AC Adapters

[Goedjn]

Power-over-ethernet, 24V, 12Watts. (thus 1/2 amp?)

[Chris Lewis]

According to mm :

The center pin or one of the rings may not be used at all, or, the two rings may be connected together. Does the wallwart have a schematic picture of the connector? They often do.

[Mark Lloyd]

Also, you can buy switchable voltage DC wall-warts with interchangeable plugs that let you use either polarity.

[Mark Lloyd]

I often look through old power wall-warts when I need one, succeeding about 75% of the time (if the voltage is common, 6V 9V or 12V).

And if you do, THAT will be the one you need.

You can combine DC supplies, but be sure to consider which side is grounded.

[Mark Lloyd]

It would.

If we has 12VAC power available everywhere, the adapters could be much smaller (or even built in to equipment).

There's a lot of things that could use standards, including button cells (used in watches, hearing aids, etc...).

[Mark Lloyd]

Equipment used to have hard power switches (that disconnected everything). Now, the power supply needs to stay active to supply power to things like clocks (even when you don't need a clock there), memories, electronic "power" switches, and remote controls. Some even have a light that glows all the time the equipment is "off".

How much current capacity? That system may be impractical, but you could use ONE transformer instead of several with your computer.

[Mark Lloyd]

That wouldn't go very far toward eliminating the cluster of wall warts behind the computer.

[mm]

I"m sure that accounts for a lot of things, but I've seen a lot of other things where none of that existed. Just one example, my wireless speakers don't have a clock, remote control, memory, or a light, and one needs to turn a knob to turn the speaker on. Yet it uses a wall wart that is on whenever it is plugged in. I unplug mine. (I have one only in the bathroom, bedroom, kitchen, and basement, so that I can listen to web radio wherever I am. But I only do that 1 to

5 hours a month. I don't need 4 wall warts runing 720 hours a month for my 1 to 5 hours.)

I don't know. Too many other projects ahead of it, but I also need the manufactures to agree on a voltage and current direction.

I think the printer, scanner, and speaker take different voltages, but for my computer, I bought (used for only 2 or 3 dollars) a box that goes under the monitor and has 4 switches plus a master switch. I use one for the printer, one for the speakers, one for the wireless speaker transmitter, and one is still empty. Because of space limitations, only every second outlet can be used for a wallwart, unless I need more, in which case I'll use a short extension cord.

[mm]

With a volt-ohmmeter, all things are possible.

[Mark Lloyd]

You can always use a switch cord. That's like an extension cord, but with both male and female ends at the same end and a switch at the other. I've seen them at the local Lowe's (no grounding cords though). I am using several of those cords now, to have switches in more convenient places.

The biggest "power strip hog" I've seen is my kill-a-watt meter. It's plugged into a power strip now (getting ready for checking holiday lights. I use so many that it's important to keep track of electrical load) , and it blocks FOUR additional outlets. That isn't a problem right now, but it could be someday.

[Mark Lloyd]

I have one 12VDC 1A power supply that is connected to 2 separate cameras. This is a regulated supply, which was needed to reduce noise in the video output of the cameras.

If one of them needed a different voltage, it would be possible to use diodes (consider current here too, diodes have current as well as voltage ratings) to drop the voltage (2 diodes in series give about

1.5V drop). If the devices have a common ground (as those cameras do), that needs to be considered when powering multiple devices with 1 adapter.

[mm]

That's a good idea. I use one for the fan on the file cabinet, so I don't have to get up when I'm on the computer.

And I used to use one to turn the tv on and off when I was in bed. Then I got one with remote control that forgot something, maybe the station list, when unplugged. The one there now might well not forget, so I should go back to using the wired switch, which is easier to find and easier to use than the remote.

Remove NOPSAM to email me..

[Mark Lloyd]

A lot of TVs forget to be on once power has been removed. Anyone using hard power switches or home automation would be interested in which TVs don't have this problem. I have 2 Magnavox sets and a Sylvania that don't. Both are 15-inch LCD TVs.

I know this is not email (and wouldn't suggest otherwise).

[PeterD]

I've found that most (smaller) LCD TVs seem to have 'better' memory when power is interrupted.

Ah, yes but will the solstice run on a wall wart?

Me, I'll wait for spring...

[Chris Lewis]

According to Mark Lloyd :

Diodes in series is a reasonable regulator, but it might not be good enough if the current through them varies a lot.

In which case, something like a three lead regulator would be better. But, they usually need more than 1.2V of headroom to operate.

[That was what I was envisaging for my "universal wallwart strip". A series of jacks at, say, 20VAC, with things that plug in that have combinations of bridge rectifiers and regulator chips.]

[Mark Lloyd]

2 diodes in series is exactly what you have with a full-wave bridge rectifier. I haven't heard of voltage drop varying with current. Perhaps you could explain.

A 78Lxx would be good if you don't need much current. Those are no bigger than transistors.

BTW, I'm using a 78L05 to power a MAX233 (RS232 interface) to control holiday lights (it worked fine for Halloween). The input to it is a

9VDC wall-wart. I can give more information on this if anybody cares.

It could be easier to use the regulator if you had to drop the voltage a lot (too many diodes).

Don't forget the filter capacitors (for DC).

[Tony Hwang]

[Tony Hwang]

Usual Si diode has a typical voltage drop of 0.2V across it's junction. If you put them in series it'll be multiple of 0.2. If current increases, you do the math acoding to the Ohm's law. Also regulator typically comes in two different flavors. Series or shunt type.

[Art Todesco]

Actually, Silicon diodes have a drop of

0.7 volt; Germanium diodes have a 0.2 volt drop.

[Chris Lewis]

Heh, Si diode forward drop is usually quoted in all the material I've dealt with over the years as .6V ;-)

Forward drop in a diode is highly non-linear relative to current flow, and ohms law doesn't apply.

Forward drop voltage tends to hit .6V at quite low currents, and then very slowly increase to a volt or more near max current for the diode.

A diode does act as regulator, but they don't regulate that well with widely varying currents. Depends on how accurate the voltage regulation needs to be.