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Now I need a Dew Heater - How to control level?

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#1 rms40

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Posted 11 December 2018 - 10:27 AM

When I first got into imaging, I thought I would need a dew strap and bought one. Dew is rarely a problem in west central Texas. I never used it. But, we have had way more rain than normal and I find dew forming or even frost the last couple of imaging runs. We are getting very near the dew point several nights and frost has been forming all over my place.

 

The dew strap I bought used has no control for the level. Will these work just plugged into a 12v system? I won't need it often so I don't want to spend a lot on a controller. Would a potentiometer work? Is there another way to control dew? I have a dew shield but it doesn't do much good when pointed up towards the meridian.

 

I know many people have to fight dew and have experience with this. I hoped it would just dry out enough out here to get back to our normal, dry conditions. But, I guess I need to figure this out....

 

Thanks, Randall.

 

 



#2 Napp

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Posted 11 December 2018 - 10:37 AM

Typical dew heaters require a controller.  They cannot and should not be plugged directly into a 12volt battery.  If your heater has an RCA connector (think stereo connections) then you need a controller.  Open your wallet wide.  



#3 rms40

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Posted 11 December 2018 - 10:59 AM

That makes sense. I will have to check it out better. It has been in the closet for over two years. Maybe it did come with some type of controller. I can see how it might cook the scope if it is just connected like a heater element. I have lots of potentiometers and connectors but setting the temp just above ambient would work best, right? I have some extra focuser temp sensors too.

 

Thanks, Randall



#4 rms40

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Posted 11 December 2018 - 12:14 PM

I just have the heat strap. I am purchasing a 12v LED dimmer to control it. Not an elegant solution but I rarely ever need it. I may look into using a heat sensor with it later. For now, I should be able to adjust the voltage and use my laser thermometer to check it's temp.

 

The products made for this do look nice. Many have dual or quad outputs for multiple dew straps. I image with my refractors unguided (thanks to a MYT and Protrack) so one lens is all I need to warm. No guide scope, finder or secondaries to worry about. I can see how this could get more complicated with Newtonians and similar designs.

 

The commercial products look like the way to go if you need to control multiple dew straps and keep the temps well regulated. I may get one if my self made solution doesn't work well or have other setups that have dew problems later on. And, it is always good to support the amateur astronomy community vendors. I have done plenty of that in the last few years!

 

Thanks, Randall


Edited by rms40, 11 December 2018 - 12:32 PM.


#5 Napp

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Posted 11 December 2018 - 01:20 PM

I just found out today that Astrozap is selling a 12volt cigarette adapter for a single dew strap - no controller.  That’s all I know.  You might check their website or call them.



#6 bill5wjw

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Posted 11 December 2018 - 04:21 PM

Plug it directly in to 12v and it will be fine. I run them all night and never had a problem. I put them on the scope as soon as I set up for imaging and turn them on right away-and no longer worry about dew. Scopestuff.com has them.

I use a 12V 100 A.H. deep cycle battery.


Edited by bill5wjw, 11 December 2018 - 06:01 PM.


#7 rms40

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Posted 12 December 2018 - 08:56 AM

The strap I have has a cig lighter plug that is directly attached to the strap. I may try it direct like that. I think the dimmer switch control will work better with it since it doesn't get real cold here (usually) and I will be able to control the temp of the strap.

 

It's always something else in this hobby. I really don't like imaging on really humid nights anyway. While the water in the air doesn't seem to affect bright planets much, it definitely scatters a lot of light from dimmer DSOs. One way I can tell how much water there is, is by looking at the Milky Way. On less humid nights, I can see it easily early but it fades away as the humidity increases at night. I have always wished to image from a desert. I may have to take a trip over to New Mexico or Big Bend with a imaging setup and see how much better that is. And, no dew problems...

 

Randall



#8 Napp

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Posted 12 December 2018 - 11:45 AM

Yep, a trip to a higher, dryer site is best.  For the rest of us there is dew control.  It’s not just cold you need to worry about. It’s a matter of the temperature dropping close to the dew point.  In Florida that’s every night since the dew point stays high.



#9 N3p

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Posted 12 December 2018 - 12:27 PM

I have my home made dew controller with potentiometer but I don't use them, the On/Off switch is good enough.. when I start to see turbulence in the eyepiece then I know it's time to shut the system off for a certain amount of time, 15 mins, 30 mins..



#10 Woodbridge_Dave

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Posted 12 December 2018 - 03:32 PM

LED dimmer switch.  $3 on amazon.


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#11 skywolf856

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Posted 12 December 2018 - 11:51 PM

Here's what I built for a controller.

Only cost about $25 total.

 

And it's 3 channel.

 

http://dslrmodificat...Controller.html


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#12 Eddgie

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Posted 13 December 2018 - 10:13 AM

While the dew strip will heat with voltage applied, the purpose of the controller is to adjust how much it heats.

 

If you are just doing an eyepiece case, then heat is heat.

 

What though if you are heating the corrector on an SCT.  Here, you want only enough heat to keep dew from forming.  Any excess heat can cause thermal currents inside the scope.

 

Also, running the heater at max current draw means well, that it draws maximum current, and that can be a lot of current, causing far faster battery drain than if the controller is used and you have the current set to just enough to be effective against dew. If you are running from a DC power supply connected to the mains and this supply delivers enough current to handle the load, then that is not a concern.  Running from a stand alone battery though, the dew strip with no regulator will likely be the highest load on the battery. 

 

This means that you might be able to get away without a controller, but it also means that you might not be able to get away without a controller.   It depends on the role the dew heater will serve.  For an SCT as and example, I would suggest a controller be used but that does not mean that it is essential to have.  


Edited by Eddgie, 13 December 2018 - 10:16 AM.


#13 MikeECha

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Posted 13 December 2018 - 08:56 PM

When I first got into imaging, I thought I would need a dew strap and bought one. Dew is rarely a problem in west central Texas. I never used it. But, we have had way more rain than normal and I find dew forming or even frost the last couple of imaging runs. We are getting very near the dew point several nights and frost has been forming all over my place.

 

The dew strap I bought used has no control for the level. Will these work just plugged into a 12v system? I won't need it often so I don't want to spend a lot on a controller. Would a potentiometer work? Is there another way to control dew? I have a dew shield but it doesn't do much good when pointed up towards the meridian.

 

I know many people have to fight dew and have experience with this. I hoped it would just dry out enough out here to get back to our normal, dry conditions. But, I guess I need to figure this out....

 

Thanks, Randall.

I use 120Vac supply as I image (no much to show yet) from my backyard. You mention 12V so my solution might not work for you. But here it is

 

For my 50mm guider I bought a USB-powered camera lens dew heater from Amazon. The size and heat output is perfect for that at least for a 35F night. It keeps the front element noticeably warm to the touch. I plug it into one of the ports of my USB hub. The power adapter for the hub is rated at 5 Amp output so plenty of juice for all othe ports.

 

For the main scope/lens, I wanted to be able to set the tempereture about 5-10F above dew point for the night and forget about it. So I bough a pack/kit of two tenperature controllers for less than $8 on Amazon and another 12V 5Amp adapter with a plug-to-hardwire terminal adater to hook up the controller. They are basically two small heat-cool thermostats (2×2×.5in) with digital screen and three small push buttons to set point and see current temp. The DIY kit comes with a clear box and hardwaee to put it together. No soldering or code programming required. Just simple control wiring of power and relay control. Of course I only wired and use the heating side. The contoller comes with a sensor that is about .125in in diameter and 1in long with about 2ft of wire terminated with a connector for the controller. I tuck the sonsor under the unheated elastic strap section of the heater and that works great. Lcd screen ligh is red and you can hear a tick when the heater is turned off. 

 

This has worked wonderfully for me so far. I hope this helps.


Edited by MikeECha, 13 December 2018 - 09:00 PM.


#14 cloudybruce

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Posted 26 December 2018 - 06:58 PM

A very clever adaptation of a LED controller.  The RGB controller might work well as a 3-channel dew strip heater controller.

 

Be careful of static electricity blowing out (shorting) the output MOSFETs.  The device's output to the LEDs (its original purpose) appears to be directly connected to the drains of the output MOSFETs.  No ESD management is seen (ESD = electrostatic discharge, i.e., static electricity).  The opened-up view of the controller is attached (as taken from skywolf856' internet link).

 

While no ESD protection might work in a fixed home application to run the illumination of RGB LEDs, lack of ESD protection in a telescope environment can be disastrous.   I speak firsthand.  See my other posts on this subject.

 

RGB controller used for dew shield.jpg


Edited by cloudybruce, 26 December 2018 - 07:01 PM.


#15 Pauls72

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Posted 26 December 2018 - 08:02 PM

Get yourself one or two of these from ebay.

PWM Dimmer Controller LED Light Lamp Strip Adjustable Brightness




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