Dew problems

[AndyWB]

Over the last couple of weeks I've had some problems with dew. Now, I'm fairly new at this, so I don't know if it's just seasonal or something, but I don't remember the spring having the same problem.

Anyway, I've been trying to figure out what to do to stop my eyepieces and secondary dewing up. Over the last couple of weeks they've been doing that on my Heritage 130p, and the secondary has been despite my using a shroud.

So I'm not sure what is a good idea? I'd prefer not to spend as much on heating systems as on the scope (that hardly seems worth it).

Thoughts I've had are:

- A couple of proper dew heaters. Seems a bit overkill for such a wee scope.

- A battery and 12v Hair Dryer - but it would mean adding a battery to my kit (at the moment I'm electricity free!), and that isn't exactly cheap.

- Try and extend the shroud well past the secondary - like the standard 'camping mat' suggestion. I'm not sure that fitting a 'camping mat' extension past the front of the tube is a good, given the tube 'opening' and secondary support not being that substantial. How are would it have to go? And I guess this won't help with the eyepieces... Could be worth trying though just 'cos it's cheap.

- Wait and see if the dew thing has just be a humid couple of weeks and goes away by itself.

Anyone have any other ideas, thoughts or observations that might help?

[Mark at Beaufort]

Andy I have a Flextube Dobsonian and occasionally I get dew on the secondary. I now have a shroud around the main body and a dew shield on the top of the scope about 15 inches long. I bought a cheap 12v hairdryer from eBay and plug it into by car portable jump starter - it works well. My eyepieces remain in their case until wanted - occasional they cloud over and I either change eyepiece or give it a quick blow with the hair dryer.

Mark

[Pig]

I am not sure what to suggest for you, I have quite a big corrector plate to consider and a heater along with the shield is the only real option for me.

You don't have to buy a controller you can just hook them up and leave them on full whack, that removes quite a big chunk of the cost.

[AndyWB]

You don't have to buy a controller you can just hook them up and leave them on full whack, that removes quite a big chunk of the cost.

Hmm. That's good to know. Heck, it shouldn't be too hard to build a pulsed controller as well, if it came to that.

 

I bought a cheap 12v hairdryer from eBay and plug it into by car portable jump starter - it works well. My eyepieces remain in their case until wanted - occasional they cloud over and I either change eyepiece or give it a quick blow with the hair dryer.

For the moment, I'm leaning towards this. The thought is, the major expense would be the battery. If I get a bigger (and better) scope, I'm likely to want a heating system, so I'd need a battery anyway. Would I be right in saying that a Leisure battery would be the right way to go? (I'm thinking of building one - batteries don't last forever, but a decent case should, and I really don't need a radio, torch, or air compressor!)

[Mark at Beaufort]

Andy if I used a lot of equipment - dew heaters, imaging cameras, mount motors etc then I think I would go with a leisure battery. A few members on the forum have made cases and have used items from Astronomiser. Here is a link to their website if that helps - http://www.astronomiser.co.uk/pwrhbx.htm

Mark

[DeepThought]

Hmm. That's good to know. Heck, it shouldn't be too hard to build a pulsed controller as well, if it came to that.

Rather than building yourself a PWM controller, you could save yourself a lot of time and effort by buying one of these:

http://www.ebay.co.uk/itm/DC-12V-8A-LED-Light-Dimmer-Brightness-Adjustable-Bright-Controller-Single-Color-/140928585939?pt=UK_DIY_Material_Electrical_Fittings_MJ&hash=item20cfff90d3

They do a perfectly good job of controlling your heater band for less than the cost of the components required to make your own.

If you're still feeling the urge to get your hands dirty then you can do what I did and buy a couple of them & install them into a project case to make a 2 channel controller...  beats watching Eastenders on a cloudy night anyway.

[Gtech]

Also being plagued with dew over the last few weeks, I looked into buying some dew heaters for my 190MN, finder and EP.

Price-wise, I would need to spend ~£100 for the heaters and ~£65 for a temp controller....Not likely for now..

Looking around my workshop, I already had some small reels of nichrome wire in various gauges and plenty heatshrink, so I set about making my own.

I based each dew heater design on ~0.18 watt/cm (same as low powered commercial products) and selected appropriate nichrome wire to yield measured full wrap(s) resistances.

I covered the nichrome wire in heatshrink, loop soldered some copper wire tails and over heatshrinked the joints.

I then sandwiched the heater between some 30mm wide cordura fabric stips (machined sewed the edges) and added some velcro at each end.

For testing, I attached the dew heater to a 12v power source for 20mins  and voila, a very gentle warmth....so no controller required for now!

Time taken = 1hour

Material cost to me = nothing......

Material cost in reality, <£3.

Next step, if needed ....source some chinese 12v dimmers and make a controller.  

[AndyWB]

They do a perfectly good job of controlling your heater band for less than the cost of the components required to make your own.

Of course! I'd forgotten that dimmer switches can be pulsed. I'm surprised by how cheap that is too.

[Pig]

The heater band can be used with this

http://www.365astronomy.com/single-dew-strip-supply-cable-p-3566.html