Switching adapter current output

[Susco]

I have a switching power adapter, which is supposed to output 5V 2A.

 

To check the output voltage is no problem, but how do I check if the current output is also actually 2A?

[Jan Dietz]

Volt meter, Amp meter and 2A load (10W resistor or a few lights), measure Amps and at 2A voltage drop should be within nominal.

 

 

This will get you into the ballpark:

https://th.rs-online.com/web/p/panel-mount-fixed-resistors/1073302

 

Little cheap meter you can leave in circuit:

https://www.lazada.co.th/products/original-dc100v-10a-i1629992789-s4492640371.html?spm=a2o4m.searchlist.list.4.29906b98Cdb0Za&search=1

 

[Susco]

4 minutes ago, Jan Dietz said:

Volt meter, Amp meter and 2A load (10W resistor or a few lights), measure Amps and at 2A voltage drop should be within nominal.

 

 

This will get you into the ballpark:

https://th.rs-online.com/web/p/panel-mount-fixed-resistors/1073302

 

Little cheap meter you can leave in circuit:

https://www.lazada.co.th/products/original-dc100v-10a-i1629992789-s4492640371.html?spm=a2o4m.searchlist.list.4.29906b98Cdb0Za&search=1

 

 

Thanks,. but ordering these things will take at least a week to deliver, and i'm in a hurry.

 

I have a multi meter. Any way I could do it using that?

 

I should add, I have plenty of appliances that are supposed to use 2A, and I can open them to measure internal

Edited November 23, 2020 by Susco

[sometimewoodworker]

13 minutes ago, Susco said:

I have a switching power adapter, which is supposed to output 5V 2A.

 

To check the output voltage is no problem, but how do I check if the current output is also actually 2A?

Buy one of these, but don’t forget that the device being charged will control the charge received/output.

Edited November 23, 2020 by sometimewoodworker

[Jan Dietz]

You will still need a way to load the power supply with 2 amps somehow. If you have a way to do that (lights, phone, random stuff) you can measure the amperage with the multimeter in series, and if you're happy you're drawing 2A, measure the voltage under load and see if it still is within specs.

 

(+) -- (Multimeter in Amp range) -- (Load)--- (-)

[impulse]

22 minutes ago, sometimewoodworker said:

Buy one of these, but don’t forget that the device being charged will control the charge received/output.

 

And don't forget that your charger may put out 2 amps during your test, only to overheat and catch fire 10 or 20 minutes later.

 

[Jan Dietz]

Then again 5V 2A (10W) is about nothing, and any switcher made in the last 10 years should easily do that without letting out its magic smoke.

 

[Susco]

2 minutes ago, Jan Dietz said:

Then again 5V 2A (10W) is about nothing, and any switcher made in the last 10 years should easily do that without letting out its magic smoke.

 

 

The adapter is functional for quite a while already, but they are rated a certain current for a reason.

 

My thoughts are that a 2A rated adapter may put out less for some reason, and in my case it is important that it doesn't, since it an Android device, and lower voltage or current may still enable the device to function, but mess up the operating system at boot up

[impulse]

9 minutes ago, Jan Dietz said:

Then again 5V 2A (10W) is about nothing, and any switcher made in the last 10 years should easily do that without letting out its magic smoke.

 

And yet, we occasionally read about people being killed by their chargers.  Whether that be sleeping on top the wire, or having the unit get hot enough to melt the plastic.  2 amps isn't much, but it's enough to smoke a tiny wire rated at 0.5 amps.  Which saves the manufacturer a penny or 2.

 

I was recently looking for a PWM LED dimmer on Amazon and one vendor offered a 30 amp rated unit.  Along with the unit, they offered a free bonus- 5 meters of 22AWG wire.  I passed on that one.

 

 

Edited November 23, 2020 by impulse

[Jan Dietz]

The only way for a power supply to limit current ("put out less") is to drop voltage. ( I = U / R ).

 

If your Android device is running and the voltage is still within a few percent of 5, it is putting out the 2A.

 

[impulse]

11 minutes ago, Jan Dietz said:

The only way for a power supply to limit current ("put out less") is to drop voltage. ( I = U / R ).

 

If your Android device is running and the voltage is still within a few percent of 5, it is putting out the 2A.

 

No longer true in these days of solid state Pulse Width Modulated (PWM).  They can still put out 5V into the load, but they only put it out for some fraction of the time.  The PWM chip that controls it can operate at a very high frequency.  And that chip can be in the power supply itself, or it can be in the device being charged.

 

[Jan Dietz]

If it's in the device being charged, you don't measure it in this scenario.

If it's in the power supply, you will measure average voltage, as the multimeter doesn't respond quick enough to show the PWM.

 

Anyway, for this to happen there will be additional negotiations between the device and charger, and the OP wants to discuss a SMPS, not a charger.

[impulse]

22 minutes ago, Jan Dietz said:

If it's in the device being charged, you don't measure it in this scenario.

If it's in the power supply, you will measure average voltage, as the multimeter doesn't respond quick enough to show the PWM.

 

Anyway, for this to happen there will be additional negotiations between the device and charger, and the OP wants to discuss a SMPS, not a charger.

 

The other name for a 5V 2A SMPS is "USB Charger".

 

[Crossy]

OK we have a 5V @ 2A power supply.

 

The output voltage will be 5V. 

 

The actual output current will be determined by the load, up to a maximum of 2A.

 

Once 2A is reached the power supply will do one of two three things:-

1. It will go into constant-current mode and reduce the output voltage to limit the current to 2A
2. It will "fold-back" and kill the output until it's reset (turned off then on again)
3. It will blow up and let out the magic smoke

 

[sometimewoodworker]

1 hour ago, Crossy said:

• It will "fold-back" and kill the output until it's reset (turned off then on again)
•  

Having watched BigClive test a variety of power supplies that is a very common mode, though the reset method is a little more simple and less drastic than turn off and on,

 

On increasing the load to to the over it’s output limit the current is clamped down to maybe 1A  but after the load is reduced enough the microcontroller in the SMPS allows the output to go back up. 

 

this performance is from memory and I would have to troll through quite a few videos and then the performance is only generally true and the 6 pin chip in the power supply could have custom programming.

[OneMoreFarang]

With any power supply it works like this:

Let's say you have a power supply which promises an out put of x Volt and y Amps (sample 5V 2A)

 

It's supposed to supply x Volts up to a load of maximum y Amps.

How much Amps is output depends on what is connected. If you connect i.e. a single LED then maybe it outputs 20mA = 0.02Amps - because that is what the load (the LED and it's resistor) wants.

If you connect a small light bulb then maybe that small light bulb wants 1A. The power supply will supply that.

And if you connect a bigger light bulb maybe that wants 2A. The power supply should do that.

Until now the output voltage should be more or less steady x Volt.

 

When you are connect anything that wants more than y Amps then one of the following will happen:

a) The power does that - at least for some time

b) It gets hot and will at some stage self destroy

c) It's "smart" and supplies maximum y Amp and keeps x Volt

d) It supplies i.e. 2.5A but the Voltage drops to 4 Volt - not good.

 

The y Amp is always the maximum amount of current which the power supply can deliver for a long period of time without getting too hot while keeping the x Volt.

You can connect anything that uses less than 2A without problem.

If you connect anything that uses above y Amp likely sooner or later there will be trouble - maybe hot destructive trouble.

 

[sometimewoodworker]

2 hours ago, OneMoreFarang said:

With any power supply it works like this:

Sorry that explanation is way too general and simplistic. There are common power supplies that do not work that way.
 

With the ubiquitous usage of a microcontroller in PSUs and the cheapness of programming them your explanation is only valid for PSUs that function that way, that certainly could be many but certainly is not all.

 

A very common mode is clamping the output down when the load is too high, no trouble.

Edited November 24, 2020 by sometimewoodworker

[OneMoreFarang]

21 minutes ago, sometimewoodworker said:

Sorry that explanation is way too general and simplistic. There are common power supplies that do not work that way.
 

With the ubiquitous usage of a microcontroller in PSUs and the cheapness of programming them your explanation is only valid for PSUs that function that way, that certainly could be many but certainly is not all.

 

A very common mode is clamping the output down when the load is too high, no trouble.

Yes, you are right.

The idea about my explanation was to tell a "normal" person how power supplies often work.

I didn't try to explain it to experts and I am sure there are many detail different in some power supplies.