Incorrect amps showing on multimeter?

In summary, the conversation discusses the creation of a circuit with 3 volts, a 330 ohm resistor, and a red LED. Using Ohm's Law, the expected current is calculated to be 9 mA, but the multimeter shows only 3 mA. This discrepancy is attributed to the voltage drop across the LED, which can be calculated using the current and resistance values. To make the LED brighter, a higher current is needed, which can be achieved by using a smaller resistor.
  • #1
jdmmade
5
0
Okay so here's what I am dealing with. I created a circuit with 3 volts and used a 330 ohm resistor and a simple red LED, and using my multimeter I tested for the current. Now using ohms law:

3/330 = 9 mA... now what I see over the multimeter is 3 mA. I must have calculated something wrong or something is different with in the circuit. Maybe because a load is there, the calculations totally change?
 

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  • #2
There will be a voltage drop across the LED.

You can calculate it like this:
Current in 330 ohm resistor = 3 mA or 0.003 amps
Voltage dropped across 330 ohm resistor = iR = 0.003 * 330 or 0.99 volts. Call it 1 volt.

So the voltage across the LED is 2 volts (3 - 1 is 2) . Diiferent coloured LEDs have different voltage drops.



So, to make the LED light up a lot brighter, you need to send more current through it.

Let us say 15 mA. So we need a resistor that will drop 1 volt when it has 15 mA flowing in it.

This is R = 1 volt / 0.015 amps = 66.6 ohms. You can get 68 ohm resistors and that would be OK.
 

Related to Incorrect amps showing on multimeter?

1. Why is my multimeter showing incorrect amps?

There are several possible reasons for this. It could be due to a faulty multimeter, incorrect settings, or a problem with the circuit being tested. Make sure to check all connections and settings before assuming the multimeter is at fault.

2. How can I fix my multimeter if it is showing incorrect amps?

If the issue is with the multimeter itself, it may need to be recalibrated or repaired. Consult the manual or contact the manufacturer for instructions on how to do this. If the problem is with the circuit being tested, troubleshoot and fix any issues with the circuit to get accurate readings.

3. Can weather or external factors affect the amp readings on a multimeter?

Yes, extreme temperatures, humidity, and electromagnetic interference can all impact the accuracy of a multimeter's readings. It is important to use the multimeter in a controlled environment and shield it from any external influences.

4. What is the range of amps that a multimeter can measure?

The range of amps that a multimeter can measure varies depending on the model and brand. However, most multimeters have a maximum amp range of 10-20 amps. It is important to check the specifications of your specific multimeter to ensure it can measure the amps you need.

5. Is it possible for a multimeter to show negative amps?

Yes, it is possible for a multimeter to show negative amps. This typically occurs when testing a circuit with alternating current (AC). Negative amps indicate that the current is flowing in the opposite direction than expected. This is a normal reading and does not indicate an issue with the multimeter.

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