Home made dew heater

[kev1204]

Hi,

Been busy during the cloudy evenings. I built myself a dew heater controller and a secondary mirror heater. The controller circuit was from a schematic I found on the web. Cheap and easy to put together. Has 4 outputs and all are independently controllable. Powered from a 12v DC source.

The secondary heater is 2 47 Ohm resistors in parallel.

Whole project cost around £30. Im going to make an eyepiece heater next when I get some time.

(click to enlarge)

controller

(click to enlarge)

circuits

(click to enlarge)

secondary heater. ( shown wired in series by mistake before gluing using araldyte)

(click to enlarge)

secondary heater terminal

(click to enlarge)

unit working

It works a treat and should beat the dew.

Kev

[blinky]

Looks the business Kev Great idea for the secondry heater as well.

[George]

Well done that looks a great job done

Which schematic did you use?

[blinky]

Here is what I use George, it looks a very similer circuit to mine.

http://www.cpemma.co.uk/555pwm.html

[George]

Well I was planning on using a Velleman PWM kit http://www.esr.co.uk/velleman/k8004.htm cos I'm a thicko when it comes to circuit diagrams, I'm quite handy with a soldering iron tho.

http://www.wilmslowastro.com/tips/dewheater.htm shows the Velleman kit controller.

Ive not decided yet on nichrome or resistors for the straps.

[blinky]

George, Maplin sell a PWM Drill Speed Controller for £15, if you are only interested in a single channel one then it would be fine.

[George]

Craig, need at least 3

ED80

Newt

Finder

[Psychobilly]

Well done Kev all ready for the South Wales meet now then

You can use more than one of the Maplin pwm units but have to watch - you have to float the outputs because of the way the circuit works....

But better of buying from Blinky...

Billy...

[kev1204]

Here is the link to the circuit I used. This was very easy to put together, and it works. I'm going to make the strip heater for the eyepiece from Nichrome wire. I got 5m of 1 Ohm per 10mm. From experimenting I reckon I need a 47 ohm heater that will give 3 Watts of heat. should be easy to knock up. I got the parts from Bitbox, you dont pay much for postage. Check the prices against Maplins is all I can say

http://www.simcoeskies.com/dew/no_can_dew.html

[George]

Well done Kev all ready for the South Wales meet now then

You can use more than one of the Maplin pwm units but have to watch - you have to float the outputs because of the way the circuit works....

But better of buying from Blinky...

Billy...

The Maplin jobby is a lot more expensive than the Velleman.

Think I will use this method for the straps http://www.iceinspace.com.au/forum/showthread.php?t=21421&highlight=dew+heaters

[Reggie]

I used this circuit, http://www.backyard-astro.com/equipment/accessories/dewheater/dewheater.html

How does your heater differ from the circuit diagram you posted Kev, are you using 556 timers instead of 555s? Too many pins on your ICs for them to a be 555s I see you used IRF510s as opposed to the TIP120s that are in the circuit I used to supply power to the bands, any heat issues at all?

[kev1204]

Hi Reggie

I used 556 dual timers for this. 2 IRF510's per circuit and 2 circuits to give 4 outputs. There are no heating issues with these MOSFETs in my set up. The secondary heater has a total resistance of 24 Ohms, this gives 6W of heating power. The IRF510s seem to cope well with this.

[Reggie]

Ahh 6W, that'll be why there aren't any heat issues, the IRF510s require a heatsink from about 24W apparently.

The 555/556 timer ICs are superb little bits of kit, so versatile.

[kev1204]

I dont envisage using anything like the 24W. The 2 47 Ohm resistors in parallel give 6W of heat. This is plenty. Once I sort heaters for the eyepiece, Red dot, and finder scope which will increase the load from the power supply. From experimenting with various resitances ( Resistors and Nichrome wire) I dont think that I will need to load any of the circuits with more than 6W.

To be honest I built this with Dew prevention in mind, not dew removal, so If I switch it on with a gentle heat when I move the scope out side for an evening it should fulfil this while still enabling a good evenings worth of juice from the power supply.

I dont know the ratings of a commercial dew heater band, probably not much difference than what Ive done here.

Thanks for the positive comments. I'd highly recommend building your own dew controllers / heaters, it is fairly easy and far more cheaper than buying the kit.

[PhillyDee]

You lot have given me a new project . . .

That makes about 6 concurrent projects, most half finished or not properly started

[Reggie]

I think between my 2 commercial heater bands I'm pulling 1.2a and 0.6a so 1.8amps at full power, I don't usually need to go above 1/3rd to 1/2 output. For my next project I'm going to make an automatic one based on ambient/ota temperatures. 2 ways to do it, all analog, pretty cheap to do ~£10 again, or digital/analog with PC feedback/control, will probably cost £30 all in including usb controller board.

For anyone that's interested in having a go with electronics in general, I found this site to be very useful, http://www.kpsec.freeuk.com/

Very informative, simple layout, loads of working examples of little projects.

the components section is useful for understanding how things work and which way round they should be connected http://www.kpsec.freeuk.com/compon.htm

And for anyone wishing to understand the little 555/556 timer ICs for making their own dew heaters take a look at the 555 page http://www.kpsec.freeuk.com/555timer.htm

I didn't have any electronics experience before this year, so as a beginner for anyone else starting out I would suggest getting a breadboard http://www.maplin.co.uk/Module.aspx?ModuleNo=5199 makes it very easy to prototype circuits without having to solder a thing, My dew heater is still using the breadboard I prototyped it on

Some jump wires would also be useful either a kit http://www.maplin.co.uk/Module.aspx?ModuleNo=2014&&source=14&doy=14m11 or 10 wire packs http://www.maplin.co.uk/Module.aspx?ModuleNo=2013&&source=14&doy=14m11

you might want to get a resistor kit too, an LED lucky bag (an LED makes a great substitute for a real heater until you know your 555 timer circuit works how it should) and last but not least, if you go in maplins and ask for a 10 nanofarad capacitor and they say they don't do anything that small, ask them for a 0.01 microfarad capacitor instead and you'll get what you originally asked for

[ChrisEdu]

That looks well neat! Good job! :hello1: Where did you get all the bits and pieces for it?

[kev1204]

Hi ChrisEdu,

Thanks.

I got the all the components from Bitsbox (google it) Very cheap, and reasonable on postage (£1.50 per order). The nichrome wire I got from Rapid online, but the spec is wrong. Try ebay for PW-Electronics ebay shop. Very good prices on nichrome and a good selection. Compare the prices on Bitsbox with Maplins. (massively cheaper)