PCVC740K Design
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The 740K Cam Housing

click to enlarge

Following is a description of the 740K cam housing.

Remembering the design considerations: Can attach to 1.25" eyepiece and to CANON SLR lenses.

I usually connect the cam via a flip mirror diagonal with a T2 thread to the telescope and therefore the CANON adapter is not only used for the SLR lenses.

The housing

Due to an upgrade for digital satellite reception I had an old alu LNB (the satellite antenna receiver part which is mounted in front of the antenna) at hand which looked like it would make a new housing for my 740K cam.

After some modification it was able to receive the components from the cam as well as a Peltier and a cold-finger with the CCD.

The tube of the feed horn was extended to fit into a standard 1.25" eyepiece tube. 

The SLR attachment is based on my 'old' design which has a removable front part with the CANON bayonet ring. It is only a alu part which fits onto the eyepiece tube and which accepts the bayonet ring front part. 

The Peltier cooling

The Peltier cooling part consist of 

a 30x30mm Peltier element (second hand so I don't know which manufacturer but it seems pretty common in specs).
an good quality alu CPU cooler with fan (ball bearing)
a cold-finger made from copper 
the power supply to drive the Peltier

The cooler is mounted on the outside of the alu die cast LNB housing of course with thermal transfer compound (actually a double sided thermal transfer tape which provides a very strong hold for the cooler - trade name is BOND PLY).
On the inner side the Peltier is mounted with nylon screws going through the LNB and the cooler.

The CCD is mounted with the double sided thermal transfer tape on top of the cold-finger which in turn sits on the cold side of the Peltier.

By design the CCD is pressed to the cold-finger and the Peltier when the cam housing is closed.

The power supply has 12V input and a LM317 linear regulator to provide 3 different power settings for the Peltier. The fan is driven by the same circuit with the intention if the Peltier does run on low power the fan can do the same...

The settings are:

Low: Ipelt=0.63A; Upelt=3.56V; Uvent=4.12V
Med: Ipelt=0.94A; Upelt=4.54V; Uvent=5.32V
High: Ipelt=1.42A; Upelt=6.12V; Uvent=7.22V

I could not place a thermometer to the cold-finger but I recognize the following effects with 20C ambient:

Low: icing on the raw pelt without any parts mounted
Med: just no icing on the CCD window - optimal ??
High: icing on the CCD of the completed and running cam (this is where I have to seal the CCD window)21

Cam assembly 

Putting everything together with insulation of the LNB housing and some pads and double sided tape to hold the PCB is shown to the right. The CCD is wired using a flat computer cable with 8 wires each side. 

The front part of the housing builds a shield and window which accepts the CCD and put a slight pressure to the whole assembly to avoid screws and other mounting parts.

And finally............

This is a picture stack of M3 taken on the day of the first light of the cam with all the modifications shown above but yet un-cooled mounted on my Lomo Astele 133.5mm telescope in prime focus.


My 'new' CCD cam


Sketch of the housing


The LNB housing


Both of them


Cold area


Cooler detail


CCD on top


Power supply circuit


Almost finished


Eyepiece & SLR


740K SC