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Will 4.5 amps do ? May 18, 2007

Posted by dorigo in computers, humor, personal, travel.

Yesterday morning I woke up at 4AM, packed my luggage, and headed to the airport. Venice to Munich, then Munich to Chicago. I got upgraded for free to business class on the intercontinental flight, and got my reservation for a compact car also upgraded to a nice Mazda 6 (the very car I own, and even the same color!) by ACE, the rental company I use at O’Hare. However, in spite these small encouragements, my mood stayed gloomy.

Spending a week on shift is not the best of worlds – you are doing something useful for your experiment, but time is spent doing nothing – no chance to use the small time fragments between a phone call and a e-log entry to concentrate on real work; the environment also lacks the necessary secludedness I have grown accustomed to, in order to have my neurons fire uninhibited and free.

And there is more: the shift is an Owl, running from midnight to 8AM.

Anyway, I am even more gloomy than I would need to be today, because as I got to my office at Fermilab I discovered I had left the power adapter for my laptop at home, 6000 miles away. I hate that! I cannot live without my laptop, and the thing has less than five hours of battery life before it runs out of juice.

So this afternoon I went to a computer store, where I found a “universal” power adapter. The thing does have the correct plug for my Sony Vaio, and it does output 16 Volts – the required voltage. However, I am now balking. The output of the transformer is 4.5A, while the standard adapter outputs 4A. The extra 8 watts of power could overheat, or melt, or ignite, my precious instrument. Should I plug the darn thing in and see what happens ? In principle, 4.5A is the maximum possible draw of current – it should not harm, but… I have burned things in the past for being overconfident!

Here is an instance when I would appreciate feedback: please tell me what to do. Should I put the laptop aside for a week, and live out of linux terminals in the lab, thereby restraining my hunger for continuous internet usage ? My blog would suffer a reduced posting rate then. Or should I plug the power in, and check carefully whether I see any sign of overheating ? Or is it really so safe to go 12.5% above the nominal power that I should not even stop thinking about it ?

There is one more option – I could try it at 15V (the universal adapter has a switch allowing the selection of 15V, 16V, 18V, all the way to 24V), which would make the wattage a bit smaller: 15×4.5=67.5W instead than 16Vx4.5A=72W. Maybe this is the first thing to try… Any hints ?

Oh, and forget advices such as “ask Sony”… They will tell me to only use their own power cord. On the other hand, the manufacturer of the universal adapter has no information on the item in their web pages… So I am really on my own here. Or not. Maybe you can help ? My laptop is a Sony Vaio VGN-T2XP, and the adapter is a “Cables Unlimited” PWR-LAP-SP11. They say “works with most notebooks” on the package… Which serves no purpose other than producing further inflamation, should the laptop get blackened in a blaze.

Update: I decided the current mismatch was not going to be a problem, and plugged the thing in… And… Nothing. The led on the transformer box is lit, but no power gets to the laptop – which only means that the provided plug (none of the nine provided, that is) does not fit well enough in the laptop power inlet (it does look like it’s not the correct one in fact). So I bought the power supply for nothing… Tomorrow I will bring it back and try to order the right one from Sony.



1. Alexander W. Janssen - May 18, 2007


using an adaptor which has more power is no problem. The machine uses only the amperes it really needs. The voltage must be exact though, so if the voltage of the power-supply is not exact enough it just might not work.

The computer takes the 16V, transforms the 16V DC using internal voltage-regulators to the needed voltage (usually +3.3, +5, +12 and some negative voltages against ground) and powers it’s components. The more juice the laptop needs the more it’ll draw in amperes from the PSU. So the PSU must be able to deliver the total energy needed. If it can deliver more: No problem. 16V * 4A would result to a maximum power consumtion of 64 Watts (DC) where your new PSU could deliver even some 117 Watts.

No need to worry about that! It won’t fry. Just be sure that the polarity is correct. But I’d guess that the laptop has a diode to prevent wrong polarity.

Sorry to hear it doesn’t work, I’d think that the delivered DC-current is not clean enough. During my own experiments I figured out that cheap PSUs just don’t deliver a constant voltage…

Cheers, Alex.

P.S.: Have fun in your night-shifts. 🙂

2. Fred - May 18, 2007

Hello Tommaso,
There is a place in Valencia, CA called atbatt.com that might have your item. A brief glance at: http://www.atbatt.com/product/2171.asp could be the ticket. It’s on sale for 45 smackers though the next day air charges will wipe out the savings. Good luck.

3. riqie arneberg - May 18, 2007

lol………….a physicist should never own an automobile or anything electronic! Voltage “pushes” electrons, and 16 volts is 16 volts. The 4.5 ampere rating is merely the amount of them which it can push before the voltage drops noticably. You could hook to an arc welder if it produced 16 volts!

4. dorigo - May 18, 2007

Hi Fred,
thanks for finding this for me. I will see how much they charge for the air shipping…

Riqie, you’re right… As Feynman would say, “in matters of everyday life a scientist is as dumb as the next guy”.
I am worried by the laptop drawing too much current, which causes a overheating. If the system is working perfectly, nothing bad should happen as you say… But unfortunately I cannot check it, due to the wrong adapter!


5. dorigo - May 18, 2007

Fred, you are right – that power supply is the one I need. It sucks to have to buy another though! I will see if they take back the one I bought first.


6. riqie arneberg - May 18, 2007

Your battery is caable of producing far in excess of 4.5 amps. If comp were to draw more than 4 amps it would be due to a short circuit, and would drain battery in very short time. If it is functioning properly, it is the load that determines current, not the supply.

7. Tom Allen - May 18, 2007

Rique is correct. The extra amperage capability of the adapter represents no harm to your computer. 4.5 Amps is what it could put out if it had to. In use it will only supply the current needed. The voltage on the other hand should match what your computer needs.

So get the right voltage and don’t worry about the Amps.

8. carlbrannen - May 19, 2007

One of the odd features of my education is that I never took undergraduate E&M as I do not have an undergraduate degree in physics. I did take a graduate course using JD Jackson’s book. But the absence of the undergraduate class left me always feeling that I was missing something on the subject, some piece of intuition that is only covered at an undergraduate level. Reading this blog entry has alleviated this feeling.

9. dorigo - May 19, 2007

Hi Tom,

thank you for your input… As I wrote above, I did try the thing after posting this, but unfortunately none of the supplied connectors work (although one of them does fit). I took the PS back to the store.


10. dorigo - May 19, 2007

Hello Carl,

you know, I took undergrad courses in electromagnetism, graduate courses in classical and quantum electrodynamics, what-not… But there still are things I fail to fully appreciate. The “intuition” you talk about can only be gained by fiddling with things in the lab.

And then, even when I think I know the answer, with a 2k$ device containing over two months of non-backed up work, I tend to play these things safer than reasonable (I burned a few devices in the past by doing silly things). Visions of my laptop (which already survived a drop on the floor recently, and might have some loose pieces or funny short circuits inside) starting to behave as a resistor led me to ask for help…


11. Quantoken - May 19, 2007


You must be joking, right? It’s a disgrace you have to discuss this thing on the web and claim to be an EXPERIMENTAL physicist, too. A person with zero knowledge of electronics at all would be able to bring the laptop and the power adapter to the store, and ask them to show you how to plug in the power adapter.
But save a trip, you just need to push it in a little bit harder, or switch the polarity.

12. dorigo - May 19, 2007

Hi Quantoken,

discussing one’s ignorance is the best way to remove it. My reputation is built on other ground than electric circuitry, and I do not fear jeopardizing the former if I show my lack of experience with the latter here.

And no – unfortunately, Sony produces quite particular plugs, and none of those provided in the package worked, no matter how hard one pushed. The female inlet of my laptop accept a central pin, and the only pinned plug in the set was too short. Switching the polarity ? Now it’s you who is kidding.


13. Fred - May 19, 2007

Your survival instincts are correct. A 2k$ can always be replaced. What’s the value of 2 months of work that can’t be retrieved? Virtualization (a corporate godsend) is still an expensive solution for the individual but there are companies in California that are starting to offer certain employees a slice of IT insurance as a perk. Eventually, we will all become members of a server farm. Moo and baa. Until then, enjoy the trials and perils while you can.

14. riqie arneberg - May 19, 2007

Is this the same Quantoken who has solvet the unified field? My comment was intended as light hearted ribbing, and i would NEVER try reverse polarity on a laptop. By the by, I have dad a similar problem with a laptop connector lately. American Autos led the world for many years as a result of standardization. It is time for the same thing to happen with computers!

15. carlbrannen - May 19, 2007

After several decades in industry, I can’t imagine manufacturing a laptop with no protection diode in the power input. The problem is that all “universal” power supplies are reversible so you have to imagine that they’re going to be plugged in backwards.

As it turns out, my crappy Gateway laptop has a faulty input power connector. Right now I can jiggle it around to work, but eventually I will have to take this laptop apart and resolder it. When I do that, I’ll check to see if they included the protection diode.

16. dorigo - May 20, 2007

Yeah Riqie, if you own 20 laptops from different brands you will also need 20 different power supplies… That is nonsense. I mean, it is ok as long as there is some technical reason – say, a 17″ monitor or a faster processor will require more power than my 10″, so it makes sense that the latter works with a smaller, lighter, more portable transformer. But the diversity of connectors makes it look as though it is done on purpose, to make the extra buck on branded accessories.


17. dorigo - May 20, 2007

Hi Carl,

ok, let me know what you find out… A good 50% of the times I take some electronic device apart to see if there is an easy fix to a problem, I then am unable to put the thing back together. I think your chances are higher, good luck!


18. Quantoken - May 20, 2007


I am not talking about familiarity with electronic circuitry. Billions of people use electronics and most of them have zero knowledge about electrinics. What you need is some common sense intelligence, average intelligence than any two legged animal walking on the street should have:

Just bring your damn laptop computer to the store and say: here is my laptop. I need a power adapter. Give me one that works and show me how to plug it in. It does not take an Einstein to figure out and they should be able to give you a power adapter that works, or the store should shut the door.

In the worst case scenary assuming you lost two months worth of work. Not much has been lost. The super string theory surely has not progressed much in two months, and you have not worked out any nobel prize worthy stuff witihin that two mouths. If you have something actually worthy saving you would have backed it up already some where else. The bottom line is if a malfunctioning power supply fries your laptop your loss is topped at $2K of the hardward cost. If your data is worth more than $2K there are data recovery services that for $2K will salvage every little bit of data on your harddrive. So your data is really not worth more than $2K.

19. Idiot's guide to handling a multi-million-$ experiment « A Quantum Diaries Survivor - May 21, 2007

[…] incompetent – and I may indeed be: the readers of this blog have a proof I even get confused with basic facts about electric circuits. But I have cooked up a recipe to shrug off that funny feeling: make a tour of the tens of […]

20. saif - May 25, 2007

when i switch off my computer there is a sound from speakers, like the computer wants to say its last words or something. this all started when i changed my psu, before i had a mecury 230watt, i am using now vip-400watt psu. i am not sure what is this causing. if any one can give me solution at the earliest it will be greatly appreciable. thanks in advance.
u can contact me get_saif@hotmail.com or post it here. anyway solution is important 🙂

21. dorigo - May 25, 2007

Hi Saif,

I haven’t a clue! I think you are worried unnecessarily, though. Just disconnect the speakers first and forget the issue!


22. Chief Redelk - August 15, 2009

Some Adapters will state a Voltage at X amps.. BUT, in fact they may depend upon the LOAD to regulate the voltage.. If you check the voltage output of any Adapter with a KNOW expected value such as 16VDC at 4.5 amps and that generic Adapter has a voltage higher than 16 volts (some are like 22 or even 28 volts) then you know that generic is NOT well regulated or filtered. NOT all power supplies are what they appear..With an expensive item I would Check the output of ANY adapter and IF the voltage exceeded 16 or 18 volts I would NOT use it. The wise thing to do is to simply check out any generic adapter by inserting the correct Resistance (works on DC where Impedence is not a problem) and use an amp meter to see if the amps are correct. IF SO.. Santa was good to you..meaning USE IT.. BUT polairty is often reversed on some things so you WILL destory your equipment.. NEVER trust the colors of wires. CHECK using a cheap volt meter and save an EXPENSIVE item. Don’t ask HOW I KNOW..To create a resistor that will carry a LOT of WATTS you can simply purchase some 10 Watt resistors and wire them in Parallell..For example two 10 watt 30 Ohms in Parallell would give you 15 Oh and 20 watts.. of course you know that..IF someone reading this DOES NOT know it, let me say.. Resistors in parallell divide their values and resitors in series Add their values but Watts is not increased like that. At the moment I am working on a Lap top that uses a 16 vdc 4.5 amp supply and I am experiementing with a few supplies I have on hand. Good luck..

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