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Eyepiece box heater

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#1 ischua

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Posted 05 January 2013 - 04:58 PM

I was thinking about heating my eyepiece box to keep the eyepieces warm.
I have a hundred feet of roof heating cable plus hundreds of 1/2watt 330ohm resistors to play with.
How big of a pad would I need to make or should I snake something around base of eyepieces?
I also have a old heater strip from a 8in SCT I could glue to the inside if that would work.
How much warmth is enough in a box ? Any ideas or thoughts :question:
Will be used with a DewBuster controller.

#2 Dick Jacobson

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Posted 05 January 2013 - 07:56 PM

Have you considered just throwing a chemical hand warmer into the box?

#3 MessiToM

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Posted 05 January 2013 - 09:00 PM

I can find the wattage of my kendric box heater out......

#4 dan_h

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Posted 05 January 2013 - 09:07 PM

An aluminun box radiates a lot of heat when under a clear sky. I throw a padded blanket over mine and use handwarmers inside it to kept it cozy.

A wooden box has some natural insulation so may not need the blanket.

Depending on the size of the box, it's construction, and how cold it is outside, I would think you may want 2watts up to as much as 10 watts or more. Since you plan on using the dew buster, why not build for 10 watts and set the buster as needed to keep things warm. In a closed box that is insulated, 10 watts is a lot of heat.

dan

#5 MessiToM

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Posted 05 January 2013 - 10:31 PM

Just checked. My Kendrick box heater is 10watts......

#6 lbsgville

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Posted 06 January 2013 - 09:48 AM

I used an old heating pad, like you would use on your back. I have my eyepieces in the aluminum tool case (briefcase style) that I got at one of the big box do it yourself stores. I spliced the wire and mounted a plug in the side of the box so I could just unplug the wire from the side of the box. I don't have any pics but could take some if anyone wants to see. It works very well.

#7 ischua

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Posted 06 January 2013 - 12:50 PM

The heating pad is great=simple but no 110 power available
so 12v. Not being in direct contact with the eyepieces I would be relying on radiant heat. I can build a 6"x4"pad underneath the eyepieces with all heat going up (approximately 4 or 5 watts max ) The dew strip I have would wrap around the ID of the box and has a rating of 25watts but would heat from the sides of the box. I'm more worried about how much is enough or am I over thinking?

#8 lbsgville

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Posted 06 January 2013 - 01:59 PM

Not having 110 is a problem at one of my dark sites. When I made my case I lived one hour from Chiefland FL and was going to Chiefland Astronomy Village for all my long term viewing and had access to 110. I didn't think about you not having it. What ever you come up with I think it may require at least two strips and its own power supply.

#9 k9yr

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Posted 07 January 2013 - 12:03 AM

I use a 12Vdc car seat heating pad. I keep my eyepiece box near the back of my SUV and the is a 12V outlet I can plug the cord into.

#10 BSJ

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Posted 09 January 2013 - 07:52 AM

Here's what I use in my small case. http://www.amazon.co...ils_o08_s00_i00

For me, the 1 star review was a bonus!

#11 gonzosc1

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Posted 09 January 2013 - 04:16 PM

just an idea, how about a small pelitier element. like they use in small 12volt coolers. one side cools and the other heats. so mount it in the lid reverse or heat side in, ad small heat sink with cpu fan on top of it to move the air around the case. only down side I can see would be the frost build up on the outside element. may not be bad but don't know for sure..

#12 Gene7

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Posted 09 January 2013 - 09:22 PM

I would make it self contained with one or two of the new #18650 Lithium batteries inside to also get heat from the battery. 4 volt cells will hold charge for about a year. Heat from power is exactly 100.00% efficient, so I would drive some LEDs to get light and heat. Would keep box small, air tight, 2 inch packed premium fine fiberglass. Gene

#13 Mike Lynch

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Posted 09 January 2013 - 09:48 PM

I'll second---or is that THIRD---the disposable chemical hand-warmers. I open one and toss it in the EP / accessory box. I put the lid down but don't lock it, and I can forget about dew throughout an observing session.

And, man, we get some DEW in Central Kentucky! (Probably like much of the central part of the U.S.)

Mike Lynch
Frankfort KY USA

#14 ischua

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Posted 11 January 2013 - 07:12 PM

I was able to scavenge elements from a bag sealer today.
12in long rated 85w 120v. I don't know if it can work with 12v without overloading/heating the wiring. Time to play!!

#15 propelller fan

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Posted 13 January 2013 - 12:56 PM

It should be workable.12 in long rated for 85w at 120v should give you 8.5 watts at 12 VDC. Even though it is rated for AC power, the heater element is not an inductive/capacitive load, so you can use ohm law, to calculate power, without having to take reactance into account.
Good luck!

#16 propelller fan

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Posted 13 January 2013 - 01:14 PM

One more thing about the heater element. It is almost certainly made of nichrome and can not be soldered. Instead of soldering, you'll need to use another way, such as crimping, to make a good electrical connection

#17 Gene7

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Posted 13 January 2013 - 05:39 PM

Mike;
Sorry Mike, but your 85 Watt element (at 120V) will only operate at about 1 watt when driven at 12V. Again and again Astro Based people's electrical advice is just astonishing!
I would use oversize 10 watt ceramic resisters instead and mix in some LEDs to give some free light.


Should you want to solder Nichrome wire use hard silver solder and an alum based flux. Must use a small propane torch for this higher melt solder. Only buy from a welding supply outlet. Hardware stores ONLY sell junk hard solder. Gene

#18 don clement

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Posted 14 January 2013 - 02:32 AM

I believe only a small wattage would be needed for an insulated eyepiece box perhaps less than 10 watts. Nichrome wire would not be necessary as has been stated can’t be easily soldered. If it were me, I would use a chain of easily obtained (I believe Radio Shack still sells small wattage resistors) small wattage resistors connected in series and/or parallel to obtain the resistance needed for the supply used e.g. 12V. Resistors can usually be easily soldered. Just make sure the wattage used for each individual resistor is less than that of each individual resistor’s stated wattage rating. For this application it doesn’t really matter type the resistor is (i.e. ceramic, metal film, carbon film, etc) as long as the wattage for each is kept at or under the stated wattage.

Don Clement

#19 gpelf

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Posted 14 January 2013 - 10:29 AM

Gene7,,,,+1 On 12v works out to .85w






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