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Digital Multimeter Failed To Measure DC Current or Resistance. Is It Broken?

Digital Multimeter Failed To Measure DC Current or Resistance. Is It Broken?

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  #1  
Old 12-22-14, 10:03 AM
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Digital Multimeter Failed To Measure DC Current or Resistance. Is It Broken?

My digital manual-range multimeter is several years old. I used it frequently to check the voltage of batteries and house AC outlets, without problem.

Recently I want to measure DC current of a battery driven motor. I used an electronic kit that has snap-on parts. I set up battery, switch, and connectors on the snap-on board. With connector, the motor runs correctly. Then I take away the connector, put the two electrode of the multimeter on the two ends that used to be snapped to the connector. To my surprise, there are no reading on multimeter, and the motor does not run.
The battery pack has 2 AA batteries. That is 3V. The motor is rated 3V, and the labeled current is from 40 mA to 70 mA. I set the range on multimeter to 200mA DC current.
I tried to place the snap-on resistor parts in the place of the motor, and tried to measure any current from my multimeter. I cannot.
I also tried to measure resistance directly on those snap-on resistor parts, without success.

When I tried to measure the voltage around the resistors or motor, I got stable readings. So the voltage measurement of this multimeter is working.

Is there any obvious mistake that I made?
If my multimeter is broken, is there any reliable and affordable multimeter available, from Radioshack or Amazon?
 
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  #2  
Old 12-22-14, 10:23 AM
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A picture of the meter would be helpful. Many have an internal fuse to protect against trying to measure too much current.
 
  #3  
Old 12-22-14, 10:59 AM
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I already looked inside the multimeter.
I did remember seeing a small glass cylinder that looks like an ordinary fuse.
I will double check later.
Thanks!
 
  #4  
Old 12-22-14, 11:07 AM
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@easygoing> "Then I take away the connector, put the two electrode of the multimeter on the two ends that used to be snapped to the connector."
This sounds like you connected the meter across the two leads to the motor and not in series with just one lead.

Bud
 
  #5  
Old 12-22-14, 12:04 PM
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Hi, Bud:
I connected my multimeter in series to the motor.
Before I used a snap-on wire connector as one link in the circuit, and tested that the motor runs correctly. Then I took off this snap-on wire connector, use the two electrode of the multimeter in place of this snap-on connector.

@easygoing> "Then I take away the connector, put the two electrode of the multimeter on the two ends that used to be snapped to the connector."
This sounds like you connected the meter across the two leads to the motor and not in series with just one lead.

Bud
 

Last edited by PJmax; 12-22-14 at 07:44 PM. Reason: removed board added link
  #6  
Old 12-22-14, 01:42 PM
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Your description still isn't sinking in, but as long as you are sure you have it in series. The next question is polarity and I'm not sure if your meter cares. My analog meters require correct direction of current flow.

Does your meter have one or two batteries? My analog has 2 and sometimes one will fail before the other. What model is your meter?

Bud
 
  #7  
Old 12-22-14, 07:47 PM
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With an analog meter the batteries are usually only used for the resistance section.

Your meter has a blown protection fuse. Maybe not today but at some point voltage was put on meter with it in the amps section. We've all done it.
 
  #8  
Old 12-23-14, 04:42 AM
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Thanks PJmax for pointing out the possibility of blown fuse.
I found a miniature ceramic fuse on this Radioshack digital multimeter (Cat. No 22-810). The labels are "50CF(UL)" and "250V315mA".
On the back of the case, there is this warning:
"For continued protection against fire, replace only with fast blow 315mA, 250V, 20mm Fuse."
I will buy a fuse and try it again.
 
  #9  
Old 12-28-14, 08:31 PM
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Problem Solved: Replacing the Fuse Makes Everything Working

Ordered some very affordable ceramic fuse from Amazon. Took several days to deliver. The fuse is of very low quality. The two caps are not aligned straight with the ceramic tube. But it works!
Thanks everyone who gave me advice!
 
  #10  
Old 12-29-14, 03:15 AM
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Thanks for letting us know the outcome.
 
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