Are electronic battery measurements better than specific gravity?

softdownsoftdown Solar Expert Posts: 3,509 ✭✭✭✭
Been measuring salt water specific gravity for 27 years. There are issues: 
1) Gauge accuracy tends to vary.
2) Measurements are wrongly effected by bubbles and solid particulates attached to the floating dial. Highly accurate measurements are not extremely repeatable as a rule.

Measuring battery s.g. is even worse. Each cell must be measured. Battery acid has a way of getting on clothes and destroying them.

Electronic battery measurement is much more convenient. Also offers very specific and highly repeatable measurements. Voltage tells a lot but resistance and aH/CCA are far more telling. Resistance tells us much about the health of the battery. Resistance goes up as batteries age and deteriorate. AH and CCA are a very specific measurement of the power of the battery. There is a very accurate correlation between battery age and battery power - that this electronic measurement accurately displays.

I'm not saying that SG is not important, I am saying that electronic measurements may be better in several respects. SG testing cost roughly 1/3rd as much and takes about five times more effort and time. Either one is cheap insurance for knowing a lot more about battery health. Electronic measurements are also highly useful on car batteries. I doubt that many measure the SG of their car batteries. 

I'm happy with this one while noting the price has recently gone up about $15. Mega inflation in many industries is now rampant. Amazon link though Ebay has older models for ~$15 less.  https://www.amazon.com/ANCEL-Battery-100-1100-Automotive-Analyzer/dp/B07Q6NBXQG/ref=sr_1_4?crid=3DTZ9CILJA6M6&dchild=1&keywords=battery+tester+automotive&qid=1600783359&sprefix=battery+tester,aps,280&sr=8-4
First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries

Comments

  • Dave AngeliniDave Angelini Solar Expert Posts: 6,034 ✭✭✭✭✭
    Anyone who is trained and understands measuring SG can get the job done with just about any decent hydrometer that has been maintained.
    It does not matter if it is electronic or analog. Below is referencing typical FLA's for offgrid.

    If you think too much about this,  you will get weird!  Each cell does not need to be measured on a regular basis either.

     Just find a pilot cell that is good and one that is the lowest. Make a note of them and mark the cells. If it is too low, .03 or greater, perform a corrective EQ.
     If the pilots are close, perform a preventative EQ per manufacturer. Keep an eye on the 2 pilots each month or so. Once every year or two, make sure all the cells were similar to the last year.

    You really are looking for large outliers and then EQing them back to close. If you catch it, it can be corrected. That is the beauty of FLA.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • softdownsoftdown Solar Expert Posts: 3,509 ✭✭✭✭
    Anyone who is trained and understands measuring SG can get the job done with just about any decent hydrometer that has been maintained.
    It does not matter if it is electronic or analog. Below is referencing typical FLA's for offgrid.

    If you think too much about this,  you will get weird!  Each cell does not need to be measured on a regular basis either.

     Just find a pilot cell that is good and one that is the lowest. Make a note of them and mark the cells. If it is too low, .03 or greater, perform a corrective EQ.
     If the pilots are close, perform a preventative EQ per manufacturer. Keep an eye on the 2 pilots each month or so. Once every year or two, make sure all the cells were similar to the last year.

    You really are looking for large outliers and then EQing them back to close. If you catch it, it can be corrected. That is the beauty of FLA.
    Hmmm, stunning science is surely found here. Nice alpha statement for sure.

    One could argue with just measuring a few cells. 

    We also have the issue of increasing numbers employing competitve battery chemistry's. 
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,034 ✭✭✭✭✭
    Not really stunning science, but practical, and also based on 300+ offgrid homes and how people really are with maintenance.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • softdownsoftdown Solar Expert Posts: 3,509 ✭✭✭✭
    Fine if you never get a bad cell - bad cells are quite common. 

    I tested all 16 batteries at 6am. Something odd happened while I was away for two weeks. Thread coming soon I hope...
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • PhotowhitPhotowhit Solar Expert Posts: 5,658 ✭✭✭✭✭
    What you've linked to is a 'load tester' I'm sure it will test car batteries just fine and tell you their relative CCA.

    I wouldn't use one that tested for 3 seconds on a deep cycle battery. It might work, but cells might be too far gone before you see a significant voltage drop in 3 secs. 
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • softdownsoftdown Solar Expert Posts: 3,509 ✭✭✭✭
    edited September 2020 #7
    Resistance is my favorite parameter - currently. Though CCA tells a lot about batteries designed for that function. Voltage says a little - but can be misleading. One of my "weaker" batteries - older but still strong - displays the highest voltage. 

    EDIT: I'm not certain the newest linked testers even test resistance. 
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,034 ✭✭✭✭✭
    softdown said:
    Fine if you never get a bad cell - bad cells are quite common. 

    I tested all 16 batteries at 6am. Something odd happened while I was away for two weeks. Thread coming soon I hope...
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • Dave AngeliniDave Angelini Solar Expert Posts: 6,034 ✭✭✭✭✭
    Respectfully disagree.

     Bad cells in a maintained offgrid bank are rare in my experience. After 7 to 10 years, the failure is usually a loss of capacity. I just do not see this with people I have trained to take care of the bank. They know that when there is an outlier cell to do a nice long EQ until the pilot cell comes back to the reference. Other cells come back also. It is at this time, after a corrective EQ one measures all of the cells.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • soloronesolorone Solar Expert Posts: 256 ✭✭✭
    SG readings at the proper time are the definitive measure of your battery condition.  I still use a glass hydrometer of 1, ONE piece construction. 2 piece glass can leak, the leak is hard to see and really throws off readings  I have been through this with an older customer hydrometer.
  • softdownsoftdown Solar Expert Posts: 3,509 ✭✭✭✭
    Here I thought battery output was the most important . Now I learn that I should look for the highest SG. 
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
Sign In or Register to comment.