DIY, making a low power lens dew heater

[Astrofriend]

I bought two new dew heaters. They are sold to be used on camera lenses and powered from USB. I have modified them to reduce the power from 8 Watt to 2 Watt which will be enough for my demand.

Some photos and documentation from this project:
http://www.astrofriend.eu/astronomy/projects/project-heating-band/05-project-heating-band.html

This will be battery operated and I try to reduce the power consumtion of the equipment.

/Lars

[Saturnine]

Excellent little project, well done. Very neat and tidy in the end and the desired output.

[Astrofriend]

Hi Jeff,
Thanks for the comment. I have now tested the dew heater a couples of nights and it work perfect. Maybe I even can reduce the power even more from the 2 Watt I have now. My shortest lenses, th 16 mm fisheye and the 50mm f/1.8 lens I know from earlier only need about 1 Watt.

/Lars

[Rerouter]

Edited

Now I get it, its a DC-DC converter powering all the USB stuff,

So about 3.1 Ohms per Dew heater, ~1.6 Amp on 5V,

For 1W per heater, you would need 4 in series, 2 per scope, might be easier to replace the wire with 1m of AWG40 magnet wire per heater for series. or 4m for parrellel, which would not actually be hard to just sew into a dew heater fabric

[Astrofriend]

yes it's correct, 3.1 ohm, before I cut the cables length it was 3.4 ohm. But because they are connect in serial of each other the voltage over each is only 2.5 Volt. It gives 2 Watt each. U^2/R = P.

If I want to have lower power I have to use the included regulator, it's like a very slow pulse width modulated device. With that I can have the 1/1, 1/2 or 1/4 setting, the last should give about 1/2 Watt at each heating band.

What power do you have on your heating devices and to what lens or telescope ?

/Lars

[Rerouter]

As I have not yet gotten my confidence up to image away from home, right now I have a zip tied coil of wire running off the same lab power supply I am using as a temporary intervalometer (could not get more unconventional)

[Astrofriend]

I have now used my new USB dew heater out in the cold night several times. Many positive things, I can reduce the power a lot. From my earlier dew heaters at 5.6 Watt I can now go as low as 1 Watt for both. Important when out on the fields and on battery.

Photos and text:

http://www.astrofriend.eu/astronomy/projects/project-heating-band/05-project-heating-band.html

/Lars

[AdamJL]

Nicely done, Lars!! That looks really neat now.
Nothing better than good cable management :)

[Astrofriend]

Yes, cables everywhere cause trouble in the dark.

These dew heaters were an important step towards the mobile observatory. With lower current, smaller battery.

Today I orderad a 24 Volts Lithium battery for my new project. I come back about that in a new thread later. 24 Volts an 12 Amph, about 300 Wh. My lead car batteries: 12 Volts and 45 Amph gives about 500 Wh but can't even use half of it, the other 12 Volt and 72 Amph gives 850 Wh. Both batteries are now destroyd because I let them uncharge too deep.

/Lars

[AdamJL]

Agreed, Lars.
Many folk still use lead acid batteries, but if I were buying now, I'd buy Lithium. Too many benefits, not enough downsides. They're fantastic batteries.

[ChrisV]

You could reduce power usage even more with feedback PWM control to set heater temp just above dew point. Then you are only using enough power to stop the mist.

[Astrofriend]

Yes, I have some thoughts to control the dew power direct from the Raspberry. I just need some dew point sensor. Do you have any idea how to design that kind of sensor ?

/Lars

[ChrisV]

There's several really good humidity/temp sensors and dew point is simple to calculate. This is my design, and others on IIS have some nice ones.
https://www.iceinspace.com.au/forum/showthread.php?t=144679

[Astrofriend]

Hi Chris,
Thank you for posting that. I have thoughts about Arduino and to control the focus motor, when I can handle that I take a look of a dew heater controller too.

I have the USB-Focuser now, it can also be delivered with a dew heater. But not interesting if I built my own focuser controller and then I have much better control over the system.

Maybe you already have a Aurdino focus motor controller ?

/Lars

[ChrisV]

I have built focus controllers. But I haven't gone to the effort of the software. There's really good stuff out there! E.g. myfocuserPro and onstep software. And they have ascom drivers!

[Astrofriend]

Hi Chris,
Sounds perfect, are there also Indi drivers available ?

/Lars

[ChrisV]

Definitely is for myfocuserPro

[mura_gadi]

Aluminium Ion batteries are very close now, should be in production by end of year. But Covid has changed a lot of dates....

Al-ion is safe, you can swallow them!, they won't catch on fire, they hold more charge and allow for more recharges than li-ion by several factors.

It may be worthwhile just getting by on what you need and wait for way better safer tech later this year/early next.


MG
https://www.forbes.com/sites/michaeltaylor/2021/11/30/asias-saturnose-could-be-first-to-commercialise-aluminum-ion-batteries/?sh=85ba11a12ebd

I think I read somewhere is was car batteries and the penny batteries. The other batteries will follow along after them...

[Astrofriend]

Yes, aluminum batteries are really exiting. I hope we have them here soon or later. But already what I have now is a big improvement.

/Lars

[joshman]

I've been using your design for a few years now, and it's been absolutely fantastic. I'm currently in the process of making my version smaller and soldering it all down to a PCB in a 3d printed enclosure, and running 4 power outputs as well, so i can run everything off the one box.

so Thank you!

[Astrofriend]

Anyone who have some examples of how much power you use to the dew heater for different mirror lens sizes ?

/Lars