How to get amps or Ma. to go through DMM ?

[petemoore]

  Been workin' at this one since I got a DMM.
 Haven't been able to detect current through it.
 Red lead into 10 amp max socket, black to common.
 Range set to all settings.
 Tried with motor, motor circuit is working 12vdc through motor.
 I don't remember having been able to measure amps or ma's.
 Having instructed others this is the way to do it and not hearing any complaints I figured I'd be able to make it work, there's got to be a goof here.

[twabelljr]

Silly question but, Did you open the circuit and put your meter in series with the circuit? Anywhere in the circuit is ok because current is the same throughout. Break the ground, put the red lead on the circuit side and the black lead on the battery or power supply side. Be careful or you may blow your meter fuse, if it is not already blown. The meter must be part of the circuit for current measurements.

[petemoore]

  spliced the DMM in an opening I created in the red wire [dual directional motor so no matter about polarity].
  Right after having run the motor, I opened the twisted red wire going to the red dot lug on the motor and spanned the openeing with the meter leads.
  I'm wondering if the current usage of the motor occasionally will pop a switching NPN.
  I'ts a little printer motor from Canon printer, perhaps the DmM can't measure a stepper motor.
  Bout time for a new DMM checker anyway.

[Gus]

When using a DMM set to current you need to keep a few things in mind

There should be a a fuse inside the meter that is in line with the leads to protect the meter.

When you have a circuit that should have a say a few ma draw you need to be mindful of the turn on current surge that might exceed the setting of the meter until it drops.  Example a large cap and a circuit that has a lower steady state current well within the meter setting.

There are ways to power up and not open the fuse.

[mattthegamer463]

A stepper motor required pulses to step, right? Your DMM probably only refreshes, at best, a couple times a second.  It won't see pulses.  You might need a data-acquisition oscilloscope for this, or some kind of purpose-built circuit.

[petemoore]

  I was thinking that also, along with it isn't turning and the TIP3055 controlling the motor circuit might make the meter at least 'hiccup'.
  For the time being it at least deserves a 'probably what it is'.
  Easy check for it is try current measuring an LED or whatever.
  I'll try that.

[waltk]

Just as a simple test, hook up a 9V battery in series with a 1K resistor - in series with your DMM in a ma range.  If it reads about 9ma, your know your meter is working.  If you get nothing, it's probably the fuse.

If your meter has a "capture min/max" kind of feature, it might be able to capture the pulse to the stepper motor.  (I guess it would depend on the sampling rate of the meter and the width of the pulse).

[Ronsonic]

This works on Fluke meters, probably on many others. To see if the fuse in the amperage circuit is good set the unit to Ohms and using the regular lead in the Volts/Ohms position touch it to the contacts in the Amp and milliAmp jacks, you should get a very low ohms reading. If you get open the fuse is blown.

[Rob Strand]

+1 on ronsonic

Usually if you use the current range and there is no reading the internal current protection fuse is blown.  There can be one or two fuses.  Different meters will behave differently with blown fuses.  The typical sign of a blown fuse, whatever the meter's behavior, is 000 reading.

If you replace the fuse make sure you use the correct fuse speed and type.  If it has ceramic body replace it with a ceramic body (these are high rupture capacity HRC fuses).   

Typically in use,
- you use the normal +/com terminals for 200mA range, setting the meter to the 200mA scale
- you use the normal 10A/com terminals for 10A range, setting the meter to the 10A scale.