[SOLVED] My multimeter reads double the AC voltage

Thread Starter

JimmyB491

Joined Mar 23, 2024
5
Hi. I build computers as a hobby and am new to the electronics direction. Thank you in advance for the help. Here's my problem. I'm installing an actuator to have my screen unhide from the back of my test-bench computer and need a 12-volt power source to activate it. So the yellow wires from my computer's power source supposedly provide the 12 volts that I need to fashion a connection from one of my unused graphics card connectors to the actuator control, so there is no issue there, but when I test the voltage with my multimeter it registers 25v which is double. I've checked other computer connectors such as the (5v USB port which shows 10v). My (3v connection displays 6v). Everything seems to work fine but the voltage seems to be double. Now when I test my 120v house outlet it tests 120v correctly. My tester is a cheap one (the voltage setting options are only 200 & 600v, so I use the 200 setting). I plan to replace it ASAP, but can you please explain what is happening? I don't want to fry my actuator or have it propel the screen across the room...LOL, by hooking it up to double-voltage.
Thanks so much again for your help
JimmyB
 

dl324

Joined Mar 30, 2015
16,988
Welcome to AAC!

Have you checked the battery? Does the meter have a low battery indicator?

Since you're new to electronics, you should pay attention to conventions. Volts is abbreviated V. When we see V by itself (e.g. 10V), we assume DC. When you talk about line voltage, that's AC and the convention would be to say 120VAC.

Also being a newbie, you should be careful probing lethal voltages.
 

MrChips

Joined Oct 2, 2009
30,925
Welcome to AAC!

I cannot fault your test meter. Post a photo so we see what you have.
You did not state whether you are testing DC or AC voltages. Show for example, 120VAC, 12VDC etc.

On most meters, the AC setting is for measuring AC Line voltages.
Use the DC setting for measuring DC voltages.
Wall adapters will commonly generate voltages that are 30-50% higher than what is marked on the label.
 

Jon Chandler

Joined Jun 12, 2008
1,070
Wall adapters will commonly generate voltages that are 30-50% higher than what is marked on the label.
This is so untrue for switch mode wall warts, which are the vast majority these days.

It is true for most supplies using 50-60Hz transformers most of which are not regulated – they depend on the load current to make the approximate "rated" voltage.
 

Thread Starter

JimmyB491

Joined Mar 23, 2024
5
Welcome to AAC!

Have you checked the battery? Does the meter have a low battery indicator?

Since you're new to electronics, you should pay attention to conventions. Volts is abbreviated V. When we see V by itself (e.g. 10V), we assume DC. When you talk about line voltage, that's AC and the convention would be to say 120VAC.

Also being a newbie, you should be careful probing lethal voltages.
Yes Thanks for your welcome reply and safety tip. I did rewire my whole house & electrical panel. Indeed I am very careful around lethal voltages...It's how I made it to 75 yrs...LOL
Anyway, I just found out what I was doing wrong. I was using the AC scale on the multimeter and getting double results. I just switched it over to the DC and all of the numbers are now right in line. So thank you again for your suggestions.
I am new here so can you tell me how to mark my question as solved, so I don't waste other's time. Thanks
 

Thread Starter

JimmyB491

Joined Mar 23, 2024
5
This is so untrue for switch mode wall warts, which are the vast majority these days.

It is true for most supplies using 50-60Hz transformers most of which are not regulated – they depend on the load current to make the approximate "rated" voltage.
I was using the AC scale on the multimeter and getting double results. I just switched it over to the DC and all of the numbers are now right in line. So thank you again for your suggestions.
 

Thread Starter

JimmyB491

Joined Mar 23, 2024
5
Welcome to AAC!

I cannot fault your test meter. Post a photo so we see what you have.
You did not state whether you are testing DC or AC voltages. Show for example, 120VAC, 12VDC etc.

On most meters, the AC setting is for measuring AC Line voltages.
Use the DC setting for measuring DC voltages.
Wall adapters will commonly generate voltages that are 30-50% higher than what is marked on the label.
I was using the AC scale on the multimeter and getting double results. I just switched it over to the DC and all of the numbers are now right in line. So thank you again for your suggestions.
 

Thread Starter

JimmyB491

Joined Mar 23, 2024
5
Hi. I build computers as a hobby and am new to the electronics direction. Thank you in advance for the help. Here's my problem. I'm installing an actuator to have my screen unhide from the back of my test-bench computer and need a 12-volt power source to activate it. So the yellow wires from my computer's power source supposedly provide the 12 volts that I need to fashion a connection from one of my unused graphics card connectors to the actuator control, so there is no issue there, but when I test the voltage with my multimeter it registers 25v which is double. I've checked other computer connectors such as the (5v USB port which shows 10v). My (3v connection displays 6v). Everything seems to work fine but the voltage seems to be double. Now when I test my 120v house outlet it tests 120v correctly. My tester is a cheap one (the voltage setting options are only 200 & 600v, so I use the 200 setting). I plan to replace it ASAP, but can you please explain what is happening? I don't want to fry my actuator or have it propel the screen across the room...LOL, by hooking it up to double-voltage.
Thanks so much again for your help
JimmyB
I found my problem I was using the AC scale on the multimeter and getting double results. I just switched it over to the DC and all of the numbers are now right in line. So thank you again for your suggestions.
 

dl324

Joined Mar 30, 2015
16,988
I was using the AC scale on the multimeter and getting double results. I just switched it over to the DC and all of the numbers are now right in line.
Meters vary in how they determine RMS voltage, but on DC you should get zero or a low reading because the voltage isn't varying much. Getting a better meter sounds like a good idea.

I am new here so can you tell me how to mark my question as solved, so I don't waste other's time
If you edit the initial post, there's an option to edit the title. I think this feature might be disabled until you get 10 posts.

I don't know if there's a special prefix for solved, but you can prefix the title with [SOLVED}.

This is what I see with the blue interface:
1711222296377.png
 
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