SBIG STF-8300en poor cooler performance

Discussion in 'STF Series CCD Cameras' started by astrodwp, May 3, 2021.

  1. astrodwp

    astrodwp Cyanogen Customer

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    You upgraded my SBIG STF-8300m to a 2 stage cooler in December/January 2020/2021.
    As we have been warming up during the nights as we head to summer. My new 2 stage cooler can only get to -20 deg C at 80% power when the ambient temp is equal or below 12.6 deg C. This is only a 32.6 deg C delta. Shouldn't I be getting better than that? My STF-8300m with a single stage cooler got a 30 deg C delta. i have been recording ambient vs cooler temp at -20 deg C, see below.

    temp
    C F Power
    -6.4 20.48 12-16
    -2.8 26.96 22-28
    -1.2 29.84 25-28
    -0.9 30.38 26-30
    -0.5 31.1 27-31
    1.1 33.98 33-36
    2.7 36.86 36-40
    2.9 37.22 36-40
    3.5 38.3 39-42
    4.7 40.46 40-44
    5.2 41.36 40-44
    5.9 42.62 44-48
    6.4 43.52 45-49
    6.9 44.42 48-51
    7.8 46.04 53-57
    8.6 47.48 45-48
    10 50 59-63
    11 51.8 62-66
    11.4 52.52 66-69
    12.4 54.32 76-80
    12.6 54.68 65-70
    14.5 58.1 49-53
    22 71.6 100-100

    The big outlier was at 14.5 deg C ambient with 49-53 % power that occurred on a warm night 1/2 months ago. The last few nights, i am getting 80% at 12.6 deg C ambient. Did the second stage quit 1/2 months ago? Second outlier was at 12.6 deg C ambient with 65-70 % power. both of these outliers measurements happen at least a month ago. I am no where near those two measurements today.

    dave
     
  2. Doug

    Doug Staff Member

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    The cooler is actually more efficient when it is warmer.

    The Delta-T spec is measured at 100% power. What temperature do you achieve with the cooler running at 100% when the ambient is around room temperature? (That will roughly replicate our test conditions at the shop.)

    Make sure there isn't some dust etc. plugging the heat sink, and that the fan is working normally.
     
  3. astrodwp

    astrodwp Cyanogen Customer

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    Ok..this is all the data i have to compare
    ambient temp 22 deg C (71.6 deg F) ..........power 100%.......sensor temp at -20 deg C.....delta 42 deg C.......taken 1/2 months ago
    ambient temp 14.5 deg C (58.1 deg F )....... power 100%.......sensor temp at -19.5 deg C...delta ..34 deg C.... .taken last night
    ambient temp 14.3 deg C (57.7 deg F)....... power 100% ......sensor temp at -20 deg C......delta 34.3 deg C ....taken last night


    other questions
    how much more noise is there at 80% power vs 100% power?
    how much more stress is put on cooler for extended operation (all night) at 100% power
    dave
     
  4. Doug

    Doug Staff Member

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    There shouldn't be any difference in noise at higher power levels. You want to make sure you don't hit 100% during normal operation because it won't be able to regulate properly.

    Stress really isn't an issue.

    It does sound like your camera isn't cooling quite as well as it used to, which is rather unusual. Be sure to check the fan etc. because airflow has a big effect.
     
  5. astrodwp

    astrodwp Cyanogen Customer

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    if it is the cooler fan .....is was just replaced 2 years ago.
    at what point would you consider the cooler performance low enough that needs to be fixed?
    thanks
     
  6. Doug

    Doug Staff Member

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    What is your camera serial number?

    As for getting it fixed... I guess when it's interfering with your ability to get good images.

    Certainly if you can't maintain -10C you would want to get it fixed. But if you're able to routinely do -20C that is more than good enough.
     
  7. astrodwp

    astrodwp Cyanogen Customer

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    stf-8300M SERIAL NUMBER 83F010777
     
  8. astrodwp

    astrodwp Cyanogen Customer

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    To continue this saga on my STF8300En cooler performance.....
    last night ambient temp was 17deg C and i cooled down to -15 deg C with about 73% power ( i could not get to -20deg c) .
    My automated script stopped around midnight, so didn't warm up. so this morning i see ambient temp is 20.1 deg C at 46% power and sensor temperature is still -15deg c.
    It seems like for some reason, the method that the 2nd stage cooler kicks in, didn't work at cooldown, but kicked in somewhere during the night??
    Is this possible? If so.....any ideas how to get 2nd stage cooler to transition at cooldown?
    thanks
    dave
     
  9. Doug

    Doug Staff Member

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    The two stages are electrically in series, so they are both always running.

    TECs are inherently more efficient at warmer temperatures, so the delta is greater when temperatures are higher. That’s helpful when temperatures get warmer, of course.
     
  10. astrodwp

    astrodwp Cyanogen Customer

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    true, but doesn't help during remote operations at beginning of session when cooler temp is set for the entire night.
    So confused......If it is helpful when temperatures get warmer......how come that is not true at cooldown? generally temp
    does not increase through out the night, so the cooler getting more efficient throughout the night provides little benefit?
    thanks
    dave
     
  11. astrodwp

    astrodwp Cyanogen Customer

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    after thinking about what you said.....it seems like, based on my performance, i need to start cool down when ambient temp is above 20 deg C to cool sensor down to -20 deg C? does this make sense?


    dave

    ,
     
  12. Doug

    Doug Staff Member

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    I'd see how cold you can get it running the cooler in the 90% range.
     

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