Strange voltage measurements on power supply

[PeterV]

Hi,

I tested (measured) some older power supplies from different devices (3.7V, 4.5V, 12V-1A, etc)
Half of them are giving much higher voltages... like: 19V instead of 12V, 20V instead of 16V, even 9V in stead of 3.7V...
So I tried a working power supply for a NiMh battery of 9.6V / 600mA.  The battery gave 10.3V and de power supply 25.6V...

Settings on meter : DC, 200V
Are these supplies or my meter broken?
Has it something to do with the fact that there is no working circuit?

It tried batteries:
3V gave 3.14V
9V gave 9.46V
new 1.5V gave 1.61V
home AC gave 224V (220V for Belgium)

Someone an idea?

[Richard Crowley]

When you say "power supplies" I assume you mean inexpensive "wall-warts".
These are typically NOT regulated, and they very commonly have a higher output voltage when NOT loaded.

I also assume that your meter is a typical modern DMM, etc.
That means that it has a very high impedance to NOT load down what you are measuring.

So what you are measuring is the "open circuit" (unloaded) voltage of low-end power supplies.
This is completely ordinary and expected. The nominal voltage ratings are typically the LOADED design target.

[Zero999]

Yes unregulated wall warts always give a higher voltage when unloaded.

It's also true that batteries give a higher voltage when fresh and unloaded.

It's very important to take the above into account when selecting components, to avoid blowing things up.

[PeterV]

Yes, I didn't know.
I have plans to work with micro-electronics...
Did you hear about the "Ardumower project" yet?

http://www.ardumower.de/index.php/en/

I want to learn and to fix my broken mower...
Big challenge...
Maybe I'll need you more in the future...

I added picture now.

So suggestions on materials for my "lab"?

Greetz

[Rick Law]

...
I want to learn and to fix my broken mower...
Big challenge...
Maybe I'll need you more in the future...

... suggestions on materials for my "lab"?

Greetz

You should consider one of those step-down (buck) converters to control your actual output voltage.  For the kind of app you are saying (under 1amp ish), The CV buck boards are well under $2-3, the CC/CV are well under $3-5.

The boost+buck is also a good choice.  It first boost the voltage to max (lm2577 max, 30volt-ish) then buck it back down to what you need.  So it can supply 2v-27v with any of DC wall-wart with enough power (watts).

These low cost boost/buck are not lab grade but they are more than adequate to power an arduino or something like that.

For a digital controlled buck, see this thread:
https://www.eevblog.com/forum/reviews/b3603-dcdc-buck-converter-mini-review-and-how-the-set-key-could-be-fatal/