22 replies to this topic

[SNH]

So, I've had this idea for at least a year. I was looking for a way to keep ALL my eyepieces warm and the idea struck me that I might be able to use an electric heating pad if I could find one that was small enough. Well, I've finally gone and done it...and I'm happy with the results!

 

Now, my situation is special because I spend 95% of my time observing within a few meters of my house under Bortle 3 skies (21.35 mpsas). So, I've got 120v electricity almost year round (pesky power outages do occur during ice storms and from high winds!). Which means my idea won't work for a lot of you folks.

 

I bought two Equate 9" x 10" heating pads off Walmart.com. They have nice, long cords and even though they will automatically turn off after 2 hours, they have two heat settings. I can place one in each of the Apache 2800 cases where I store my eyepieces and simply lower the lid.

 

I used them for the first time two nights ago when it was around 32F and they managed to keep my eyepieces decently warm while on high! It was a great feeling to reach for one and find it comfortable to hold with my bare fingertips.

 

Scott H.

 

 

 

[SNH]

Just sharing all this in case someone else could use the inspiration. I HATE a cold eyepiece...

 

Scott H.

 

[Knasal]

Great! And when the back gets sore, or *you* get cold, you’re all set  

 

Kevin

[TOMDEY]

Yeah... looks like the thermostat starts cycling off and on at 110^oF. The rapid heat up means the wattage (when heating cycle on) is probably pretty high. This is fine, provided the thermostat works and the pad is all around the same temperature. For milder continuous heating I use pet bed warmer pads... which draw only a few watts. The newer high wattage pads (yours) have the now required auto shut off so it is far less likely to start a fire if left on and unattended somewhere. I had one of those (old ones continuous on) in my observatory turned on for months on end under a tub of eyepieces and... when I checked it --- it had scorched the wooden table underneath!     Tom

 

Picture of pet pads >>>

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[ButterFly]

I tried that for a while.  Fogging is the issue it staves off.  Cold eyepiece with a hit of hot breath equals fog.  The plug in heating pad is way too much power though.

 

I made the 3-6-9 watt heater below instead.  With the lid closed like above, it provides plenty enough heat to stave off fogging.  One could, in theory, just place this in the case itself, with sockets for power leads coming out the side.  One lead gives me 3W, and the other 6W.  A Y-cable connecting the two gives me 9W.  I rarely need more than 3W to keep the eyepieces maintained hot enough in the closed case, but the 9W for a little while gets them going.

 

 

The innards are just two separate sets of 330 ohm resistor ladders.  The powered on resistors within one ladder are arranged as knight's moves apart.  That way, I can double the number in one ladder, without overlapping in any of the other ladder.  I avoid hot spots with a layer of smoothing insulator between the ladders and the outer duct tape housing.

 

One could use nichrome wire, salvaged from a toaster, instead.  That will more easily prevent hotspots.  Just be careful to avoid burning through the insulator, and keep the wire secured to prevent shorts.

[slavicek]

Well, I took it one step further....

 

 

Heated pad, holds 3 Ethos, runs on 12V. The only think I have to upgrade was the 9 AH battery which runs the DOB and the heated pad. Battery was getting old anyways. So I upgraded it to 18 AH. It will last looong time (more then me). Works like a charm.

 

[csrlice12]

Just use a harvest gold crock pot....and only a harvest gold crock pot.

[Scott99]

We need something like this with a battery!  Great product idea for someone.   For long sessions in winter I"ll often drape a heated dewstrip across the inside of my ep case, it does the trick too.  Just need to keep them a little warmer to avoid fogging.....

[SNH]

Tom Dey is correct that my heating pad is a bit powerful considering it draws 26W. So, the "small" pet bed one he has might be a better alternative for some people. However, there's a difference between keeping large, heavy eyepieces warm and warming them up after having been in the focuser for 20 minutes with a below freezing air temperature. And at the moment, I'm pretty happy with mine since I think it can do the latter quite well. But I recognize now in hindsight I might not have needed to get the one I did.

 

Scott H.

[ButterFly]

I'm below freezing here from September through April!

 

These things help before they go into the focuser.  Using an ordinary dew strap on a cold eyepiece won't cut it, so preheating them helps.  Even with the four step CVS version I had (52 W max), it only went down to 13W at its lowest setting.  That's way too much to get the job done.  Once the eyepiece goes back in the case, it just came off of the dew heating strip, so it's warm enough for the dew strip to do its job.

 

After it's out of the focuser (and off the dew heating strip), it doesn't really matter.  It's capped and already above ambient, at wherever the dew heating strip left it.  The case heater at that point is just getting it even higher.

 

My concerns with overheating are destroying the rubber eyeguards by drying them out even more.  My ambient relative humidity is usually very, very low already.  The effect on the cement between the elements can be terrible if the heating is very localized.  Dumping 26W evenly across the area may be fine, but concentrating those 26W into a small area can lead to trouble.  If there are hotspots, consider adding a piece of rubber between the heater and the eyepieces to prevent dumping a lot of heat to one part of an eyepiece.

[Ac2aj]

The dew strips for eps work great. Warms them up. I have one for 1 1/4 and one for 2" eps.


Brian

[ButterFly]

The dew strips for eps work great. Warms them up. I have one for 1 1/4 and one for 2" eps.


Brian

Only when they're already warm enough, though.  That's where having a case heater helps.

 

Preventing dew on an eyepiece is easy.  Just cap it when not in use.  Preventing fogging from breath is much harder, and needs much more heat.

[quilty]

Makes a difference, he?

[Scott99]

Only when they're already warm enough, though.  That's where having a case heater helps.

 

Preventing dew on an eyepiece is easy.  Just cap it when not in use.  Preventing fogging from breath is much harder, and needs much more heat.

the way it works for me is that I'll typically have 2 eyepieces of each magnification - low, medium, high ,very high, in the case, and observe with one of them till it fogs.  Then it's back in the case with the dewstrip and use another one from the case, until it fogs.   This keeps me from needing a strap on the eyepiece at the scope

[slavicek]

The dew strips for eps work great. Warms them up. I have one for 1 1/4 and one for 2" eps.


Brian

Yes but the dew strip cables tangle up and catch on everything.

My experience...

[Mike Q]

Yes but the dew strip cables tangle up and catch on everything.

My experience...

Proper cable management is a art form lol

[triplemon]

The heatpad in the original post isn't overpowered.

The way its used the vast majority of its heat is going into other places than the eyepieces. Its surface is large. It will barely be adequate because of this poor efficiency.

 

10W / squarefoot barely makes things feel nice, even if there is good thermal insulation on BOTH sides:



If you want to efficiently heat the EP, make a metal holder with the usual hole sizes, add insulation on the sides and below and heat that metal 'heat spreader". This not only transfers some heat directly to the metal parts of the EP, but any warm air rising also envelopes the rest of the EP.



Technical data: Temp rise of the EP casing +12C, eye lens +7C at 5.4 watts in still air.

Edited by triplemon, 07 January 2025 - 03:35 PM.

[ButterFly]

The heatpad in the original post isn't overpowered.

The way its used the vast majority of its heat is going into other places than the eyepieces. Its surface is large. It will barely be adequate because of this poor efficiency.

 

10W / squarefoot barely makes things feel nice, even if there is good thermal insulation on BOTH sides:
 

 

What makes you think this 9x10" heater is giving off less than 10W?
 

[CrazyPanda]

This thread has inspired me.

 

Idea:

 

1. Take one of my current cases with Kaizen foam and use my 3/4" cutting tool to poke a bunch of holes in the cavities where the eyepieces sit (maybe like 3-4 per eyepiece).

2. Extend the holes of all my 1.25" finger pulls down to the bottom so they each act like vents to the top layer of the case.

3. Make some additional strategic holes throughout the rest of the foam.

4. Make a 12v heating pad out of nichrome or resistors and place it in the bottom of the case - perhaps between the foam holding the eyepieces and another thin layer of foam just to insulate the heating pad a bit and prevent it from warming the ground.

 

The holes will allow warm air to rise and heat the eyepieces, as well as rise up into the space with the convoluted foam to heat the top of the eyepieces as well. The finger pulls are at the tops of the eyepieces, near the eye lenses, which is exactly what you want to have a little bit of warm to prevent fogging.

 

The foam itself will also get warm and in turn warm the eyepieces, but foam is a good insulator so I don't expect it to be that effective in this regard (I wonder if there's such a thing as thermally conductive foam)

 

As long as I keep my case closed when not in use, it should make for a fairly effective warming solution for the eyepieces.

Edited by CrazyPanda, 07 January 2025 - 10:25 PM.

[Usquebae]

Here's my heated EP case, made from Dow 2" foam board and duct tape.  The green padding is high density foam from Joann Fabrics.  The heating element is an Ororo heated seating pad, intended for bleachers or something.  Powered by any USB battery.  I got 30,000 mah power bank that will run the pad all night.  Control button hangs out, conveniently.  I've got foam padding between the heating pad and the EPs, so the EPs don't get hot, but they stay well above ambient all night. 

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[ButterFly]

You can even make the lead come out of the side, or have a female lead flush with the outside.  For reasons pertaining to my knowing I'm an idiot, I like to keep the case closed with only one of the latches engaged.  That way, when I dump the case over, at least the eyepieces won't come spilling out.

 

There is indeed thermally conductive foam, but you don't really need it.  As the insulated foam itself gets hotter, so do the eyepieces.  That's the benefit of trapping the heat in the case - it has nowhere to go.

[triplemon]

What makes you think this 9x10" heater is giving off less than 10W?
 

Did I say such ? I'd bet the scope on a 26W heater giving off 26W of heat ... its not glowing, making noise or radiating much at any other much different wavelength.

 

The 10W per sqft (a power density, not absolute power) example with the two furry sensors shows that power density its barely rising from room temp to "irresistably nice".  So the temp rise of eyepieces from near freezing would be 2-3x that much, so power needs go up by that much as well. The towels and 1/2" cyanoacrylate underneath the cat toasters and overall dimensions look pretty comparable to me to the towels and foam in the eyepiece case. Plus, eyepieces will add a lot less heat of their own than my furry sensors. So that is how I conclude with nerdy engineering methods that the cat toaster example, scaled to the eyepiece case creates about the same overall effect.

Edited by triplemon, 08 January 2025 - 03:09 PM.

[ButterFly]

Did I say such ? I'd bet the scope on a 26W heater giving off 26W of heat ... its not glowing, making noise or radiating much at any other much different wavelength.

 

The 10W/sqft example with the two furry sensors shows that power density its barely rising from room temp to "irresistably nice".  So the temp rise of eyepieces from near freezing would be 2-3x that much, so power needs go up by that much as well. The towels and 1/2" cyanoacrylate underneath the cat toasters and overall dimensions look pretty comparable to me to the towels and foam in the eyepiece case. Plus, eyepieces will add a lot less heat of their own than my furry sensors. So that is how I conclude with nerdy engineering methods that the cat toaster example, scaled to the eyepiece case creates about the same overall effect.

So it's 26W?  That's still too much power.