Puppy Linux Discussion Forum

I own two 30-year old AC/DC adaptors.

Specifications:
Input: 220V, 50/60HZ AC
Output: 1.5-3-4.5-6-7.5-9-12V DC
Current: 500mA, 9W

The wall socket has a current of 230V.
I recently measured their parameters with a meter and found that the output voltage is almost 10V higher on each range, e.g. instead of 12V it is 20V.

Is this due to the old age of these power supplies or the 10V higher input current?

puppy_apprentice wrote: Sun Apr 07, 2024 7:07 pm

Is this due to the old age of these power supplies or the 10V higher input current?

The capacitors are all dry there.

Yes, in the 90s and early 2000s, such Chinese adapters were sold on every radio market. The quality then was you know what. Throw it all out the window. You have the leadership of the party buying a Black Panther in South Korea, and you are messing with these adapters

I got it along with a videotape rewinder and a walkman from my American uncle.
I sometimes tested computer fans with them. Now they are going to the rubbish heap.

With no load except a voltmeter, AC/DC adapters with unregulated outputs will have much higher output voltages than their specified output voltage. The specified output voltage is measured at the specified output current. Load the 12 Volt output (with a 100 ohm 1 Watt resistor for instance) and you should see the output voltage drop. A 100 ohm resistor across 12 volts will get very hot very quickly, so don't delay measuring the voltage.

puppy_apprentice wrote: Sun Apr 07, 2024 7:33 pm

I sometimes

I found such an adapter in the pantry. The only good thing there is the polarity switch But the designation on the case did not always correspond to the correct polarity... "Why, why doesn't it work?! Ah!!! There's a plus and a minus mixed up..."

Flash wrote: Sun Apr 07, 2024 11:04 pm

With no load except a voltmeter, AC/DC adapters with unregulated outputs will have much higher output voltages than their specified output voltage. The specified output voltage is measured at the specified output current. Load the 12 Volt output (with a 100 ohm 1 Watt resistor for instance) and you should see the output voltage drop. A 100 ohm resistor across 12 volts will get very hot very quickly, so don't delay measuring the voltage.

Yep. Fresh AA (LR6) batteries have ~1,65V/1.7V and ~2,4A on my multimeter. But I think the differences between the voltmeter reading and the nominal values for my adapters are too high.
I'm planning to buy an RPi and a contact/prototype board so maybe I'll keep those adapters and try to make myself some electrical circuits.

Grey wrote: Sun Apr 07, 2024 11:38 pm

"Why, why doesn't it work?! Ah!!! There's a plus and a minus mixed up..."

I had a Lego Technics set that had a motor in it. You could build a crane and, by changing the polarity, pull the rope up or down.

puppy_apprentice wrote: Mon Apr 08, 2024 7:57 pm

Yep. Fresh AA (LR6) batteries have ~1,65V/1.7V and ~2,4A on my multimeter...

It sounds like you shorted the batteries through the Amp scale of the multimeter. Normally this would have blown the fuse that all multimeters have in their Amp scale to protect their circuitry from someone connecting a voltage source across the Amp terminals. Apparently, AA cells can't put out enough current to blow the fuse in your multimeter. Try measuring how much current a 12 Volt car battery can put out with your multimeter and you'll see what I mean. Don't ask me how I know.

I'm planning to buy an RPi and a contact/prototype board so maybe I'll keep those adapters and try to make myself some electrical circuits.

I suggest starting out with the 78xx and 79xx 3-terminal voltage regulators. You'll be making a regulated power supply and learning while you do it. These regulators have been available since the '70s so they are cheap and there's tons of information about how to use them. Start by reading the fine print of the data sheet.

Flash wrote: Mon Apr 08, 2024 9:42 pm

It sounds like you shorted the batteries through the Amp scale of the multimeter. Normally this would have blown the fuse that all multimeters have in their Amp scale to protect their circuitry from someone connecting a voltage source across the Amp terminals. Apparently, AA cells can't put out enough current to blow the fuse in your multimeter. Try measuring how much current a 12 Volt car battery can put out with your multimeter and you'll see what I mean. Don't ask me how I know.

I connected the battery to the multimeter for 2 seconds and set the scale to 10A. I have a Chinese multimeter bought for $3. If it burns out I'll buy a new one

Flash wrote: Mon Apr 08, 2024 9:42 pm

I suggest starting out with the 78xx and 79xx 3-terminal voltage regulators. You'll be making a regulated power supply and learning while you do it. These regulators have been available since the '70s so they are cheap and there's tons of information about how to use them. Start by reading the fine print of the data sheet.

Flash wrote: Mon Apr 08, 2024 9:42 pm

These regulators have been available since the '70s so they are cheap and there's tons of information about how to use them. Start by reading the fine print of the data sheet.

puppy_apprentice wrote: Mon Apr 08, 2024 10:24 pm

I have a Chinese multimeter bought for $3. If it burns out I'll buy a new one

Flash is right. By the way, electronics flourished in Poland in the 70s, people did everything with their own hands, and did not buy Chinese Now there is also - I do not argue - but like us, it is not massive.

Here I have a translated book by Janusz Wojciechowski from 1977. Not the one who is a European official in agriculture, but an old Polish writer and technician "(Radio)Electronic toys":

I don't have a prototype board yet and had to hold the wires and bulb in my left hand and the phone in my right

The measurement result is 0.21A