How does Heating Pad work?

[kangyunmei]

Hi, let me start by saying that I do not have any formal degree in electronics, but I love taking thigs apart in order to understanding how things work. Presently I took my heating pad apart to understand how it works. I have been having a hard time understanding how the switch mechanism works. The pad has a button that enables the user to turn the pad: OFF->WARM(green LED)->LOW(yellow LED)->MED(orange LED)->HI(red LED)->OFF . . .

Regardless of the Warm/Low/Med/Hi setting the output Voltage and Current never changes but the pad temperature still changes per the setting. How is that possible?

 

[KlausST]

Hi,

As in your other post: a forum can't replace scool.
Thus I recommend to first study electric / electronic basics.

*********
To your question:
There is almost just useless information:

You need to learn to focus on the problem.
The problem here is just "power".
Learn how to measure/calculate electrical power.

We can not know how and where you measured voltage and current. Thus it's impossible to answer your question in detail.
Learn to give useful informations.
A schematic or even a hand drawn sketch is good information.
What meter did you use?
The values you measure are they: measured on AC or DC or pulsed wavefirms.
Are they peak values, average values, RMS values?

Klaus

 

[betwixt]

But in essence, the heating elements are switched in and out. There will be more than one and they can be switched in combinations of some on, some off, in series or in parallel. The voltage may be steady from the PSU but the current will change under different heat settings. It has to, W=VxI so if you change W and V stays constant, I has to change.

Brian.