Finally found a simple heating pad to test for the contact heating experiment.
It’s a plain Sunbeam 3-setting pad, $15 in the pharmacy section of Smith’s which appears to be associated with Kroger grocery. The SKU on the package appears to be specific to the retailer, but it looks like this one from walmart.
The kill-a-watt reads ~43w when it’s cycled on, so probably a 45w pad. Quite hot when it’s cranking so I’ll probably use it under a towel or something.
I watched the wattage and tried to figure out what the pad is doing. It’s hard to tell, but I think the pattern is something like this:
low - on for 30 seconds, off for 60 seconds, 50% duty cycle followed by 60 seconds (on/off/on/off every couple of seconds), repeat
medium - on for 60 seconds, off for 60 seconds, 50% duty cycle followed by 60 seconds (on/off/on/off every couple of seconds), repeat
high - on, at least for the couple of minutes I watched it.
During the 50% cycling some of the ON cycles are only 7-8w. I wonder if it’s running a small amount of power through to check temperature via increasing resistance. Dunno.
The wattage is just about right, and it’s cheap. I think it’s more robust than the heated car seat cover and vest so it will be my go-to for contact heating. I like the vest for working at the desk, but at $50 I’m afraid to damage it.