I have found myself needing small heaters, in the 5-10 watt range for various applications in diy projects, preferably powered from 120VAC. The exact wattage is not important, and doesn't have to have a thermistor.

Ideally, I would love to just use a 3k/10 watt resistor and call it a day, but for safety reasons I know you must use an isolation transformer.

So can I just find the smallest 1:1 0.05A iso transformer I can, fuse it at 0.05 A on the wall side and call it good?

There might be an even better solution though, maybe even something just off the shelf.

  • 5
    \$\begingroup\$ Consider an incandescent lightbulb. \$\endgroup\$ – glen_geek Feb 25 at 0:28
  • \$\begingroup\$ an 8 watt bulb or a 35W soldering pen with a dimmer.... I once used a soldering iron suspended by wire in air in a picnic box to make a portable Tenny "cheap & dirty" oven for widget testing then dry ice cubes with a 1W fan to stir and test to -40'C \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Feb 25 at 0:49
  • \$\begingroup\$ you don'r need an isolating transformer if you have sufficient isolation or use a grounded enclosure. \$\endgroup\$ – Jasen Feb 25 at 6:38
  • \$\begingroup\$ a usb phone charger isn't a bad way to go, probably cheaper than a copper-heay transformer. \$\endgroup\$ – dandavis Feb 25 at 18:25
  • \$\begingroup\$ The bulb is a fantastic idea, I will use that. Thank you! \$\endgroup\$ – cat pants Mar 5 at 5:40

You don't need a 1:1 iso transformer. Just get a doorbell transformer and pick a resistor to suit your needs. Although you can get better prices for lower-power transformers if you go to a distributor such as digikey.com and search.

Going to a lower voltage (say, 24 volts or less) will also be safer, since even if it's isolated, 120 VAC is perfectly capable of killing you if you mess up.


You don't need an isolating transformer if you have sufficient insulation or use a grounded enclosure.

A hot glue gun uses electrical insulation of the heater, electric blankets, and heating pads do this too.

A soldering pencil uses an earth connection for safety, same with portable hotplates, and some electric jugs.

Mount a 10W resistor inside a grounded metal emclosure,


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