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Author Topic: 314L+ Mono Cooling Question?  (Read 3286 times)

NorthBoundTrain

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314L+ Mono Cooling Question?
« on: January 31, 2013, 10:31:17 am »
Hi everyone,

I have had my 314L+ for close to a year now, and have never really got a straight answer to what I would think is a simple question.

I have read in several places that it is best to keep the cooling at a point where you are using it at less then 90%. This typically allows me to get around -10c of ambient.

Is it a power consumption reason, or is there a danger of damaging the camera if run at a higher %, say 150% and up?

Power consumption is not an issue for me, hence the reason I ask. 

I typically get conflicting answers or an "I dunno" whenever I ask, so it would be nice to have a solid answer.

TIA!
And hope someone is having clear skies, going on 2.5 months of clouds, wind or rain here...
Clear Skies - Chris
----------------------------------------
Atlas EQ-G/Orion SVPro w/ Dual Axis Drives
Stellarvue SV80ST-25SV APO Triplet
Orion 50mm Mini Guide Scope
Baader Planetarium-LRGB/HaOIIISII
Atik 314L+ Mono/SSAG
SPC900NC
Bortle Scale Class 3/4-Blue/Green Zone

MikeM

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Re: 314L+ Mono Cooling Question?
« Reply #1 on: January 31, 2013, 01:48:11 pm »
Hi Chris, I too have wondered and always have thought it was an issue of making the cooler work too hard. But in my search I've found this:

"Whatever method is used to cool your camera, the goal is always the same: cool the
CCD well below the ambient temperature so that noise will be minimized.
When cooling is active, CCDOps gives you information about cooling efficiency. You can
use this information to control the amount of cooling. CCDOps provides two numbers
related to cooling efficiency:
•  Detector temperature, in degrees Celsius
•  Percentage of total cooling capacity in use 
Total cooling capacity is the “delta-T” of cooling available. (The Greek letter delta—∆ or
δ—refers to “change,” and the “T” stands for temperature. So “delta-T” means “change in
temperature.”) For example, the cooling system built into the ST-10XME camera
provides about 30 degrees Celsius of cooling below ambient temperature. (This is a
nominal value; actual cooling might be slightly above or below this number for a specific
camera.)
For example, suppose that the ambient temperature is 10ºC. That means that the
maximum cooling should bring the detector temperature down to approximately -20ºC.
You might be tempted to pick -20ºC as your setpoint temperature, but that’s not the best
strategy. If the cooler is working at 100% of its capacity, there is no reserve capacity and
it will not be able to maintain a steady temperature.
Why is a steady temperature important? Let’s return for a moment to those creeping
electrons. The rate at which electrons creep into the pixels varies with the temperature.
When the temperature is warmer, more electrons creep in. When it is cooler, few
electrons creep in. If the temperature is held steady, the rate of electron flow is also
reasonably steady and predictable. (The rate will vary from one pixel to the next, but it
will be predictable for each pixel.)
Here’s the payoff: if temperature is steady, CCDOps can measure the electron flow (dark
current) and subtract it from the image. Electron flow is measured by taking an exposure
with the shutter closed (dark frame). The dark frame is subtracted from the light image to
create a low-noise result. CCDOps includes tools to make dark subtraction simple and
efficient. See the section “Dark Frames and Flat-Field Frames” for more information
about dark frames and dark subtraction. "

It comes from the SBIG CCDOps user guide.
In short I guess it means that if the cooler is pinned at 100% ( you won't be able to go higher) then the cooler has no room to "regulate" the temperature.
It may not answer your question totally but it's the best I could find.
Clear Skies!!
Mike

FSQ106N - AT8RC
G-11

NorthBoundTrain

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Re: 314L+ Mono Cooling Question?
« Reply #2 on: February 01, 2013, 01:05:05 pm »
Thanks for the input Mike,

To clarify:
In warmer months I run -10 typically, which keeps it around 90%.
Winter is a little easier to get it down to -15 of ambient, while maintaining it at 90%.
Clear Skies - Chris
----------------------------------------
Atlas EQ-G/Orion SVPro w/ Dual Axis Drives
Stellarvue SV80ST-25SV APO Triplet
Orion 50mm Mini Guide Scope
Baader Planetarium-LRGB/HaOIIISII
Atik 314L+ Mono/SSAG
SPC900NC
Bortle Scale Class 3/4-Blue/Green Zone