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Jon Chandler has written a fantastic getting-started article on selecting an AC-to-DC power supply for your home electronics project over at Digital DIY. It covers the very basic details of voltage and current selection, and goes on to clearly and succinctly explain what “linear,” “regulated,” and “switching” power supplies are, and, most importantly IMHO, gives a bunch of practical tips on how to identify the various species of wall warts, in the wild, and determine if they are suitable for your own application. [via Hack a Day]

Sean Michael Ragan

I am descended from 5,000 generations of tool-using primates. Also, I went to college and stuff. I write for MAKE, serve as Technical Editor for MAKE magazine, and develop original DIY content for Make: Projects.


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  1. Anonymous says:

    An excellent technical article, and thank you for it, but I didn’t see it answer a simple question that has often bugged me: up to ~20 years ago all mains-powered electronic devices had their AC-to-DC in the project box, and no competition for the area around the wall plug was seen. so why has this function been moved out to the wall? It’s probably something simple like, “it’s cheaper that way”, but i’d love a simple explanation – thankee!

    1. The wall wart is a power interface between your gadget and whatever the local voltage standard is. Say company A makes routers. If all models require 9 volts DC at 60 mA, then the only extra requirement is to make a selection of wall warts that convert the “local” mains supply to 9vdc, 60ma. The manufacturer ends up getting an economy of scale for the routers, which are presumably more expensive to make than than the wall warts.

      1. Anonymous says:

        Thank you for that. I’ve had the “globalized market forces” hinted at me before. But I find it hard to believe that the “wart” still couldn’t be closer/attached to the device; just run the cord out the other side and still swap out for each market. It would help the plug area quickly becomes a tiling problem with all the form factors that have to compete – plus it gets a bit warm there due to inefficiency. ah well, ‘hey you kids, get off my lawn!’ etc.

        1. kalleguld says:

          If they use existing wall warts, they also get the “economy of scale” from the wall warts (i.e. lots of stuff uses a 9v DC, 60 mA).
          Also, if your device doesn’t touch high voltage at all, you don’t have to certify that it complies to those safety regulations, as the power adapter is certified already.
          Some power adapters are made in the “brick”-type, with a cable coming out of each end of the “brick”. But they are more expensive because of the higher part-count.

        2. Anonymous says:

          Some Lexmark printers have the ‘wart’ at the printer. I agree that it would be much nicer if this was the case for other devices as well.

    2. It’s partly due to safety regulations, and partly due to internationalisation. A manufacturer can design and build a device with a DC input and then select a ready-made wall wart to suit the mains voltage, connector standard(s) and regulatory approvals according to the country where the device is sold. Then, the device designer need not worry about mains voltage design and can concentrate on the low-voltage stuff.

      But it’s a shame that the wall warts themselves are often too bulky to use in adjacent sockets on an extension lead. And it’s a shame that the on/off switch on the device (if it has one) can only switch the DC off, and not switch the mains off.

    3. Dan French says:

      One reason is that the project can be smaller, lighter, and cooler if the power supply is external. Of course then you have a lump of a power supply out there…

  2. Some devices have the bulky part (excuse my lack of technical lingo) near the device end, and just a small plug going to the wall. This still allows for most of answers to herrnichte’s question, e.g., international standards, economy of scale, while avoiding the bulky plug taking up space on the wall outlet / power strip.

    If my memory serves me, the Nintendo 64 has a small outlet plug and all the bulky parts attaching to the device, while being removable.

  3. l says:

    he forgot to mention that there’ also wall warts that output low voltage AC, pretty much every adsl modem I’ve seen uses an AC wall wart so it can easily generate a -/+ supply

  4. Logan says:

    I really would love to see a nice DC bus powerstrip that I could use to replace all the wall warts and which could perhaps run with a more efficient conversion rate.

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