multimeter help

[testas86]

hey i got 2 of these multimeters and the voltage reads find but i cant get anything with the amps, it flashes for a second saying around 1 amp then goes to 0 am i just using it wrong? any help would be great thanks!

[selldoor]

Re: multimeter help

Try google??

securitest pro meter instructions

[testas86]

Re: multimeter help

on the site all i get is this which doesnt help

http://www.idealindustries.com/prodD...?prodId=33-892

[vinceroger69]

Re: multimeter help

ignore same link you found

[stj]

Re: multimeter help

what the fuck are you doing?
you dont set a meter to Amps and short a psu with it!!!!!!!

that could trash the psu or meter or blow the meter fuse!

[selldoor]

Re: multimeter help

Ok well it is some help, bearing in mind we have no idea what you are doing.
If we assume you have the leads in the correct sockets there is are 3 manual settings for current testing so I think you should have it on 10A.?
If you have I guess where you may be going wrong is that you are testing a portable dc power supply which may be rated around 4A ? You havent given us many clues.

I believe that these type of psu only output the amperage required by what it is connected to. So connect to a portable hard drive say 2A and it will output 2A- connect it to a TV it will output say 4A. and so on up to its maximum.

Try testing the amps with a load connected

[stj]

Re: multimeter help

let me explain how the current function works,
you conect the meter in between the power source and the device being powered.
as if the meter was a fuse.

it then reads how much power is flowing across the leads.
you DO NOT put it across the power source.

[selldoor]

Re: multimeter help

Here is a youtube - using a simple meter but the same applies to yours

http://www.youtube.com/watch?v=7lwZkl0yBqA

[testas86]

Re: multimeter help

Ok well it is some help, bearing in mind we have no idea what you are doing.
If we assume you have the leads in the correct sockets there is are 3 manual settings for current testing so I think you should have it on 10A.?
If you have I guess where you may be going wrong is that you are testing a portable dc power supply which may be rated around 4A ? You havent given us many clues.

I believe that these type of psu only output the amperage required by what it is connected to. So connect to a portable hard drive say 2A and it will output 2A- connect it to a TV it will output say 4A. and so on up to its maximum.

Try testing the amps with a load connected

its a 1 amp output sorry i though i included that photo and yes i had the meter set to 10 amps unfused. so if thats not how you test the output amps of a PSU then how do you test them? i have tons of PSU that i need to test to make sure they are putting out what they rated at before i can connect them to any devices.

[stj]

Re: multimeter help

energy doesnt work that way.

the rating on a psu is how much you can pull from it without it overheating or blowing up.
they dont "push" power out.

if you want to stress them you need a variable load - maybe a reostat.
but your only risking the psu's because your going to be winding up the load till they do something bad.
and it's not much use to know that a 4a psu can go to 4.8a if you blew it up in the process.

you also need 2 meters.
one to watch the current your pulling,
the other to watch the voltage incase it suddenly jumps or more likely drops.

[mariushm]

Re: multimeter help

So to recap.

A power supply produces energy on its output which is defined by voltage and current.
The rating on the power supply is simply saying that the power supply is designed to be able to output up to that much current to a device connected to it.
You can't measure with a multimeter the maximum current in a simple way, you have to attach something to the power supply that will "eat" energy and connect the multimeter in the circuit to measure the current.

So you measure voltage by putting the multimeter on Voltage and one lead on + and one lead on -
You measure the current by placing the multimeter in series with the power supply :

power supply + -----> multimeter probe black ---> multimeter ---> multimeter probe red ------> + device - -----> power supply -

In order to measure how much power supply is capable of, you have to measure voltage AND current at the same time.
As the device starts to consume more energy, some power supplies slowly lower the voltage so that the total output stays below a certain level.
For example, the power supply in your picture is saying on label 12v 1A, which would imply it's designed to output up to 12v x 1A = 12w.
However, if your device needs 1.1A, the power supply may lower the voltage to 11v in order to keep the total power below 12w (11v x 1.1A = 12.1w).
Other power supplies are overrated, they could in practice only be capable of 8w, so when your device goes above 0.75A, the voltage may go down all of the sudden.


You need a device that would eat up that energy. You could build or buy an electronic load, but if you're not good at electronics or don't feel like paying, you can fake it.

If you want to test a 12v power supply, you could simply buy a few 12v light bulbs. By adding bulbs in parallel, you increase the power drawn from the power supply.
Search for such bulbs at a cars/motorbike store, you'll find plenty. Even on amazon there are many.

For example, here's one rated for 12-14v 1watt : http://www.amazon.com/Eiko-40478-Min...dp/B002CYUADE/

1w/14v = 0.07A so one of these lightbulbs will consume about 0.07-0.1A from your power supply. Now you can add one bulb at a time to the circuit (put bulbs in parallel) and with each step, the power supply will have to deliver up to 0.1A more current to the circuit.

There's also 3w lighbulbs : http://www.amazon.com/Eiko-40304-Min...dp/B002CYS8MY/ 3w / 12v-14v = ~ 0.21-0.25A for each bulb

Another method is to use resistors, which are basically lightbulbs, same thing. Lightbulbs have the resistive element inside a bulb and it gets so hot it produces light, resistors have the filament inside a cement or epoxy body and doesn't produce light.

You can put a resistor between + and - of the power supply and that resistor will consume power.
You have basic formulas : voltage equals current times resistance and power equals current squared times resistance ( V = IxR , P = IxIxR )

So let's say you have a 27 ohm resistor rated for up to 7w of power.

voltage (12v) = I x R (27 ohm) , therefore current I = 12v / 27 ohm = 0.444 A
The power dissipated in resistor is P = 0.444 x 0.444 x 27 = 5.33 w

So a 27ohm 7w resistor (cheap, you can get 5 for a dollar or something like that) is equivalent to a 12v 5w lightbulb.

If you want finer control, you increase the resistance value.
For example, 100 ohm means I = 12/100 = 0.12A , P = 0.0144 x 100 = 1.44w so you buy a 100 ohm 3w rated resistor (the rating of the resistor must be above the power dissipated in resistor otherwise resistor breaks down) and you basically have a 1.5w lightbulb

[budm]

Re: multimeter help

I had a guy trying to find out if the AC OUTLET is puttIng out 15A or not by hooking up his meter setting to AC amp, should have seen what happen! It blew up and he blamed it on the meter. Basic knowledge is a MUST.

[stj]

Re: multimeter help

too bad he wasnt testing a 415v 3phase 63amp outlet with a friend recording it.
it would have been a smash on utube.
probably better than the guy dropping a steel bar across a car battery!!!!!