Quote:
Originally Posted by Inmykombie
Thanks Chris, Your heater is in exactly the same place as I fitted mine ( yours looks a lot neater than mine though )
May I ask the wattage of your heaters ?
Thanks for the tips.
Geoff.
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Geoff - I ran 50 390 ohm, 1/2 watt resistors in parallel. If you take 50x390 ohm resistors you have a total of 7.8 ohms over the whole lot (divide the resistance by the number of parallel resistors in the circuit). This results in an 18 watt unit at 12 volts DC. I then use my home made PWM controller to limit that to 0, 1/8, 1/4, 3/8, 1/2, etc, etc to get a nicely controlled output. At 1/8th of a power cycle I can linearly estimate that it's running at 2.25 watts at that setting.
I have to respectfully disagree with putting heaters INSIDE your OTA, I'm sorry. It's not required in my experience, and introduces warm air tube currents where you don't want them. It doesn't matter that you lose heat if installed on the outside where we have ours, because you merely compensate by cranking it up a tad more. We aren't looking for efficiency - just a small layer of air that's slightly warmer NEAR the corrector. Remember - it's the temperature of the
air near the corrector which is the important thing - irrespective of the temperature of the corrector flange ring, which will be much warmer than 1-2 degrees above ambient. Dew shields, by themselves, almost work well - without any heating devices. They work by trapping air close to the corrector (or objective on a refractor) which settles at the transmissive surface and is hopefully unaffected by circulating ambient air at the end of the tube/dew shield assembly. Because this air is trapped it remains slightly (and I mean slightly) warmer than the outside air above it. That's all that's needed. The heater just helps by raising that same air another notch or two.
Here's another one I made for my C8. Works a treat - super efficient and only needs to run at around 1/4 power on the controller - even on the foggiest, dewey nights. This one even has a layer of felt in between its outside edge and the corrector flange to limit the heat transfer. I want to warm the air, remember, not the flange itself.