Weird voltage readings

Other Hardware General Electronics
1

Hi！

I bought an Arduino power adapter on Amazon. According to the label, it outputs 9V, 1000mA. I connected it to the DC jack, then tried measuring the voltage between the 5V pin and GND on the Arduino Mega—it showed 6.75V. That seems really off, right? What could be causing this?

Thanks in advance!

2

Please post a link to the adapter that you bought.

3

Probably just no-load voltage.

4

If you are reading 6.75 volts between the Mega's ground and 5V pins, my first second thought would be that that Mega is toast. That's measuring the output of the onboard 5V regulator, not your adapter.

What should have been my first thought is what @LarryD writes below.

5
  • Make sure the batteries in your Meter are good.
6

And that should have been my first thought, as I've been bitten by that one before!

7

The multimeter should be fine—I tested it on other Arduino boards and everything looked normal.

8

But this board still works just fine.

9

Time to buy a new Mega?

10

This is the power adapter I bought. After testing, the adapter turns out to be working fine, so it’s probably the board that has an issue.

11

But the board still works fine. I'm still using it to control five stepper motors and everything runs fine. Do you think I should still get a new board?

12

It shouldn't.

bild
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0.75 V isn't much, but it can damage the MCU partially and it'll show later. Besides, manufacturers don't encourage to use Maximum ratings at all.

13

It seems more probably to me that the figure "6.75V" is not correct.

Could you show a clear picture of your measure process, such that the multimeter, arduino and connections are visible?

15

I directly connected the power adapter to one Mega board, then used a multimeter to measure the voltage between the 5V pin and GND—it showed 6.75V. Then I tried two other boards: one showed 4.97V, and the other 5.05V.

16

Sounds like a broken voltage regulator. The two others are good.

17

So even if the voltage regulator is broken, the board can still run normally?

18

Sorry to asking that - are you sure you know how to use a DMM?
Did you measure it in a DC voltage mode?

that was the reason why i asked for a photo

19

No worries, feel free to ask anything. I'm pretty sure I didn't use the multimeter incorrectly, because I also measured the other Arduino boards I have, and those readings were normal.

20

Power the Mega with a 5volt cellphone charger, connected to the USB socket.
That bypasses the built-in 5volt regulator of the Mega.
Leo..

21

Hello why don´t you try to Read the voltage By a Multimeter?

Carefull with general VCC PowerSupply