cooling a c11 help please

[icytailmark (Mark)]

can someone please give me some tips on how to cool a C11? I am going to buy a c11 and losmandy g11 mount sometime this year for mostly planetary imaging. I will be using a DMK21 ccd camera.

Does anyone know a retailer that would be able to install fans for me without voiding the warranty?

[sheeny (Al)]

G'Day Mark,

There's obviously a lot you can do with active cooling and SCT coolers etc. I can't answer your direct question there, but if you will have the C11 installed in an observatory, a humble small electric fan blowing ambient air over the OTA will help heaps without the expense of an SCT cooler or active cooling fans.

I was very disappointed when I first got my C11 to find that an hour or two of cooling still resulted in strong thermal currents in the OTA, when they would've been long gone in the C8. I tried the electric fan blowing across the OTA, and ever since I haven't seen evidence of a tube thermal. There obviously must be early on, but its a low tech solution that is worth exploring.



Al.

[icytailmark (Mark)]

i dont have an observatory i just use my backyard. I use a 5amp 13.8VDC regulated power supply for all my power requirements.

[asimov (John)]

Right now it's very easy to control. There's only 2 planets worth shooting (Saturn & venus) in the AM which gives you plenty of time to setup just after dusk, point the OTA corrector down, bung in a cheshire with 3 winds of flywire & a rubber band around it to allow heat from the mirror to escape, tarp her up & walk away until 2AM.

It gets more difficult as the object becomes a PM object.

The flan blowing on it works wonders too. I keep my OTA in the shed with a big fan blowing on it 24/7 when not in use.

I have more trouble with seeing, more so than I'll ever have with not being at ambient. Once you've seen really good seeing (8+) even WITH internal thermals you'll wonder what the fuss was all about.

[casstony]

I've been keeping an eye out for easy solutions to cooling my C11; a guy on cloudy nights found that simply removing unused screws from the ota gave a large improvement. I'm going to do this once I find some filter material to stick over the holes, maybe something like the plastic mesh used to filter airflow into computer boxes.

There are up to eight screws that can be removed from the rear end (including the handle and finder mount screws) and two at the front, depending on what accessories are mounted to the ota - mine is the Chinese model with the sculpted back end.

The rear port could be left open initially (covered with stocking) and air will naturally flow through the ota, but even while observing air can still escape from the ota through the screw holes.

Regardless of the degree of success it's a painless and reversible experiment to try.

Note: be sure not to unscrew anything with a nut on the inside of the ota.

[casstony]

If anyone would install fans it would be Bintel - you'd have to call them.

One thing I don't understand is why people bother to drill into the castings rather than mount a fan on the side of the aluminum tube blowing across the mirror face.

[pmrid (Peter)]

Originally Posted by casstony

I'm going to do this once I find some filter material to stick over the holes, maybe something like the plastic mesh used to filter airflow into computer boxes.

There are up to eight screws that can be removed from the rear end (including the handle and finder mount screws) and two at the front,

I have used a variation on this method. To filter the holes but still allow reasonably unobstructed air flow is the trick. My solution was to get some of both types of adhesive-backed velcro - the one with the hooks and the one with the soft pad that the hooks grab. I cut short sections of the hook, then folded it in half and using some little side cutters, cut a diamond-shaped hole in the middle roughly the size of the holes in the OTA rim. I removed the adhesive protector and stuck that on the OTA so the hole was open and under the diamond hole I had cut. It tyhen cut sections of soft velcro the same length and without removing the adhesive backing, lightly positioned it over the hook velcro on the OTA. My plan is based on the fibres of the velcro being sufficiently open to act as an airflow but sufficiently dense to act as a decent filter.
Seems to work OK but I also use an SCT cooler - having a bet each way.
Peter

[Paul Haese]

HI there,

try this if you dare. I did this 2007, I was the first of now quite a few. It is easy to conduct and just requires some care.

Click here for link to peltier cooling an SCT.

[casstony]

Hi Peter,
I think I'll try your velcro idea, but cut a hole through both pieces of velcro and sandwich some stocking fabric between the velcro; I think this might allow better airflow along with better filtering.

I like Al's idea of the fan blowing onto the outside of the tube too.

Not so keen on Paul's major surgery .