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Ask HN: On-Demand Phone Charger
2 points by egberts1 on Sept 26, 2022 | hide | past | favorite | 5 comments
When you have 6 phone chargers around the house, napkin-math is showing me $22.00/month in electric bill.

Not to nitpick, but surely there is a charger out there in the marketplace that can apply electrical load once the iPhone/Android gets connected to the charger. That is assuming that Energy Saving Trust accurately assert that it is eating electric cost wether the device is connected or not. [1]

Perhaps with a big zenier diode or something instead of an always-on wounded transformer coil sucking electricity …

Is there such a thing? I could imagine some type of mechanical (or even electronic) relay to kick in that coiled transformer load but as a tiny consumer product?

Does one exist? If so, how would one search for such a product on search engines?

Napkin Math:

35W/hour (rated phone charger)

24 hours x 365 days (always on)

306.6kW/year, total usage (1 charger)

$0.149/kWh electric rate

$45.68 per charger

or $274.10 annual electric bill for six(6j chargers

of course, Energy Saving Trust claims the chargers are essentially always on, whether you have the device connected or not.

[1] http://monopolybuysellrent.co.uk/advice/energy-saving-tips/



Note that a cell phone charger use 5-10W when the cell phone is charging, but it uses only 0.1W or less when the cell phone is not connected. I can't get official numbers, but this article has some info https://www.howtogeek.com/231886/tested-should-you-unplug-ch...


what's your napkin math? because switching PSUs if well-done are pretty darn efficient even if idle (and the most efficient topology overall)


35W/hour (rated phone charger)

24 hours x 365 days (always on)

306.6kW/year, total usage (1 charger)

$0.149/kWh electric rate

$45.68 per charger

or $274.10 annual electric bill for six(6j chargers

of course, Energy Saving Trust claims the chargers are essentially always on, whether you have the device connected or not.

updated OP.


no phone charger is going to use the rated power if nothing is connected, I'd expect more like something in the range of 0.2-2W


Newest Apple 35W Dual Charger “no-load power consumption of the charger at 220V 50Hz is 0.063W”[1]

[1] https://www.chongdiantou.com/archives/157270.html




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