AC Adapter Voltage Question

[goombawaho]

How come when I test a Linksys router's AC adapter output, it registers 16.5 volts DC??? The rating on the adapter is for 12VDC output. I got the same reading with 2 different routers of nearly the same brand/model.

Meanwhile, my laptop power supply puts out 19.6VDC and is supposed to put out 19.5VDC - spot on.

Does this have anything to do with not being under load while testing?? But, both measurements were made while NOT under load so that doesn't make sense.

The reason this came up: Somebody was asking me if they could power a router (temporarily while they try to find a new AC adapter) from a 12 volt car battery since the router power supply was rated at 12VDC.

 

[gbaughma]

Does this have anything to do with not being under load while testing??

Very likely.

Voltage will drop as load increases, unless it's a regulated power supply; and the regulation on wall-warts is minimal.



Just my 2¢

"What the captain doesn't realize is that we've secretly replaced his Dilithium Crystals with new Folger's Crystals."

--Greg

http://parallel.tzo.com

 

[BadBigBen]

Somebody was asking me if they could power a router (temporarily while they try to find a new AC adapter) from a 12 volt car battery since the router power supply was rated at 12VDC

almost same principle as a UPC...

short answer: should be doable... Car batteries have more than 12v anyway, they usually run around 12.6V (2.1v per cell) fully charged...

right now, I am using a Switch, whose PSU (internal) has died, and it is hooked up to my external FireWire Case as the power supply... What I am saying her is, look around there may be different electrical devices that may fit the bill, or it could be powered over the PSU from a PC, instead of messing with a LEAD ACID battery...

I generally learned that if you are within the 10% +- volt range you should be fine...

but I will bow to more knowledgeable people here on the Forum, who have more training in electronics than I prolly will ever have...


Ben
"If it works don't fix it! If it doesn't use a sledgehammer..."
How to ask a question, when posting them to a professional forum.
Only ask questions with yes/no answers if you want "yes" or "no"

 

[paparazi]

Short answer is REGULATED or UREGULATED.
The designated output is likely 12 volts when so many amps are being drawn so higher voltage when there is no amp draw. where as a regulated supply (in theory) should give the same voltage whatever ampage is being drawn (up to it's max stated rating of course)
Martin

On wings like angels whispers sweet
my heart it feels a broken beat
Touched soul and hurt lay wounded deep
Brown eyes are lost afar and sleep

 

[goombawaho]

UPC??? Do you mean UPS?

And actually, it's not the same right - because that's an inverter (DC to AC), whereas this would be straight DC to DC if you used a battery to power a DC-requiring device.

I'm not worried about it. It was just a random conversation with someone. He'll probably fry the thing.

 

[edfair]

As long as polarity is OK it should work well. I suspect that the 12 it is expecting is still enough over requirements that it is pulled down further.

Done it lots of times with all sorts of equipment. I keep radio shack adjustables on hand for emergencies.

Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[G0AOZ]

As said by others, REGULATED or UNREGULATED...

Try checking it under load and tell us the reading you get.

If you look inside the router you may find that it has a voltage stabiliser chip on the pcb. This seems to be the trend these days, which is probably why many routers get so darned hot!

ROGER - G0AOZ.

 

[BadBigBen]

Yeah, I meant UPS... DOH, proofreading is not my forte...



Ben
"If it works don't fix it! If it doesn't use a sledgehammer..."
How to ask a question, when posting them to a professional forum.
Only ask questions with yes/no answers if you want "yes" or "no"

 

[Sympology]

Of course getting a short on a Car Battery will, shall we say, be more interesting than a short on the output end of of a adapter

Robert Wilensky:
We've all heard that a million monkeys banging on a million typewriters will eventually reproduce the entire works of Shakespeare. Now, thanks to the Internet, we know this is not true.

 

[goombawaho]

I'm not going to do any testing - it's more of an academic point at this time instead of real world experimentation.

Thanks for the info on the regulated vs. unregulated.

I guess the thing to worry about using a battery to power a router or swtich would be if the battery voltage dropped down and created a brown out situation.

Don't know if these devices would be more sensitive to that condition that others when their batteries drop down.

 

[goombawaho]

As a corollary to this post, when I tested the voltage for my laptop AC adapter (just for this post), I managed to short out the little pin in the very bottom of the Dell adapter which tells the laptop about the power supply connected to it.

Thus, I got the dreaded error "The AC power adapter type cannot be determined. This will prevent optimal system performance." So, for my trouble, I got to purchase a new AC adapter.

Kids, don't try this at home.