Check my ac adaptor

[KanedaFr]

Hi there,
I have several AC Adaptor to check.

I need to be sure they could output the 10V 1.2A they were sold to.

For the 10V, I thought to simply connect the adaptor to the wallplug and test with my multimeter.
But I read the value won't be valid until I plug it to a load.
Volt will drop as soon as current will be drawn...
Can you confirm me this ? what's the easiest way to mesure the real output ?

For the 1.2A, it seems to be very difficult.
I found 2 ways :
- connect the adaptor to a circuit and mesure in serial the current with an ampermeter
- connect the adaptor to a load, use a low precise resistor on serial and mesure volt at resistor. Since V=RI, just divide V/R to get I

What I don't understand is what should be the circuit/load to plug to be get full power ?
If I connect a led with a small resistor, it won't ask the full 1.2A of the adaptor....no ?
If I connect a 10V 5A device, it will blow out the adaptor !


So, what should I do to measure the correct values for volt and current ?!

thanks for any hint or link

[foobat]

The only way to check to see if they can provide the rated current is to connect them to the rated load. The tool to do this is called a "dummy load" or sometimes (paradoxically) a "load generator". It's effectively a series of resistors, and that's basically the same thing as an electric heater.

You can test the voltage with your multimeter. It will probably read high with no load connected. There's a minimum load you need to get the rated voltage out of one of those little wall wart transformers. If you have a datasheet there will be charts and graphs and one of them will show the minimum required load and the maximum allowed load. If you draw more than the maximum load either the voltage will sag or it will melt and catch fire.

Have fun

[KanedaFr]

thanks for the details...

"dummy load" was the term I was looking for, thanks

Now I have to understand how you define the power of the dummy load needed.

In fine, I'll need a dummy load (high power) and a very small resistor to measure current.

[Charles MacDonald]

thanks for the details...
Now I have to understand how you define the power of the dummy load needed.

In fine, I'll need a dummy load (high power) and a very small resistor to measure current.

If you want to verify that the adapter can provide 10V at 1.2A:

R = V / I = 10V / 1.2A = 8.3 ohms
P = I*V = 12 watts

A common type of power resistor is 8 ohms and 50W which should be ideal, this will allow 1.25A which is close enough.
Get the kind that has solder lug terminals (eyelets you can thread the wire through and solder to on either side of the resistor) like this:

https://upload.wikimedia.org/wikipedia/ ... sistor.jpg

It will get rather hot, so be careful.

[KanedaFr]

so I need a dummy load per adaptor I want to test, if current/volt is different ?

I don't know if it worths the money, perhaps I should simply plug it on the device and check current flowing
If the genny doesn't even power up, trash !

[Charles MacDonald]

don't know if it worths the money, perhaps I should simply plug it on the device and check current flowing
If the genny doesn't even power up, trash !

Oh I thought you were testing multiple units of the exact same AC adapter. Are these all Genesis power supplies you are testing, Or something else? Do you know what they'll be connected to?

Most consoles use a 5V regulator, that requires DC input which is at least 2V higher. Typically a 9V to 10V supply is used as this gives more headroom to handle power fluctuations and such then using exactly 7V. The 5V regulator is what powers the load. So the input voltage isn't critical.

I don't know much current the Genesis draws on average, but I can measure it if you want to know how close to 1.2A it gets.