9v power adapters read 12-13v

  • Thread starter Thread starter Steenamaroo
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Steenamaroo

Steenamaroo

...
Hi all,

I bought a little ipod dock recently which has a hardwired unmarked power supply.

Testing showed the power supply to be 8v DC.

I want to be able to move the dock around, and for convenience i'd probably want power supplies in different rooms to save me hoking around at plug sockets.
So....... I've removed the power cable from the unit (it was a little 2 pin molex behind a rear panel) and fitted a socket to the unit, and a jack to the power supply like you'd get on guitar effects pedals etc.

Plugged it in, and of course, it works.






Problem is, I have stacks of 9v dc adapters from various appliances and they all read somewhere between 12 and 13.5v on a meter, but i have a few 5v ones and they read 5.

So what am i missing? I don't want to run the thing on the wrong psu and do damage in the longterm.


I've read that unregulated supplies will show a higher voltage without load, whereas regulated should be bang on, so
do you think my original supply is likely to be 5v or 6v unregulated or 8v regulated?

Any guidance is appreciated.
 
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I've read that unregulated supplies will show a higher voltage without load, whereas regulated should be bang on, so
do you think my original supply is likely to be 5v or 6v regulated or 8v unregulated?
Click to expand...

Correct, usually switching converters are regulated and linear converters (your 9V guys) are not (although they can be), and linears will thus sag under load to the rated voltage. The linear type are fast becoming obsolete; the really tiny and lightweight ones are the switching dudes. I would expect an iPod deck to use a switching supply (which would be 8V regulated), but you never know . . . post a pic of the PSU in question.

The other thing to do is stick a dummy load on the PSU and see if it sags. 100 ohm 1W resistor ought to do (assuming the PSU is rated at least 100mA).
 
Thanks for that MSH.

I don't have any 1watt, but i've a stack of 1/4watt.

Tried it with higher values in parallel which showed a drop on my 9vpsus, but not on the 8v one in question.

That proves it's 8v dc regulated then right?

Here's the psu.
 
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Steenamaroo said:
Here's the psu.
Click to expand...

Well there is your problem Paul those tongs on the PSU are all wrong! I'd never be able to plug that into the wall socket. :D

I too have a mountain of PSU's ..... to the point where I don't collect them any more and should start to weed out the ones that will never be used ever again.
 
I've some experience with wall/floor warts. Here' some of what I have observed:

Once put a meter on all the ones I had, and made labels (primarily so I could find the right one without having to squint at the little bitty writing on them) reading their actual voltage output. Every one tested higher than "advertised.

This may be obvious, but I have found that power rating match (wart to device) was at least as important as voltage- in fact, I find you can be a few volts off and things often still work, but if the power rating (watts) from the wart is low, chances are the device being powered won't work right.

Oh, and you should NOT us an AC-output wart for a DC-powered device, or vice versa.

YMMV.
 
Well, to be exact, the one that came with the dock reads 8.4, so i bought a few 9v dc regulated jobbies.

Couldn't see any 8v on ebay, so i figured 9 was just much more common.

The ones i bought read 9.4 under load or not, but that worries me much less than reading 12 or 13.

I'm happy :) Thanks MSH et al.
 
mshilarious said:
...linears will thus sag under load to the rated voltage. The linear type are fast becoming obsolete...
Click to expand...

Hmmm. I know some guitarist like to use batteries instead of warts with some pedals (distortion pedals, AIR,) b/c they like the sag they get. (Personally, I think they are fooling themselves, but whatever.) But wouldn't that make for a market for the linear types?

Just asking, I don't care that much either way.
 
stevieb said:
Hmmm. I know some guitarist like to use batteries instead of warts with some pedals (distortion pedals, AIR,) b/c they like the sag they get. (Personally, I think they are fooling themselves, but whatever.) But wouldn't that make for a market for the linear types?

Just asking, I don't care that much either way.
Click to expand...
The 'sag' on the power supplies isn't a dynamic sag, it just sags to the rated output when it's plugged into what it's supposed to be powering. It's not like battery sag that changes as the load changes.
 
See, that's what worried me.
I can't say you're wrong; I don't know about this stuff, but i used a 9v unregulated supply (reading 13), and tested it while the ipod dock was plugged in and turned on.
It still read 13 so that's why i wasn't happy.
 
Gosh I have a multitude of these wall warts!
Maybe I'll make some sort of art sculpture out of them and sell it for big bucks to some rich industrialist.
 
Electrical devices aren't that fussy.
And most stuff in the real world doesn't care.

A few volts over doesn't matter. AC/DC and total watts (having
more available than the device pulls) is more important.
 
I don't believe we've met Tim.

I'm Steenamaroo; Stuff breaks when I look at it! :p
 
TimOBrien said:
Electrical devices aren't that fussy.
And most stuff in the real world doesn't care.

A few volts over doesn't matter.
Click to expand...

That cannot be assumed. Portable devices these days are getting very small and most of them anticipate using their rated supply. They will likely have some sort of regulation on the power input; it may be a linear regulator which must shed the excess voltage as heat. A 5V margin may be more than the designer allowed for, given space restrictions in the device. Hopefully the regulator will go into thermal shutdown and recover when the power is removed, but it could be damaged.

Another option is a switching supply at the input, which mostly eliminates the thermal problem, but such devices may have a maximum voltage input before they are damaged, or there may be passive components that will exceed their rating.

It's possible to design a power input robust enough to survive anything, but it takes space and money to do so. What decisions did the designer make? You won't know until you try and exceed the rated input. Maybe you'll trip a shunt and blow a fuse. Minor damage . . . if you can get the device open and find the correct part to replace the fuse . . .
 
Thanks for all the replies.

I picked up a few supplies as discussed and everything's tip top, plus I learned a little something :)

Cheers Msh.
 
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