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ideas for EP case heater ?

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#1 Bob4BVM

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Posted 15 December 2019 - 06:16 PM

Any ideas ?

I am looking to keep EPs warm for my cold damp winter nights

 

EPs are always cased when not in use. Case arrangement is foam pockets to hold most EPs vertical, top up.

Ideally would like some kind of mat heater in bottom of case below the foam, something like a small heating pad.

 

Battery power will be small 1S or 2S LiPo, so could easily fit inside case

Wondering if a small 120V heat pad might work, generating a very low heat on a low voltage DC source

Something like 250W @120Vac  to 7.2Vdc or 3.6Vdc:   250:120=x:3.6  =7.5Wx1.414 =10.6W

Havent looked at pad wattage or sizes so this is just a guess right now. If I can find a pad that (ideally) fits in my EP case I might give this a go.

 

Anyone done something like this?. I can add a little PWM ckt to control current, but would like to find a match between pad R and battery V so just a switch would be the only other thing in the ckt.

 

Thx

Bob


Edited by Bob4BVM, 15 December 2019 - 06:28 PM.


#2 N3p

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Posted 15 December 2019 - 07:38 PM

You can check this website to get additional ideas, it's a plan to build a controller and heating straps using a 12v battery. I've built one and it's working fine, it's possible to fabricate many kinds of heating surfaces.

 

https://www.deepskyw...dew-heater.html


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#3 Bob4BVM

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Posted 15 December 2019 - 09:55 PM

N3p,

Nice collection of ideas there, thank you.

I have built a lot of dew control stuff over the years and have used some of those same ideas, but never anything specifically for an EP case.

A little looking and I have found heat pads in the 12x15 inch range, rated for from 4W to 50W on 120Vac. I was thinking of an internal case battery, but maybe it makes more sense to just use 12V since I usually have that avaikable for other stuff anyway. I could just install a '12V input' jack on the EP case an plug it is as necessary.  That also simplifies the power calculation since a heater on 12v is 1/10th the 120Vac rating, plus the 1.41 multiplier in going from AC to DC.

I guess now I just need to see what wattage gets my case slightly warm... 



#4 RaulTheRat

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Posted 15 December 2019 - 10:04 PM

Don't forget power won't be linear with voltage. The current will drop linearly (I=V/R so for the same resistance you'll have 1/10th the current at 12v compared to 120v), but P=IV so you'll have 1/10th the current at 1/10th the voltage for 1/100th of the power.

#5 BGRE

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Posted 15 December 2019 - 10:06 PM

Wrong. The power dissipation at 12 V is 1/100 that at 120V for the same resistance heater. There is also no 1.41 multiplier as the heating effect of 120V rms AC is exactly the same as 120V dc.



#6 Bob4BVM

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Posted 15 December 2019 - 10:18 PM

Well you are both right, thx for catching my mistake.

1/100th the wattage for a give element.

And I missed the RMS value, somehow I had the 170Vac Peak value in my head and then factored it (1.414) against the rms, which as you said is already the dc heating value of the 120VAC line voltage.

Guess I've been retired too long :)



#7 Starman47

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Posted 10 January 2020 - 09:10 PM

I know this may not be exactly what you want. But I have put Hot Hands (chemical hand warmers) in my eyepiece case. They last all night.



#8 StevenYood

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Posted 11 January 2020 - 05:25 AM

I use terrarium heaters, but I have 110v at my observing site.  Tech 2000 make nice looking battery options.

http://www.tech2000a...my.com/radiant/




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