Suggestions For Low Voltage Heating Element

Thread Starter

eirman

Joined Aug 18, 2017
14
My Samsung intercom/doorphone unit at the front gate is housed in a surface metal box.
Dimensions: 12 x 15 x 4 Centimeters (80% empty space inside)

During the winter period it is prone to occasional ring of it's own accord (Usually at some godforaken hour).
I'm 98% sure that it's being caused condensation/moisture.

I'm going to run an extra pair of wires into the housing and fit some type of heating element.
I have a bunch of DC transformers available to me (Up to 12v - 2 Amps)

I'm looking for suggestions as to Voltage/Current and the heating element.
(An old car filament bulb or a wirewound resistor was what initially occured to me)
 
Last edited:

DickCappels

Joined Aug 21, 2008
10,153
upload_2017-8-18_21-49-16.png
Yes -resistors, especially those in heatsink cases are wonderful heaters. They come with voltage and power ratings so you can easily and safely get the wattage you want.
 

OBW0549

Joined Mar 2, 2015
3,566
I'm going to run an extra pair of wires into the housing and fit some type of heating element.
I have a bunch of DC transformers available to me (Up to 12v - 2 Amps)

I'm looking for suggestions as to Voltage/Current and the heating element.
(An old car filament bulb or a wirewound resistor was what initially occured to me)
Just get one or two chassis-mounted power resistors. One of these powered by 12V will dissipate ≈6 watts; two in parallel will give you ≈12 watts. I imagine one will be enough.
 

AlbertHall

Joined Jun 4, 2014
12,345
You will need to try something and monitor the temperature inside the box. You need enough heat but not enough to fry the electronics in there.
You could include one of these which will automatically turn off the heater if it gets too hot in the box.
 

Alec_t

Joined Sep 17, 2013
14,280
For a box that small I would guess 1W or less would be adequate, unless you live in an extremely cold, high humidity climate zone.
 

Thread Starter

eirman

Joined Aug 18, 2017
14
Great information so far - thanks.

I live in Ireland so it's never too hot. (Min -4c Max 24c)
The housing is never in direct sunlight

6 watts may be excessive. 1-2 watts would be better - What do you recommend?
(I'll be using intruder alarm wire by the way)
I use http://ie.rs-online.com/web/

@OBW - Would 2 of those aforementioned chassis-mounted power resistors in series output 3 Watts?
 

wmodavis

Joined Oct 23, 2010
739
How difficult is it to move to max direct sunlight? Is that option better/worse than running power wiring for heating element?
 

ian field

Joined Oct 27, 2012
6,536
You will need to try something and monitor the temperature inside the box. You need enough heat but not enough to fry the electronics in there.
You could include one of these which will automatically turn off the heater if it gets too hot in the box.
Not if you use a PTC thermistor - the degauss posistor in olt CRT Tvs could be the best known application, but they turn up in various kinds of ceramic heater.

The degauss circuit takes advantage of the cold current of the PTC to dump decaying AC into the degauss coil. heating elements reach equilibrium at a certain temperature, they draw more current in a hard frost, but throttle back when nothing takes much heat away.

The Polyfuse is a PTC element - but probably designed for too sharp knee curve for this application.
 

tcmtech

Joined Nov 4, 2013
2,867
You only need to keep the average internal temperature a few degrees above the local external ambient temperature to keep condensation from forming.

As others said, for the size of box 1 - 2 watts should be more than sufficient.
 

Thread Starter

eirman

Joined Aug 18, 2017
14
RESULTS
These are my results after a long wet and cold 2017/18 winter.

12 Volts with a 100 Ohm resistor (1.44 Watts)
Failure. Two false activations in September 2017.

12 Volts with two 100 Ohm resistors in parallel (2.88 Watts)
100% success!
- Zero false activations to date.
 
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