Powering dew heaters from remote train transformer?

[Rusted]

Hi,

In winter am losing hours of solar imaging in recent mornings to heavy dew on my refractor objectives.
Wrapping the business ends in thick mattress foam hasn't helped at all. The dew is on the lens inner surfaces too!

My recent purchase of a secondhand hair drier only works on the front surfaces with the low heat setting.
Heating the cells and tubes with the hot setting had no obvious effect on the inner, dewed surfaces.

I am tempted to use one of my old 12VDC train transformers for power.
I have several of these by different makers. Including one with a "speed controller." Might be useful?

I don't like having mains connected overnight in the observatory so isolate both legs with a two pole switch.
A 30m long "mains" extension lead will run back to the 12VDC train transformer indoors.

Is this workable or is there something I haven't thought of? Voltage drop shouldn't be a problem.

[Dr_Ju_ju]

I take it there must be some air flow, from outside to inside, for the condensation to appear ? if so then ensure good air-flow else silica gel\tablets may help to  'mop-up' the air-borne water.

Have you considered using a dew band, wrapped around the outside of the lens\ota, Its what I have on my ED80\canon lenses, with no issues, but then I keep them on at a low level... 

[Rusted]

Hi Julian and thanks for your response. I had better try to be clearer:

My two storey, 3m domed observatory is deliberately well ventilated at all levels to aid seeing conditions.
I have my 6" and 7" refractors permanently mounted in there.
Literally everything is dripping wet with dew after a light frost.
Inside the OTAs as well judging by the heavily misted inner lens surfaces.

So I was going to buy suitably sized heating bands to combat dew by wrapping the objective cells.
No idea which bands yet. I have never tried heating bands before now.
I'm hoping one or more train transformers will supply enough current.
The bands will need suitable connections rather than USB.

I doubt a barrow load of silica gel would make a dent in the quantities of dew involved.
Even the timber and plywood construction materials are wet!

[Dr_Ju_ju]

Dew likes to 'form' in still-air conditions, so make sure there's plenty of air flow & provide fans as necessary.

My system is open to all the elements, on the garden pier, and while on good imaging nights i.e. cold no wind etc. the heating bands wrapped around the lens cells etc., keeps everything clear, even when the rest of the equipment bodies may be saturated.

I bought ready made dew bands, but the controllers are 'home-made', which I'm about to upgrade to Arduino ones, so that I can have better remote control....

[Rusted]

Thanks Julian.

Just had a look at the FLO blurb on Astrozap dew bands.

It would seem that larger diameters are temperature self-regulating.
Whereas only smaller bands might become warmer than needed.
I'm trying to avoid costly regulators to start with and lack your electronics skills.

Can they be run in series to self-regulate by rising resistance with temperature?
Or are these new-fangled heating devices non-resistive?

[Dr_Ju_ju]

Currently I just use a pair of these to drive the heater bands https://www.ebay.co.uk/itm/DC-12V-24V-8A-LED-Bulb-Dimmer-Switch-Adjustable-Brightness-Dimming-Controller/153681027217?hash=item23c81a6091:g:bokAAOSwwb9doGxd

Driving suitable length bands, similar to these https://www.ebay.co.uk/itm/Dew-Not-4-Dew-Band-Heater/124007058111?hash=item1cdf658abf:g:FSAAAOSwdndd8KMi  

 

[Rusted]

Thanks Julian. 

[Dr_Ju_ju]

FYI, the dc controllers are easily dismountable (a simple PCB, & a plug-in potentiometer) so I've mounted a pair in a small container, with a single input & a pair of outputs on each controller....