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Self-regulating heat trace cable as a dew heater?

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#1 Waynerplays

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Posted 16 February 2020 - 08:32 PM

Hello friends,

 

I work for an electrical wholesale company where we sell 120V self-regulating heat trace cable for roof and downspout de-icing  or pipe freeze protection. It comes in 5W, 8W, and 10W per foot and I'm hoping one wrap around the tube at the corrector plate with a cold lead to a controller of some kind(?) and likely having a GFCI male cord end.

 

Has anyone tried to adapt this type of cable for use as a dew heater? I have a Super C8 and use a 450W UPS for remote power, so between the Byers drive and the heater, I still should get a good number of hours operation.

 

Am I dreaming?



#2 wrnchhead

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Posted 16 February 2020 - 08:45 PM

My solution was to get a 12 V heated blanket from Walmart and took out the elements and fashioned my own straps and it was $20 invested. I don’t know how easy your solution is but this one was pretty easy. The elements are basically thin white wires that are obviously insulated and I used some medical tape similar to ace bandage to attach it and it has a nice high and low switch which I usually just run on low.
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#3 RaulTheRat

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Posted 16 February 2020 - 08:49 PM

Since P is proportional to i^2 you'd get 1/100th as much power running it at 12v vs 120v, and I certainly wouldn't put 120v anywhere near a damp, dewy metal tube outdoors, so I don't think it's such a great idea.

Dew heaters are fairly easy (albeit a little fiddly) to make with nichrome heating wire, kapton tape and something to encapsulate the contraption in.

#4 jnomura

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Posted 25 March 2020 - 10:49 AM

I would be very careful about placing 120V line voltages on your mount or Ota. You could introduce electrical noise and current leaks to ground through your OTA. Might try the 12 volt versions sold on amazon and eBay. This is used to heat car batteries and such. It is very cheap and is sourced out of China. I have used it on the secondary and primary of a early 16” IDK. Seems to work in California weather. Not sure about freezing weather thou.

Good luck. Keep us informed.

Jim



#5 Jii

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Posted 25 March 2020 - 11:05 AM

I have used 2m long ready-made version (20W/230V) around my scope and mount during this winter and it has worked fine. Easy to remove when I start imaging and fast to put back after it.



#6 John O'Grady

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Posted 25 March 2020 - 11:23 AM

A quick google search turns up two different hits as to the maximum temperature these top out at.

One source reports 140 degree F and another 160 degree F.  That's the upper limit.

One search result describe the trace cables as 'low-temperature self-limiting devices'  

 

What you have to understand is that the temperature regulation in these devices is designed to work while keeping the manufacturing cost as low as possible (i.e. cheap).

So just because the regulation turns off, it doesn't mean it turns off at a temperature that's healthy for optical equipment.

Heating up a copper pipe more than necesary... adds a margin of safety that ensures the pipe won't freeze.

 

Maybe the cable will run at a lower temperature - you can test it out with a temperature probe to verify.

But you'll want to do so across various temperatures to simulate changes to the outside temperature and for an extended period (think 8 hours minimum, over several nights).

Since it is working well for Jii, possibly he has already done this type of testing and would be willing to share his data on it?

Or maybe he has a unique approach that doesn't use the integrated temperature controllers most of these come with.

 

It's a novel thought, but given some of the reasonably cost-effective dew heater options already available on the market, I would recommend sticking with one of those instead.

Will it work - probably.  Will it work well - likely not, at least not without some effort and customization. 

As always YMMV.   

 

Good luck.


Edited by John O'Grady, 25 March 2020 - 11:24 AM.


#7 jnomura

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Posted 25 March 2020 - 11:35 AM

John,

 

The heat strip I am referring to is a self compensating heat source where the current increases as temperature drops. It only produces a few watts per foot and can be cut to any length. They use a polymer that has a negative resistance property like doped silicon. What is nice about it is it is not a series resistance but works across the cross section so can be cut up and still maintain its operational voltage.

 

I will see if I can find the link to it and post it.

Jim


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#8 jnomura

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Posted 25 March 2020 - 12:32 PM

https://www.ebay.com...0.c100148.m2813

 

Hope this works! Tested link seems to work

on Ebay

12V24V36V110V220V380V Self Regulating Heating Tape Trace Cable Freeze Protection
Snow Melting Flame retardancy Drain Water Pipe deicing.

 

How to use:

Cut to desired length 1 or 2 wraps depending on heat desired. I use 1 wrap.

Strip about 1/2" off one end.

fold back and tin the leads and solder you power cable to the leads

Insulate connections with shrink tube.

cover entire end (leads extending away from the end) and allow about 2" extra beyond the end.

stick the free end in the 2" section and heat shrink the tube so as to make a loop with the shrink tube holding it together. When cool slide out the free end of the tape and stuff a small piece of Qtip stick cross wise inside the now open heat shrink ( prevents shorts). Place around the object to be heated and insert the free end of the tape in the pre shrunk heat shrink tube to hold it all together. If needed a little can be trimmed off the tape to make it tight.

 

NOTE: This tape provides a some what self adjusting heat output ( the higher the temp the lower the heat output) that gets only warm to the touch. best results was to use a dew strap heat controller on high or directly to 12V. it is best to use this as a continuous heat source rather than on/off control. I orders both the 24V and the 12V and the cable marking are the same. so I am not sure exactly what I received. they both worked.


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#9 Jii

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Posted 25 March 2020 - 12:47 PM


 

Maybe the cable will run at a lower temperature - you can test it out with a temperature probe to verify.

But you'll want to do so across various temperatures to simulate changes to the outside temperature and for an extended period (think 8 hours minimum, over several nights).

Since it is working well for Jii, possibly he has already done this type of testing and would be willing to share his data on it?

Or maybe he has a unique approach that doesn't use the integrated temperature controllers most of these come with.

I have used this kind of cable (local manufacturer, I think):

 

frostvakt-10_4.png

As it has max 20W heating over the 2m length, it does not get too warm. I asked around in local astroforum before buying one and there were one or two guys who had used similar cables without issues.

 

My telescope stays roughly +7C warmer under cover than air in the shed it is placed and that's enough to keep humidity away. I have also stick-PC running constantly on top of the scope and that will naturally contribute somewhat to that figure.

 

But yeah, I can guess that there are various kind of solutions/cables in market so be careful when selecting the cable and also test it properly to see how hot it will get.

 

Edit: Forgot to mention but these models can be inserted into inside of the pipe.


Edited by Jii, 25 March 2020 - 12:50 PM.

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#10 Waynerplays

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Posted 26 March 2020 - 01:23 PM

Thanks to all for your informative responses fellows.

 

After considering them and having done some further research, I believe it's best I shy away from using the 120V heat trace cable, which aside from the voltage, is the same as that in the link you included Jim, mostly due to the inherent danger it may pose, higher current draw, plus the difficulties temperature control may present. And Jim, I do appreciate your instructions on how to use this cable and your input Jii.

 

I am still working out the math to build an appropriately sized nichrome strip, but as John said, a prefabricated strip may be worth the extra dollars spent. There are also a number of articles for building controllers using 12VDC PWM LED dimmers that would be much less expensive than others on the market.

 

Clear Skies



#11 John O'Grady

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Posted 26 March 2020 - 03:57 PM

I use one of the following 12V PWM controllers to drive a light box I built:

While I paid $3 CDN originally, $6CDN is like what almost free in US dollars these days??? wink.gif

 

It works well for the custom DIY light box I built.

 

With the terminal blocks I have it wired with an 2.3 x 5.5mm Female power plug that I can power from a battery pack.

I just use one of the cigeratte lighter to 12VDC power plugs.

 

Good luck with your build and post back to update us once you've got a solution.

 

John


Edited by John O'Grady, 27 March 2020 - 02:15 PM.


#12 Waynerplays

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Posted 27 March 2020 - 12:03 AM

Hey, thanks again John,

 

The PWM controller is the one I planned to use, but sadly the link to your light box didn't arrive where it was intended.

I'm not sure how soon I'll get to this project but I'll keep in touch.

 

By the way, lovely 8 you've got there

 

stay healthy


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#13 John O'Grady

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Posted 27 March 2020 - 02:19 PM

Thanks - I hope I was able to fix the links.

 

The C8 was a great scope but unfortunately I no longer have it.

I installed TEMP-est fans in the OTA - that was fun and quite functional.

 

At the time, I had a C9 and C11 and knew I had to let one go. So I sold the C8.  I still have the C9 and C11 for now. lol.gif

 

Clear skies and good health to you. flowerred.gif




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