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Hand held 12v hair dryer for dew

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#1 Ira

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Posted 14 February 2013 - 06:21 PM

Do the hand-held 12v hair dryers sold for astronomy do a decent job of removing dew? Dew here is light most of the year but can be heavy during the winter. I deploy two scopes on an iOptron MiniTower Pro so I have been reluctant to get dew strips because I would have wires hanging everywhere with this set-up, a pair on each scope for the objective and eyepiece. Also, how much power do these dryers use? I'm using an Astrotech 250 amp power tank as the main power source.

/Ira

#2 johnnyha

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Posted 14 February 2013 - 07:12 PM

These things REALLY eat up power although they do the job.

#3 Jim-M

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Posted 14 February 2013 - 07:55 PM

The unit that I use draws 10 amps at 12 volts. It clears the dew quickly but it does not last long.

Jim

#4 FebStars

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Posted 14 February 2013 - 08:09 PM

Ira,
They sell 12v hair blowers/dryers for recreational vehicles that can be found sometimes in WalMart. I have one that runs around 175 to 200 watts. It takes a little while for it to work, but it is effective.
TomH

#5 JayinUT

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Posted 14 February 2013 - 08:44 PM

Harbor Freight sells a 12v auto heater/defroster that works really well. I used one for 2 years before getting a dew heater system. Here is the link.

#6 Paul Hyndman

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Posted 14 February 2013 - 10:30 PM

Maybe it's just me, but I cringe at the thought of using a hair dryer or heat gun to control dew on a 'scopes optics (insert sound of fingernails scraping across a chalkboard here).

You need only keep the surface heated a miniscule amount above the dew point to inhibit its formation (a single degree will usually suffice). Anything more is not merely overkill but can, at the very least, degrade the image and, at worst, cause permanent spotting and, if over-zealously applied, fracturing of the optics.

Lastly, why create the headache of having to constantly fritter with dew removal as opposed to having an automated solution?!?

Perhaps I am just too darn persnickety, but only use controlled dew heater strips with a cable management system (velcro etc) to prevent tangling, which allow precisely applying a minimal amount of heat.



Paul

#7 Ira

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Posted 14 February 2013 - 11:03 PM

Those are all good questions I ask myself. But I have to set up and tear down every night, and I already have cable management issues with a bundle of wires to a Mallincam and two monitors, so adding 4 more cables to manage is a big issue. And it all adds time to set up and tear down. I don't think anyone has cracked an optic by heating it to remove dew without going way overboard with heating, and perhaps not even then.

/Ira

#8 DaveJ

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Posted 15 February 2013 - 08:53 AM

Those are all good questions I ask myself. But I have to set up and tear down every night, and I already have cable management issues with a bundle of wires to a Mallincam and two monitors, so adding 4 more cables to manage is a big issue. And it all adds time to set up and tear down. I don't think anyone has cracked an optic by heating it to remove dew without going way overboard with heating, and perhaps not even then.


It's not that the optics will crack, it's that you're baking on crud captured in the moisture that has formed. FAR better to prevent the dew from forming than to bake it off with a hairdryer. I agree wholeheartedly with Paul on this one. Get a legitimate dew prevention system: Dewbuster controller and Dew-Not heater strips will serve you well.

#9 dan_h

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Posted 15 February 2013 - 08:55 AM

Paul is right about this one.

In my experience, using a hair dryer to remove dew is a temporary fix at best. Because only the surface of the glass is warmed, the dew will return in short order. You may get a half hour between use but you may not get even that, depending on conditions and your setup.

A hair dryer plugged into the wall outlet consumes about 10 times as much power (1500watts versus 150 watts) but still only provides temporary dew relief unless you warm the glass way beyond the point of evaporating the dew.

If you allow the lens to dew up repeatedly, you will eventually get spots and a cleaning will be forced. And besides, who knows what else is in the dew besides water? Better to prevent the dew and keep your glass in pristine condition.

If you use a 12volt dryer three times in an evening, you will discharge a 7ah battery. Better to use that effort to prevent the dew and enjoy viewing. It takes a little effort to set up but not as much as chasing dew and dragging around the extra batteries and gear.

Put on your dew strips and dress the cables neatly with some decent ties so that removal and replacement takes minimal effort. You will enjoy your observing far more.

dan

#10 cliff mygatt

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Posted 15 February 2013 - 09:39 AM

I have a portable propane Catalytic heater like this one I use in the field to keep me warm and I discovered it fits my SCT corrector quite well to remove dew and does not "blow" anything on the corrector you might want to try that and you have some heat to keep your feet warm. Good Luck

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#11 Ira

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Posted 15 February 2013 - 09:54 AM

Cliff,
Where did you get this?

/Ira

#12 dan_h

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Posted 15 February 2013 - 10:09 AM

Don't try to use this in an enclosed space. It uses a catalyst to reduce the propane to heat and water. We had a similar unit in our warm up shed at our club site. I fired it up one night to have a warm place to take my scope and binos so they could be dew free. The instant I took the cool equipment into the shed, everything dewed up like never before and was literally dripping wet everywhere. The room was warm but it was more like a sanau.

It was not what I wanted but it was to be expected.

dan

#13 Eddgie

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Posted 15 February 2013 - 10:20 AM

Bite the bullet and learn to manage the dew heater cables.

You may think some of these other solutions have promise, but nothing works as well as a dew heater.

A 12 VDC blower will suck a car battery dry if you use it enough to keep dew off

The heat from a propane unit will cause such strong thermal currents that you will induce more local seeing than all 5 miles of atmosphere above you does.

A 115 volt hair dryer will require you to run out AC, so now you have an extension cord to deal with.

Dude, if you want to image and need long periods of dew free operation, there just really isn't a substitute for the dew strip approach. Nothing else is as effective, and in the long run, you will spend more time taking dew off of your optics using a hair dryer than you will plugging in your dew strip.

My dew strip stays on my OTA all the time. It adds almost no weight and stay out of the way (proper mounting is just behind the corrector cell, not on the corrector cell, so it goes under the dovetail).

My dew controller is Velcrod to the mount. When I put in the scope, I only have to plug in the wire (which I ran under the dovetail to the rear of the scope) to the controller.

Since the controller stays on the mount, I only have to plug in the power plug.

In fact, I have many times considered just tapping it into the power wire for the mount so that I don't even have to do that.

Not sure where the "Four more wires" deal comes from, but there are only two, and plugging them both in takes all of 20 seconds.

Don't kid yourself, there is no better way to manage dew on an SCT than with a dew heater system.

Like most things, if you spend a bit of time planning your installation, you can get it neat and tidy and down to one connection to make.

#14 Jim Romanski

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Posted 15 February 2013 - 02:56 PM

If you have a constant dew problem I agree with Paul that you should find an automated solution. That said, I don't use a SCT and I don't have a problem with dew most of the time. I keep a 12V hair dryer in my observing kit and it can really bail me out on the few nights when I need it.

They do not get very hot (no where near as hot as a 120V unit) so I'm not worried about the effect on my optics.

I went to CSP a few years ago and was able to keep me and a couple of neighboring observers going for several additional observing hours with my little hair dryer.

#15 Paul Hyndman

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Posted 15 February 2013 - 05:00 PM

Considerable time, effort, and money is often expended to figure high quality optics from which we hope to squeeze the most oomph. Many of us astro-geeks set up equipment hours beforehand to allow sufficient time for thermal equilibrium. Years have been spent (and countless seminars given) seeking to find better ways to mitigate thermal currents and minimize effects of temperature changes. Heck, many of us are even concerned as to what kind of surface (cement/lawn/etc) we set up on or what we must view over (buildings/water/forest/etc) so as to deliver the best from our scopes.

Dew and temperature stabilization are two of the easiest degradation factors over which we have control, so why skimp or look beyond proven and (relatively) simple and inexpensive techniques? To use harsher abatement methods, one may as well just save the money spent on a well-figured scope and observe with an eyepiece and a shaving mirror (well, I did mention I sometimes tend to be persnickety with my equipment).


Paul

#16 Paul G

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Posted 15 February 2013 - 05:25 PM

Just like acid rain dew can be acidic, particularly in urban areas and those east (downwind) of major industrial areas. Preventing dew in the first place with a proper dew prevention system is preferable to allowing it to collect and then baking off the water. Since you already have a bunch of cables to manage, what's a couple more? :)

#17 Jon Isaacs

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Posted 15 February 2013 - 08:19 PM

Lastly, why create the headache of having to constantly fritter with dew removal as opposed to having an automated solution?!?



For some of us, dew is relatively uncommon, a hair drier is useful on those rare occasions when there is dew.

I have had a couple of 12volt hair driers for use as dew heaters. The standard 12 volt hair driers are 120 watt, that's 10 amps. It's pretty feeble, a typical 120volt hair drier is about 1500 watts...

Jon

#18 Lane

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Posted 15 February 2013 - 08:56 PM

If you have to deal with a serious dew problem it is much better to go with a dew strap and controller. Uses a lot less energy and its much easier because you just turn on the power and forget about it.

#19 D_talley

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Posted 15 February 2013 - 11:12 PM

Where I live on the east coast, dew is a major problem. Even with dew straps and shields I would get dew on my 14 inch SCT with the dew straps at full power. Too much glass to keep warm. So at times I would have to resort to the 12 volt dryer to make up for it. Power is not a problem since I have 4 x 125 amp hour batteries tied together to provide the power.

#20 Lane

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Posted 16 February 2013 - 02:00 AM

Same problem with the C11, after 4 hours or so the center of the corrector would still dew up. Does not seem to affect the views all that much so I just leave it alone. Kind of like having a giant central obstruction. Amazing how much of the center can be covered and still result in good DSO views. I suspect planet viewing would be in the toilet.

#21 rmollise

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Posted 16 February 2013 - 10:17 AM

Same problem with the C11, after 4 hours or so the center of the corrector would still dew up. Does not seem to affect the views all that much so I just leave it alone. Kind of like having a giant central obstruction. Amazing how much of the center can be covered and still result in good DSO views. I suspect planet viewing would be in the toilet.


Doesn't have to be this way. I use a C11 down here on the Gulf Coast where dew is incredibly heavy, but my corrector stays clear all night. Secret? A temperature controlled dew system like the DewBuster or one of the newer Kendrick controllers...

#22 DaveJ

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Posted 16 February 2013 - 03:37 PM

Same problem with the C11, after 4 hours or so the center of the corrector would still dew up. Does not seem to affect the views all that much so I just leave it alone. Kind of like having a giant central obstruction. Amazing how much of the center can be covered and still result in good DSO views. I suspect planet viewing would be in the toilet.


Doesn't have to be this way. I use a C11 down here on the Gulf Coast where dew is incredibly heavy, but my corrector stays clear all night. Secret? A temperature controlled dew system like the DewBuster or one of the newer Kendrick controllers...


Also, as you've mentioned many times in the past, keep the dew heater strap BEHIND the corrector plate rim, not on it.

#23 Ira

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Posted 16 February 2013 - 05:01 PM

I need four leads. I mount a C8 and 80mm refractor on an iOptron MiniTower Pro, so I have two objectives and two eyepieces I need to de-dew. The eyepieces get wetter than the objectives because they are more exposed. I use a large plastic dew shield on the C8 and the built-in dew shield on the refractor.

/Ira

#24 DaveJ

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Posted 16 February 2013 - 05:15 PM

I need four leads. I mount a C8 and 80mm refractor on an iOptron MiniTower Pro, so I have two objectives and two eyepieces I need to de-dew. The eyepieces get wetter than the objectives because they are more exposed. I use a large plastic dew shield on the C8 and the built-in dew shield on the refractor.


No problem. I run 5 dew heater strips all the time. I use a Dewbuster controller which has all the outputs I need. The five cables that run from the heater strips to the controller are bundled to keep them out of the way. I keep these bundled which makes setup & teardown easy. The outside air temperature sensor is bundled with the heater strips. The controller attaches to the mount with Velcro. I plug the bundled heater strips into their proper connectors and plug the temp sensor into the top. There's only one cable leading down from the mount and that's to the 12V supply for the controller. The entire heater controller/temp sensor/heater cables might add as much as two minutes to setup time, but I doubt it. I use this heater setup with multiple mount/scope(s) setups with total success regarding due prevention.

#25 George N

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Posted 16 February 2013 - 05:55 PM

While I agree that a dew strap is the “ultimate solution”, I have used the following when for some reason I don’t have a dew strap available: rubber-band or duct tape chemical hand warmers on. It works best for eyepieces, bino-viewers, and smaller optics, like DSLR lenses and 80mm binoculars. There’s not enough room in the dew shield for my 5-inch refractor, but I’ve seen a friend duct-tape a hand warmer or two inside the dew-shield of his 6-inch achro and it worked!

BTW…. Dew?? Where I live the problem is just as likely to be frost. On many cold nights I’ve ended up with my Obsession 20 looking pure white – covered in thick frost. With heat on the secondary and eyepieces, there was no problem….. except slipping on the frosted-up ladder.






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