DC adapters

[Bassalisk]

Hello,

I have this old Nintendo AC 220 V to 24 V 550 mA DC.

it has this

one full line followed below with dotted ones.

Can you help me read this? And how do these adapters behave. Do they ALWAYS give 550 mA, no matter how much voltage drop is connected to the end?

I am thinking of using that adapter for powering LED diodes, lots of them. I am expecting for a such adapter to behave like a battery.

THanks

[schip666!]

I'm not sure what "one full line followed below with dotted ones" refers too. If it is the output wires of your adapter, the usual convention is to mark the + wire with a white stripe or dots. A DC voltmeter will be of great use in validating this...

As to the 550mA thing, could be or not be. Some wall-warts are regulated, such that they will always produce, e.g. 24v -- at least until you try to draw more than, e.g., 550mA from them. Others are not regulated, the markings refer to their _maximum_ rating so you should be able to get 550mA at 24v, or less current with a somewhat higher voltage. The way to tell is, again, with your voltmeter and some variable loads, like a set of interestingly valued resistors.

And yes, you should be able to run LEDs, lots. Just start with a few in series with a resistor that would limit the current to around 20mA and see where to go from that.

[Bassalisk]

http://pokit.etf.ba/get/a787fa53bd2848ee1b18b170d920e204.jpg

Here is the image, does this help?

[tiny-tim]

Comparing it with the line above, it looks as if ~ denotes AC and those straight lines denote DC. :smile:

[Bassalisk]

Comparing it with the line above, it looks as if ~ denotes AC and those straight lines denote DC. :smile:

Yes i get that, but do i have steady current or steady voltage or both?
http://en.wikipedia.org/wiki/Current_source
http://en.wikipedia.org/wiki/Voltage_source

[berkeman]

Yes i get that, but do i have steady current or steady voltage or both?
http://en.wikipedia.org/wiki/Current_source
http://en.wikipedia.org/wiki/Voltage_source

The wall adapter will act like a voltage source with a finite output impedance. At no output load, you will read the source voltage, and as you load it more towards the 550mA, the output voltage will drop (but should still stay within spec).

[Bassalisk]

The wall adapter will act like a voltage source with a finite output impedance. At no output load, you will read the source voltage, and as you load it more towards the 550mA, the output voltage will drop (but should still stay within spec).

I get it now, thanks folks !

[berkeman]

BTW, the better DC adapters will have a voltage regulator at the output, so there may be a pretty low effective output resistance. The cheaper ones just have a rectifier and output capacitor, so they have a fair bit of sag from no load to full load.

One adapter that I use a lot runs about 13Vdc at no load, and just meets its spec of 9Vdc output at its full rated load of 500mA.

[Bassalisk]

So, can you suggest me a good power source for lets say 25 LED diodes which run on 3,3 V and 20mA, alternative to DC adapters?