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You’d think electric blankets would use a 12V DC adapter to step down the 240V AC to 12V DC. It has the potential to be just as effective while also being safer. Do you think it’s because of the additional cost of the wall adapter?

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  • \$\begingroup\$ A heater doesn't care if it's AC or DC and DC doesn't mean safer. DC just means more work in this case. Safety is in the magnitude of the voltage and whether it's isolated or not. What do electric blankets use? \$\endgroup\$ – DKNguyen Feb 24 at 2:46
  • \$\begingroup\$ DKNguyen is it not true that at a DC signal at an equivalent magnitude to an AC signal is just as safe but also provides more power? Therefore you’d need to increase the AC voltage magnitude to deliver the same quantity of power as that specific DC signal, thus making it less safe than the DC signal? \$\endgroup\$ – gorge Feb 24 at 3:21
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    \$\begingroup\$ Your phrasing is ambiguous and could be more specific with regards to ratings. RMS voltages, whether AC or DC, will provide the same resistive power. But the peak voltages for the RMS AC will be higher than the RMS DC. But then let me ask you this: If you're going to step it down why go to the trouble of stepping it down to 12VDC when you could just step it down to 12VAC? Is 12Vpeak from 12VDC really any safer than 17Vpeak from 12VAC? Is 120VACrms (170Vpeak) really any safer than 120VDCrms (120Vpeak)? \$\endgroup\$ – DKNguyen Feb 24 at 3:32
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Converting 240Vac to 12Vdc involves a lot of subsystems. You need an EMI filter, rectifier, and then a step down switching converter (buck, or H-bridge, etc.). Electric blankets just produce heat and you can cost-effectively due that by just putting the incoming AC on a resistive load and avoid power conversion completely and greatly reducing the cost.

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  • \$\begingroup\$ Electric blankets run directly off the mains? How do they handle the safety issues? \$\endgroup\$ – DKNguyen Feb 24 at 2:45
  • \$\begingroup\$ I've never taken one apart but with proper insulation it should be safe. Lower voltage doesn't mean safe. Low voltage DC can be unsafe if the current is too high. I would think to provide different levels of heat they are just switching in/out more resistive loads in parallel. \$\endgroup\$ – SPieiga Feb 24 at 2:50
  • \$\begingroup\$ @DKNguyen probably by meeting the double layer of insulation requirement. \$\endgroup\$ – Solar Mike Feb 24 at 5:20

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