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EOS 1000D extreme modding

yesyes

By yesyes
in DIY Astronomer

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Gina

Gina

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That had occured to me, Gina but I thought that the simple approach might be easier overall. I've used this method with a number of power amps and I incorporated it in the output stage of my own dew heater controller. It doesn't need to be super accurate as long as it reduces the drive to keep it within the SOAR of the output device :icon_salut:
Yes, I agree with that. The charger uses voltage and current control to provide optimum charging and preventing possible damage to batteries being charged. The charger was designed to cater for car batteries as well as the very heavy duty tractor batteries. The application in this thread doesn't need such sophistication, I quite agree.
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yesyes

yesyes

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That looks fine to me, Chris :icon_salut:

Thanks a lot. I shall test this as soon as the MOSFETs arrive...

Also thanks again for this suggestion that I had not considered. Better safe than sorry.. ;-)

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rcheshire

rcheshire

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I used one of these from element14/Farnell

NXP - PSMN1R6-30PL, Logic Level N-Channel MOSFET, very low Rds(on) 0.0014ohms (0.14mOhms), with a high power rating. No heat sink required, but it has its own in any case, just in case.

I see you've attached a display - very nice. Dew point calculation would make PWM scheduling automatic. I tend to set about 2C above DP.

The PSU I bought is very noisy, so much so, that just plugging it in, even without switching it on at the mains causes interference - grounding the camera chassis fixed that. I use the same 22uf cap across the Gate pull down resistor as your design, and although I was advised not to do this, the system runs very well. Any ideas you have on noise reduction on the MOSFET side will be most welcome.

I notice that Pixinsight rejects the odd interference line which appear from time to time.

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yesyes

yesyes

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Ah, about the noise, I will have to check that when I've build all this and noise/interference becomes a problem... What I've read is that all cables to the peltier (i.e. everything carrying the high PWM switched current) should be shielded and the shield grounded. The braided shield stripped out of a length of coaxial cable could be used.

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Gina

Gina

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Been looking at the cold finger mod and see that the 1000D is much easier to mod as there is a separate circuit board to the left of the sensor that isn't needed and can be removed so that the cold finger can go straight through the side of the body. On my 1100D the main board goes right round the left side and has the USB connector etc. on it, completely blocking cold finger access that way. So that is an advantage of the 1000D over the 1100D even if it does have a higher noise level. As I recall, the 1000D has about twice the noise of the 1100D so 7C lower temperature will make them equivalent.

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rcheshire

rcheshire

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Ah, about the noise, I will have to check that when I've build all this and noise/interference becomes a problem... What I've read is that all cables to the peltier (i.e. everything carrying the high PWM switched current) should be shielded and the shield grounded. The braided shield stripped out of a length of coaxial cable could be used.

I think it helps, moreover a good quality PSU wont be so problematic.

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Gina

Gina

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I'd be inclined to suggest a low switching rate for the Peltier TEC to reduce the noise. Thermal devices have a long time constant - you could probably use several seconds per cycle. I'm thinking of using a simple thermostat circuit to control mine. A hysteresis of something like a degree C would be alright I would think.

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yesyes

yesyes

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I read that this is exactly what one should *not* do with peltiers. Between cycles the peltier should not have enough time to significantly cool or heat as that would drastically reduce the life span of the peltier. It is recommended to use PWM above 2kHz but no less that 100Hz IIRC. The Arduino PWM is around 500Hz, so that should be fine-ish.

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Gina

Gina

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This is a thermostat circuit I designed for stopping my rain gauge from freezing. The same sort of thing with op amp inputs reversed and maybe the BD681 replaced with a power MOSFET. Oh, and the supply would be 12v rather than 24. Hysteresis is controilled by the 1M positive feedback resistor and is several degrees C for this value.

Heater_Thermostat_4.png

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Gina

Gina

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I read that this is exactly what one should *not* do with peltiers. Between cycles the peltier should not have enough time to significantly cool or heat as that would drastically reduce the life span of the peltier. It is recommended to use PWM above 2kHz but no less that 100Hz IIRC. The Arduino PWM is around 500Hz, so that should be fine-ish.
Oh I see, I didn't know that. :icon_salut:

I guess I could use the PWM o/p of my USB interface board (I'm not into Arduinos). Or perhaps a 555 timer.

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yesyes

yesyes

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That is almost the same PDF as the one I linked to 2 posts before... :)

This describes more or less what I had in mind. I'll make a case from 3mm black acrylic and add automated cooling control and a few more temperature sensors.

It looks like the author of that PDF has also removed the viewfinder mirror. Too bad he didn't describe how and what needs to remain in place (does it have a switch?)....

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rcheshire

rcheshire

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Home / DSLR cooling modification | Gallery - synergous.com

Unless you intend installing a dew heater on the front of the low pass filter there doesn't seem much point to the reconstruction of the camera. The cold finger is easily formed to exit the camera body without the removal of any parts - as in my mod linked above and here - Canon 1000D/XS/Kiss F DSLR cooling modification - images and overview FlatPress

Cheers

Rowland.

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