What is a dew heater?
A dew remover system is designed to eliminate dew from telescope optics by keeping the optics slightly warmer than ambient, or above the dew point. Power is applied from a dew controller via flexible dew heaters, usually wrapped around the telescope tube, near to the cell housing the optics.
Dew is one of the stargazer’s most noticeably awful foes. On the off chance that no precautionary measures are taken – dew can pretty much ruin an ideal watching night, as it shapes on mirrors and focal points.
All telescopes are liable to “the dew issue”.
Open cylinder reflectors (for instance Newtonians) have some favorable position over refractors or catadioptrics since their fundamental mirror is all around secured. Anyway their auxiliary mirrors get dewed effectively.
Along these lines it’s required for pretty much every beginner space expert to have some sort of dew control solution for his gear.
Table of Contents
The Theory of dew heaters for telescopes.
Dew can frame on surfaces when they get cooler than the surrounding temperature, beneath a specific “dew point” (which relies upon dampness).
At the point when a surface is pointed up, into the sky, it emanates its warmth away (for the most part by means of infrared) however gets nothing consequently.
Accordingly its temperature can drop low enough for the dew to frame. A surface which is pointed down, into the ground, likewise emanates. Anyway the ground emanates back superficially, and some kind of harmony is come to.
That is the motivation behind why dew is framed all the more effectively on unshielded surfaces pointing upwards (in spite of the typical conviction that dew “gradually tumbles down” like a downpour).
The Solution – Dew Heater.
How to keep telescopes warm.
Video by Jeff Lucas Astrophotographer
Thousand Oaks Four-Channel Digital Dew Heater Control Unit.
Each heater output is controlled independently and has a full range of adjustment from 0-100%.This eliminates the problem of overheating or not reaching desired temperature regardless of heater size and combination.
Thousand Oaks 1″x 15″ Heater Band (.94amp) for 2.5″ to 4″ Telescopes, used with 4-Channel DDHC Digital Heater Control Unit.
Find all the customer reviews and latest price on Amazon here.
- Use with 2.5-4″ (60-102mm) Telescopes
- Requires Dew Heater Controller DDHC or similar
- Consumes 0.94 amps @ 12 Volts DC
There are a few ways to deal with dew control: Dew shields or dew tops, blowing air from time to time, and so forth. I’m utilizing the third methodology, which is the best one: Heating the optical surface over the dew point.
Dew Heater Strips (With and Without)
Video made my Chuck’s Astrophotography
There is a lot of solutions commercially available for warming, of different costs and sophistication. A few of the organizations which offer them are “Astrozap“, “Kendrick”, “Thousand Oaks”, “Dew Buster”.
I’ve went for a straightforward, home-made arrangement, which intently takes after “Astrozap” items.
My system depends on PWM 4 channel dew controller, 10Ah Lithium-Ion battery, and a few warming components utilized for: Newtonian auxiliary mirror, 2″ and 1.25″ eyepieces, discoverer and the objective focal point of 80mm refractor.
The controller itself is anything but an obligatory segment, since the warmers can be connected straightforwardly to any 12v power source. Anyway it’s valuable to have variable power.
The general expense of segments for making this arrangement (barring the battery) was roughly $25. Comparable commercial arrangements would be around 250-300$.
Nichrome Heating Straps:
I utilized nichrome warming straps, as a superior option in contrast to resistors. Nichrome is a compound with high electrical obstruction, and regularly utilized in warming components.
The thought is to utilize circles of the Nichrome wire of explicit length (a “warming circle”). Each circle has a particular resistance and will draw a particular current from a 12V source.
It’s essential to ensure that the wire doesn’t get excessively hot. In the event that you require more power however the calculations demonstrate you are getting high temperatures – simply join two longer circles in parallel.
You can utilize the accompanying table that is available with your package for various warming components for a 33 and 26 AWG wires, which guarantees that the wires will stay under 60°C at room temperatures.
Regardless, after you assembled the heater, it’s a smart move to test it at full power and ensure it’s not setting your telescope ablaze.
Stage 1:
I put a channel tape of required length on a table, with the sticky part confronting upwards. At that point deliberately put the pre-cut Nichrome wire on it, ensuring that there are no covers.
The circle should start and end at a similar side of the stripe. In the event that there is trouble to protect portions of the circle from one another – another layer of duct tape can be connected.
Stage 2:
Cut another stripe of tape and spread the wires with it. Ensure the two stripes are solidly held together.
Stage 3:
I like to fold the entire thing over with tape once again.
Stage 4:
Connect the copper wires to nichrome – this can be somewhat dubious. I made a little “V” overlays on both copper and the nichrome, hooking them together and squeezing the endings.
After that I fastened the intersection. Note that the wire can accompany a type of “covering” and should be cleaned with a sharp blade, or a sand paper, before the patching methodology.
Stage 5:
At the end of my cable I associated a RCA plug (the sort which is utilized for segment video).
Stage 6:
It’s ideal to sew a textured fabric strap with some sort of “pocket” for the warming component, and fix it with some velcro stripes. Utilizing a wipe protection (on the external side of the warming component) is a smart move to anticipate heat misfortunes that might occur.
In the event that there is no sewing choice – basically glue velcro stripes to the warming component.
It’s a smart move to test the strap for a couple of minutes on full power, to ensure it doesn’t overheat. In the event that it does – utilize longer circles and ensure the wire is all around protected inside the strap and doesn’t cover.
In the event that you are extremely worried about setting your telescope ablaze – apply a layer of protecting tape over each circle of the wire.
PWM Dew Controller.
The PWM 4 channel controller I made is extremely straightforward. PWM (pulse width moderation) is a productive method to control. There are a ton of variations of dew controller schematics over the web.
Mine is practically like the controller made by Astrozap, and is perfect to their radiators.
AstroZap AstroZap Dual Channel Controller for Telescope Dew Heaters.
It highlights 4 yield stations, with two sets controlled independently, On/Off switch and a 6V yield attachment (which I required for my past telescope).
It depends on a 556 double clock chip, 2 TIP31 and 2 2N2222 transistors, 2 red LEDs, 6 RCA female connectors, control switch, two potentiometers, a little project box and a couple of discrete parts. Circuit is assembled on a little wire-wrap board.
What you need:
- Input: 8-18V (suggested 12V).
- Output: same as input, pulse.
- Connector type: RCA (segment video type).
- Most current for each pair of channels: 3A (1-2A prescribed).
Notes:
H1-H2 and H3-H4 channels are combined. The LEDs for each channel pair will squint gradually, as indicated by provided control.
At the point when the LED is consistently “on” – at that point full power is provided to warmers in comparing channel pair.
Since this controller has no input (no temperature settings) – a consideration ought to be taken not to overheat the optics.
Likewise i’ts exceptionally prescribed to utilize a 3-5A fuse. I’m utilizing this controller for quite a long while now.
Dew controller Ebay alternatives.
As of late some extremely inexpensive (~5$) 12V dimmers and different controllers wound up to be readily accessible on eBay.
You can look for the accompanying catchphrases: “12v PWM controller” or “12v dimmer”.
They are additionally founded on PWM strategy (don’t waste power) and can be utilized as an option in contrast to commercial or home-made dew controllers.
Simply ensure that the yield current rating (Amperes) is sufficient for the majority of your warmers.
Warming straps from resistors.
On the off chance that you can’t discover a nichrome wire – you can utilize a “ladder” of resistors as a warming component. Generally speaking radiator control between 1 to 4 watts ought to be sufficient, contingent upon conditions.
You can utilize information from commercially available warming straps so as to decide the required power.
Power (P) of a resistor “ladder” is determined the accompanying way:
P = (Supply voltage ^ 2) / (resistor value in Ohm/number of resistors).
Number of resistors and their worth may shift as per size of the ties, connected voltage, and anticipated encompassing temperature.
To counteract overheating – ensure that genuine power on every resistor doesn’t approach their most extreme evaluated control (generally 0.25 or 0.5 W). The genuine power is determined by partitioning the general intensity of warmer component by number of resistors (on the off chance that they are associated in parallel).
Optional Mirror Heater.
There are 2 different ways of warming the optional reflection of Newtonian telescope: Attach a type of warming component to back of the mirror itself, or wrap a warming tie around mirror holder.
I chose to for all time append a warming tie with a power connector to the mirror holder, in a way it doesn’t meddle with telescope’s aperture.
Warming component can be produced using nichrome wire, in a way referenced above, or from resistors. I’ve utilized both of these strategies for various telescopes.
I additionally put some flocking paper around the strap, so as to keep away undesirable reflections from the tape.
An increasingly exquisite method for driving the warmer is to conduct electricity straightforwardly through the spider vanes, anyway this requires protecting atleast one of them.