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USB powered hand warmers as dew heater strips?

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#1 Analemma

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Posted 14 December 2019 - 11:47 AM

Hi, Im new to the hobby and looking to save some $$ if possible. I found these USB powered hand warmers online:
https://m.aliexpress...c2-78d3c041b47b

I just bought a nexstar 8SE which hasn't arrived yet. But, I live in central florida and suspect dew will be a challenge for me.

These hand warmers are 5 v and a little less than 5" long each. There are 2 pads to each usb plug so my questions are:

1) the circumference of my corrector plate is about 25". Would just 1 of these warmers be ok with 2 pads that are 5" long each. So only about 10" of the total circumference would be warmed?

2) also, these warmers have no regulation. Will that be a problem? Will it be too much heat? Or too little?

3)any other recommendations? Alternatives? I cant really spend hundreds on a dew system right now, but I want to be able to use the scope.

Thanks for your help,
Anais

#2 RyanSem

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Posted 14 December 2019 - 11:57 AM

I'd imagine it would be very hard to control how much heat is actually being applied, and if that heat is being dispersed evenly.

 

Reviews aren't too great on aliexpress. But for the price it might not hurt to try, I suppose. 


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#3 Eddgie

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Posted 14 December 2019 - 12:22 PM

I doubt that these will be sufficient for three reasons.

 

First, I doubt that these produce enough heat.  When your hand is in a glove, it takes very little added heat to keep your hands comfortable.   The SCT corrector though is insulated.

 

Second, the current capability of the standard USB port is probably not high enough.

 

Last,  the heat is best applied to the tube where it meets the corrector cell and the dew strip completely encircles the cell, ensuring that the corrector is evenly heated with the lowest possible heat required to do the job.  These look like they could generate thermal currents.

 

Now that does not mean they won't work.  I don't know.  I have never tried using them.  I have owned a bunch of SCTs though, and based on that ownership, I recommend a good dew system.  

 

My advice?  Spend the money on a good commercial system.  It is possible to make your own if you are handy and have a bit of electronic build experience, but a good dew system is not really all that expensive.   Now you also need power, and depending on your location and conditions, that could mean extra battery, but if you are running from the mains, just make sure your power supply can handle the current draw. 

 

https://www.cloudyni...diy-dew-heater/

 

http://www.deepskywa...dew-heater.html

 

https://www.skyandte...diy-dew-heater/


Edited by Eddgie, 14 December 2019 - 12:24 PM.

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#4 Analemma

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Posted 14 December 2019 - 12:43 PM

Eddgie,

This will be my first telescope and I don't really know exactly what I will need. Though, from what I gather here on CN and elsewhere, my location will probably require it. I live in central florida.

I have a 12V Li-ion 20000mAh battery that will be my main for the scope. I think that should be enough to run everything?

I could just buy more pads so that they encircle the whole tube. Say 3 sets?

Also, if I understand correctly the heater strip should go right behind the black ring at the front? Is that what you mean? Im not familiar with "corrector cell" and "thermal currents"?

Im just exploring this idea , but if you guys don't think its a good idea, my husband has a little bit of experience with electronics. He could probably make it for me.

Thanks for your help and patience, these questions might sound a little silly to more experienced folks such as yourselves.

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#5 RaulTheRat

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Posted 14 December 2019 - 01:05 PM

Yeah making them yourself might be better. I made a bunch a while back using nichrome wire in kapton tape, then sewn inside strips of old denim. Ideally do what I did and add an online fuse to each. Soldering copper wire onto the nichrome properly isn't really possible as the nichrome won't take solder properly but you can ball up the nichrome and copper together and get a blob of solder onto it in such a way that it'll be fine.

To be honest, it's a bit of a job and I'm not sure I'd do it again, given the expense of everything else in astronomy although dew heaters are overpriced they are probably not much worse than many other things we buy. If you don't already have a sewing machine and soldering iron then it may not be worth the trouble.

The ones I made are decent though - I expect just as durable and effective as commercially bought items and probably less than a quarter the cost so it's definitely an option.
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#6 Analemma

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Posted 14 December 2019 - 01:18 PM

Yeah making them yourself might be better. I made a bunch a while back using nichrome wire in kapton tape, then sewn inside strips of old denim. Ideally do what I did and add an online fuse to each. Soldering copper wire onto the nichrome properly isn't really possible as the nichrome won't take solder properly but you can ball up the nichrome and copper together and get a blob of solder onto it in such a way that it'll be fine.

To be honest, it's a bit of a job and I'm not sure I'd do it again, given the expense of everything else in astronomy although dew heaters are overpriced they are probably not much worse than many other things we buy. If you don't already have a sewing machine and soldering iron then it may not be worth the trouble.

The ones I made are decent though - I expect just as durable and effective as commercially bought items and probably less than a quarter the cost so it's definitely an option.

Thanks a lot for the info. I have a sewing machine and husband has soldering equipment. I might go that route. I just didn't want all the trouble having to make it. Definitely a good and affordable option though. Thanks again

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#7 petert913

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Posted 14 December 2019 - 01:47 PM

This review is not great: -->  It's "working" but not efficient at all, it's more a gadget than a real device, it's not worth it.  Even for this price, don't buy it ;)


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#8 ButterFly

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Posted 14 December 2019 - 02:58 PM

my husband has a little bit of experience with electronics. He could probably make it for me.

 

The strips are fairly easy to make: Homemade Heater Strips.  The info is based on 12V sources, but could be modified for others so long as the power requirements are met.  Look around at the commercial offerrings to get a sense of how much power is good for a particular application (power = voltage * current used, for resistive heaters).  That 5V hand warmer won't give you nearly enough power (or uniformity) and merely plugging it into a 12V source to get more power is unsafe.

 

A controller is good to have, but often not necessary, especially in a high humidity area.  They just send current for a part of the time, essentially shutting it off and on quickly.  Others use a temp sensor to shut off completely at thresholds.  You don't need all of that right away.  These just save battery, but you can just shut them off yourself.

 

I do suggest that the power plug on the homemade heater match your battery's output.  The commercial ones use RCA inputs to use with controllers.  If you do get one down the line, just change the input plug.


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#9 RaulTheRat

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Posted 14 December 2019 - 03:18 PM

Thanks a lot for the info. I have a sewing machine and husband has soldering equipment. I might go that route. I just didn't want all the trouble having to make it. Definitely a good and affordable option though. Thanks again

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Yes they are pretty decent if you're willing to put in the time. I'd recommend checking first what resistance you need to get the power you want, you can look up commercial heaters and the wattage used for different applications, for example a secondary on a newt needs quite a bit less power than a front corrector on an SCT, and a maksutov needs yet more because of the thick meniscus. Then just use ohms law to figure out the resistance you need through either P=IV and I=V/R along with P=I^2 x R and that will allow you to calculate (knowing the resistance per metre of different thicknesses of nichrome wire, and the convenient length of your finished strips with 1/2/3 etc runs of wire going through them) what thickness of wire you want to order.



You want to aim for about the power of the commercial ones IMO which means you'll typically run them about 50% and have some headroom for very dewy nights to turn up higher. You can control them with the very cheap PWM dimmers that you can find on eBay meant for LED lights, I use these with DC 2.1/5.5mm jacks but in retrospect it would have been better to fit the dew strips with RCA plugs to match the standard connection used by the commercial ones, so that my strips would be compatible with a commercial controller, and I could then have just made an adapter from jack plug to RCA socket to connect them to the cheap PWM dimmers.

I used cable ties tightly around the copper power wires, then sewn inside the ends of each strip to strain relief the soldered connections.

There's a few guides around if you Google DIY dew heater strips that may help give you some more ideas.

Incidentally, and I can't remember where I saw these but after I made mine I found some Chinese made heating strips that use exactly the same principle and were cheap. They were made I think as anti-frost heaters for plants in greenhouses and came in strips that could be easily adapted for dew heater use. They were nichrome wire moulded into some sort of rubbery insulating foam. They would definitely be worth a look imo if you could find them.
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#10 v3ngence

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Posted 15 December 2019 - 02:21 AM

I love these camera lens heater strips, they even have a temperature control!

https://www.amazon.c...duct/B07WJG9B5P

 

I use 2 and they work for any configuration: one for the 70mm refractor and one for the guidescope, or with the 8" I stick them together end-to-end and they fit perfect! The 8" has an OAG so no guidescope to worry about.

 

I leave them on low power and they work great, you only need to be a few degrees above the ambient, if you heat up the scope too much you can get tube currents.


Edited by v3ngence, 15 December 2019 - 02:14 PM.

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#11 cytan299

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Posted 15 December 2019 - 08:47 AM

Hi Ana,

 

  I’m not sure that dew strips are the way to go at this stage of your Astro adventure. I’d suggest just making a dew shield which is heck of a lot simpler and costs around $10. Until you’re sure that you’d stay in the hobby I’d forego dew strips for now.

 

cytan


Edited by cytan299, 15 December 2019 - 08:48 AM.

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#12 rdmarco

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Posted 15 December 2019 - 10:24 AM

I love these camera lens heater strips, they even have a temperature control!

https://www.amazon.c...duct/B07WJG9B5P

 

I use 2 and they work for any configuration: one for the 70mm refractor and one for the guidescope, or with the 8" I stick them together end-to-end and they fit perfect! The 8" has an OAG so no guidescope to worry about.

 

I leave them on low power and they work great, you only need to be a few degrees above the ambient, if you heat up the scope too much you can get heat currents

+1 on these. They work for me.


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#13 Eddgie

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Posted 15 December 2019 - 11:07 AM

Eddgie,

This will be my first telescope and I don't really know exactly what I will need. Though, from what I gather here on CN and elsewhere, my location will probably require it. I live in central florida.

I have a 12V Li-ion 20000mAh battery that will be my main for the scope. I think that should be enough to run everything?

I could just buy more pads so that they encircle the whole tube. Say 3 sets?

Also, if I understand correctly the heater strip should go right behind the black ring at the front? Is that what you mean? Im not familiar with "corrector cell" and "thermal currents"?

Im just exploring this idea , but if you guys don't think its a good idea, my husband has a little bit of experience with electronics. He could probably make it for me.

Thanks for your help and patience, these questions might sound a little silly to more experienced folks such as yourselves.

Sent from my Pixel 3 using Tapatalk

I would say that no matter where you live, if it is an SCT, you need a plan for dew.  That does not mean you always need to use it, but I live in Austin Tx, and even as dry as it is here, I had to run my dew heater on my C14 just about every session. .

 

20 Amp hour should be enough for a decently long session running a dew heater for a C8.

The corrector is the Schmidt Plate at the front of the SCT and yes, the black ring is the cell it is mounted in.  Many people think the strip goes on the cell itself, but because the plate is recessed in the cell, if you put the dew strip around this rim, much of the heat just radiates off through the inside wall. 

 

The correct placement of the strip is on the tube just behind the black cell.  This way, the heat radiates trough the tube wall and and is trapped under the corrector, where it does the most good with the least amount of heat applied.

 

Thermal currents are heat plumes inside the scope (in this context).  Now the reason that you don't want a thermal current in the scope is because as the light passes trough it, it is slightly refracted, and this damages the image.   This is why you want the strip as close to the corrector as possible.  Because it is very close, you need only a minimum of heat, and it is being applied very close to where you want it to go.  The large radiating surfaces of the pads you showed would put the radiating surface deeper inside the tube, and since you would probably need to use more heat for these, then you have a much bigger chance of having a small column of heat developing and rising in a concentrated column across the light path would do much more damage than the very even and very low heat applied by the band.

 

And as to whether you want a dew controller or not.  I can give you the arguments for and against them.

Against is easy..  They are expensive (not really.  I mean considering the price of a telescope, a mount, an obsever's chair, and a case of eyepieces, they are really dirt cheap). 

 

For:

The goal of the heater is to apply only exactly enough heat to prevent dew from forming. If you use a lot more than this, what happens is that you create enough excess heat that you can generate thermal currents as a blanket of warm air builds behind the corrector.  Again, the goal is to put just enough into the corrector to keep it slightly above the dew point.  The heat is radiated out through the corrector almost as fast as it is applied.  

If you use a non controlled heater, the tendency will be to either leave it one, producing a lot of power and heat that is not radiating away, or only turn it on when the dew is forming, which means that you have to over-heat the internal air volume to dispel the already forming dew, and once again, you get some amount of disturbed air in the tube. 

 

Now you could of course just turn the heater on and off from time to time, but that is what dew controllers do for you. Once you put it on and set it for the conditions, you go about your business of observing and don't worry further about it.

 

The second reason is closely related to the first.  If you use a strip without a controller and you leave it on, you may be using a lot more power than you would with a controller, drawing more current from your battery than is needed.   Now if you are running off of the mains, that does not matter, but if you are running off of a portable source, you have to ensure you calculate for the amount of amperage it will take to complete your session. 

 

To be fair though, you don't need a controller.   If you don't want to run the strip 100% of the time, you will need to periodically check that you are not dewing up because once the dew stars, you have to apply a whole lot of heat to recover and if you calculate to low on the wattage of the dew strip, you may not recover.  This is because temps tend to be constantly falling at night, and it is easy to get behind the power curve, though with a C8, the problem is not a serious as it would be with a larger SCT.

 

Now I don't sell dew strips or dew controllers, but I do recommend them because they work well, and once you get a feel for the right settings for a given set of conditions, you can set the controller when you set up the scope, and not worry about it until the end of the session. 

 

And people mention dew shields.  These can be effective at delaying dew and in refractors can be all that is needed in many locations, but again, they can delay dew, but once it forms, that is that.  

The best combo is a dew shield and a dew prevention strip. This can reduce the power consumption and has the added benefit of blocking some off axis light (useful in subruban and brighter environments) but if you are going to run the dew heater anyway, and have the capacity to get through your session, a dew heater alone may be all you need. 

 

So, a lot of the argument for a controller is that you set it at the beginning of the session for the conditions you expect (get the temp and dew point from your local weather) and mostly you are done.   It still helps to check the corrector every half our or so just to make sure you have it set high enough, but once you get to know your observing conditions, you can usually pick a setting that will keep you dew free thought your session and not use excessive amounts of current or build up excessive heat in the tube. 

There are two accessories that I recommend most.  For all observers, I recommend a good observing chair.   For SCT owners, I recommend a dew prevention system, whether it be home made, or commercial.  I included the links to DIY in my first post because it is possible to roll your own, but I also think that the cost of a controller offers good return on investment.  As astro-stuff goes, it is pretty cheap.


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#14 cytan299

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Posted 15 December 2019 - 11:25 AM

Hi Edgie,

  I agree with what you posted. But since the op is new to the game and wants to save money, I’d suggest a dew shield first. As you know, lots of people buy a new scope and only use it once or twice and then the scope becomes a decorative piece in the home smile.gif

 

As usual YMMV

 

cytan


Edited by cytan299, 15 December 2019 - 11:26 AM.

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#15 Analemma

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Posted 15 December 2019 - 11:36 AM

Thank you all for the tons of insight. I am so thankful for cloudy nights. I've learned so much already.

I think I'll start off making a dew shield. Start simple and work my way up. I'll see how much of a problem dew is for me and then decide on which route to go with an actual heater strip and controller.

I'm pretty confident I could make a dew strip if I decided to go that route, or I might decide that the investment in a full commercial solution would be well worth the investment.


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#16 AhBok

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Posted 15 December 2019 - 02:59 PM

I use the camera lens USB heater for my 60mm guide scope and it works great for that. I image with a newt so no other heaters are needed and the USB heater is a cheap and effective solution for that. No way would it work on anything larger. I use a C6 for visual and I find a dew shield is all I need. If a dew shield isn’t enough then there is really no substitute for dew straps and a controller.


Edited by AhBok, 15 December 2019 - 11:40 PM.

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#17 jcj380

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Posted 17 December 2019 - 09:26 AM

You can buy a controller for $10 on Amazon.  I've not tried them myself, but others have written that they work well with DIY heater strips or motorcycle glove heaters, etc.




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