Multimeter amps problem

[e44-72]

Hello there

I measure volts all the time with my DMM and ohms. I know when measurig volts your put it across (in parallel) with the component and for amps you need to put it in series.

I wanted to see if I could measure the amps of a 12v amber led, so I connect positive to the anode of the led then the cathode to the probe and the other probe back to neagative.
The negative probe is in common and the positive is in volts, ohms, mA (200mA max). I set it to 200mA on the rotary switch and noting happens, led does not light and no reading on meter.

I also did the same for a 12v bulb and a motor, same problem occurs.

Is this because the fuse in the meter might of burnt out or I am doiong something wrong.

Any replies I am grateful for.

 

[colin55]

The 200mA fuse is blown

 

[Jaguarjoe]

I don't understand how you are using 3 leads. Your first sentence explains it......amps you need to put it in series. Current from the (+) terminal of the power source goes to the (+) probe of the DMM. The (-) probe of the DMM goes to the (+) terminal of the load. It's all in series. The (-) terminal of the load connects to the (-) terminal of the power supply. There is no third lead.
DMM fuses are very easy to pop and quite pricey. One $11 error teaches a lifelong lesson!
Always start on a very high range and dial down to a reasonable one.
If your DMM can not read high enough, you can use a current shunt, or current sensing resistor in the loop. The big parts houses sell them fairly cheap. Use ohm's law to work out the value of it, or pick a standard value and calculate the voltage across it. Be mindful of the power dissipated and use a shunt/sensor of at least twice the wattage dissipated. I grew up using 2.5-3X

 

[KeepItSimpleStupid]

I'm having a hard time interpreting just what the OP tried to do.

However. MOST if not all DMM's use a separate connection for measuring current. The Fluke 77, for instance has two. One for less than 300 mA and one for 10 Amps.

Your LED probably doesn't require a series resistor, however it might.

The meter should be in series with the power supply. Check to make sure your using the right terminals.

 

[e44-72]

Thanks for replies

Sorry if I confussed you Jaguarjoe, not three leads, a wire from positive of power supply to load (led) then the meter in series back to negative. As you said but I did it with the meter in series after the load as apose to before as you described. The third your thinking of is just a wire not a probe lead. image of i what I mean below.

 

[e44-72]

On my dmm there is one for 10A as well as the one for up to 200ma. I would not think my led would draw anything near an amp more like 8mA, thats why I used this instead of the 10A terminal

 

[Roff]

An LED without a current limiting resistor is basically a short circuit on a 12V supply. Your fuse probably saved your LED. You must have a series current limiting resistor, unless the LED package has an internal one.

 

[Dean Huster]

This would be the first DMM I've heard of that DIDN'T have a separate jack for measuring current. Even my ancient Heathkit IM-102 had a "third jack" for current.

RON!! Where've ya been? Haven't heard from you for a while. Is retirement as great as you were hoping? At least your ticker is still ticking, huh?

 

[Roff]

Dean - check your PMs.

 

[e44-72]

The led was run on 9v, pp3 battery and it does have an integrated resister in the led, Thank you roff and others for your help.

So why is it the fuse would blow on the 200ma port when leds don't draw anywhere near that much current.

 

[Roff]

The led was run on 9v, pp3 battery and it does have an integrated resister in the led, Thank you roff and others for your help.

So why is it the fuse would blow on the 200ma port when leds don't draw anywhere near that much current.

Is this the first time you have used you meter to measure current? If so, you could have burned out the fuse a long time ago while trying to measure voltage. If you really only have two jacks on your meter, just setting it the switch to current accidentally while having the probes connected across a low impedance source could have done it.

 

[Reloadron]

A picture of the meter or maybe Make & Model # would maybe help? As Ron mentioned, the fuse could have cooked long ago and gone unnoticed.

Ron

 

[KeepItSimpleStupid]

Just take the meter apart. Look for the fuse. If it's obviously broken, your done.

If not, reassemble the meter without the ammeter fuse and test with the ohmmeter.

If it tests bad, it's bad. If it tests good, it may not be. I had that happen to me twice in my life time, so far. The fuse would open only under load. It would test OK with an ohmmeter.

 

[e44-72]

My multimeter is a UNIT, UT30B meter.

Thank you for your replies, as roff said I may have at some point accidentally put it in amps testing while testing voltage. I will open it up and take a look at the fuse. The fuse required is givern in the manual for the meter.

Thanks for the replies

 

[tvtech]

My multimeter is a UNIT, UT30B meter.

Thank you for your replies, as roff said I may have at some point accidentally put it in amps testing while testing voltage. I will open it up and take a look at the fuse. The fuse required is givern in the manual for the meter.

Thanks for the replies

Good for you...and good luck. I hope you learn't something here on this great Forum

Cheers,
TV Tech

 

[colin55]

Just solder a single strand of wire from hook-up flex across the ends of the fuse.