DIY Dew Controller

[Stevie P]

Sorry for rubbish pics...

[mikeobrien]

Hi guys,

I have made a dew controller and heater straps about 4 months ago using nichrome wire and led controllers here is a picture it can be seen just to the right of the synscan hc I used the top of the existing cases and fitted them to a large project box lid. Works great for me.

Mike

Sent from my Nexus 7 using Tapatalk

[Dave_D]

so being the unremorseful scavenger i am, i managed to snaffle a broken toaster some local guy had sat on top of his bin

just tested the nichrome wire and it shows it's resistance as 7.4 ohms/m. is this a bit too low? as according to the spreadsheet on Blackwater Skies, i'd need  just over 13 turns for a strap for my 50mm guide scope which seems a lot of turns in a small space to me.

[JamesF]

It's a bit low for a small scope such as a finder.  I think I used some stuff that was about 19 ohms/m for that (SWG 32, perhaps?).  It's much closer to what you'd need for a larger SCT though, from memory.

James

[Dave_D]

yeah after a bit more study i think it's too low resistance as well, but as nichrome is so cheap anyway i guess it isn't an issue.

on a sidenote, and pondering the cabling and tripping over stiff in the dark, i stumbled across these which look interesting from a safety (of your equipment) point of view:

Magnetic Electrical Connector Pair

http://www.ebay.co.uk/itm/Magnetic-Electrical-Connector-Pair-/290998676210?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item43c0df6af2

[StuartJPP]

I have made a few dew straps using nichrome wire and Velcro loop strip (50mm wide).

The Velcro I chose has a (very) sticky side and if you stick it back to back it isn't budging. You can then use a small piece of hook to keep it held together once wrapped around the lens.

By choosing a suitable amount of wattage per lens area (my largest is only 3 Watts) and appropriate thickness of nichrome wire and length I find it is not necessary to adjust the heat, or at least I haven't until now.

Total cost £2.50 for nichrome wire, £2 for Velcro and £1 for 10 meters for the wire to the battery (enough for 5 straps).

People really seem to go overboard with dew heaters and controllers. Most important to me is the dew shield (or in my case lens hood) and a little bit of heat to stop the front element getting colder than the ambient air temperature which doesn't require much with a decent dew shield.

Of course these are my experiences and yours may differ.

[JamesF]

yeah after a bit more study i think it's too low resistance as well, but as nichrome is so cheap anyway i guess it isn't an issue.

on a sidenote, and pondering the cabling and tripping over stiff in the dark, i stumbled across these which look interesting from a safety (of your equipment) point of view:

Magnetic Electrical Connector Pair

http://www.ebay.co.uk/itm/Magnetic-Electrical-Connector-Pair-/290998676210?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item43c0df6af2

That's something I'd not thought of before.  Magnetic couplings could be really handy, especially if they came in an insulated housing with two connectors for instance, so you could connect up a positive and negative at the same time.

James

[mhard26339]

I built mine in a similar manner using an RGB 3 channel Dimmer s the basis of the chassis plus a hobby box from Maplin, some phono panel sockets and a couple of hours with a drill and soldering iron. the link on ebay is http://www.ebay.co.uk/itm/151055417940?var=450181429166. has proved perfectly capable of heating a 9.25 SCT

Regards

Mike