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I am planning to make a dew heater for a camera lens to get rid of condensation, using resistors wired in parallel, then distributing them around the circumference of the lens. Diameter of lens: 65mm

Total power output: 6W

Power Supply(powerbank): 5V, 2A, 20Ah

Resistance for each resistor: 120 Ohm

Resistor power rating: 0.25W

Power output for each resistor: 0.21W

Number of resistor required: 29

I Will probably insulate the wire with tape, and wrap the resistors in cloth around the lens. Is 6W too much or sufficient for this use? Any suggestions? Thanks.

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  • \$\begingroup\$ If you run your quarter watt resistors that close to their limit they're going to get very hot, probably like a 100 degrees Celsius hot... You may want to add more resistors so that each one is run a little cooler... \$\endgroup\$
    – MadHatter
    Commented Aug 8, 2020 at 18:37
  • \$\begingroup\$ @MadHatter Noted. I will try to find resistors with higher power rating. \$\endgroup\$
    – radastro
    Commented Aug 9, 2020 at 0:33
  • \$\begingroup\$ if they are attached in a way that there's good thermal conductivity to the lens or the lens housing then you're probably fine, but I'm not sure how you do that with standard leaded resistors... Have you looked at kapton heating elements, they are like a film with a double sticky tape that you can attach to things. It might actually work better than resistors in your case they're readily available on eBay and Amazon \$\endgroup\$
    – MadHatter
    Commented Aug 9, 2020 at 2:08
  • \$\begingroup\$ @MadHatter I am using iceinspace.com.au/…. as a guide. Scroll down to see the finished work. I will buy resistors first as they are cheap and available near my place and see if things work. \$\endgroup\$
    – radastro
    Commented Aug 9, 2020 at 5:11

2 Answers 2

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6W sounds like a good staring place for your experiment, but I would use more resistors run at a lower power.

buy 100 cheap resistors and connect most of in series and see if that's good

GW at 5V is 1.2A so 41.7 ohms total so

maybe start with 89 0.47 ohm resistors in series.

by connecting them in series there string will be more flexible.

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5W-6W seems in the normal range for lens dew heaters.

You could consider adding a PWM control circuit to adjust the power from 0 to 6W. Easy to make with a 555 and logic-level MOSFET.

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