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Many of us have lots of devices that uses AC mains (110V/220V) to DC (typically 12VDC) adapters. There's my LED table lamp, my Wi-Fi router, my Gigabit switch, my powered USB hub,.....

Such AC/DC adapters are dirt cheap from China, so I highly doubt efficiency is built into them.

So here's my idea. Can I somehow combine all these into a single device; do the AC/DC conversion once and have everyone tap the DC line, instead of each doing the conversion themselves?

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  • \$\begingroup\$ Be aware that some devices that appear to be just voltage sources may be more complex. this is rare but not unknown. \$\endgroup\$ – Russell McMahon Jan 13 '12 at 14:45
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    \$\begingroup\$ It would just be nice to create a bulk adapter with usb ports or so to have only one converter, but you would lose in flexibility, so i don't know if it's worth. \$\endgroup\$ – clabacchio Jan 13 '12 at 14:53
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Yes, devices of the same voltage can be run from the same supply.

For this you would need a (preferably decent quality regulated) 12V supply that is capable of sourcing more than the total (max) current draw of all your devices combined. If you have other devices at e.g. 9V you would need a supply with a 9V and 12V output.
The required info re current draw is usually written on the device somewhere, or in it's manual. You can also use the rating info on the adapter it came with as a guide.

For instance (for 12V devices) if device 1 draws 100mA max, device 2 200mA max and device 3 500mA max, you need a supply capable of supplying at least 800mA @ 12V.

For high current draws, a SMPS will be preferable to a simple linear supply. These will be much smaller/lighter in comparison.

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  • \$\begingroup\$ From the answers on this page so far, it seems my idea is not so crazy after all. That there can be economy of scale by having one big efficient supply (switched-mode power supply) instead of multiple AC/DC adapters. (thinking aloud: if I were to expand on this idea, we're talking about running a DC supply through-out the house, isn't it? BTW, I'm also eyeing using LED lighting everywhere) \$\endgroup\$ – Ivan Jan 14 '12 at 6:54
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    \$\begingroup\$ A PC's power supply is switched-mode isn't it? As it's a commodity, a PC's power supply should have better price/performance than specialized SMPS. My question then, can I repurpose a PC power supply for this task? \$\endgroup\$ – Ivan Jan 14 '12 at 6:58
  • \$\begingroup\$ Yes, given their high power, low price and availability, many people do repurpose ATX supplies for things like this. Google has plenty of info on the subject. \$\endgroup\$ – Oli Glaser Jan 14 '12 at 7:54
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Largely "connect away".
As long as the voltage is as required and the current supply is at last capable of meeting the maximum load current then it should work.

BUT

Be aware that some devices that appear to be just voltage sources may be more complex. This is unusual but not unknown.

eg If the output voltage measures a steady 4.1 to 4.2V open circuit and does not change much when loaded with eg a 20 ohm resistor then it is quite likely that it is a Lithium Ion charger. Using a simple higher current capable 4.2V source in its place would probably be utterly disastrous. I once needed to charge a LiIon battery when I did not have the correct charger while in China. I took the first available no-name power pack and measured its voltage, intending to make my own lashup charger. Eureka! 4.2V :-). As long as current max at 4.2V <= 1C for battery concerned it will probably charge OK.

Some few pieces of equipment need several voltages simultaneously and may care about applied and removed order or voltage ramp up rates etc. This is rare but happens. Examples may be printers which may have a 20 to 30 V supply (inkjet printhead?) and a 5V supply.

Some supplies have a complex current / voltage / time map that enables communication between supply and powered device re supply capability and device needs. An example is older Ericsson cell phones which accept 5V to 9V in but make decisions about subsequent charging which depend on how the charger responds to initial loading. Use of a much higher current supply than needed would probably be OK. Probably.

Some manufacturers make it hard in some or all cases to connect supplies other than their own. Unrecognized supplies will usually just not work rather than producing magic smoke. But caveat experimentator.
Apple is well known for this, Dell in some cases, Motorola in some cases, others perhaps.

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  • \$\begingroup\$ I usually don't worry about grammar and spelling too much (I am just as bad sometimes) but this was difficult for me to read. I have fixed most of the stuff I saw, but there are still a few things that I wasn't sure what exactly you were trying to say. It would be very helpful to write your answer a little more readable as sometimes I feel like you just threw up on the screen... All of the info is there, just difficult to read. \$\endgroup\$ – Kellenjb Jan 13 '12 at 21:28
  • \$\begingroup\$ @Kellenjb - Hmm 6 hours ago, that would have been 4:30am here and not yet abed. Thinking works. Seeing and typing may be shutting down a bit :-). Will fix. Thanks. \$\endgroup\$ – Russell McMahon Jan 13 '12 at 21:28
  • \$\begingroup\$ don't take it personally or anything, just wanted to point it out, just as I would hope someone would do the same to me. \$\endgroup\$ – Kellenjb Jan 13 '12 at 21:29
  • \$\begingroup\$ @Kellenjb - Tidied. Original actually didn't look too bad for 4am I thought :-). \$\endgroup\$ – Russell McMahon Jan 14 '12 at 0:35
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Such AC/DC adapters are dirt cheap from China, so I highly doubt efficiency is built into them.

au contraire -- almost all of them are switching converters nowadays (the high frequency magnetics + controllers are smaller and cheaper than a 60Hz transformer)

So here's my idea. Can I somehow combine all these into a single device; do the AC/DC conversion once and have everyone tap the DC line, instead of each doing the conversion themselves?

Yes, just make a box with a bunch of cables + connectors that match the devices you want to plug into.

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