Hello everyone.
I have one of those multi voltage power supplies, similar to this



If it is rated for eg. 1000mA at 12V (12VA), may I assume that it can source 4A at 3V for example?
Or the limit remains 1A due to wire thickness?

Thanks

 

With SMPS types, you cannot take anything for granted. !

 

If it is rated for eg. 1000mA at 12V (12VA), may I assume that it can source 4A at 3V for example?
Or the limit remains 1A due to wire thickness?

Current is limited to 1A because that's what the supply is rated for. Good supplies will actually provide 1A, or a little more. Cheap ones might not provide 1A reliably.

You can reduce the voltage to 3V by using a voltage regulator, but you can't increase current above 1A.

 

hi kil,
The module photo shows the voltage output is selectable, but I would estimate all settings are 3000mA max, for that module.
Post a photo shot of your module.
E

 

The label says 3A max for 5V to 12V. It does not say the max current for 3V or 4.5V output settings.

 

hi agu,
It clearly states 3Amp for all settings, BUT I did not say I believe it.

Note the 'back slash' between ALL the values.
E

 

I look at that USB adapter and cringe.

BE CERTAIN the voltage is set to 5 volts before plugging it in to a USB connector.


Also, this is a modern regulated switching supply. Beware of older "battery eliminators" that use a line-frequency transformer. Most ARE NOT REGULATED and depend on the load current and transformer impedence to make the resulting voltage kind of near what it's supposed to be.

 

BE CERTAIN the voltage is set to 5 volts before plugging it in to a USB connector.

I don't have the one in the picture, was just an example

The label says 3A max for 5V to 12V.

Actually the label in the pictur above says

"3V/4.5V/5V/6V/7.5V/
9V/12V -- 3.0A max"

They just started a new line there but I guess 3.0A is referred as a limit for even the low voltages. Probably due to wire sections or other components current capability

 

If you don't have the one pictured, it may be a non-regulated type as I described. The output voltage could be far greater than expected under light loads.

Best to measure no-load output voltage to be sure.

 

The output diode will be the limiting factor, as it tends to be the part that creates the most heat in a small flyback converter.
So 1A for all voltages.
It is probably not an unregulated supply, as that would imply it would have a 50Hz/60Hz transformer, meaning it would be much bigger and heavier. Although it is not impossible to make an unregulated flyback converter, with the plethora of control ICs available it would be highly unusual.

 

Looking at the blurry photo, I was wrong. It says 3A for all voltage outputs:

 

I don't have the one in the picture, was just an example

You stated succinctly in your initial post that the picture wasn't what you had.

I have one of those multi voltage power supplies, similar to this

And then you said:

If it is rated for eg. 1000mA at 12V (12VA), may I assume that it can source 4A at 3V for example?
Or the limit remains 1A due to wire thickness?

Probably due to wire sections or other components current capability

Wire gauge would only be a limiter in poorly designed power supplies. I bought 4 of them from Ali Express. They have built-in volt meters that don't provide accurate readings if any significant current is being drawn.

 

kiltro, can I ask - what is your plan with this mystery Chinese wonder-supply of yours? This may be the real question that needs addressed. As for these sorts of supplies in general, trust nothing, as MaxHeadRoom had stated, and others have agreed to.