Do I ‘Need’ a dew heater controller?

[AntHart]

Hey

I’ve been wondering about dew heaters and controlling.

Why would I need a controller?

Whats wrong with just plugging it in and leaving it at ‘full power/not controlled’?

There must be a reason for a controller to exist and the only reason I can think of is that if the scope gets ‘too hot’ it’s bad?

I know the idea is to keep just above ambient to avoid dew.
These little bands draw only a few watts, I’ve even got one that’s usb powered for dslr lenses, that’s got no controller.

Id be using on a 2” guide scope and a 3-4” refractor 

 

I’m still new to this so might be obvious  but If someone could please explain a bit more about it I’d really appreciate it...I’ve searched around but can’t seem to find the answer 

 

Thanks,

Ant

[SyedT]

There's a theoretical risk of overheating the optics. I haven't personally come across this happening to anyone, but I feel it's better to be safe and invest in one instead of risking damage to expensive equipment.

[zcapp96]

I may be wrong about this as I don't have a scope with a dew heater but am looking into a C9.25 purchase in the near future so would be interested in the answer as well! Would it be because if it heats it more than slightly above ambient temperature it will cause thermal currents and disrubt the view? As we wait for the scope to cool before use it would seem logical that heating it back up again would be counterproductive! 

[JG777]

I use a dew controller with my C9.25, generally have it set as low as possible, just enough to keep dew at bay. If you turn it right up you risk seeing thermal currents. Use it in conjunction with a home made dew shield. Never needed one for my refractors, they all have dew shields built in or retractable. Cats and Maks are more at risk of dewing as the corrector plates are very exposed, it also depends on local conditions where you are observing from. Most weather apps will give you the dew point as well. 

[jiberjaber]

I hadn't considered the thermal currents aspect when I built mine years ago but through some experimentation at the time I came across a figure of 20(ish) degrees above the dew point seemed to be right for my equipment to keep the dew off, that's a temperature measured in the actual dew strap, the temperature near the optics will be quite different as this is wrapped around an alu dew shield plus loss of the actual dew band outer material - perhaps leaving it at 5 degrees above DP at a guess.

Without a controller of some sort it would be hard to adjust it relative to the actual DP at that time, some will be fully automated (like mine measuring ambient temp & humidity to get to DP and then adjusting the measured temperature in the dew band to something) or just a dial to change the output and through experimentation you can set it to keep the dew at bay.

If you don't have a controller then notwithstanding the above notes on potential effect on optics, you are also just wasting energy, which might be a consideration if you are running off batteries perhaps.. 

[MarkAR]

Better to have a controller that none.

One option is a Pegasus PowerBox or similar that has built in control via software, that way you aren't drawing unnecessary current from your battery, also has the benefits of tidying up a lot of cables.