Celestron dew heater rings?

[5ash (Philip)]

Can any one who uses one of these suggest options for powering and controlling one , that doesn’t cost too much . I enquired about the cost of one for my C11 , I wasn’t phased by the $225 price for the heater ring (it’s not cheap) but was taken aback when I was told that the recommended celestron controller was $750.I understand the frustration of dewing on a corrector plate but was suprised at the cost of this answer. My telescope is in an observatory of sorts and is protected by a dew shield that works well so I can probably get away without one. Would be interested in suggestions and discussion about this product . Regards philip

[gregmc (Greg)]

I’ve read over time lots of stories about people powering those rings and essentially having issues with too much power applied. The manual might indicate you can (I forget as it’s a long time ago I read it) but you will have issues.

The controller measures ambient temperature and humidity. It uses these to calculate the dew point which is the temperature of a surface that dew forms.

The controller will provide power to the ring while measuring the temperature of the glass with a built in sensor. It uses that measurement as a feedback to adjust the power to the ring.

You use the windows app to adjust the aggressiveness of this control if you like but the app is not needed otherwise unless you want to see the graphs or control the 12v port. You just ignore the other celestron stuff in the app if you don’t have other celestron gear (which I don’t)

Manual control of power to the heater can be a bit of hit and miss without knowing the dew point and without any idea of the approximate temperature of the glass

[carlstronomy (Carl)]

I have a band heater around the end of my 9.25" SCT. This has a very simple manual controller and to be honest I was surprised at how little heat was required to keep the corrector clear. I am not a fan of having heaters connected at all times so as the dew sets in I turn on the unit and monitor in between shots to ensure I am not under or over cooking. Knowing how little it takes to heat the corrector to prevent due build up I can understand the previous comment about people having issues after all you do not want to heat up the interior of the tube, this causes even more issues. In my observatory I find a due shield usually does enough for my imaging nights to keep my corrector clear, I would personally not spend $750 on fancy controller than will probably not achieve anything special.

There is a lot of money to be made from our hobby and if the companies think they can suck $750 out of us for an item that probably cost less than $40 to make they will We seem to love the shiny pretty stuff and they know it!!!

I like you looked at the pretty corrector plate heater and thought, nice I would like that. But at the end of the day thought why bother, expensive setup which can be achieved for a lot less money.

[JA]

One could use a simple ON/OFF* temperature controller with a 12V high current relay with the often supplied thermocouple situated on or near the glass to control the heater to be at or slightly above the ambient temperature to ensure that the glass temperature does not reach the dew point temperature for the conditions.

One thing of interest to the above in terms of determining a crude temperature set point: If you heat the glass to the ambient temperature it will always be above or equal to the dewpoint temperature. (It will be equal to the dewpoint point temperature when the air's relative humidity is 100%.) You could use less power if you finessed the air's condition, but that would require some assumptions and/or at least one other air parameter, such as its relative humidity, wet bulb temperature, etc... and using say a psychrometric chart for air to determine its condition.

*If you want it more sophisticated you could also go for a PID type controller with PWM type output.

A bit of a project.

Best
JA

[ChrisV (Chris)]

Like this
https://www.iceinspace.com.au/forum/...d.php?t=144679
He said in a self aggrandising sort of way. Actually I must update it as it's changed a lot since then.

It's an Arduino pwm controlled heater. Measures ambient temp/humidity using one of several available sensors, heater temp using the ds18b20, and can use cheapo MOSFET modules as you don't need much power.

Can set power manually, variable according ambient temp relative to dew point, or feedback control of heater temp relative to dew point.

Chris

[JoeyJoJoJr (Adrian)]

I built my own dew heater ring and controller for my Celestron C8 very simply using nichrome wire wrapped in duct tape and a cheap PWM controller from Amazon. The PWM is nice because it's more efficient than controlling current in other ways so somewhat offsets the loss off any battery usage for using a higher temp than necessary.

I followed the instructions at https://www.deepskywatch.com/Article...ew-heater.html for the heater strap. I ran two wires in parallel to fir the internal circumference of the OTA, I then connected this to a 5.5/2.1mm DC plug. I just taped it on the inside of the OTA making sure I left enough of a gap at the front to be able to use the cover. I added velcro to the cover and the end of the plug so that I could attach it to the cover and reduce the amount of contact the wiring might make with the optics when the cover is closed.

I mounted the PWM inside a small enclosure, and wired it up with 2 5.5/2.1mm DC sockets and then attached it to my dew shield next to a small hole through which the plug can run.

I played with the temperature a little bit and have found a 'max' value where there is slight star distortion due to the heat. That value will depend on the input amps.

All up it cost me approx $30 and most time was spent running the fiddly nichrome wire along the duct tape so that I had a consistent, straight ring.

Nichrome: https://www.jaycar.com.au/nichrome-r...-pack/p/WW4040

PWM I used: https://www.amazon.com.au/Controller...d=AXQ2EGXUO12M