Announcement

Collapse
No announcement yet.

Battery Temperature Sensor Placement

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Battery Temperature Sensor Placement

    I got sucked into a youtube video where this homesteader was having issues with his PV charging which seemed a bit mysterious until it came to light that he had not installed the temperature sensor which came with his inverter/charger. (It was winter in Idaho.) When he installed it, he installed it on the terminal post of the battery - and to be fair, that is exactly where it looked intuitively where it should go, it had a tab with a hole that looked suspiciously the same size as a ring terminal for a battery.

    That seemed wrong to me on many levels. It prompted me to do a little googling on battery temperature sensors, and I found that many of them physically look just like that. A tab at the end with about a 3/8" or 5/16" hole, perfect size to add to a battery post.

    I had always thought that ideally a sensor would be mounted about half way up vertically on the warmest cell of the warmest battery in the bank. As batteries are frequently packed together pretty tight to save space and reduce inter-battery cable length this is frequently in the 'interior' of the bank.

    So I guess three questions came to mind about the practical installation of a battery sensor.

    1. How important is the placement? Obviously one anywhere in the battery compartment is better than one coiled up in the equipment or in the shipping box, but once it is in the battery compartment, how big of deal is it exactly where it is?

    2. Given that the terminals of a battery is the most likely place in a system where unwanted heat is likely to be generated, isn't attached to a battery terminal among the worst places in the battery box? Wouldn't having it in 'free air' somewhere in the box be better than bolting it to a terminal? If it is bad, why do so many manufacturers have the tab/hole design?

    3. For the person wanting to mount the sensor on the side of a battery, what are good and bad ways of doing that? It would seem to me that anything as permanent as epoxy is dumb. Perhaps some silicone RTV makes sense? The only time I had opportunity to install one, and I don't even recall what it physically looked like, I attached it to the side of a middle battery with a big 'X' of duct tape - was that dumb for any reason?

    School me please.

  • #2
    Easy Peasy.

    CENTER MASS. Quit watching Screw Tube. Not on a Term Post. Center of Thermal Mass. So if you have a stack, right in the center of all the cells on the side of a battery. It should be a Ceramic Thermistor in the shape of a coin. You use silicon grease to paste to the side of the cell.
    MSEE, PE

    Comment


    • #3
      I have two brands of temperature sensors: one for the Outback FlexMax80 CC, and one for the Apollo Solar Turbo 80 CC. Both companies sell sensor replacements with attached cabling. I reused the sensors upon replacement of the batteries in August 2016. As mentioned, they were set about halfway up from the base of a battery ensuring that the sensor is picking up the temperature of the liquid acid. I used 10 mil pvc pipe wrap to tape the sensor to the battery. I precleaned the battery surface with rubbing alcohol prior the placing the tape.

      As previously mentioned in other posts, solar does do not have enough hours in a day to worry about thermal runaway on FLA batteries, and I see little value in the temperature compensation because seasonally, I tweak both the absorption hours and charge voltages slightly, sort of as needed. At 7,000 ft in New Mexico, I have observed battery temperature of about 53 deg F in the winter and at about 95 deg F in the summer. The batteries are stored in an well ventilated, unheated out building with the propane fueled generator. I wrapped the outer perimeter of the batteries with 2-inch blue board insulation to help moderate temperature variation due the daily temperature swings.

      Comment


      • #4
        Wouldn't it be great if there were Temp sensors/hydrometers that sat in the tank as opposed to external. They could be mounted to the caps and send info wirelessly. You would be able to get exact temp/SOC readings on a full time basis.
        Disclaimer, OK you heard it here first, folks
        2.2kw Suntech mono, Classic 200, NEW Trace SW4024

        Comment


        • #5
          Originally posted by citabria View Post
          I have two brands of temperature sensors: one for the Outback FlexMax80 CC, and one for the Apollo Solar Turbo 80 CC. Both companies sell sensor replacements with attached cabling. I reused the sensors upon replacement of the batteries in August 2016. As mentioned, they were set about halfway up from the base of a battery ensuring that the sensor is picking up the temperature of the liquid acid. I used 10 mil pvc pipe wrap to tape the sensor to the battery. I precleaned the battery surface with rubbing alcohol prior the placing the tape.

          As previously mentioned in other posts, solar does do not have enough hours in a day to worry about thermal runaway on FLA batteries, and I see little value in the temperature compensation because seasonally, I tweak both the absorption hours and charge voltages slightly, sort of as needed. At 7,000 ft in New Mexico, I have observed battery temperature of about 53 deg F in the winter and at about 95 deg F in the summer. The batteries are stored in an well ventilated, unheated out building with the propane fueled generator. I wrapped the outer perimeter of the batteries with 2-inch blue board insulation to help moderate temperature variation due the daily temperature swings.
          +1. I agree Temp Comp is of no value in a solar system using FLA. with one exception and that is extremely cold climates and the batteries are exposed to the elements. By cold I mean well below 0 degrees fahrenheit. Does it get cold in Phoenix or Sun Valley? Flagstaff maybe few times a year.

          As for AGM, not much value anyway. The whole point of using Temp Comp is to prevent Thermal Runaway on AGM batteries. Unless your panel wattage is grossly oversized, it is impossible for solar to cause Thermal Runaway. As you said, solar is not capable of fully charging batteries in over 90% of systems installed.. Thermal Runaway is way after the battery is fully charged and being severely overcharged. Only commercial AC Chargers are capable of doing that. So Temp comp has very little if any value using solar to charge Pb batteries. Will not hurt if you use Temp Comp, but nothing gained, just cost money.

          If you are going to use it, use it correctly by placing the Sensor in the Center of the THERMAL MASS. Quit watching You Tube, it will make you a stupid and ask silly questions. .
          Last edited by Sunking; 11-03-2017, 02:15 PM.
          MSEE, PE

          Comment


          • #6
            Originally posted by littleharbor View Post
            Wouldn't it be great if there were Temp sensors/hydrometers that sat in the tank as opposed to external.
            They make Temp Sensors that are emerged in the Electrolyte. Nearly every utility that uses FLA batteries has one in what is called a Pilot Cell located in Center Mass. On paper it is possible to have an electronic hydrometer installed in a cell electrolyte. However two huge problems exist doing so, thus why there are none on the market I know of. Electronic Hydrometers are not very accurate, and unless every part is made of gold or glass, the acid corrosion will eat any electronics alive, and that will contaminate the battery.

            So when you use a hydrometer, make darn sure it is cleaned before and after each use with distilled water.

            Last edited by Sunking; 11-03-2017, 02:29 PM.
            MSEE, PE

            Comment


            • #7
              I kinda thought the corrosive environment would be problematic. Maybe someday.
              2.2kw Suntech mono, Classic 200, NEW Trace SW4024

              Comment


              • #8
                Originally posted by littleharbor View Post
                I kinda thought the corrosive environment would be problematic. Maybe someday.
                That someday maybe now, I just do not know of any, nor would I use it if available until I am convinced of accuracy.

                This is one area electronics cannot compete with accuracy in a good ole fashion Float Hydrometer. Go to any Calibration Lab that calibrates hydrometers of any kind use what is called a Master Hydrometer, or measuring Specific Gravity of a known liquid and Temp. In practice you cannot calibrate a hydrometer, you can only apply a Correction Factor against a known source. Two ways to do that.

                1. Master Hydrometer is a just a regular Glass Tube with a weighted bottom to float in the test liquid.
                2. Use pure Water at known temp. Example pure water at 70 degrees should read .998. At 77 degrees 1.000
                MSEE, PE

                Comment


                • #9
                  Originally posted by littleharbor View Post
                  Wouldn't it be great if there were Temp sensors/hydrometers that sat in the tank as opposed to external. They could be mounted to the caps and send info wirelessly. You would be able to get exact temp/SOC readings on a full time basis.
                  Disclaimer, OK you heard it here first, folks
                  Such instrumentation is readily available for temperature measurement/monitoring and used all the time in power/process industries. Commonly RTD's (Resistance Temperature Detectors) are used, but other methods/materials are possible. I specified/designed them all the time. Any reasonable/desired level of accuracy is possible depending on requirements. Some pressure boundary design consideration(s), instrument location/placement and calibration against a known standard may be necessary for high accuracy/precision. I've never done RTD designed tempSpace may be a limitation for battery applications.

                  As for hydrometers, and as SK notes, real accuracy comes from bulb type immersion hydrometers. However, they have physical limitations for size and location as well as perhaps for material/corrosion considerations, and, although most bulb hydrometers use glass, making them less subject to corrosion, they are also more prone to breakage. Still, for the right amount of $, any desired level of accuracy is possible with glass hydrometers.

                  Comment

                  Working...
                  X