Dew heater for a 250px

[AndyWB]

Hi,

I'm thinking about trying to lay my mitts on a Kendrick split secondary heater for my 10" dob. However, I'm stuggling to figure out what size! Looking at this page - http://www.kendrickastro.com/newtonian.html#Split - it seems that none of these split secondary heaters are small enough to my secondary (though my measurements are a bit rough - I didn't take the mirror off, and the measurements were 'tricky' with it mounted). Even the smallest seems  a fair bit longer than my secondary mirror.

I'm figuring this must be muppetry on my part. Has anyone ever tried fitting a kendrick split heater to a 10" f4.8 skywatcher? Which heater did you use?

Or does anyone happen to have the exact dimensions of such a secondary mirror?

Thanks for any help,

Andy

[MattJenko]

Hi Andy - what has prompted you to get a dew heater (other than the obvious) - has it been regularly dewing up?

I have not had my secondary dew up much, but not had massively long observing evenings recently, so wondering what circumstances have led you to get one for yours?

[AndyWB]

Um, yeah, pretty much that it's dewing up sometimes. Dewed up after about 2.5 hours a few weeks ago. It's not always by any means, but sometimes. And I've recently found that the travel hairdryer approach means starting my car before it supplies power to it - and starting the car generates a lot of light.

If it's a lot of hassle, well, I might not do it, but I wanted to investigate.

[AndyWB]

For future information for anyone finding this, yes, split ring dew heaters are too big for 250pxs and, I suspect, 200ps also. I'm going to look into stalk heaters. I know there is a small air gap to the mirror; I may also be looking into thermal conducting paste like you put on computer CPU heat sinks...

[MattJenko]

Seeing as I side-tracked this thread in the first place, and I am also interested in this, I will add my searchings:

There seem to be homebrew solutions involving resistor chains, which means the wire can be threaded along a spider without any increase in obstruction size.

http://www.dewbuster.com/heaters-330ohm-resistors.html

Kendrick do a wrap around for smaller secondaries that the split ring ones won't fit for people like me who get panic attacks when faced with electrical wiring.

http://www.kendrickastro.com/newtonian.html

[michaelmorris]

My advice would be to contact Kendrick and ask them which one will fit, they may well know.