Dew heaters.

[Arthur Alchin]

I have had a great deal of satisfaction from dew heaters that i have made from nichrome wire and a pulse width modulator, and i must say that these are very inexpensive when compared to commercially available units.

I have just acquired 2 x 120w (yes 12v, 10 amp) units from overseas for less than $20 and 30m of 32g (10 ohm/ foot) nichrome from the USA for about $10.

Th current unit i am using delivers 14 watts off 12 v. This is much easier than fiddling with soldering resistors together.

Feedback welcome

[rcheshire]

Hello Arthur. I bought 0.33mm nichrome this week, along with a humidity sensor from Jaycar. About $5 / 4 metres, 13.77R / metre. My first dew heater. I will pwm a MOSFET from an Arduino in response to humidity and scale the heating that way. No doubt fine tuning will be required. I'm quite happy with the prototype. It's as warm as holding a mug of hot tea. Quite warm but not so hot you need to let go. Aiming for 18.4R, I finished up with 17.8.

[Arthur Alchin]

Love the concept, built on a "heat needed" principle rather than just let it burn all night.

I do have some nichrome which i scavenge from disused toasters but find it's 5ohm/ foot to vicious. Although still only drag 1 amp for about 14 watts

[rcheshire]

It worked well at the SVAA camp last weekend - 3C at 4am.

At Alistair's suggestion, a dewpoint calculation in the code switches heating near dewpoint to maximum. The rest of the time heating is scheduled in response to humidity as a convenient reference. The lens suffers from moisture ingress and condensation on an internal element - running heating all the time seems to help keep it dry.

[TechnoViking]

do you have any Photos of the setup??

[rcheshire]

I'll post, but there's not much to see.