Does this seem normal temp compensation

rake1
rake1 Solar Expert Posts: 173 ✭✭
I added a remote temp sensor to my tristar 60 it is only 5 feet from the TS-60 in the same room. The Ts-60 dumps at 14.8 volts (wind and solar system) since I put the RTS on, it dumps alot higher. Went into my camp on the weekend and the temp inside was -17C and the TS-60 wouldn't dump until 15.8V, I knew it would change but that seems high to me. I cupped the RTS in my hand and after about 45 seconds it was back to dumping at 14.8V. I realize I may have answered my own question but I am a little concerned about the 15.8v compensation the TS-60 is doing.

Comments

  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Does this seem normal temp compensation

    -17C is very cold.

    1V difference that you see is 167mV/cell, or divided by 42 degrees, about 4mV/K/cell. This is about right.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Does this seem normal temp compensation

    Where do you have the RTS attached? Battery temp is always higher than ambient, but if the RTS is exposed to air even on one side it will read colder than the actual battery temp.

    If one side of it must be in open air (instead of tucked between two batteries) cover it with some rigid foam insulation. You're trying to get an accurate reading of the internal battery temperature here.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Does this seem normal temp compensation

    Remember that batteries have huge (relative) thermal mass. If your camp is -17 and has been there a while, it will take a LONG time for the temp of the battery to equilibrate. When I return from a while away in the winter, it takes my batteries days to stop frosting and sweating, regardless of loading and charging. Not to argue with 'coot, but the batteries can be much colder than the air for a good long while.

    Tony
  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Does this seem normal temp compensation
    icarus wrote: »
    Not to argue with 'coot, but the batteries can be much colder than the air for a good long while.

    I keep batteries in my garage, which is at 12C. When I wasn't cycling them they were around 10C. However when I started cycling then, their temperature rose to about 20C.

    I guess with proper insulaton, the cycling can easily heat them up to 15, or even 20C, above the ambient temperature.
  • rake1
    rake1 Solar Expert Posts: 173 ✭✭
    Re: Does this seem normal temp compensation

    I had it attached to the battery terminal. I have taken it off now and it just hangs beside the battery.
  • rake1
    rake1 Solar Expert Posts: 173 ✭✭
    Re: Does this seem normal temp compensation
    icarus wrote: »
    Remember that batteries have huge (relative) thermal mass. If your camp is -17 and has been there a while, it will take a LONG time for the temp of the battery to equilibrate. When I return from a while away in the winter, it takes my batteries days to stop frosting and sweating, regardless of loading and charging. Not to argue with 'coot, but the batteries can be much colder than the air for a good long while.

    Tony
    I agree my batteries when cold may read 14.8v when I walk in the door but as soon as I turn on say 6amps of power they drop to 12 .2 in 20 min. Two days later in the heat of the camp and fully charged they stay at 12.5 for almost 1 hour same load. And yes they sweat for a couple of days so I know they are cold,Especially these Surretts which are a large battery with a lot of electrolyte in them.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Does this seem normal temp compensation

    It all sounds normal to me. If your batteries are -20 thier capacity to produce power is diminished considerable, perhaps by 50% or more, (don't have a chart in front of me) when they return to +20 they now have near 100% capacity. The cold won't hurt them one bit, it is just that thier capacity drops.

    Tony
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Does this seem normal temp compensation

    The purpose of the RTS is to read the internal temp of the battery and adjust its relative Voltage to the charge controller's settings so that the charge set points are relevant to the battery temp. It does not matter that the batteries have sat and got cold, because when the current from charging goes through them they should warm up well above ambient on the first charge cycle.

    Thus when Absorb is reached the battery Voltage is read as "14.8 @ 25C" but the cooler temp sensed adjusts the Voltage downwards to "14.2 @ 25C equivalent" causing the charge controller to push the Voltage higher in "25C Volts". This is similar to temp compensation on a hydrometer.

    If your RTS is just hanging out in open air its reading is going to be quite wrong, especially with very low ambient temps. Fasten it securely to the side of a battery, tightly between two if possible or with some foam blocking the outside face. If the RTS thinks your batteries are at ambient (especially -17C) it will allow the charge controller to push the Voltage too high.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Does this seem normal temp compensation

    Once again, not to argue with 'coot, but if you bolt the temp sensor to the post, it will BR good enugh. The post will conduct heat out of the electrolyte better than the case. That said, glued or taped to the case is just as good int he real world. Even tucked between two batteries will give a pretty close reading, as the batteries will radiate the heat (or cold) off the cases.

    I suspect if you take a good temp reading of the battery case, and compare it to free air (without draft) 1" away from the case you wouldn't find much difference.

    Tony
  • rake1
    rake1 Solar Expert Posts: 173 ✭✭
    Re: Does this seem normal temp compensation
    icarus wrote: »
    Once again, not to argue with 'coot, but if you bolt the temp sensor to the post, it will BR good enugh. The post will conduct heat out of the electrolyte better than the case. That said, glued or taped to the case is just as good int he real world. Even tucked between two batteries will give a pretty close reading, as the batteries will radiate the heat (or cold) off the cases.

    I suspect if you take a good temp reading of the battery case, and compare it to free air (without draft) 1" away from the case you wouldn't find much difference.

    Tony

    It has a type of sensor that bolts to the terminal and that is where I had it originally, but moved it to just beside it. I will put it back on the terminal all the camp should be the same temp all through so no drafts. Should I wrap it with a little insulation also?
  • Muskoka
    Muskoka Solar Expert Posts: 103 ✭✭
    Re: Does this seem normal temp compensation

    I have mine (2) attached to the battery terminal, and checked last night with my temperature probe. Temperature at the middle of the battery case (L16) idle state, 0 deg Celsius, Morningstar RTS, 0 deg Celsius, ambient temperature in battery room from thermometer, 4 deg Celsius. I will test again under a charge state, and see the temperature difference between the "case", and the "lug", to see the difference, if any.

    Glen
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Does this seem normal temp compensation

    I think you are over thinking this a bit. Bolt it to the post and be done with it, is what I would suggest.

    Tony
  • rake1
    rake1 Solar Expert Posts: 173 ✭✭
    Re: Does this seem normal temp compensation
    icarus wrote: »
    I think you are over thinking this a bit. Bolt it to the post and be done with it, is what I would suggest.

    Tony

    Done deal thanks