finding out the amp usage of a part

You need a multimeter that measures current. Disconnect the power supply line going to the Peltier Cooler and insert the multimeter in series with the Peltier cooler. Some multimeters do not measure current, so your may not be able to. Having said that, it is a fairly common measurement and most multimeters do have the ability to measure current.

Have a look at this multimeter:

http://www.newark.com/fluke/fluke-87-5/digital-multimeter-dmm-handheld/dp/96H6287

You can see there are four ports on the bottom. One is ground or common, one is for voltage or resistance measurements, the other two are for different scales of current measurement.

Follow this:

thank you your diagrams were great i didn't add the meter in series silly mistake

Another way is by measuring resistance, and doing some math.

Someone corect me if i am wrong, it has been a while sence i took my law exam, but.

If you put your meter into the ohm setting, and with no power on, and the device unhooked from other circuts,

take the two meter probes and get a reading of the ohms that it has.

than using the middle formula, Take your voltage, (12) I am guessing and divide that into the Resistance (50) "Just using 50 as an example, i have no idea what it really will be".

And you should have amps, ( 12/50=.24 amps.....) Just using as an example!!!

TADA!

hope it helps.

i will give this ago in the morning great help thanks guys

Gotta part company with you on this idea, Lupe.  The Peltier cooler acts like a diode rather than a resistor.  The Peltier cooler isn't linear and so Ohm's law cannot be applied well.

You gotta do what the other guys said and break the circuit and insert the ammeter.

"The ideal voltmeter has infinite input impedance.

The ideal ammeter has zero input impedance."

Well, i understand, but than we have another proble.

From Shanes origional post, the pelter is overloading his available power supply.

"Hi all,

im working on the camping chair rebuild and i have came acroos some issues with the electronics im not sure if there a problem on my part or on the parts side.

firstly i hooked up the fans and smoke detector tothe psu and to a 12v 500ma power supply everythink worked fine the fans were running at half speed due to the fans both trying to use 500ma each so i then unhooked this and attached the peltier to the psu... this is where the problems started.

firstly the led on the psu was flashnig and there was a humming comming from the psu i hooked a temp monitor up to the cooler and i noticed it wasnt cooling i then tested the voltages the smoke detector was 5v and the cooler was only at 9.8v i had believed that the peltier was 12v.

so i hooker the coller up to the 12v supply and hey presto the cooler dropped from 20 celcius to 15 in about a minute this was a dry run with the probe on the heat sink then problems again the power supply failed so i am guessing that the peltier uses more than 500ma?

anybody have any ideas?

and if ben happens to read this i would greatly apreciate  the volts of the peltier as i cant read the peltier because someone epoxied it inplace

shane"

In which case, i don't think the ammeter will work ether.

Example: If i have a circuit that requires 1.5 amps, and i have a supply that will only supply 1 amp, will the meter only read the 1 amp of current flowing through the circuit?

If the OHM  meter wont help, than the only other thing i can think of is to place a known resistance in series with the peltier, and measure the voltage drop difference between the the resistor than calculate the amperage that way?

I am trying to help.

The current rating on a power supply tells us the amount of power we can hope to get out of the supply without harm.  For a moment, depending upon its design, it may supply more.  If the supply features foldback limiting, it will just drop the output potential when challenged.   Ammeters can read the amount of current they are rated for.  Except that it can be a little lossy, inserting a series resistor to measure the drop and infer the current will work fine.  A ten Siemens conductor would probably work fine, provided it could handle the power.  Hall effect current sensing is also a possibility.  Sensing based on magnetic saturation is a possibility at higher current densities. 

Our inquirer should find himself a larger PS.  It is perfectly okay to use a PS rated for more current than needed.  In a hot environment, if might even be a good idea.

I think that's his goal, finding out what size power supply he needs for the circut.

So he can buy the supply he needs.

But he don't know the requirement of the circuit.

Peltiers are notoriously power hungry. If he has a variable power supply he could start at a low voltage and measure the current at successive points inorder to graph the power curve of the peltier. If his ammeter or power supply can't handle the full draw at the 12 volts he can interpolate the graph in order to estimate the current at the 12 volts. As Don pointed out don't expect the graph to be a straight line.

John

ok that was a lot of reading to wake up to I'm going to see if i can find a better power supply with more amps to test again i don't have a variable bench power supply i will be looking into getting one of these I'm currently using left over power supply from previous projects and devices I'm going to go out on a limb and look for a 2 amp power supply as both of the parts run on a 1200ma power supply so hopefully 2 would be more than enough think i might do my electronics at college after christmas i need a brush up