What is a Dew Heater?
A dew heater works by applying a small, controlled amount of heat to an optical element or its housing. You usually only need to be 1–3°C above ambient temperature—just enough to keep the surface temperature above the dew point.
So, why not buy a good quality product available on the market? Well, most of the dew heaters available online are expensive (around 4K) or frequently out of stock. As a hobbyist, why spend money and wait when you can build your own?
The parts are easily sourced, and it typically takes less than 30 minutes to build (though patience is required!).
Parts that you need:
- Nichrome/resistance wire (32 AWG)
- Masking tape / Duct tape (Non-Conductive)
- PVC electrical tape
- Aluminum foil tape
- DC barrel connector
- Dual Core wire
I recommend getting a 5-meter or 10-meter roll of Nichrome wire; you can use it for many purposes or to build multiple dew heaters.
Specs for Nichrome Wire: This is a bit tricky, as most online sellers do not specify the resistance per meter/foot. A dew heater needs some resistance to function properly without melting your lens housing. Pay attention to this!
You only need approximately 3 Watts of power for your dew heater to function properly. Looking at the specs of commercial products, I found that they typically allow you to vary the temperature from 1.5 Watts (Low) to 3.5 Watts (Medium) and 7 Watts (Max). With that in mind, I found this product, which is in our “sweet spot.”
So, how much wire do you need? Let’s break it down using some simple calculations.
It depends on your power source and how you plan to power it. Remember: resistive loads often don’t work well with power banks if the resistance is too low; the power bank will auto-cutoff if the current draw isn’t within a certain limit. With that in mind, I chose a 12V power supply.
Using a simple calculator, I determined how much resistance I need from the Nichrome wire.
I know I need to limit my resistance to less than 48 Ohms. I measured the biggest lens I own (the glorious Samyang 135mm) so that I can reuse this for all my lenses. Wait, the guide scope needs a dew heater too! I measured the distance to wrap both scopes, and it came to about 2 feet.
Here is the catch: the product I bought has 22.44 Ohms/foot, but I need 2 feet of coverage. Laying this wire in a straight line won’t spread the heat evenly. The solution is to lay it in a zig-zag pattern. Calculating the exact length is bit tricky, but here is how to do it.
I’d suggest settling with 2x the length of the band so we can space the Zig-Zag pattern more efficiently without worrying of running out of wire or patching it. Never ever path the wire in between as its prone for uneven heat distribution.
- Take 4X the length of the Dew Band you want to make
- (Refer Image1) Using a Nail or door handle tie the split ends of the wires, Grab a pencil or a stick for the other end and start twisting it. Don’t apply too much of force while twisting or the NiChr will break.
- Now if you measure the resistance it should be Approx 2x the original need i.e ~44 Ohms, which is close to our need.
(Images shown using enamel copper wire for better visibility)
After Twisting you should have a strand like this.
Cool ! now let’s prepare the base, Have patience during this step and additional hands will help you !
Peal off the protective layer form the Aluminum duct tape and place the sticky end facing towards you. We need to protect the sticky layer, reason is the aluminum underneath the sticky gum is conductive.
Grab Insulation tape and slowly unwrap it, don’t stretch the whole length all together as insulation tape is elastic in nature and would contract and will cause the whole band to wrap, So take the desired length and place it on an even surface with the sticky layer facing towards you, let it settle for a minute or 2 and the lay it over the top of the aluminum foil, don’t force it to stick yet. We will slowly work our way out and needs patience else it’s going to become a mess.
Now repeat the above process and lay another insulation tape on top of the first insulation layer by overlapping at least 1/6’th of the same. You might have repeat the process 3-4 times until the whole aluminum tape is covered. Now the sticky part of the insulation tape will act as out guide layer for NiChr wire.
We don’t need the whole part of the band to be wrapped in NiChr, So protect the Edges by using Duct tape or Masking tape, at least 1/6 of the corners. Lay the duct tape (cut its width as required) and place it on a flat surface and place the Aluminum tape on top of and wrap the other end towards the insulation tape and end result should be as shown in image 2
Join the Electrical wire and Nichrome by soldering or twist it for at least one Inch and use heat shrink wrap or insulation tape , Place this at least 1 Inch away from corner.
Add small piece of insulation tape as a guide to hold the Nichrome wire in Zig Zag pattern and lay the entire band as shown and ensure to leave 1 Inch empty space on both the ends | Dont force place the Nichrome on the insulation sticky part as you might need to adjust the entire length to match the resistance we needed.
Once you are satisfied with the layout and resistance, join the other end using a hobby Multi Strand wire, Don’t use single core wire as it will add more stiffness. Lay the wire with some guide insulation piece and bring it back to the start. Measure the final resistance it should be close to our desired 44 Ohms.
Complete the circuit to the electrical wire using soldering or twist it for half inch and insulate it / heat shrink it. Now remember the initial insulation layer we layed with sticky part facing upward? start covering it with Insulation tape on top, so both the top sticky layers will hold the Nichrome wire permanently. it is impossible to separate 2 sticky insulation tape without force ! this layer is going to hold it for ages. Let’s add another layer of Masking tape/Duct tape to protect it. End result should look like this.
Now cover both the corner with additional layer of Masking Tape / duct tape so it lasts long.
If you have come this far Congratulations !!! You Dew Heater is ready, Add the female DC Jack and test it out. It should now produce ~3+ watts.
Don’t worry about Nichrm shorting / melting the gums. Trust me i’ve been using this for almost 2+Yrs and gave away 4 of these bands to Club members and they have been using it without any issue. The way how we placed it with guide tapes and Nichrome in between sandwich layer of insulation tape will keep everything intact.
Caring: while unpacking, wipe off any moisture and roll the band along with its wire. This will give long life to it.
Clear Skies !!!