1
\$\begingroup\$

Newbie to electronics here.

I have a simple circuit consisting of just a 9V battery and an 820 ohm resistor. I was trying to measure the current with a multimeter (by opening the circuit between the positive battery terminal and the resistor and placing the leads in there.) According to my calculations, the current should be 0.011A = 9.2v / 820ohms.

My ammeter is reading values anywhere between 0.030A and 0.200A. I'm assuming my multimeter is faulty, but could it be something I have done wrong or is there a way to fix it?

the open circuit

the multimeter showing the reading When I set the range to 20m the meter reads 1.

instructions on how to read current

I'm making the connection just by touching the clips onto the wires, making sure to not touch any wires with my fingers. And the resistor is reading 810ohms. I've tried two different batteries in the multimeter, both fully charged. The voltage across the battery terminals measures 8.64v while the circuit is closed and the current is flowing.

\$\endgroup\$
7
  • 2
    \$\begingroup\$ How well are you making connection? Alligator clips and battery holders can be handy to get good connections. The battery has internal resistance too so you have to re measure voltage while the current is flowing if you want the numbers to really match up. \$\endgroup\$
    – K H
    Jan 31 '21 at 12:33
  • 4
    \$\begingroup\$ Post a photo of the setup showing the meter switch, display and sockets. We might spot something. \$\endgroup\$
    – Transistor
    Jan 31 '21 at 12:33
  • 6
    \$\begingroup\$ Are the probes in the right sockets on the multimeter and is it set to the correct range? Have you confirmed the resistor by measuring it? \$\endgroup\$ Jan 31 '21 at 13:11
  • \$\begingroup\$ I've added photos and some more info in the question. \$\endgroup\$
    – Ricardo
    Jan 31 '21 at 15:15
  • 2
    \$\begingroup\$ No, it's on hold in the picture because I couldn't take a pic and hold the leads on at the same time \$\endgroup\$
    – Ricardo
    Feb 1 '21 at 12:04
0
\$\begingroup\$

That meter is switching the current being measured through the rotary switch contacts. These are sprung wipers that brush along the main PCB.

enter image description here

Figure 1. Inside of The World's cheapest multimeter.

You may be able to resolve the problem by rocking the switch back and forth. Disassembly and application of switch contact cleaner would be a better treatment.

\$\endgroup\$
6
  • 3
    \$\begingroup\$ The best treatment would probably be getting a less cheap multimeter. \$\endgroup\$
    – Hearth
    Jan 31 '21 at 15:16
  • \$\begingroup\$ If I put the dial half way between the 2m and 20m ranges, I get an accurate reading of 0.01A. \$\endgroup\$
    – Ricardo
    Jan 31 '21 at 15:45
  • \$\begingroup\$ That's probably a 10 A range reading so it's useless as the meter will have probably +/- a couple of least significant digit error. Once you're happy it's actually an 820 ohm resistor switch to 20 mA range and take a reading. \$\endgroup\$
    – Transistor
    Jan 31 '21 at 15:48
  • \$\begingroup\$ I am happy that it's an 820 ohm resistor and the ammeter reads 1 when in the 20m range. I've corrected a typo about that in the question. \$\endgroup\$
    – Ricardo
    Jan 31 '21 at 23:30
  • \$\begingroup\$ @Ricardo, I see you've updated your question to indicate that you're getting a 1 "Overrange" indication at 20 mA. That either means that you're doing something wrong or the meter is "banjaxed" as we say in Ireland. (You can guess the meaning.) the meter should be reading 10.9 mA. I think you should unaccept my answer until you sort it out. \$\endgroup\$
    – Transistor
    Jan 31 '21 at 23:31

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.