DC Power Supply - going over current rating and high pitch noise

Thread Starter

dirusptalot

Joined May 12, 2017
2
I'm freaking out over a high pitch noise (very faint) coming from my power supply and wanted to clarify some things so that I can be sure i'm safe.

I have a 12V DC power supply (1A) that has 2 components connected in parallel. The circuit works perfectly but I'm pretty certain that this circuit is trying draw more current than power supply can provide.
What happens in this instance?
  • Does the power supply just continue working while limiting current draw to 1A?
  • Is there any danger either to the power supply or components in this case?
  • Why am I hearing this slight screeching noise? Another thing to note is that shaking the power supply you can hear some sort of small piece inside moving around.
 

#12

Joined Nov 30, 2010
18,222
1) Power supplies don't limit current, they regulate voltage. The resistance of the load limits current.
2) What danger? The danger that you can hear the magnetostriction of the transformer core? The danger that it's not overheating? The danger that it's working perfectly?
3) Look up, "magnetostriction".
3b) Open it and find the loose bit and take it out...or just quit shaking a perfectly working power supply. You could also consider why you think emotions have any purpose in a wall wart size problem which is working perfectly.
 

Hypatia's Protege

Joined Mar 1, 2015
3,226
Why am I hearing this slight screeching noise?
Seems the over-current/current limiting condition entails a pulse-width modulator mode productive of audible harmonics (not at all uncommon in such systems outside designed dynamic range)

  • Another thing to note is that shaking the power supply you can hear some sort of small piece inside moving around.
That wants investigation ASAP...

  • Does the power supply just continue working while limiting current draw to 1A?
  • Is there any danger either to the power supply or components in this case?
Better to address the problem than muse upon the imponderables...

Best regards and good luck!
HP:)
 

Hypatia's Protege

Joined Mar 1, 2015
3,226
) Power supplies don't limit current, they regulate voltage. The resistance of the load limits current.
Current 'foldback' protection is not uncommon:confused:

Best regards
HP:)

PS
Of course SMPS topology doesn't implement current limiting via 'foldback' per se -- thus it seems manufacturers appreciate retro-analogy:rolleyes: -- Point being, I've seldom encountered switch-mode PSUs sans provision for over-current protection...
 
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Thread Starter

dirusptalot

Joined May 12, 2017
2
Here a picture of the inside of the power supply. It's the very generic ACDC PSU you get. I opened it up, there is as I thought not a loose bit or anything. I wasn't able to identify where the rattling noise is coming from.
http://imgur.com/a/khZWt

Unfortunately i'm just a beginner in electronics some of these comments are going to just go past me :) i'm trying my best to make sense of them though.
I'm quite certain that it needs more current as there were tests on the component before and at 12v it drew more than 1A. I didn't really get an answer though on whether a power supply can safely handle a component that requires more current. And the main worry there is does the PSU die or catch on fire i guess :D
 

#12

Joined Nov 30, 2010
18,222
there were tests on the component before and at 12v it drew more than 1A. I didn't really get an answer though on whether a power supply can safely handle a component that requires more current.
That answer is, "no". Either it will overheat or go into self protect mode. Both of those are bad. If your load wants more than one amp, buy a power supply that can provide more than one amp.
 
I opened it up, there is as I thought not a loose bit or anything. I wasn't able to identify where the rattling noise is coming from.
The sound may owe to flexation of a lead or a loose piece of glue/glass in the fuse cartridge... In any event it should cause you no difficulty so long as you are certain the enclosure is free of metallic (or otherwise electrically conductive) debris.

As for the rest? Well... As per your own assessment, the PSU is not 'up to the job' -- Your next move would seem obvious...

Best regards and, again, good luck!
HP:)
 

#12

Joined Nov 30, 2010
18,222
Current 'foldback' protection is not uncommon:confused:
SMPS topology doesn't implement current limiting via 'foldback' per se
I've seldom encountered switch-mode PSUs sans provision for over-current protection..
I haven't let the smoke out of enough of them to have a gut level estimate of their self protecting qualities. I'll have to take your word on this until I have the opportunity to test a few. I do have a bucket full of wall warts. They are probably cringing into the back corner of the box even as I type here.:D
 

Dodgydave

Joined Jun 22, 2012
10,040
Here a picture of the inside of the power supply. It's the very generic ACDC PSU you get. I opened it up, there is as I thought not a loose bit or anything. I wasn't able to identify where the rattling noise is coming from.
http://imgur.com/a/khZWt

Unfortunately i'm just a beginner in electronics some of these comments are going to just go past me :) i'm trying my best to make sense of them though.
I'm quite certain that it needs more current as there were tests on the component before and at 12v it drew more than 1A. I didn't really get an answer though on whether a power supply can safely handle a component that requires more current. And the main worry there is does the PSU die or catch on fire i guess :D


The noise is likely the large transformer (yellow square object) going onto saturation or the transistor on the heatsink, and inductor.
 
I haven't let the smoke out of enough of them to have a gut level estimate of their self protecting qualities. I'll have to take your word on this until I have the opportunity to test a few. I do have a bucket full of wall warts. They are probably cringing into the back corner of the box even as I type here.:D
In my experience, FWIW, overloaded SMPS units tend to either 'shut down' (thereafter requiring a PD-PU cycle to reset) or 'sing' (while holding current to non-destructive levels)...

Careful you don't have a linear supply among your test subjects! -- They tend to smoke like legionnaires when overloaded!:eek:

Best regards
HP:)
 

SgtWookie

Joined Jul 17, 2007
22,221
What is the peak current requirement for your load? Your power supply should be rated for at least 20% more than your load peak, otherwise you will likely shorten the life of your power supply.

If your load exceeds the rating of your supply, the transformer will likely saturate as has already been mentioned.

When a transformer (or any inductor wound on a core) saturates, it acts as if it is short-circuited, which causes high current flow through it and the switching transistor or MOSFET or IGBT, resulting in high power dissipation as heat. This is undesirable.

Also, if your load draws more current than the supply is rated for, the voltage will no longer be regulated. This may cause unpredictable load behavior, and may damage both the load and the supply.

You should always use a fuse between a power supply and your load, to protect both.
 
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