Cold Finger design

[libraryman]

Hi all, there's a lot of experience on this forum with respect to cold finger cooling, can i tap into that by asking.

1. what's the best material, copper or aluminium...i know some of the relative merits of both, at this time i suspect aluminium will suffice because i       don't really want to go below - 2/3 deg's C

2 what thickness of cold finger is good, i know that i have to have 1.2mm for insertion into the sensor gap but what about the Peltier contact           area..how thick is good for this area?

3. is Condensation a real problem in cold finger design and is it really necessary to employ some kind of preventative measure?

That's all folks, hope that you can advise.

Ray

[starnut]

Watching with interest as I want to go down this road with a future webcam.

[Guest]

Well Meade have been using this method for over 15 years with their DSI cameras, cold finger cooling with no peltier or fan, and I can say it works great on my DSI Pro III.

So go for it

Olly

[libraryman]

Hi olly, I believe that the dsi uses a heatsink only..attached to the sensor just to get rid of excess heat!!

I of course can not use that method for reason of space but a cold finger should be more efficient.

My question about what material would be best is probably not the best way to ask, I need to achieve a delta of 15deg C, which Material would achieve that drop consistently?

Ray

[skybadger]

Hi Ray.

It's not a question of material,it's a question of cooling. it's a question of the ability to suck heat first and foremost. Most heatsinks I have used have been copper. Pc heatsinks are aluminum. You need to insulate the heatpath to prevent condensation and ensure that you only pull heat from the source, not the rest of the environment. Closed celll foam, polystyrene or lagging will do. Then you need to ensure you can dissipate the heat , mostly by putting a fan across the heatsink or using watefcooling. Otherwise a pc modders water pump and heat exchanger will do this really well.

Hth

Mike

[astrovirus]

Hi Ray,

From my own experience I would say copper is the prefered material as it is a better conductor of heat compared to aluminium (which is also heavely dependant on the type of alloy used). With regard the the thickness of the copper at the peltier connection I don't think it needs to be really big, 1 mm should be sufficient, but it is important to have a large contact space, so the copper should connect over the complete size of the peltier element. Finally, dew is a real big problem and if you can incorperate some form of dew heating system I would do it for sure. In my Dutch setting I can usually go about 5-10°C below the dewpoint, if I go lower, I get dew on the sensor within minutes.

Good luck,

Regards Tim

[libraryman]

Some good points here, I had not fully appreciated the reason for the insulation, I will go with 2mm for the finger thickness to retain rigidity and a decent pad size for contact area!

Is there a preferred way of applying heat to the sensor to reduce condensation, I am initially considering nichrome wire!!

Ray

[faulksy]

copper is the best conducter of heat out of the 2 gold would be better though, use some heat sink compound as well

[libraryman]

He he, I'll look around to see if anyone will let me have 4 inches of 24 carrot gold plate!!!

Ray

[Mr TamiyaCowboy]

webcams become warm for one reason, lack of a decent heat spreader internally on the main and secondary chip sets

they tend to be the power hungry part of the system as they have to do all the work ONBOARD, also the fact they are thrown into a small none vented case.

there are a couple ways to help, liquid mask is one, we use it in the hobby scene to mask of paint areas.

this could be used and applied by brush to the rear side of the board, 

cooling could become two finger heat spreader with a very small TEC unit fitted 40mmx40mm 

taking those chips down in temp will help they ARE the main cause of heat and couple the fact webcams are getting smaller and smaller.

more , usb controllers etc etc are all being added to a single chip.

i would look more at cooling the workhorses of the camera system, mainly the chip sets on the rear of the board.

the sensor will not get as hot as those chips do.