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Dew strap with short cable?

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#1 WadeH237

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Posted 05 October 2019 - 07:17 PM

I have a quick question:

 

Does anyone know of someone sells dew heater straps with short (or no) leads?  I route my cables through the mount, and want to be able to swap OTAs without disassembling the mount.  It would be ideal to be able to disconnect the dew heater from its cable.

 

I'm currently using Kendrick dew straps and have cut off the existing cables at about 6" from the straps and installed PowerPole ends.  This works, but since the Kendrick power cables are coaxial, the connection to the PowerPole is awkward.  I'd like to switch to something a little better suited, and less likely to give me trouble down the road.

 

If I can't find something off the shelf, I may need to look at opening up one of the straps and seeing how difficult it would be to just solder on my own cable.  But I'm not awesome with a soldering iron, and in this case, I'd be happy to pay for one that is made the way I want.

 

Thanks,

-Wade



#2 TOMDEY

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Posted 05 October 2019 - 07:38 PM

I've done that too. Could never figure out why they use coax... it's just joule heated resistive nichrome wire, after all, with a bit of circuitry if thermostatically controlled. Coax is usually used to prevent RF coupling/interference (in and/or out). But the meanders in the heater part would still be emitting a LOT of RF! Maybe some wizard out there knows (not guessing but actually knows)... I'm guessing those connectors are just what they decided on long ago, just because they liked the feel or something, and have become the non-official/casual convention?    Tom



#3 Nicole Sharp

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Posted 05 October 2019 - 08:24 PM

Not exactly sure what you are asking, but the Omegon USB dew heaters may be shorter than the RCA dew heaters, since USB loses power more quickly.


Edited by Nicole Sharp, 05 October 2019 - 08:25 PM.


#4 Migwan

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Posted 05 October 2019 - 09:39 PM

Just about anything involving electricity can cause rf under various circumstance, but coax on either side of the nichrome won't prevent it.

 

jd



#5 WadeH237

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Posted 06 October 2019 - 06:38 AM

Not exactly sure what you are asking, but the Omegon USB dew heaters may be shorter than the RCA dew heaters, since USB loses power more quickly.

I route all of my cabling through the mount.  It's a large mount that comes apart into two halves - an RA half, and a declination half - for transportation and storage.  It's almost impossible to fish a cable through it without actually separating it.  Oh, and it may not have been clear, but I have a semi-permanent setup - not quite an observatory because I cover the scope instead of having it in a structure.

 

To change a telescope, I disconnect all of the cables at the telescope and then remove it.  I then reuse the same cables for a different telescope.  This works fine for everything but a standard dew strap.  Since the cable is normally fixed permanently to the strap, I have to take the mount apart after removing the telescope to pull out the cable for the first dew strap and fish the cable through the mount for the dew strap on the other telescope.

 

What I want is a dew strap that basically has no cable permanently attached, but instead has a connector so that I can separate the cable from the strap.  It seems odd to me that nobody (that I have found) makes them like this.

 

I hope that this makes sense,

-Wade



#6 t-ara-fan

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Posted 09 October 2019 - 08:59 PM

Just about anything involving electricity can cause rf under various circumstance, but coax on either side of the nichrome won't prevent it.

jd


The power to the dew heater is chopped at 100kHz. Which creates MHz harmonics. Maybe the coax stifles the noise.

I thought Kendrick used the coax because it is very flexible - even in the cold. Or maybe because it looks good with the RCA plugs?

#7 t-ara-fan

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Posted 09 October 2019 - 09:13 PM

 

What I want is a dew strap that basically has no cable permanently attached, but instead has a connector so that I can separate the cable from the strap.  It seems odd to me that nobody (that I have found) makes them like this.

 

In the past I ran a Kendrick dew heater extension cable up though my mount.  About 3" of it with the female end was hanging out of the mount. 

 

On my two scopes, I just wrapped the excess long cable coming out of the dew strap around the OTA tube a few times, then plugged it into the 3" stub coming up from the dew controller. 

 

Simple? I sure as heck didn't fish the cable through the mount every time.

 

The pic below shows two dew heater cables and a USB exiting the mount. I have since changed my setup to have my dew heater controller mounted up on my OTA.

 

4fxuDDb.jpg


Edited by t-ara-fan, 09 October 2019 - 09:14 PM.


#8 Migwan

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Posted 09 October 2019 - 09:34 PM

The power to the dew heater is chopped at 100kHz. Which creates MHz harmonics. Maybe the coax stifles the noise.

I thought Kendrick used the coax because it is very flexible - even in the cold. Or maybe because it looks good with the RCA plugs?

Coax has a center conductor and an outer shielding, the later being either foil or wire and acting as a Faraday Cage to the center conductor.   There's nothing to shield whatever current (+ or -) that is carried on the shielding.  Besides, the nichrome has no shielding. 

 

Think the choice of coax probably has more to do with expense and durability of the jacks, but could be wrong. 

 

Like your routing.  Pretty slick. 

 

jd



#9 StevenYood

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Posted 10 October 2019 - 03:55 AM

R Sky made me some heaters with custom cables a while back. It might be worth checking with him. His pricing is very good also.

#10 wrvond

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Posted 10 October 2019 - 06:43 AM

You could simply cut the leads to the length you want and install your own solderless RCA connectors. Here's some fairly inexpensive ones:

https://smile.amazon...0707680&sr=8-22


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