Different current in 2 strings

jcheiljcheil Solar Expert Posts: 722 ✭✭✭
Ok, so I have had my new system up and running (well) for 3 weeks now. All looks good.

Since I have 2 strings of batteries, I decided to wire it in a way so that I would be able to have an amp meter on each "string" to see if there would ever be any imbalance issues. I also wired it with all of the cables being the exact same length/size, etc.

So the meters finally came in yesterday and I hooked them up temporarily (see below) and noticed a REALLY big difference in the current in one string vs the other. I verified that the meters are working properly as the values they show match what my DC clamp meter shows. I also got a mv reading across the shunt and did the math and it all jives.

I double checked all the connections and 2 of them (at the battery post) on the bank that is showing the low current were loose (not sure how I missed them I swear I torqued them twice when I installed them). So I thought that would fix it, but it didn't. The pix below are from a few mins ago.

Could the fact that there was a loose connection in one bank somehow have effected this in a way that perhaps THAT bank was never really being "used" and is therefore more 'charged" than the other (the one showing high current)? If so, I would expect the condition to go away "tomorrow" after a cycle?

I tried to take hi-res pix as attached so you could see the detail of the connections, etc.
I am going to get some SG readings right now but was wondering if anyone had any thoughts. Thanks!
Attachment not found.Attachment not found.
Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Different current in 2 strings

    Loose connect = higher resistance = lower current.

    It may not go away in one cycle, but it should improve if this hasn't been going on for a long time.
  • jcheiljcheil Solar Expert Posts: 722 ✭✭✭
    Re: Different current in 2 strings
    Loose connect = higher resistance = lower current.

    It may not go away in one cycle, but it should improve if this hasn't been going on for a long time.

    I have a feeling it may have been going on since the install (which was just under 3 weeks ago).
    Like I said, I could have sworn I double-checked all the connections. lesson learned - THREE TIMES.

    And I just checked SG on a few cells from each bank and yup, the left bank (good connections) is way down and the right bank (lose connection) is way up.
    So that was confusing the controller and must have been dropping it out of absorb thinking the "whole" bank was full.

    I know master yoda, one of the negatives of more than a single string :) But at least I only have 2 and I think these meters will help me identify if something like this happens again.

    Since the Mate3/FNDC shows 100% and it just dropped out of absorb into float and the SG's are still low on the other bank do you recommend an EQ at this point?
    If I "had" to I technically could disconnect the "good" bank (as you see from my wiring, I overkilled it and made it easy to work on). But I would rather not.
    Thoughts?

    And thanks again, you guys really rock!
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Different current in 2 strings

    How far apart are the SG's between the two strings?
    If it's greater than 0.015 then disconnect the high string and charge the low one to bring it up. When you get them close to equal, reconnect and charge up as normal.

    If left for a long time it becomes a bit of a race to see which bank dies first: the one suffering from persistent self-discharge or the one being drawn down too much because it's having to do all the work.
  • jcheiljcheil Solar Expert Posts: 722 ✭✭✭
    Re: Different current in 2 strings
    How far apart are the SG's between the two strings?
    If it's greater than 0.015 then disconnect the high string and charge the low one to bring it up. When you get them close to equal, reconnect and charge up as normal.

    Quite a bit :( 1.210's on the one bank and 1.260's on the other. Ugh...can't believe I missed that loose connection.

    I think I will take your advice and EQ it now but perhaps leave both connected at first, and when the "good" bank gets to the 1.280 I'll disconnect the good bank and then let the "bad" bank catch up to 1.28, then reconnect the good bank and let it ride for a while.
    Hope that sounds like a good plan. My only concern is my max charge rate. I don't want to cook the "single" bank. or will that not hurt for this "short" charge?
    Hopefully since this has only been (at most) 3 weeks, it's not permanent...time will tell I guess.
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Different current in 2 strings

    You've got Outback equipment; turn the current down and fully charge the low bank. EQ if it won't come up all the way or comes up unevenly.
  • jcheiljcheil Solar Expert Posts: 722 ✭✭✭
    Re: Different current in 2 strings
    You've got Outback equipment; turn the current down and fully charge the low bank. EQ if it won't come up all the way or comes up unevenly.

    10-4. Thanks, I just set the global charge limit to 55amps (for when the single bank is connected). Will Put it back up to 110 when both get connected later.
    (That is a good number correct?)
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Different current in 2 strings
    jcheil wrote: »
    10-4. Thanks, I just set the global charge limit to 55amps (for when the single bank is connected). Will Put it back up to 110 when both get connected later.
    (That is a good number correct?)

    Is your signature correct? You're running 740 Amp hours of battery? If so 110 Amps would be just short of 15% and that would certainly be the maximum.

    For half that bank, 370 Amp hours, I'd advise turning it down to 37 Amps and letting it Absorb for a long time as you're trying to recover lost capacity. Longer time at a lower rate works better for this.
  • jcheiljcheil Solar Expert Posts: 722 ✭✭✭
    Re: Different current in 2 strings
    Is your signature correct? You're running 740 Amp hours of battery? If so 110 Amps would be just short of 15% and that would certainly be the maximum.

    For half that bank, 370 Amp hours, I'd advise turning it down to 37 Amps and letting it Absorb for a long time as you're trying to recover lost capacity. Longer time at a lower rate works better for this.

    Yes SIG is correct.

    PS - SG's are all coming up evenly now and quite fast actually, up to 1.275 on the bad side already.
    I will do what you said and once both banks get reconnected do a nice long slow absorb at 37amps.

    Thanks again!
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • jcheiljcheil Solar Expert Posts: 722 ✭✭✭
    Re: Different current in 2 strings

    What's the max recommended temp the batteries should not be allowed to go over when doing an EQ?
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Different current in 2 strings
    jcheil wrote: »
    What's the max recommended temp the batteries should not be allowed to go over when doing an EQ?
    It varies from Manufacturer, 115 - 125 F , I use about 110 F, but I have never been above the high 90's. You can always let them cool overnight.
  • vtmapsvtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Different current in 2 strings
    jcheil wrote: »
    I could have sworn I double-checked all the connections. lesson learned - THREE TIMES.

    You may well have torqued all the connections properly and not missed any. That doesn't mean a loose connection can't happen.

    Copper flows. After torquing a copper connection it is important to go back the next day and torque again.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • gww1gww1 Solar Expert Posts: 963 ✭✭
    Re: Different current in 2 strings

    I have never found a way to measure temp that I felt comfortable with. I have fork truck and using a sears clamp meter the battery maker said 100 degrees f would be fine. I think the highest I have seen is about 92 degrees.
    gww
  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Different current in 2 strings

    I built these for all my banks. It's a standard cap, glass vial and $4 indoor / outdoor thermometer. They seem to be pretty accurate. In GC-2's it'll go into the electrolyte, not in a tall case, but it seem's to work in the tall cell ok.

    Attachment not found.
  • gww1gww1 Solar Expert Posts: 963 ✭✭
    Re: Different current in 2 strings

    Blackcherry, thats cool, where did you get the glass vial?
    gww
  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Different current in 2 strings
    gww1 wrote: »
    Blackcherry, thats cool, where did you get the glass vial?
    gww
    It's a perfume vial, PM me with a mailing address and I'll mail you a couple. I think I bought 100 of them and used<10. it's small enough it doesn't interfere with the venting of the cap.

    I thought I had some extra caps here, but they must be at the shop at the lake. I don't go there much in the winter and working on a medical issue this winter.

    .
  • gww1gww1 Solar Expert Posts: 963 ✭✭
    Re: Different current in 2 strings

    Blackcherry
    Cool, and thanks.
    gww
  • jcheiljcheil Solar Expert Posts: 722 ✭✭✭
    Re: Different current in 2 strings

    OK, all is good now. At one point the battery temp got to 104, but I put a box fan in there blowing down on the batteries and it dropped down to 95 within a few minutes. Remember I am also in FL so it was in the 90's outside today to begin with!

    After the single bank EQ and then a short dual bank EQ all the SG's are back up where they should be (actually a tad higher, most are 1.290 with a couple 1.285+ readings and couple of 1.300 readings). And at that point the charger was only putting in 9 amps max.

    And the current between the banks is now no more than 1amp difference and that might just be meter calibration differences.

    Phew...that was a close one.

    Thanks everyone for the advice.
    And I LOVE the battery temp cap thing. I might just go make one myself!
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • CDN_VTCDN_VT Solar Expert Posts: 492 ✭✭✭
    Re: Different current in 2 strings
    It's a perfume vial, PM me with a mailing address and I'll mail you a couple. I think I bought 100 of them and used<10. it's small enough it doesn't interfere with the venting of the cap.

    I thought I had some extra caps here, but they must be at the shop at the lake. I don't go there much in the winter and working on a medical issue this winter.

    .

    + 1 Blackcherry , great tip , & the acid smells nice :-)

    VT
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