K3's AstroPhotography
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Philips Vesta (PCVC675) LONG EXPOSURE cooled SC2 camera

A, Introduction
B, Technical data
C, Peltier cooling system power requirements
D, Detailed photo-documentation of modification
E, Electronic thermostat


Introduction
After five months of using my Philips Vesta 675SC camera I decided to modify it to stage 2 (software switching long exposure mode, switching CCD amplifier on/off) with cooling. The inventor of this modfication is Steve Chambers and you can find on his pages schematic diagram and information about this modification. The cooling system was built according to nice idea of Peter Vasey.

!WARNING! You can use the following information on your own risk. Author is not responsible for any damage of camera or computer equipment. The following procedure was done successfully by author, but he cannot guarantee, that your modification will be successful.

Technical Data

Weight
(incl. USB cable)

309g
(non modified Vesta has 175g)

Dimensions
(length x width x height)
90mm x 65mm x 40mm (without radiator)
90mm x 65mm x 80 mm (with radiator)
Maximum usable exposure time 15-20 min
Temperature difference
(difference between ambient temperature
and temperature of alloy chamber arround CCD)
~28C
Cooling down time 8-10 min
DarkFrame
(15min, gain 100%, white balance - Indoor,
cooled, ambient temperature 25C)


Peltier Cooling System Power Requirements

Peltier unit - Supercool PE-127-10-25
Imax 2.0 A
Umax 16.4 V
PCmax 19.3 W
DTmax 74 C
THot max 80 C
Dimensions
(l x w x h)
30mm x 30mm x 4.8mm
Voltage Current consumption Power consumption
12V 1.26A 15.12W
9V 0.96A 8.64W
6V 0.63A 3.78W
5V 0.46A 2.30W
4.5 0.39A 1.75W

Note: Power consumption was measured with ventilator switched ON.


Detailed photo-documentation of modification

Detailed description of procedure of modification camera for Peltier cooling you can find on Peter Vasey web site.
Here you can find detailed photos, which illustrate, who the modifaction was done.


Alloy casting housing the LED, Microphone, CCD Chip and lens. Note that end part of PCB carrying only model information was trimmed off.

Detail view of alloy part, which must be cut down to cube.

Truncated PCB with CCD, microphone and LED.
The with of module is 20mm.

Another look at CCD. The second pin from left must be cut.

Detail of hand-worked alloy part. Abrasive paper '400' was used for final treatment.

Detail from PCB side. Note the small recess on the left side which has been cut to allow the passage of a wire from cut CCD pin 9.

Another side of alloy part. The recess is for microphone.

Hand-made aluminium parts for cooling system together with alloy box.

Detail vie of aluminium plate, which is connected to cold side of Peltier unit

Small spacer between aluminium plate and alloy box.

Small clamping plate for gripping alloy box to aluminium plate.

Peltier module (Supercool PE-127-10-25)

Top view of plastic case with filed out openings.

Front view of plastic case with detailed view of opening for alloy box with CCD unit.

Aluminium plate attached to plastic box

Cold plate with Peltier unit. Note black plastic spacers on both sides of aluminium plate.

View from inner part of plastic case

Gripping of alloy box part by means of clamping plate and bolts

Rear side with holes for connectors and LED

Cut pin 9 of CCD.
Unfortunately, I had a bad day - I cut the pin 13 accidentally. You can see repair on right side

Camera's main board mounted into case

View of connector part situated on rear side

Top view of inside parts

Switching transistor of SC2 modification is soldered directly to CCD's PCB (prevention from unwanted interference). Note green 2k7 resistor
   

Metal part from Vesta camera with tripod thread was modified for attaching to bottom part of case

Bottom part of case with tripod thread

The final result

Rear side of camera - green LED (from CCD PCB), connector for 12V power for Peltier unit and ventilator, CANON 9 connector for computer control and USB cable

Detail of Peltier unit with radiator

Ice created on cooled metal parts after 1 hour of cooling. (Ambient temperature 26C)


Electronic thermostat

The Peltier cooling system of my webcam is able to generate temperature difference about 28C (between ambient temperature and temperature of cold chamber). It is very powerful cooling. But there may be a problem in colder nights, when cold chamber can become too cold. In freezing nights it is not a problem to get tempereture of -30C or even lower, which is even under allowed storage temperature!
According to SONY datasheet the CCD chip used in Philips Vesta cameras (ICX098AK) has the following temperature conditions:

Storage temperature 30C to +80C
Operating temperature 10C to +60C

I decided to design an electronic thermostat, which would protect the CCD from very low temperatures.
The thermostat should satisfy the next demand:
1, Low power loss (i.e. low production of heat)
2, Small size and weight - the best solution would be to put the electronics into camera case
3, Adjustable temperature threshold
4, Precision about +/-1C

The most difficult criteria are 1, and 2,. The problem is to switch the current about 1-1.5A without loss of power. I tried several solutions - bipolar switching transistors, relays - but without success. In case of inbuilding thermostat in camera case, it is unwelcome for electronics to generate additional heat. Finally I decided to use power MOSFET. The IRFR024N type has the resistance in on-state 0.075Ohm. It enables to achieve power loss only 75mW (1A current).
The costs of the whole electronic thermostat is not more than 5,-Euro.

Here is my final version of thermostat for Peltier cooling system:


Click the picture to see full-sized schematic diagram.
Note: Supply voltage is 12V. Inputs of the second operational amplifier must be handled (+ input to VCC, - input to GND) to avoid its oscillation.

The principle of function:
The temperature sensor IC2 (LM335) generates voltage which represent temperature (10mV/K). The voltage from IC2 is compared with voltage adjusted by R8 trimmer. IC3a (one half of LM393) serves as comparator. R11 and D1 provide hysteresis of the control loop. The hysteresis is necessary for securing the transistor T1 (IRFR024N) is working in switching mode (only in this mode the power loss is very low). D2 LED is indicating that Peltier is switched on (I like blue LED for indication of cooling ;-))).

The contruction notes:
I built the module on experimental piece of PCB. I protected the temperature sensor from water/ice by putting its end with pins into heat-retracting insulator (see a picture below). The voltage from IC2 is led out to connector on rear camera panel. It enables me to measure temperature of cold chamber.
As the thermostat consists of the sensitive measuring part and power switching part, the PCB must be carefully designed. You must pay attention for current loops - you have to design two separate grounds for each part. In case of violation of this rule, the thermostat will not be sufficiently accurate.

The adjustment procedure:
At first it is necessary to do fine adjustment of IC2. I used mixture of water and ice (which has temperature 0C while ice is not melted). I put the temperature sensor into this mixture and by means of trimmer R7 I set the voltage on the IC2 (between cathode and anode) to 2.731V (which represents 273.1Kelvins). Then I set the voltage in R8 trimmer according to required temperature - in my case I set 2.551V, which represents -18C. With current values of R2, R4 and R8 it is possible to set the temperatures between -19-+2C.
That's all.

According to my tests the termostat is holding the temperature in required range -18+/-1C.

And here are some photos of implementation of the thermostat:


The temperature sensor (LM335) put into heat-retracting insulator

The holder of temperature sensor (made from piece of plate) with hole for M3 bolt

The thermostat electronics built in bottom side of camera's case

Fixation of sensor to cold chamber. The sensor is fixed under M3 nut.

The rear panel of camera. Notice the bottom part:
On the left side there is a blue LED (Peltier indicator) and on the right side there is a connector for measuring temperature (by means of digital multimeter).
 


Have a look at tests of my cooled SC2 camera

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Last Update: 14.09.2005