1
\$\begingroup\$

I have a cheap multimeter called "Branford" and I would like to measure the current used to charge a phone. As a power supply, I use a DC generator, which I rotate by hand. Then I have a DC/DC Step Down Converter to get constant 5.2V. Then I use the power to charge the phone. It works perfectly fine and the phone is charging as it should.

However, I would like to see how much current goes through, but I get very small values. I think I'm doing something wrong, because I'm a noob in this field, therefore I would like to ask if what I am doing is correct. The multimeter front panel looks like this:

enter image description here

and the connections are like in the picture below. I've been looking around the internet and it looks okay, but considering that the multimeter is not the same, I would expect that there might be some other set-ups.

enter image description here

As you can see, I get that 0.7 (A?) which stays constant and that is where the suspicion starts. I also tried to turn the knob to the "20A" option, but there is no change. The generator has the following specs:

  • Output voltage: 5V-24V
  • Max load voltage: 40V
  • Max output current: 1500mA
  • Max load power: 20W

So, can anyone help me to figure out if it is the measurements that I'm doing wrong or the generator can't deliver more?

\$\endgroup\$
2
\$\begingroup\$

If you use the "20A" socket, the meter must be set to "20m/20A" for a correct reading. If the switch is set to any other position, the reading (if any) may or may not be meaningful.

Since you say you read 0.7 in both the 20m/20A and 200m positions, I expect the current is really 0.7 Amp. That is a reasonable current for the phone to draw when charging. The charging current will vary, depending on the state of charge of the battery, and can be limited by the charger circuit in the phone.

\$\endgroup\$
1
\$\begingroup\$

Note the mA socket is on the right and dial has only 1 position for 20Adc and another for 20A Ac (~) using left jack.

You will want to test Vdc shunt when charging vs RPM then Idc in series vs RPM. Count revs/minute and record results! Then report here.

\$\endgroup\$
1
\$\begingroup\$

You're using the wrong jack on the meter.

The jack labelled "20A" is ONLY used when the range selector is in the 20A position.

For all other current ranges, you should have the red plug in the "->|-ΩmAV" jack on the right.

\$\endgroup\$
  • \$\begingroup\$ In this case, since the current appears to be 0.7 amps, the OP should not use the mA jack since it is fused for only 200 ma. \$\endgroup\$ – Barry Dec 16 '17 at 0:51

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.