# power supply for a printed resistive flexible heater

Discussion in 'The Projects Forum' started by sidneo, Jun 13, 2013.

1. ### sidneo Thread Starter New Member

Jun 13, 2013
1
0
Hi I am a newbie I would like to get an advice for a printed resistive heater I am working on . The heater is a heat resistant thin film on which I printed patterns made out of resistive ink carbon/ graphite/ ferrous material each connected to the power supply via a more conductive ink (silver ink).
My goal is to do some kind of multiplexing to turn on and off certain areas my patterned circuit .Here is my questions is there an idiot proof way to calculate the power needed to turn my half millimeter resistors red hot ?

I Have Seen people turning graphite leads into incandescent light with 24volt 2 amp
How can one build a simple power supply to produce the Power Required will A joule thief do The Job ? If yes how ?Because I have tried I don't know what I am doing wrong I am getting 5 volt from a 9 volt battery the only think getting hot seem to be my transistor . My ideal solution would be to pulse high current to the resistors from capacitors connected to a usb power supply but I don't know if that's possible and I surely don't what Kind of capacitors to use

Apologise for my lack of knowledge and I hope to get a feedback soon .

2. ### GopherT AAC Fanatic!

Nov 23, 2012
6,321
4,046
24v at 2 amps is 48 watts. You cannot supply more than about 0.9 watts with a 9 volt battery.

A joule thief cannot get more power from a battery than a battery is able to put out at a given time. It can only bump up the voltage while sacrificing current. You are likely asking your thief to supply too much current. Therefore it cannot maintain the voltage you are hoping for.

Last edited: Jun 13, 2013
3. ### wayneh Expert

Sep 9, 2010
12,392
3,246
Almost nothing is idiot proof! But the definition of power in the electrical world is volts x amps, which is the same as amps^2*resistance since resistance=volts/amps.

So you need to know how much voltage and current gives the desired result for each "pixel". From that you can easily calculate power.

Do you have any data at all? If not, I'd suggest starting with a 12V supply and then try to heat a test pixel through a 100K resistor. I'm guessing that the resulting current won't be enough to make it hot. Then start cutting the resistance in half, over and over, until you start getting heat. Maybe it'll be at 1kΩ, who knows. Then make smaller increments. When it's heating the way you like, measure the voltage across the resistor and calculate the current flow using Ohm's law.

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