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What component should I use to modulate an heating pad ? Answered

Rheostat, variable resistor, potentiometer, pulse width modulator, or dimmer, to my understanding I can use any of them to control the heat in my heating wire. I have a 19V 3.16A ouput and my heating wires resistance is 6.6 Ω (1.27 Ω/m).

Thanks in advance for your reply.

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Jack A Lopez
Jack A Lopez

Best Answer 4 years ago

Rheostat, variable resistor, and potentiometer, are, as far as I know, three words for the same thing. These are typically not a good idea for limiting power to a heating element, because they are resistive. They dissipate power as heat, and when you do the math, you will discover it is usually an amount of power (in watts, as heat) comparable to the power (in watts, as heat) dissipated by the heating element itself.

Lamp dimmers, the usual triac based kind, require AC, alternating current. They won't work with DC.

So that leaves PWM, pulse width modulation, and that will work with a DC, direct current, supply, and I am guessing that's what you've got there.

I mean, your, what you call "19V 3.16A". I am guessing this is old charger for a laptop, or maybe a surplus one, if you bought it from some place selling it as a power supply. It is a regulated DC power supply. It tries to keep its output voltage regulated, at a constant 19 volts DC. The spec given for current, 3.16 amperes, is a maximum value. The actual amount of current that flows depends on the load to which it is connected.

Anyway, there exist PWM modules that are good match to a 19 VDC supply. Moreover, there are people selling these things on eBay, and maybe other places too. Typically the best prices come from people selling them directly out of China, with not a lot of documentation. I mean typically all you get is a picture of the board with some labels on it, showing which pins are inputs, outputs, and which potentiometer controls what, and that picture you have to rip from the eBay listing itself.

Note that when you do the math for power dissipated by a 6.6 ohm resistor, R, with a voltage of V = 19 V across it.

I = V/R = (19.0 V)/(6.6 ohm) = 2.9 A

P = V*I = V^2/R = (19.0 V)*(19 V)/(6.6 ohm) = 55 W

When you go shopping for PWM modules, these modules will be rated for some maximum current, or some maximum power throughput, and that's why we are doing math to estimate power and current, because you want to pick a PWM capable of comfortably handling that much power and current.

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ninazz
ninazz

4 years ago

Thanks so much for your reply! I need to read again (and again) your reply, and try to understand these PWM before coming back. Meanwhile I found an interesting thread talking about this: https://www.instructables.com/answers/What-is-the-advantage-of-PWM-vs-supplying-variable/

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Yonatan24
Yonatan24

4 years ago

I think PWM in the simplest. Look for a cheap one on eBay...

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steveastrouk
steveastrouk

4 years ago

If your supply is DC then NOT a rheostat, variable resistor, potentiometer or dimmer.

Yes to PWM. Your heater can only draw 2.9 A, so you won't need anything too expensive

If its AC, then a dimmer might work, if you feed the primary of the transformer with it.