DIY cooler for asi178

[D4N]

I've decided to have a play around with some DIY cooling and bought a 5V peltier cooler to do this.

Now I went for 5V as I wanted to be able to power it from a USB port, I have some battery packs that are designed for charging up phones and tablets that will come in handy for portability.

 

The ZWO cameras are quite well designed for this type of thing as they have a large flat backplate that the cooler can be attached to.

 

I used a thermal interface pad to attach the TEC to the back of the camera and another one to attach a CPU heat sink with fan from an old computer.

The fan and cooler are then connected up in parallel to two battery packs or to a single 5V mains adaptor.

 

 

Now for the testing, I ran the camera in video mode for a while and the temperature settled at 36.7°C with no cooling on.  I kept the gain at 255 throughout the tests.

When I turned the cooling on the temperature quickly dropped down to 16°C.

Next I did some longer exposures, after a 5min exposure with no cooling it reported that the temperature was 32.2°C and on inspection the average pixel value was 1187.

Now with the cooling on I took another 5min exposure and it reported the temp as being 10.2°C and the average pixel value was 216.

 

I took some 1min exposures as well, these came up with a pixel value of 198 for uncooled and 17 for cooled.

I noticed that a lot of this noise was in the corners, I assume that this is amp glow or other interference from the internal electronics so I cropped it and the average pixel value dropped to 180 for uncooled and 8 for cooled.

Cropping the 5min exposures brought the average pixel value down to 1038 for uncooled and 80 for cooled.

This seems to be a resounding success so far as noise reduction goes, I expect that the amp glow can be dealt with using dark frames as it isn't random noise.

I also noticed that the majority of the noise is in the same pixels in the cooled exposures, as such it should respond well to dark frames or a bad pixel map.

 

I plan to use this with some camera lenses I have as a super portable setup, maybe it will be portable enough to take somewhere with no cloud

[Gina]

I've thought of doing this for my All Sky Cam.

[ChrisLX200]

Sounds like a successful experiment.

ChrisH

[Gina]

Yes indeed   Think I'll try this with my present ASC camera once I've finished the new case and mast fitting.  I already have one or two Peltier TECs.  A relatively small reduction in sensor temperature should do it - I don't think it warrants a cooled version of the camera at an extra £300 or so!!  The exposed position of an ASC is not suitable for a cooled camera version anyway.

[D4N]

Indeed and these tests were carried out indoors so I expect the noise will be even lower when used outside.

 

I was considering the uses for an ASC and it would be handy if the heat from the TEC could be transferred to the lens area to prevent it from fogging up.  A small lens is likely to cool down to much when attached to such a cold camera housing.

 

Hopefully I don't need to build a dew heater for this setup but if it becomes necessary I will as I have some bits leftover from when I made the heaters for my scope, I can just design it for 5V and parallel it off the same supply.

[ChrisLX200]

Do you have any photos of this mod?

ChrisH

[D4N]

Yep, here it is.

The fan and heat sink are out of an old Compaq desktop PC I had laying around and the peltier cooler is this one:

Cooler

The USB power cables are salvaged from old keyboards.

[D4N]

I had planned to use a smaller round heat sink I have but then I found out how much heat this thing can kick out I had to switch to something a bit more efficient.

[ChrisLX200]

OK thanks! I'll have to look for a 12V Peltier as that would be more convenient for me, I could work with 5V if I had to but 12V would be much easier..

ChrisH

[Gina]

Trouble is 12v Peltier TECs tend to be higher wattage and a lot less efficient.  I would definitely recommend buying from RS or Element14 etc. rather than the cheap ones often offered on ebay.  The ebay ones are very inefficient.  They are cheap cheap rather than good value.  I have quite a bit of experience with Peltier TECs.

[Gina]

Going through some of my threads I've found a seemingly reasonable 12v Peltier TEC from Farnel Element14. 

MULTICOMP  MCPE-127-10-25  PELTIER COOLER, 19.6W

Quote

Internal Resistance: 6.9ohm
Power Rating: 19.6W
Series: PE
Temperature Difference Max: 75°C
Transducer Function: Thermoelectric Module
Voltage Max @ Diff Temperature Max: 15.7V
DC Current Max: 2A
External Depth: 4.8mm
External Length / Height: 30mm
Height: 30mm
Input Voltage Max: 15.7V
'Further Manufacturer's Details (for this range)...PE series, max operating temperature for short term 110°C, recommended max 90°C for long lifetime Good reliability in ON-OFF power cycling mode Recommended operating current 0.7 Imax for long life

I should have this one around somewhere - be good to try in my all sky camera.  I've found one TEC but its 5v and only 25mm square.  Takes up to 5A.  Might use an old PC ATX PSU and this could run off the 3.3v rail.

[ChrisLX200]

Thanks Gina, I found that item is also on Amazon a couple of quid cheaper - if that matters. Anyway, I ordered one. I can machine my own heatsink from a chunk of alloy, not sure if I have a vibration-free fan but there are loads of CPU and case fans lying about.

ChrisH

[D4N]

Since I'm running a 12V CPU fan at 5V it is very quiet indeed, I suspect that if you run one at 12V it will be a bit shakier so you might need some damping.

[Gina]

Yes, I often run 12v fans at 5v - I do this on my 3D printers.

[D4N]

An outdoor test last night proved that dew will certainly be a problem with this level of cooling.  Time to make another dew heater.

[Gina]

On 05/08/2016 at 20:56, ChrisLX200 said:

Thanks Gina, I found that item is also on Amazon a couple of quid cheaper - if that matters. Anyway, I ordered one. I can machine my own heatsink from a chunk of alloy, not sure if I have a vibration-free fan but there are loads of CPU and case fans lying about.

ChrisH

I couldn't find it cheaper on Amazon.

[ChrisLX200]

58 minutes ago, Gina said:

I couldn't find it cheaper on Amazon.

https://www.amazon.co.uk/PELTIER-COOLER-19-6W-MCPE-127-10-25-MULTICOMP/dp/B01186NYAC/ref=sr_1_64?ie=UTF8&qid=1470523811&sr=8-64&keywords=MULTICOMP++MCPE

That's £28.99 as opposed to the £31.96 it cost me to order it from Farnell (inclusive prices including delivery)

ChrisH

[Gina]

I have it down as about £27 with free delivery from Farnell Element14 but I haven't gone all the way through to actual payment lately.  If I can't find the one I have already I'll probably order another as it's a better option than the smaller 5v one.

[Gina]

AH... Just checked the price again and it's £26.63 ex VAT - so that's £31.56 inc VAT.

[ChrisLX200]

I guess the fact the cold end is covered in ice means it's working   What's the best way of controlling these things - PWM?

This heatsink isn't quite as heavy as it looks, and the fan is running at low speed so no vibration that I can detect.

ChrisH

[D4N]

I think the TEC isn't fussy about its supply but PWM is probably the most efficient way of having a manual control, a rheostat would be cheaper and smaller but inneficient so not ideal for battery powered setups.

Otherwise you can have a controller with feedback that will keep a set point but this would be a lot more complicated and more expensive.

 

I'm planning to just leave mine on full, if I find it gets too cold I will have to rethink this but the combination of dew heater and the heat from the sensor should be enough I think.

[Gina]

A constant voltage/current is best but I have used PWM.

[ChrisLX200]

I have a drawer full of NANOs and plenty of thermal probes so I guess I could cobble together a control circuit. I'm a bit worried that on colder nights the whole thing would freeze - the USB3 connector is right next to where the cold plate would be.

ChrisH

[D4N]

USB connectors work fine at -25°C, I have imaged with no problems at that temp.

I doubt the TEC could bring the casing down to a temperature that would damage it unless you have seriously over-specked your cooler.

[Gina]

I have built and programmed several automatic set-point coolers in the past.  I use DS18B20s for digital thermometers.