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Practical solution to Mak dewing in UK?


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Either get yourself some dew heaters or a dew shield (or both). Cheap alternative which works well for normal use would be to cut up some camping mat and wrap it into a tube to act as a dew shield. A hair dryer does the job as well assuming the neighbours don't mind the noise.

James

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I don't know the maths but when I've used it with my 100ah leisure battery via an invertor it drained the battery quickly, too quickly to be practical. So its only something is recommend when there's a mains supply close by. I have an astrozap heated dew shield and a few heater strips which I use with a hitec astro 4 port controller and tend to use these when in my obsy or out in the field.

James

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How much drain would a 12 v hair dryer cause ?

12v at 180 watts for example ? 15 amps ? I did this at school a long long time ago but does that sound correct ?

I think that's correct. Seems high, but as I remember it, Power = current x voltage?

Stu

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I use a long dew shield, it's the only way to go.

I've never seen the sense in spending hours letting your scope cool down only to heat it up again!

It is always a fine balance applying just enough heat to keep the dew off but not so much it heats the tube.

Dew shields alone have not kept maks corrector plate clear so I do need dew strips too.

Stu

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In the main I found a decent dew shield was sufficient for my 127 Mak.  It still dewed up eventually, but usually only after several hours.

My C9.25 on the other hand seems to dew up within about half an hour, even with a dew shield.  I am constructing a heater and controller for it at the moment.

James

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In the main I found a decent dew shield was sufficient for my 127 Mak.  It still dewed up eventually, but usually only after several hours.

My C9.25 on the other hand seems to dew up within about half an hour, even with a dew shield.  I am constructing a heater and controller for it at the moment.

James

Good stuff James.....I was going to ask if there were any wiring diagrams or parts lists so anyone with a soldering iron could construct their own?....I mean, £50 plus for a controller seems a bit steep!, For that matter why would you pay £23 quid for a piece of foam???

Where did I put that RS catalogue?

Clive

Clive 

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I have been making up heater "tapes" using nichrome wire based on the details here:

http://www.blackwaterskies.co.uk/2013/05/making-your-own-nichrome-dew-heater.html

although in my case I have constructed them by putting the nichrome in the shrink-wrap, sticking it to duct tape and then laying dense foam matting over the top to create a strip about an inch wide (in the case of a single loop of nichrome).

For the controller I'm using some 12V 8A PWM LED controllers I bought from ebay for a few quid.  People have said in other threads they've had a few problems with reliability, but I intend to remove mine from the case and put them inside a larger project box so hopefully the better air circulation will help with keeping them cool:

http://www.ebay.co.uk/itm/LED-Light-Dimmer-Modulator-Brightness-Adjustable-Control-12V-24V-8A-JT1-F8s/331092006155

(I didn't get them from that seller -- mine came from the UK).

Thus far I've made up strips for my 127 Mak and C9.25 and tested them by plugging them across a 12V supply.  They get too hot to hold comfortably on the "hot" side, so I'm hopeful that they should work ok.

(Unlike the instructions in the first website I also managed to thread the nichrome down 1.7m of shrink-wrap in a single hit.  It was a bit tricky for the last 20cm though.  Whether you can do it in one go or have to do it in pieces may depend on the ID of the shrink-wrap and the size of the nichrome.)

James

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Hi,

I tend to tackle dew with three lines of defence, firstly with a decent dew shield to prevent dew settling on the optics and not leaving the scope pointing upwards when not in use. Secondly I have dew heaters on the eyepiece and behind the secondary on my newtonian, and thirdly I have a cheap 12 v camping hair drier if dew does settle and this clears the optics in about 30 seconds. Id never use a 240v hairdryer due to the risk of shock and the amount of battery drain it causes but the 12v  ones seem to be sufficient and are only used in short bursts.

The worst challenge I had was at kielder in November when I woke up at 12 midnight to a frozen up scope and optics, but 2 minutes with the 12v hair dryer ad the dew control on full whack for a while had me viewing in about 10 minutes ...... I now consider dew control as one of he priority things I need on hand if Ive traveled to a dark site etc

12v dryers are only cheap , Go Outdoors do one for £14.99 http://www.gooutdoors.co.uk/12v-hair-dryer-p182790?gclid=CNvA-qSOxbsCFQcTwwodjDcABg

Cheers

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Or...  choose your observing nights wisely, often a good weather forecast might include the dew point so you should be able to tell if you will get dew or not.  Looking outside at street lights or security lights is also a good tell-tale sign, if you can see a light cone underneath them that's usually moisture falling from the sky since the sun went down.

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Or... choose your observing nights wisely, often a good weather forecast might include the dew point so you should be able to tell if you will get dew or not. Looking outside at street lights or security lights is also a good tell-tale sign, if you can see a light cone underneath them that's usually moisture falling from the sky since the sun went down.

Also decreases the limited nights of viewable weather from 10 to 5 nights per year ;-)
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