My take on DSLR peltier cooling

[Gina]

My peltier is unregulated at the moment simply cause I don't have a clue of what do to to regulate the power to it....what do you use for this, I must buy some components

I'll post what I do when I've done it (if you see what I mean) Haven't quite decided yet.

P.s. Yup....like I said Gina is a brave, going fot this mod with no fear he he he

Not exactly no fear! But I do have a fair bit of experience in electronics and dealing with the hardware.

[martin_h]

Any good?

[martin_h]

PWM control for the cooler perhaps?

[yesyes]

PWM control for the cooler perhaps?

That's what I'm doing.

I posted the circuit diagram for my cooling controller in my 1000D cooling thread

http://stargazerslounge.com/diy-astronomer/183121-eos-1000d-extreme-modding-4.html#post2245170

[Mr TamiyaCowboy]

PWM control for the cooler perhaps?

not sure on the electronics side but i could not see why.

but that foam sheet is a good way to go in insulating and could have possible other uses when heated up.

light weight dew shield lol

[Gina]

I'm afraid Chris's design of PWM controller is too complicated for me - has to be fairly simple at my age

[Gina]

Not sure yet whether to go for a separate controller or via computer. The latter would be more accurate and provide settings and display in the warm room rather than near/on the mount. I have an old laptop running Linux Mint which I could program to read a 1-wire DS18B20 thermometer and control a MOSFET for PWM. The laptop would also run my weather station software and possibly other things while my newer netbook running Windows XP does the mount control, guiding and exposure sequences.

[Auntystatic]

How about using the venerable 555 timer with a power mosfet to pulse the voltage, you could vary the pulse width of the "on" period with a pot and mark a dial for the temp.

[Gina]

How about using the venerable 555 timer with a power mosfet to pulse the voltage, you could vary the pulse width of the "on" period with a pot and mark a dial for the temp.

Yes, that's what I thought of first of all but I'd like to provide feedback from a thermometer to provide set-point control. I may make up the 555 controller to start with in place of my bench PSU.

[yesyes]

How about using the venerable 555 timer with a power mosfet to pulse the voltage, you could vary the pulse width of the "on" period with a pot and mark a dial for the temp.

That would be one easy way. However, somehow I think that the same PWM duty cycle will not always result in the same temperature. It will depend on the ambient temperature. So you could easily control the "intensity" of the cooling but not the actual temperature.

What I'm aiming for are a few repeatable sensor temperatures. The controller will cool down to that temperature and then hold it. This will allow me to make a library of darks for only a few specific temperatures. Of course this makes the controller more complicated.

But it's not as complicated as it looks. The bottom right looks complex but that's only the weird wiring for the display which is not really necessary. The rest is just an Arduino with a few sensors, a transistor for PWN cooling fan control and a MOSFET with current limiting circuit.

[Gina]

I did think of using a thermistor to measure the cold finger temperature and put that in a comparator circuit with a variable resistor (pot) to adjust the set-point temperature. The following op-amp arranged as a standard amplifier (rather than with hysteresis) then compared with a triangle wave to operate the MOSFET. I'll post circuit diagram later.

[Gina]

The other idea is to use the digital temperature sensor and feed that into the computer. the TEC being controlled by MOSFET fed from the PWM output of my USB interface board. (The other inputs and outputs would be used for other controls such as filter wheel and electric focuser motor.) Then the temperature set-point would be input to software and compared with the temperature read from the cold finger and the PWM output changed to bring the temperature back to the set-point value.

[Mr TamiyaCowboy]

am not good with that sort of electronics but i had an idea.

maplins sell these electronic kit modules, i was going to use

Temperature Activated Switch Kit : TR Kits : Maplin Electronics

with it wired to a TEC to control when it was switched on and off, they also sell a 555 timer module and a thermostat. could all these small units be wire into one multi purpose unit

[Gina]

Unfortunately it seems Preltier TECs don't like being allowed to change temperature too much. A PWM control running at over 100Hz is fine. But the temperature cycling of a thermostat control wears them out.