Resistance heater

[Father Haskell]

Need a small, 10 - 25 watt heater to keep a
houseplant container warm. Currently using a
plywood box surrounding the pot, with a light
bulb under the pot, which sits on a metal drip
pan to catch spills. Works well, but could
be more compact. Thinking of replacing the
bulb with several ceramic block power resistors
connected in parallel, set around the pot for
more even heating, powered by a 12v transformer.
Ohm's laws I = ER and P = IE should tell me
what component values I need.

Will this be safe to leave running constantly?

 

[Archon]

Father Haskell wrote:

Need a small, 10 - 25 watt heater to keep a
houseplant container warm. Currently using a
plywood box surrounding the pot, with a light
bulb under the pot, which sits on a metal drip
pan to catch spills. Works well, but could
be more compact. Thinking of replacing the
bulb with several ceramic block power resistors
connected in parallel, set around the pot for
more even heating, powered by a 12v transformer.
Ohm's laws I = ER and P = IE should tell me
what component values I need.

Will this be safe to leave running constantly?

You may be better off considering heat cable, as supplied in pet stores
for keeping reptiles warm, I think they are about 25W, buddy of mine
used it to warm up his home made wine fermentation. Also available for
pipe lagging in cold countries. Try Ebay in your respective country.

JC