February 10th, 2012

What does electric heating pad and electric chair have in common?

To keep myself warm, I purchased nice "beurer hk25" heating pad. According to their manual, it is "thoroughly tested" and "high-quality" product. It was supposed to have three temperature
settings... but in fact it has three power settings, with emergency overtemp fuse that renders the pad useless. Uncool :-(. [Pad is connected by two wires to the control unit]. It was not exactly cheap, either.

I expected some kind of switching/tyristor control, but apparently control unit just contains resistors, so it "may heat up" and "may not be covered". Oops. I thought that controlling 100W of heat is not a rocket science.

But that was not biggest surprise. Biggest surprise was that heating pad is actually able to induce enough electricity in the human body to be felt. Just touch another person, and her skin appears appears to vibrate very rapidly.

Now, the manual does have a lot of warnings; but "don't touch another person while using this" is not there. (Ok, the warnings mostly say "this can not be used at all"). One of warnings describes possible pacemaker interference, and lists electrical specs: 5000V/m electric
field strength, 80A/m magnetic field strength, 0.1mT magnetic flux density.

Except that values listed are not actual values produced by the pad, but limits from health regulations. So this does not do help me determining if this device is designed to introduce interesting sensations, or if my device is somehow faulty.

(Not sure how I should be measuring this, anyway. So far I know that multimeter indicates cca 2V AC between me and ground when it is on, so I know I'm not imaginging this, but....)

Now, I don't think this is unavoidable. Including AC/DC converter would be one possible solution... right?