Dew Heater for Refractor

Post by **weixing** » Wed Jan 11, 2006 9:15 pm

Hi,

your design only draw 0.2 A (1.76W) which is too low to generate enough heat.

Err... W= (V x V) / R = (9.6 x 9.6) / (8 x 5.6) = 2W

you should consider using a 12V Gel battery pack or use 10 NiMH batteries instead and reduce the total resistance from 45 to 30 ohms.
that should give you 0.4A (4.8W). A 4AH Gel pack should give you about 9-10 hrs while the Sanyo 2500mAH NiMH battery should yield about 6 hrs.

Hmm... 4.8W... will it be too high?? Anyway, will try out using slightly less resistance, but first need to get some 1W rating resistors first.

Hmm.. have you measured the temperature of the lens? A temperature increase of 1 to 2 deg C over the ambient temperature is usually sufficient to prevent dew formation. You also know that too much heat will generate tube currents. If you need to measure your tube temperature I have the sensors. Let me know when you are free!

Hmm.. how you measure the temperature on the lens?? Quite uncomfortable in putting sensor on my lens to measure it temperature. Also, as what I mention, I can't feel the heat in the dewshield without putting the lens cap on for a while and also can't feel any heat on the dewshield itself.

Anyway, will review my dewshield design again after it go through a few observation session.

Thanks and have a nice day.

cataclysm · Post by **cataclysm** » Wed Jan 11, 2006 10:20 pm

tyre warmers in the real world are as it is name described, to warm up tyres. Normaly used on formular one cars prior to the start of race to keep the tyres nice warm and soft. Of late, it has caught on by remote control car enthusiast in miniaturize form. Can buy off the shelf from hobby shop in a set of 4 ( yes miniaturize car has 4 tyres too). they looks identiclal to standard scope heaters, but shorter in length. Used singlely is good enough for large 2 inch eyepiece. I velcro 2 together for my 4 inch apo. objective. You can change the connector to phono jack form and they will works wonderfully on standard heater controller.

jermng · Post by **jermng** » Wed Jan 11, 2006 10:32 pm

Hi, how much would a kit of tyre warmers cost? Would they be enough for an 8" OTA?

Post by **Airconvent** » Wed Jan 11, 2006 10:45 pm

weixing wrote:Hi,
Err... W= (V x V) / R = (9.6 x 9.6) / (8 x 5.6) = 2W
Hmm... 4.8W... will it be too high?? Anyway, will try out using slightly less resistance, but first need to get some 1W rating resistors first.

heh heh, weixing, you're more accurate. I rounded off too many times in the calculations. Should be I*Squared R for power, i.e. 0.21*0.21*44.8 = 2W
I used 0.2 *0 .2 *44 = 1.76W....

4.8W may be too high for you as your refractor is much smaller than an 8" SCT...so you may want to tune your resistors for around 0.3A instead.

anyway, for my design, I am using parallel home made series resistor strips. If its becomes too hot, I cut power off to one of them via a switch...

cataclysm · Post by **cataclysm** » Wed Jan 11, 2006 11:54 pm

The tyre warmer cost about $80/$90 for a set of 4. It may too small for c8. More ideal for refractors and eyepieces.

Post by **weixing** » Wed Jan 11, 2006 11:57 pm

Hi,

standard heater controller.

What type of "standard heater controller" do you mean??

Have a nice day.

Post by **Airconvent** » Thu Jan 12, 2006 12:00 am

weixing wrote:Hi,
standard heater controller.
What type of "standard heater controller" do you mean??

Have a nice day.

likely the usual brands like Kendrick and astrozap....i think