Author Topic: Quick question about AC-AC adapter voltage  (Read 630 times)

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Offline Mp3Topic starter

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Quick question about AC-AC adapter voltage
« on: September 14, 2019, 01:02:08 am »
Hello,

I have four AC-AC adapters here. One didn't work, so I decided to check the voltages on all 4. I used my multimeter on AC Volts mode, definitely not DC.

One is dead completely. (0v)
One is labeled 9v but the meter says 12v.
Two are labeled 12v but the meter says 16v.

Is this a problem or is this normal? I know often older (80s/90s) DC power supplies put out a couple volts above what the label says.

Like for a device that wants 12VAC, I would think I should use my "9v" adapter that reads 12v on the meter, instead of either of my AC adapters which read 16v?
High school graduate
 

Online mariush

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Re: Quick question about AC-AC adapter voltage
« Reply #1 on: September 14, 2019, 01:18:45 am »
Your multimeter doesn't put a load on the power supply.

Go to some car / motorbike parts store and get a cheap halogen/tungsten/anything working on 12v AC lightbulb (should be less than 1-2$) and use the lightbulb as a load and measure voltage at same time with your multimeter.

 
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Offline forrestc

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Re: Quick question about AC-AC adapter voltage
« Reply #2 on: September 14, 2019, 01:24:47 am »
Hello,

I have four AC-AC adapters here. One didn't work, so I decided to check the voltages on all 4. I used my multimeter on AC Volts mode, definitely not DC.

One is dead completely. (0v)
One is labeled 9v but the meter says 12v.
Two are labeled 12v but the meter says 16v.

Is this a problem or is this normal? I know often older (80s/90s) DC power supplies put out a couple volts above what the label says.

Like for a device that wants 12VAC, I would think I should use my "9v" adapter that reads 12v on the meter, instead of either of my AC adapters which read 16v?

Most unregulated wall-warts (AC or DC) are rated for both voltage and current.    Generally they will read high unless you are drawing the rated current.  For instance, a 9V@300mA wall transformer will read high until around 300mA is drawn from it. 

So it's completely normal.     One other trap for new electronics people is that if you decide to use one of those AC power transformers with a diode rectifier and a capacitor to make DC, you'll find that not only is the voltage from the 9V transformer going to be high due to the 12V 'unloaded' voltage, but you'll also end up charging the capacitor up to the peak AC voltage which will even be higher.   
 
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Offline Mp3Topic starter

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Re: Quick question about AC-AC adapter voltage
« Reply #3 on: September 14, 2019, 01:34:17 am »
Thanks to all for the helpful responses. This is what i had hoped to find out. When i googled i just got answers about measure mains voltage, so i appreciate it.
High school graduate
 


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