laptop charger testing

[moss99]

Hi all
I have an asus laptop on which the charger broke i got a new one and wanted to check volts and amps were ok tested volts fine (19.2) but cant seem to get a stable amp reading i am using a fluke 77 iv meter and the bar at the bottom go's right up to max then back down again
any help would be great
thanks..

 

[KJ6EAD]

That sounds like you're overloading the meter. Do you have it connected in series with the load with the leads connected to the correct terminals on the meter?

 

[moss99]

i just had the test probes in the dc jack center positive red lead to 10A socket black to com and meter set to ( not milliamps)
thanks for reply
mark..

 

[KJ6EAD]

i just had the test probes in the dc jack center positive red lead to 10A socket black to com and meter set to ( not milliamps)
thanks for reply
mark..

I'm having trouble understanding your meaning since you don't form sentences with correct capitalization and punctuation.

 

[moss99]

Terribly sorry didn't realise I would be scrutinised on my grammer on this forum.
Ok I have the red test lead in socket 10A on meter, black lead in socket com on meter .
The meter is switched to A .
Test probe (black one ) connected to dc jack outer test probe (red one) connected to dc jack inner .

I hope this makes it easier for you to understand , english was my worst subject at school .

 

[KJ6EAD]

That's what I was afraid of. You've got your probes attached to the power supply in parallel so the current will always read as an overload on the meter. Current measurement must be done with the probes connected to the circuit under test in series. See page 8 in the manual.

http://assets.fluke.com/manuals/77iv____umeng0000.pdf

P.S. It's sentence structure, not grammar. We all are scrutinized on our ability to communicate in all aspects of our lives whether we like it or not. I was blessed/cursed to grow up with a father who was a remedial reading instructor and had a degree in semantics. He was kind of the American version of Professor Henry Higgins.

 

[jackorocko]

no one here is trying to scrutinize your grammar, but if you want help then you will need to communicate so that people can understand what you are trying to say.

Why do you want to check that the new power adapter? If it was made for the laptop then it shouldn't be a problem. If you was worried about it being a piece of crap because it came form china, then why didn't you buy it from asus?

Also, wouldn't the power adapter need a load before you can measure the amperage?

edit: nm, kj hooked you up with the appropriate information.

 

[davelectronic]

Testing charger psu

Hi moss99.
It sounds like your meter leads are correct on the meter, red + to 10 amps DC socket, black to common - volts socket, use a load to measure a current, a lamp 10 watt halogen will do, establish + and - volts on the chargers jack plug, once you have done that make up a series circuit where the red meter lead is at the highest potential to + volts on the supply's jack, then wire your lamp between the common - volts, one end lamp on this lead, then other lamp lead to common on the jack, read the measurement, and do the maths to check if you want.

Expect some tolerance if you do the maths, + or - % in power, lamps are none critical for power.
Dave.

 

[Resqueline]

It sounds like your meter leads are correct on the meter, red + to 10 amps DC socket, black to common - volts socket,

That is correct for the meter itself, but if connected straight to the supply it constitutes a short-circuit for the supply, which then starts pulsing in order to protect itself.
I'm saying it just for the record, to prevent any misunderstandings. I misinterpreted the statement the first couple of times I read it.
The rest sounds ok to me. In essence, measuring Amp's has to be done in a series string with a load. Polarity is not important for digital meters though.

 

[davelectronic]

measuring polarity

No polarity not to important in a digital multi meter, as the reading will give the same, but if reversed polarity this will show on the display - showing negative orientation, if you get in the habit of connecting the meter in series, one is you wont be head scratching looking at the display, and secondly if you ever use an analogue meter, this reverse of poles will blow the meter fuse, or worse damage the moving coil, needle, good practice positive to the highest potential + volts for a series reading in amps.
Dave.
PS don't forget a load of some kind, lamps resistor, other.

 

[Resqueline]

I'll bet that many won't even notice the - in front of the numbers.. But in battery circuits involving charges it's useful to keep track of which way the current flows.
Negative polarity won't in itself damage analog meters, but it prevents you from seeing if you're overranging it, so as a secondary cause it could still be damaged by that.

 

[moss99]

Hi guys thanks for all the replies very helpful so basically it needs to be supplying a load , I assumed the meter would be the load .
As for why I wanted to test it, it was not a genuine asus one although it was not a £5.00 ebay one either but I still wanted to test volt / amps for my own peace of mind ( arent asus made in china anyway) & i am trying to learn a bit about electronics (complete beginner if you hadn't noticed LOL )
sites like this are a real benefit ..
thanks again all

 

[Resqueline]

Yep, that's right. But you actually had a load there, only a zero ohm one instead of 4 ohms (or more, depending on the power rating of the supply).
If you had been testing a laboratory power supply that way it would have delivered a steady current of whatever it was set to, but laptop supplies are different.
In your case a 24V 55W headlamp could have been a suitable load, but you still wouldn't have needed to measure the exact current, only the voltage.