I’m getting tired of wall warts (AC adapters). Isn’t it about time we came up with a standardized DC power outlet? I realize different devices use different voltages, but that’s partly because of lack of standardization. I can’t imagine many electronic devices which can’t run off +/- 12V and +5V. Have there been any such proposals/attempts? If not, any good reason why not?
The reason is that you cannot “transmit” there is probably a better word but I can’t think of it,DC very far without a lot of loss. It is because of the resistance of the wire.
Some RVs have DC outlets in them.
Yes, I understand you can’t run DC power through transformers to obtain high voltage (thus low current, and low transmission loss). I was thinking more along the line of a huge regulated DC power supply in the basement (or under the desk) which converts normal AC into DC.
Is there a standard for DC power on RVs? Is it different from the cigarette lighter socket in normal cars? Those work OK, but too unstable to use directly in most electronics.
The reason why DC current does not flow through your wall outlets is because AC is cheaper than DC. It is cheaper for the power company, and for you. DC electricty requires much more equipment than AC does.
Look at this page and at its links to see how the power distribution works.
There’s no reason why scr’s idea of a regulated DC supply in a house wouldn’t work- you could put it in the same room as the hot water heater, etc. You could run the DC to each electrial outlet, and have a special plug in addition to the standard AC plug. However, this wouldn’t eliminate the reason why so many devices use wall-warts (wall transformers).
The main reason for using a standard wall transformers with a product (instead of building the power supply into the device) is to eliminate expensive and lengthy UL approval. If the wall transformer itself is UL approved (and you just buy them from a supplier that already has gone through it), your product doesn’t need to be, because it’s not directly connected to the AC line. If you had an in-home DC power distribution system, it’d have to be fairly high power (enough to power everything you might plug in at once), high powered enough to get UL and the National Electric Code people involved in setting up regulations, which would probably mean new products that plugged into it would need some sort of approval, which defeats the main purpose of the wall adapter!
That, plus the complications of different DC voltages (anywhere from 3V to 28V DC or more, and designing a 28V DC to 3V DC power supply isn’t always fun given heat and size constraints), and the fact that some wall adapters are designed to put out AC voltage, not DC (some products need low voltage AC) makes it too much of a mess.
Arjuna34
So you are saying devices that get connected to high current power sources need safety certification, not just high voltage… Thanks, I did overlook that. And now that I thought about it more, I guess it’s hard to beat the cost performance of wall transformers anyway. Too bad though, standardized DC power would reduce buisiness travel luggage a lot, and also make it easier to build power outlets into airliners and cars.
By the way, I’ve never seen a wall adapter that outputs AC. What kind of devices are they for? Synchronous motors?
So you are saying devices that get connected to high current power sources need safety certification, not just high voltage… Thanks, I did overlook that. And now that I thought about it more, I guess it’s hard to beat the cost performance of wall transformers anyway. Too bad though, standardized DC power would reduce business travel luggage, and also make it easier to build power outlets into airliners and other vehicles. Maybe even desks in conference rooms and offices.
By the way, I’ve never seen a wall adapter that outputs AC. What kind of devices are they for? Synchronous motors?
My grandmother’s house, built in Spokane in 1908, had DC outlets. Not all of them – most were AC, but there were DC ones as well. You could use them for table lamps, not much else. That turned out to be very convenient when she had me install a doorbell for her – I just hooked it into the DC wiring, no transformer/rectifier required.
Edison’s original electrical distribution system was DC, as is well known. They used images of the (AC) electric chair to frighten people away from Westinghouse’s AC system.
So the answer is that you certainly could have DC power outlets, as Arjuna pointed out. But it doesn’t seem to be economically justified right now.
Generally, power sources that present a shock hazard (i.e. high voltage) or a fire hazard (i.e. high current) need some sort of safety certification. Standard (in the US at least) 120V AC sources are both shock and fire hazards. A “whole house” DC supply would be a fire hazard-type electrical supply, due to the high current capacity it would need.
AC output wall adapters could be used for synchronous motors, although I’ve never seen one for that. The ones I’ve seen are used when multiple DC supplies are needed, and it is cheaper to supply low voltage, isolated AC power to the product, and convert it to multiple DC voltages internally. The decision to use an AC output adapter and internal AC-DC supplies vs. a DC adapter and internal DC-DC supplies depends on details such as power requirements, how regulated and noise-free the DC needs to be, costs (an AC output adapter is usually cheaper), etc.
The other times I’ve seen AC adapters are in very low-cost consumer stuff, where it was cheaper to have a SUPER el-cheapo supply in the product rather than pay for a DC wall adapter with the normal el-cheapo DC supply.
Arjuna34