Using heaters on a Newtonian??

[Peje]

Getting everything prepared for this autumn/winter and I was planning to add a dew heater to the outside of my main scope to avoid the secondary misting when the scope is out all night. I already have one on the ST-80 which works well, currently have a 4ch controller with only one port being used.

My question would be; I am right in assuming that I just strap the heater around the top of the scope and this will be suficient? I'm concerned that with me having a steel tubed scope most of my heat is going to travel down the tube and very little (if any) heat will reach the secondary. I have been looking at the dedicated secondary heaters, there seems to be varying opinions on these due to difficulty in getting the right amount of heat to keep dew away without affecting optical performance. I am aiming for a set and forget system as I generally can't sit out past around 1am.

@Shelster1973

[andrew s]

With my Newtonian I had one strap round the main mirror with a temperature probe and a simple resistor chain behind the secondary. Both were controlled by a Kendric controller which allowed easy setting up of the power supplied. This worked well for me for imaging/spectroscopy.

Regards Andrew

[Peje]

Just now, andrew s said:

With my Newtonian I had one strap round the main mirror with a temperature probe and a simple resistor chain behind the secondary. Both were controlled by a Kendric controller which allowed easy setting up of the power supplied. This worked well for me for imaging/spectroscopy.

Regards Andrew

So you put a heater at the base of the scope to heat the primary? I might have to bite the bullet and buy one of the secondary heaters also

[andrew s]

1 minute ago, Peje said:

So you put a heater at the base of the scope to heat the primary?

The main heater strap was wrapped directly round the primary but going round the cell supports that hold the side of the mirror. 

Regards Andrew

[Peje]

Just now, andrew s said:

The main heater strap was wrapped directly round the primary but going round the cell supports that hold the side of the mirror. 

Regards Andrew

Thanks. I haven't had any problems with the primary misting but if it happens I'll have to look into heating it also. Going to start digging into secodary heaters to see what options are available in the UK, not really fussed on making something myself.

[andrew s]

I know you don't want to DIY but this is worth a read to understand the issues http://www.blackwaterskies.co.uk/2013/05/making-your-own-nichrome-dew-heater.html and http://www.blackwaterskies.co.uk/2013/05/a-cheap-multi-channel-dew-heater.html

Good luck - Andrew

[Peje]

Thanks Andrew, I had looked at the first guide but figured I'd just buy something as doing that for the secondary could be very fiddly.

I think I'm going to order this one as it looks like a well made solution and gets good reviews online.

[Peje]

Ended up getting this one as the previous one wouldn't fit my secondary. Took the dew controller into work today and hooked it up to one of the bench PSU's, marked the dial position that gave 1 and 2 watts to the heater, all being well it should be left at 1w forever.

1w with the heater floating in free air at ambient 23 oC had the heater at 32 oC, 2w was 42 oC. Maximum load was 3.7w which I can't see me ever needing. Hopefully I'll get some time to fit it this weekend, also planning to mark the centre spot on my primary so once that is done I'll spend a few nights getting the collimation bang on.