 12.64v and B) 12.61v.
At 9:44 pm , the two batteries showed A) 12.54v and B) 12.51v.
At 10:44 pm, the two batteries showed A) 12.43v and B) 12.39v.
At 12:33 am, the two batteries showed A) 12.21v and B) 12.18v.
At 1:44 am, the two batteries showed A) 12.07v and B) 12.03v.
That is part of what I sent them. They were suppose to call me today but did not. I'll see if they call me tomorrow.....
The interesting thing is -- as can be seen in my results above -- even with lower voltage during ABSORB, the 'good' battery holds voltage better than the 'bad' battery under load.
Two batteries within 0.3volt of each other after several hours loading :o
I think you will be darn lucky if the battery supplier entertains a warranty replacement as both these batteries look good to me.
If you are expecting dead on identical performance from two same model batteries from the same manufacturer (and even from the same manufactured batch) then I fear you are always going to be disappointed.
I recommend you forget this issue and only make a warranty claim if one of the batteries fails
dgd
dgd, thanks for your input. The 0.03v difference after several hour loading isn't what worries me. It's the great divergence in voltage between the two batteries at the end of ABSORB. Neither batteries are absorbing properly. One is absorbing at 13.7v and the other absorbs between 14.7v to 15.2v, depending on what I set ABSORB to -- i.e. 28.5v to 29v. But I do appreciate the input about 0.03v not being a big deal.
On a more positive note, changing PV panel config to (2) parallel strings appears to have improved efficiency by quite a bit.
Previously, I've observed 435w as about the highest I've been able to obtain. Today, I saw the KID go as high as 536w at one point. I was able to snap a photo at 532w to document the milestone. ;D This is awesome! 536w definitely makes me smile. It does have to be noted that today's weather is cooler (lots of intermittent clouds) and a bit breezy so I think that is definitely helping to cool down the panels to produce at optimal output as well. :)
Just an update...
It took a while working with the seller but finally today the manager gave the approval to send me 3 new 125Ah batteries for the price of 2. That part is not surprising as that's what I proposed. What did surprise me is that they're allowing me to just keep the 'bad' battery instead of shipping it back to them. Wow! That was unexpected.
But before I get too happy, I need to wait and see how the 3 new batteries perform. If they perform properly, connected in series-parallel into my battery bank, I'll be extremely happy with their customer service and warranty servicing.
So let's wait and see what happens.