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How to pick the correct size dew heater strip?

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15 replies to this topic

#1 joelin

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Posted 14 January 2019 - 07:12 PM

I'm a bit unsure how to pick the correct size for a dew heater strip. Here is where I'm not sure

 

1) Can I pick a dew heater strip that I know will be a bit too big and just wrap the excess around?

2) If I have a lens that accepts a 77mm filter, will a 3" dew heater strip work (just a hair under 77mm)?

3) What is the correct size needed for a 60mm refractor? How about 80mm?



#2 Kunama

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Posted 14 January 2019 - 07:57 PM

Get a strip of paper and measure the actual circumference of the eyepiece, lens or scope.

Then do to the DewNot site where they provide the lengths of the various dew heater straps....

 

https://www.dew-not....cifications.htm

 

and if you don't have a controller then I would recommend the DewBuster waytogo.gif


Edited by Kunama, 14 January 2019 - 07:58 PM.


#3 Starman47

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Posted 14 January 2019 - 07:59 PM

http://www.kendricka...ierheaters.html



#4 joelin

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Posted 14 January 2019 - 08:00 PM

Also, will lens heaters work such as: https://www.amazon.c...ns heater&psc=1



#5 Kunama

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Posted 14 January 2019 - 08:12 PM

Also, will lens heaters work such as: https://www.amazon.c...ns heater&psc=1

They should be fine as well, they are 1Amp at 5V and have a USB cord.  



#6 Fernando134

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Posted 14 January 2019 - 08:12 PM

I'm a bit unsure how to pick the correct size for a dew heater strip. Here is where I'm not sure

 

1) Can I pick a dew heater strip that I know will be a bit too big and just wrap the excess around?

2) If I have a lens that accepts a 77mm filter, will a 3" dew heater strip work (just a hair under 77mm)?

3) What is the correct size needed for a 60mm refractor? How about 80mm?

I was in the "same page" as you. Check the Agena website. They have detailed and complete instructions on which size for

your telescope dimensions. It worked just fine for me. Hope this helps.

 

Regards, Fernando



#7 WarmWeatherGuy

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Posted 14 January 2019 - 08:16 PM

Go to this Agena Astro page and scroll down to section D Specification Table where they list the exact size you need for each scope.


Edited by WarmWeatherGuy, 14 January 2019 - 08:16 PM.


#8 joelin

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Posted 14 January 2019 - 08:30 PM

well i was also wondering if its ok just to buy a larger one for a smaller scope...and then wrap the excess around...

 

it doenst cost much more to go from 4" to 6" for example...and the 6" is more versatile for stuff in the future



#9 Starman47

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Posted 14 January 2019 - 09:20 PM

I was told by a dew heater maker that I should not use an oversized heater because the overlap could cause overheating at the overlapped parts of the strip. I, of course, do not know if the information is correct.


Edited by Starman47, 15 January 2019 - 07:42 AM.


#10 mkirk76

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Posted 17 January 2020 - 05:11 PM

I was told by a dew heater maker that I should not use an oversized heater because the overlap could cause overheating at the overlapped parts of the strip. I, of course, do not know if the information is correct.

Bumping this old thread with this question:

 

My Evolution 6 has a 22" circumference.  The 6" Dew-Not heater measures 20.5", while the 7" Dew-Not measures 25" - these measurements don't include the velcro attachment.

 

Is it better/safer to have a 1.5" gap using the 6" heater or have a 3" overlap using the 7"?

 

Thanks,

Mike


Edited by mkirk76, 17 January 2020 - 05:14 PM.


#11 junomike

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Posted 17 January 2020 - 07:34 PM

Bumping this old thread with this question:

 

My Evolution 6 has a 22" circumference.  The 6" Dew-Not heater measures 20.5", while the 7" Dew-Not measures 25" - these measurements don't include the velcro attachment.

 

Is it better/safer to have a 1.5" gap using the 6" heater or have a 3" overlap using the 7"?

 

Thanks,

Mike

Were you measuring the OTA behind the Corrector Plate?  This is where the Heater fits best.

If so I would go with the larger Heater although either should work fine.



#12 mkirk76

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Posted 17 January 2020 - 08:11 PM

Were you measuring the OTA behind the Corrector Plate?  This is where the Heater fits best.

If so I would go with the larger Heater although either should work fine.

Yes, I measured the outside circumference just behind the corrector plate.

 

Is a 3” overlap going to damage the heater? Or, is a 1.5” gap going to increase the chance of dew forming?



#13 junomike

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Posted 18 January 2020 - 09:33 AM

Yes, I measured the outside circumference just behind the corrector plate.

 

Is a 3” overlap going to damage the heater? Or, is a 1.5” gap going to increase the chance of dew forming?

I have and still do both options (short and too long Heaters)
IME the "too short" option may take a little longer to clear the dew as it might dissipate in a normal circle pattern with a small spike sticking out where the

 Heater is missing. This "spike" will clear, but be slightly larger than the circle pattern.

 

A 3" overlap is going to add almost double the heat to that 3" portion, however I've never noticed an issue and it seemed better to me than having a gap.


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#14 GrandadCast

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Posted 18 January 2020 - 02:36 PM

I been using one that fits all three of my OTAs, from a 8” SCT (1.5 or 2 wraps, sorry not looking at it right now) down to wrapping it onto a 80mm (definitely three wraps) and never a problem. Just set the adjustment to what is needed to slightly warm things up. I guess if I would cranked it up it may get warm to slightly hot, but not hotter than sitting out under a cover during the hot Texas sun.  

Jess



#15 mkirk76

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Posted 26 January 2020 - 01:29 PM

I have and still do both options (short and too long Heaters)
IME the "too short" option may take a little longer to clear the dew as it might dissipate in a normal circle pattern with a small spike sticking out where the

 Heater is missing. This "spike" will clear, but be slightly larger than the circle pattern.

 

A 3" overlap is going to add almost double the heat to that 3" portion, however I've never noticed an issue and it seemed better to me than having a gap.

I ended up contacting Dew-Not and asked for recommendations on 6” vs 7”.  Like you mentioned, they thought that depending on weather conditions, some dew may form due to the gap, if I went with the 6” heater. 
 

They suggested making a custom size so there’s no overlap or gap, and had it in the mail to me the same day.  Fits perfectly!

 

Excellent customer service from Dew-Not. 



#16 junomike

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Posted 26 January 2020 - 04:21 PM

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