My astronomy project:
Making of heater band
1: Introduction to making a heating band
This miserable condensation on the front lens! What to do about it?
Out and look for suitable material to the mantle. Boat accessories, car accessories yielded nothing, after a while I was into BEA at Enskede here in Stockholm. They usually have various odd things. Today's finding was a sleeping mat in black, price 8 Euro.
This will probably last for my telescopes lifetime.
A moderately large piece was cut for the 165mm lens.
Transformation to the cylinder shape by tape, the tape must be replaced with a higher quality before the test in the cold to be made. This is made 150mm long 110 mm of which extends beyond the ordinary lens hood. The lens has a diameter of 60mm (always set to f4) and hoods inner diameter is 75 mm, shall suffice, provided it is straight. This lens is made for the medium format film size of 60x70 mm contrast to the small full frame 24x36 mm I have.
Summer, steering wheel's mantle of.
Winter, steering wheel's mantle on!
I have ordered components to build a heating element as well, so there will be both hood and heating band for safety. The black plastic was handy to work with, only to remark is perhaps that it was really dull on the surface. The heating element, chose to build this by myself to get it tailor-made for this lens.
The day after I ordered the resistors they showed up in the mailbox, 100 parts of 470 ohms. To this dew heater, it takes 10 parts and gives a resistance of 47 ohms when in parallel and a power of 3 to 4 watts. The cost 0.022 Euro pieces!
Fix the ten resistors at equal distance on the 27 cm distance corresponding to the perimeter of the front of the lens.
Cut and strip the cable that feeds the resistors. All resistors are connected in parallel.
Insulating tape so that no live parts is in contact with the metal parts of the lens.
An extra touch was to connect an extra outlet for more accessories to be connected in future.Back to contents
2: Attach heater to cap and cables
Dew heater. It goes forward, now heat element tape mounted inside in the dew cap.
Here attached heating elements against the insulation in the dew cap, regular duct tape used.
The power is a little over 3 Watts which I wrote earlier. Now when the elements are mounted so there is a small risk that they overheat, the insulation makes the cooling effect limited. So should not be powered on during warmer weather.
Mounted on the lens and the equipment has been completed with one more connector. The idea was to test it during yesterday evening, but the weather put a stop as usual.Back to contents
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3: Heater band for 5" telescope
Now we turn our attention to the larger refractor and to manufacture a heat band to the telescope, the tube diameter is about 160 mm. I have it to sit just behind dew cap where it is usually recommended.
I calculate the power needed, it becomes 23 pieces of 470 ohm resistor would make an power of 8 Watts at 13 volts, it is 2 cm between the resistors. The selected effect gives a little margin so that a power control can be installed later.
The resistors are attached to an isolation band outside so that most of the heat is delivered inside to the tube. Even better might have been to just heat the lens holder. That had been a completely different structure and it will have to wait for the future. The disadvantage of this solution chosen is that the entire tube is heated unnecessarily and drains the battery faster.Back to contents
4: Fieldtest and modification of 5" heater band
Now at last I have been able to test the equipment under real conditions. Concluded fairly quickly that the heat tape is not warmed enough to keep condensation off. It was mounted behind the lens hood where you usually place it as you see in previous images. With aluminum that conducts heat well, it means, unfortunately that it heats the entire telescope tube. One can compensate for it by increasing the effect, but I don't want that since it involves other negative things.
After some quick thinking there during the night, I found this solution that I am fortunate could manage in the dark to modify it. Between the lens hood and lens holder is a gap that was big enough for the electric heat band to fit in. Now I don't to heat the entire telescope tube, only the lens holder, very effective. Just as I wanted it from the beginning.
A small problem added, however, now I had a cable that came out ahead of the front lens, thus could not mount the protection cap. Was solved by making a separation wall placed in front of the lens for protection, there is now space between the lens and cap so that the cable can be rolled up and thus protection cap can be mounted again.Back to contents
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Part 5: New, USB heater band 1
As you maybe have read on other place here I have purchased a new light weight mount earlier this year, a Star Adventurer. The idea is to have this mount as light and easy to use as possibly. Still I need a dew heater band on the lens and that heating band needs power. My power source today is a car battery that I use to my EQ6 mount, and that weights more than 25 kilogram and that's far to much.
The last years it has come a lot of USB power units, often called powerbanks and the use of them is mainly to charge mobile phones. Here I will try to use a powerbank and build a heater band to it.
There are already over the desk equipment for this to buy, but the camera lenses, at least the ones I have has very limited space to mount a heater band. I need someone that is more narrower to fit.
Note: This is just a test, if it overheat or something similar happen the equipment can be destroyed, maybe even burn your house down! Take the information with caution! I do not take any responsibility! Don't try to copy my ideas if you don't have the knowledge and understand this very well of what you are doing!
Warning! Don't connect it to your PC's USB port, it take to much current for that!
don't have the knowledge or don't want to build your own control equipment you can write to Vincent at USB-Focus:
The heart of my new heating system, the power bank. It has the capacity of 10000 mAmph and cost only 15 Euro (Webhallen Sweden).Webhallen (Sweden)
The cable you see is for charging and it takes about 10 hours. There are two USB outputs and you should not load them with to much Amps! 0.5 Amp is standard for one USB output.
To my earlier heating band I used resistors as heating element and solder them together too get the right size and power. Now I want something that's easier to build. I search for different kinds of solutions.
Kanthal wires which is what you normally use when building heating elements. But they need to be encapsulated in something.
Then I started to look after stainless steel wires and found them in electric band for electric fences. Is it possible to use them? I found the above band at the Swedish company Biltema.Biltema (Sweden)
It has the resistance of 15 ohm per meter. 200 meters of this electric band cost only 12 Euro, I have a supply for my lifetime if it works! There are three wires of 45 ohm each per meter, maybe useful if I want to reduce the power later.
I bought 6.3 mm flat male connectors to connect the heating band and the USB cable together when I do this test. I will use other connectors later.
I also took one of my old USB cables and cut it and mounted two 6.3 mm female connectors. Use a volt meter to see which wires that has the power, don't shortcut them! You should read 5 volts when you find the right ones. The cable area is very small on a USB cable, keep it short to reduce the looses.
I guess I need about 3 Watt of heating power (later reduced to 2.5 Watt) to keep the dew away from my lens, maybe less. With 5 volt from the powerbank the resistance has to be about 8 ohm (later 10 ohm to get 2.5 Watt).
It's of course very important to not overheat the lens, it can melt down! The wire has 15 ohm per meter and I cut off 0.5 meter and then got the resistance of 7.5 ohm. Note: This are steel wires, use tools that can handle that! I mounted the flat connectors. Each of the three wires gives about 1 watt with this length of heating band.
My first test too see what heat I get from the heating band. It feel a bit too hot, if I put thermal insulation of the heating band on the outside it certainly will be too hot! Maybe use of a power regulator or only use two of the three wires will get the right amount of power. To much heating power can destroy the equipment and it also will let the battery last for shorter time. You should of course have fuses installed to protect the equipment, a fuse of 0.5 Ampere, the battery is of very high capacity and can get on fire if it's overloaded, be careful ! Remember it's just a test I'm doing here, the final construction will be much better.
The metal wires of the heating band is open and has to be electric insulated to not give a shortcut. Here I have put a electric insulation tape on front and backside of the heating band. Maybe better to find a plastic tube to have around the heating band. But it should not isolate it for heat, the heat must come out from the heating band to heat the lens to get the dew away.
Here I have wound the heating band around the lens, a Sigma 150mm f2.8 APO. Two turns. The lens has a very limited space to mount this heating band on it. You must also have the mechanical focus to rotate free, otherwise the lens focus motor can be destroyed!
Here is the heating band connected. What I feel 3 Watt is too much. I reduced the power by just use two of the three wires, it will then give 2 Watt. Maybe later I can reduce the power to only 1 Watt if I put a thermal isolation outside the heating band. I must do some outdoor test to figure out how much power I need. Maybe it will be smart to have switches so I can adjust the power by selecting how many heating wires that will be connected.
In some way I also must have the dew shield mounted, here I have just pressed it on, maybe it will work without falling off.
Ready for a first test, in a few days we have the Perseid shower coming!Back to contents
Part 6: New, USB heater band 2
Now I done some test and I see that I need 3 Watt of heating power or less. I made the length of this new electric heater band longer, 0.65 meter (10 ohm) and then reduced the power to 2.5 Watt. I decided to built a control box that can let me choose one, two or three heating wires in the heating band to be connected. That correspond to 0.8, 1.6 0r 2.5 Watts of heating power from my heating band.
I also have too built an enclosure for it, ordered a box and some components that arrived the day after, bought it from the Swedish company Electrokit.
After some work it look like this:
Three LEDs and switches and one fuse of 0.5 Ampere. I also ordered a special USB connector that let me solder 0.75 mm2 cables to it.
No PCB board, just air mounting. What's missing here are the clamp holder of the cables, didn't had any at home. Have to do a complement later. The black component up to right is the important fuse holder with a 0.5 Ampere fuse, it must be there and correctly connected!
I mounted LEDs as indicators of which heating wires that are activated.
The light output from the LEDs are a bit high, I will increase the serial resistors to them to about 1 kilo ohm later, now they are 470 ohm. Or maybe it's handy to have the red light in the dark?
Don't try to solder the stainless steel wires, better to use crimp connectors.
Here is all that is needed to have an anti dew heating band on my camera lens. Heating band, cables, control box, battery and charger. The weight are about 0.5 kilogram together. Note that it are four cables connected to the heating band now, one black common to one end, and three red cables to the other end, one for each wire in it. The black cable has a connector so it's possibly to take it apart and wrap it around the lens/tube.
I will be back with more information of how well it works. Later in the winter it will be much colder, will 2.5 Watt be enough then? And how long will the battery last?Back to contents