Working with a dew heater strip

jermng · Post by **jermng** » Thu Dec 21, 2006 12:31 pm

I'm getting a dew heater strip but I'm not ready to get a controller yet.

Is there a way to build something/connect it to a battery power supply to maximise its use for now?
What kind of battery cell do I need to get? Do I need to build some resistor thing to control the power?

One last thing, is it ok to use an 8" strip on a smaller tube? something like a 6" or even 3"??

Thanks for looking!

rlow · Post by **rlow** » Thu Dec 21, 2006 12:44 pm

One last thing, is it ok to use an 8" strip on a smaller tube? something like a 6" or even 3"??

No problem, I have used the 8" dew heater strap before on my C5. Just wrap around a bit more, as the Dew-Nots Dew Heater has an elastic band with Velcro. I even plan to use my 1.25" strap on a 2" eyepiece. It does not need to be a perfect match as long as enough heat is supplied to keep dew away and not generate noticeable 'tube currents'.

jermng · Post by **jermng** » Thu Dec 21, 2006 3:07 pm

How do I connect it to a battery? I think if I connect directly it'll be too hot ...

Post by **Airconvent** » Thu Dec 21, 2006 8:41 pm

Jeremy,
If its that easy, Kendricks would not be selling their controllers at cut throat prices. these heaters are designed for max use, hence if there is no controller, it would simply deplete your battery faster.
Of course you can build your own controller but this would not be as sophisticated as the bought ones.
My home made one uses a series of resisters to control current.

rlow · Post by **rlow** » Thu Dec 21, 2006 9:21 pm

Jeremy, you can also check with Canopus who has built a DIY controller.

Clifford60 · Post by **Clifford60** » Thu Dec 21, 2006 9:30 pm

Jeremy/Richard, is the so called heater make of resistor, if yes you can make a transistor's monostable or bistable to control the on/off duty cycle to prolong the battery life. The circuit can be built may be under $10/-

jermng · Post by **jermng** » Thu Dec 21, 2006 10:19 pm

Clifford, can you elaborate a little?

Richard 1 - I agree with you, it would be nice to have a Kendrick controller

But I missed a good price from rlow and recently bought too many things so it's time to cut back on astro purchases.

Anyway, lots of astro stuff are sold at cut throat prices and people seem to be able to build them DIY with some effort. Only problem now is, I'm not really a DIY sort of person.

So I need you guys for help!

Canopus Lim · Post by **Canopus Lim** » Thu Dec 21, 2006 10:25 pm

I use a variable voltage regulator to control the current. I haven't used my DIY dew heater controller for quite a while so I don't know if it is still working. The last time it worked was a few months back at Mersing with my C5. It works well though. It just requires a bit of heat to keep off the dew. If you directly connect the heating pads, I think it would be wasting energy because the power would be a bit too high and also it may cause tube currents.

As Clifford said, if you construct a circuit that switch on/off with a predetermined or configurable duty cycle, your battery can last longer and you can connect more dew heaters to it.

jermng · Post by **jermng** » Thu Dec 21, 2006 10:33 pm

Thanks Yang Beng.

What do I need to build a simple circuit? I'm a total noob at electronics. The furthest I go is theory at JC physics.

Not so much of the practical ...

kingkong · Post by **kingkong** » Thu Dec 21, 2006 11:10 pm

i've just started to build a variable duty-cycle dew heater controller. and enough nichrome wires to build a few heater straps for all the 8", 4" 2.5" 50mm scope, ep, finder, etc. i have...
i actually already bought components for two circuits...
one controller + heater will end up costing less than 100myr... i think it will be worth the effort...