Dew Heater Advice

[Scooot]

I need to protect my secondary from dew and I've been looking at options. With my secondary it seems to be between the kendrick wrap around version or one I attach to the back of the mirror. If I choose the second option I have to remove the secondary and then unglue it from the stalk to put the heater on. I'm known here as a Do it Wonky expert so I'm not very keen on this option although it's probably the best solution. Re the wrap around version I wonder whether it obscures the view at all, I don't really want to do this if it would reduce contrast.

The Kendricks look good but the dew controllers seem expensive and using others void the warranty, I don't know if this is a sales ploy or whether other dew controllers don't work with there's.

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

So I'd be glad of any thoughts/views or other options.

This is my mirror.

[Tommohawk]

Quite a few threads on dew problems at the moment - its that time of year I guess!

The heaters that wrap around the stalk are probably easier - I can't say I've fitted one myself - but to get the heat to the mirror they have to produce more heat than you really want wafting around in your OTA. It s especially a problem if the secondary is fitted on a pad cos that doesn't conduct the heat very well. 

Kendrick do a split elliptical one which can fit to the mirror direct, but the stalk on yours looks too big to give sufficient space for that. HAve a look at the website - it has the dimensions - maybe type 2029-XL?

With regards to controllers, you should be able to rig something without risk to the heater pad - just make sure you dont exceed the voltage which the recommended controller operates at. 

I've just done a mod on my secondary - its quite pretty if I say so myself, BUT I scrated the mirror in the process, so wouldnt recommend this method!

I'm looking at an alternative method which doesnt involve so much handling of the mirror, but not sure how this wil work out yet.

TBH on balance if your mostly doing visual I think the waft of the hairdryer is the simplest/lowest risk/lowest cost option.

[Scooot]

Quite a few threads on dew problems at the moment - its that time of year I guess!

The heaters that wrap around the stalk are probably easier - I can't say I've fitted one myself - but to get the heat to the mirror they have to produce more heat than you really want wafting around in your OTA. It s especially a problem if the secondary is fitted on a pad cos that doesn't conduct the heat very well. 

Kendrick do a split elliptical one which can fit to the mirror direct, but the stalk on yours looks too big to give sufficient space for that. HAve a look at the website - it has the dimensions - maybe type 2029-XL?

With regards to controllers, you should be able to rig something without risk to the heater pad - just make sure you dont exceed the voltage which the recommended controller operates at. 

I've just done a mod on my secondary - its quite pretty if I say so myself, BUT I scrated the mirror in the process, so wouldnt recommend this method!

I'm looking at an alternative method which doesnt involve so much handling of the mirror, but not sure how this wil work out yet.

TBH on balance if your mostly doing visual I think the waft of the hairdryer is the simplest/lowest risk/lowest cost option.

Many thanks for this. I think I'll steer clear of the wrap around now. I think one of the split ellipticals would fit size wise but my mirror is glued onto the stalk at the very edge in at least three places so I'd have to remove the mirror and glue to fit it in which case of course I might as well go the full hog and get one of the others.

I've been borrowing Jane's hair dryer but it's a bit of pain getting the extension lead set up running from the garage and I'm sure she'd rather I didn't. I've been googling for a battery operated one with no luck so far but maybe I'll just have to look a bit harder. If anyone knows of one........?

Thanks again.

[Tommohawk]

I think the split ones are a bit bendy , so you can open them a little to fit round the stalk without having to remove the mirror. Check this first, but I think thats correct.

This is the option I would go for, but my secondary is only 52mm min ax) wide so too small for any of the Kendricks so far as I can see..

[faulksy]

Hi,Richard, make your own mate. I did, I used I think 330 ohm resistors 1/4 watt around 15 in total, wrapped around the stalk. Control is simple pwm. As long as you insulate the stalk there's no heat currents, as all the heat goes into the mirror

sent from my fone using fingers

[Scooot]

Hi,Richard, make your own mate. I did, I used I think 330 ohm resistors 1/4 watt around 15 in total, wrapped around the stalk. Control is simple pwm. As long as you insulate the stalk there's no heat currents, as all the heat goes into the mirror

sent from my fone using fingers

Cheers Mike,

Make my own eek, I'm a Do it wonky expert Lol. you didn't read my post properly.

Seriously though, I've just googled some pics of resistors and looked up what a pwm is. So if I wrap the resistors around the stalk how does the heat get into the flat, and why doesn't it heat the air around it?  You can see my knowledge in this field

PS

Ah just realised you mean wrap insulation around the outside of the resistors Doh. Still not sure how the mirror heats, presumably its transferred through the stalk?

[estwing]

If it's that simple you can do mine Mike!!

[Daniel-K]

Richard the split one work fine any controller. yes the kendricks are or much higher quality but you can just use the astro zap of hi-tech astro single channel controller. 

[Daniel-K]

Many thanks for this. I think I'll steer clear of the wrap around now. I think one of the split ellipticals would fit size wise but my mirror is glued onto the stalk at the very edge in at least three places so I'd have to remove the mirror and glue to fit it in which case of course I might as well go the full hog and get one of the others.

I've been borrowing Jane's hair dryer but it's a bit of pain getting the extension lead set up running from the garage and I'm sure she'd rather I didn't. I've been googling for a battery operated one with no luck so far but maybe I'll just have to look a bit harder. If anyone knows of one........?

Thanks again.

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

[Sporadic Dobstronomer]

...I've been borrowing Jane's hair dryer but it's a bit of pain getting the extension lead set up running from the garage and I'm sure she'd rather I didn't. I've been googling for a battery operated one with no luck so far but maybe I'll just have to look a bit harder. If anyone knows of one........?

Thanks again.

I use what is allegedly a travel hairdryer with a car cigar-type plug which is rated at 168W.  In English that means you die of old age before your hair gets dry, but the unit is very good for zapping dew.  The one I have is the Monsun 12V Hair Dryer:

http://www.amazon.co.uk/gp/product/B000YKZ9JS

I run it of a 7Ah Skywatcher power tank (the smaller one).  According to the specifications, the power tank should pop a fuse or circuit breaker or something as the (168W / 12V=) 14A required is more than the 10A rating of the power tank but in practice it seems to work just fine.  It may be relvant that it only needs to be used for a few seconds at a time.

It occurs to me that if you have to blow from the front end, a cunningly modified cardboard tube might help direct the air where it is needed.

[Sporadic Dobstronomer]

It occurs to me that if you have to blow from the front end, a cunningly modified cardboard tube might help direct the air where it is needed.

  By the way, do not do anything that will significantly reduce the amount of air that passes through the hairdryer or you will burn out the heating elements and that will not be approved of!

[Scooot]

I use what is allegedly a travel hairdryer with a car cigar-type plug which is rated at 168W.  In English that means you die of old age before your hair gets dry, but the unit is very good for zapping dew.  The one I have is the Monsun 12V Hair Dryer:

http://www.amazon.co.uk/gp/product/B000YKZ9JS

I run it of a 7Ah Skywatcher power tank (the smaller one).  According to the specifications, the power tank should pop a fuse or circuit breaker or something as the (168W / 12V=) 14A required is more than the 10A rating of the power tank but in practice it seems to work just fine.  It may be relvant that it only needs to be used for a few seconds at a time.

It occurs to me that if you have to blow from the front end, a cunningly modified cardboard tube might help direct the air where it is needed.

Thanks very much, I've just found this as well.

http://www.telescopehouse.com/acatalog/Orion_Dew_Zapper_Gun.html

I'd just point it down the focusser.

[Daniel-K]

Thanks very much, I've just found this as well.

http://www.telescopehouse.com/acatalog/Orion_Dew_Zapper_Gun.html

I'd just point it down the focusser.

Richard although these work "eventually" a heated secondary is the easiest way to cure the problem. i have just got OO to stick a kendrick dew heater onto my secondary stalk for me this will be rand from an astrozap dewcontroller powered by the 4AH Tracer battery. very light dew heating set up

[Sporadic Dobstronomer]

Thanks very much, I've just found this as well.

http://www.telescopehouse.com/acatalog/Orion_Dew_Zapper_Gun.html

I'd just point it down the focusser.

You can't point it down the focuser because that is far too sensible and easy. (nearest equivalent to facepalm smiley)

[Scooot]

Richard although these work "eventually" a heated secondary is the easiest way to cure the problem. i have just got OO to stick a kendrick dew heater onto my secondary stalk for me this will be rand from an astrozap dewcontroller powered by the 4AH Tracer battery. very light dew heating set up

Yes thanks Dan, I think I'm going to get one of the split elipticals, I need the 2029-XM. It doesn't look is if many stockists have them over here, just emailed Altair Astro.

[Tommohawk]

 In English that means you die of old age before your hair gets dry.....

Hmmm. Once upon a time, when I had lots of hair that would have been true. Now, my hair is dry before I step out of the shower.

On the other hand.... being somewhat older.... it might still be a close run thing.

[Tommohawk]

Scooot, theres another thread on budget controllers at the mo:

http://stargazerslounge.com/topic/229886-dew-heater-controllers/#entry2481355

About £14 for a three channel - I've just ordered one, so will let you know how (if!) it works.

Also, what size is your secondary? In your photo, the mirror looks only slightly larger than the stalk.

[Scooot]

Scooot, theres another thread on budget controllers at the mo:

http://stargazerslounge.com/topic/229886-dew-heater-controllers/#entry2481355

About £14 for a three channel - I've just ordered one, so will let you know how (if!) it works.

Also, what size is your secondary? In your photo, the mirror looks only slightly larger than the stalk.

It's 63mm according to OOs spec, I spoke to them today and they haven't changed them. I measured the diameter of the stalk with a compass today and that's 64mm , which seems odd as the flat sticks out. I gave this measurement to Kendrick in an email and they replied saying the 2029XM would be the right one?

[Tommohawk]

It's 63mm according to OOs spec, I spoke to them today and they haven't changed them. I measured the diameter of the stalk with a compass today and that's 64mm , which seems odd as the flat sticks out. I gave this measurement to Kendrick in an email and they replied saying the 2029XM would be the right one?

Ehh? As you say, the stalk diameter can't be bigger than the minor axis of the secondary! The secondary size of 63mm (minor) sounds correct.

From the photo, it looks to me that the secondary diameter is just larger than the stalk, but only be about 10mm - which would leave a width of only 5mm either side. Seems too narrow to me for that heater pad. The spec for 2029XM is:

2029-XM

Wire length: 610 mm (24")

Connector: RCA plug

Wattage: 7 watts

Center hole dimensions:

45 mm x 64 mm

Minor axis dimension: 80 mm

Major axis dimension: 110 mm

So it's way too wide - and they cant be trimmed BTW.  Having said all that, the photo seems to show quite a gap between the stalk and the mirror - rather as though they are separated by 5mm? Maybe the mirror is attached by a thick sticky pad?

If that is so, providing you get a heater pad which is the right width (63mm max) and if the sticky pad is somewhat smaller than the stalk diameter, there may be clearance to get the inner edge of the heater pad between the mirror and the stalk. Does that make sense?

Can I suggest you re-measure the stalk dia for starters? It looks more like 53mm. If its definitely 64mm, then the mirror must be larger - more like 80mm Maybe thats whay Kendrick say that the 2029XM heater is correct?? Can you measure the actual secondary ...... carefully!?

[Scooot]

Ehh? As you say, the stalk diameter can't be bigger than the minor axis of the secondary! The secondary size of 63mm (minor) sounds correct.

From the photo, it looks to me that the secondary diameter is just larger than the stalk, but only be about 10mm - which would leave a width of only 5mm either side. Seems too narrow to me for that heater pad. The spec for 2029XM is:

2029-XM

Wire length: 610 mm (24")

Connector: RCA plug

Wattage: 7 watts

Center hole dimensions:

45 mm x 64 mm

Minor axis dimension: 80 mm

Major axis dimension: 110 mm

So it's way too wide - and they cant be trimmed BTW. Having said all that, the photo seems to show quite a gap between the stalk and the mirror - rather as though they are separated by 5mm? Maybe the mirror is attached by a thick sticky pad?

If that is so, providing you get a heater pad which is the right width (63mm max) and if the sticky pad is somewhat smaller than the stalk diameter, there may be clearance to get the inner edge of the heater pad between the mirror and the stalk. Does that make sense?

Can I suggest you re-measure the stalk dia for starters? It looks more like 53mm. If its definitely 64mm, then the mirror must be larger - more like 80mm Maybe thats whay Kendrick say that the 2029XM heater is correct?? Can you measure the actual secondary ...... carefully!?

I told you I was a DIW expert

It's not that easy to measure the diameter of the stalk because I can't lay anything across the centre but had another go and cut out a paper template to check, it's actually 56mm as you suspected. The depth of the stalk along the back is 64mm.

You're right about the gap between the mirror and stalk but it's caused by thick blobs of the glue. I can easily slide a piece of card between it where there's no glue. There are 3 blobs forming a triangle, one in the middle at the primary end and two at the wire end of the elliptical heater.

I'm not sure now if any of them will fit now.

Ps the blobs of glue are roughly opposite the three collimation screws but near the edge of the mirror.

[Rustysplit]

Hi Richard,

I would go with Faulksy's solution. Dead easy and non invasive. I used the 330 ohm resistors to make my secondary heater too. Mine is between the stalk and mirror though, as my stalk is wooden.

[Rustysplit]

Or, another possibility is getting a dew strap for a 2" ep and wrapping that round the stalk? Would need to make sure that it did not bulge out past the mirror though.

[faulksy]

Hi Richard,

I would go with Faulksy's solution. Dead easy and non invasive. I used the 330 ohm resistors to make my secondary heater too. Mine is between the stalk and mirror though, as my stalk is wooden.

good man should of shown you mine at dobfest richard, or alan could of shown his

[Scooot]

Hi Richard,

I would go with Faulksy's solution. Dead easy and non invasive. I used the 330 ohm resistors to make my secondary heater too. Mine is between the stalk and mirror though, as my stalk is wooden.

Hi Alan,

My stalks wooden as well, but I could fit something between the mirror and the stalk, so making something makes sense but it won't be easy for me. How many do I need, if more than one how do I connect them? Do they just heat up when a 12v dc goes through them, in which case do they just rest against the mirror. Something like these? https://www.google.co.uk/?gws_rd=ssl#q=330+ohm+.25watt+resistor&tbm=shop&spd=11105007870415251855

[Scooot]

Hi again Mike & Alan,

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

I'll have a good read.

Thanks everyone for all the help!