Is my new (aftermarket) power adapter safe for my laptop?
November 13, 2008 6:21 AM   Subscribe

Can I damage my laptop by using a power adapter that has a slightly higher wattage than the original adapter? The original adapter was 65W, and the aftermarket one is 70W. The voltage is switchable. My original adapter had a voltage of 18.5V, this one says that if I need 18.5V, I should choose 18V. Any chance of damaging the computer by using this one?

The computer is a few years old -- it's an HP Pavillion dv1040us model.

Also, one additional detail -- I bought it in the US but now am living in Europe. I've been using the US plug with an adapter end for the EU socket. This one I bought here will automatically have the EU plug. That doesn't make any difference right?

Thanks for any help/answers. I've tried to research online and I think I'm safe, but I really don't know anything about electrical things, so some expert confirmation would really be appreciated.
posted by leticia to Computers & Internet (8 answers total)
No chance of damaging anything, no. The rated wattage is the maximum power that an attached device should draw. Higher is always fine.
posted by kindall at 6:38 AM on November 13, 2008 [2 favorites]

Seconding Kindall.

The voltage supplied must be correct or very close. Higher voltage risks damaging the equipment because it'll cause too much current to flow, generating more heat than the laptop is designed to handle and maybe burning out circuitry. Going slightly lower should be OK, although it's possible it could confuse your laptop battery's charging circuits slightly. Personally I'd give it a try and just watch out to see if my battery takes the same time to charge and discharge, but I'm not an expert. I think the worst case scenario has your battery failing to charge and/or your computer being a bit unstable when trying to do lots of power-intensive things (burning a CD, running fans, screen on maximum brightness, etc) at the same time. I doubt a drop of 0.5v would make that much difference though.

Also important is the connecter's polarity. IIRC, my laptop expects the centre of the connecter to be positive and the outside to be negative. Check this for your laptop (it should be written next to the socket, certainly somewhere on the case) and make sure that the charger agrees. Getting these the wrong way around could do some damage.

The figure of "70W" is the maximum current that can safely flow through the power supply without overheating, etc. You want this to be higher than the amount of current that your laptop will try to draw, so in this case 70W is as good as -- and arguably slightly better than -- 65W.

Side question to any experts:
Are laptop power supplies standardised? All the ones I've seen and bothered to check say they supply 18-19v up to around 70W and -- I think -- use the same connecter. Is this coincidence, or is there an industry standard?
posted by metaBugs at 6:58 AM on November 13, 2008 [1 favorite]

Response by poster: Thanks for the responses so far... I'm feeling more confident about it.

But, @metaBugs... I didn't quite follow the bit about the connecter's polarity. Not sure how I would check that.
posted by leticia at 7:10 AM on November 13, 2008

Higher power is fine, and maybe even good. My wife's macbook charges noticeably faster when using my macbook pro's power supply than when using her macbook's brick. No harm has come of it.

Most modern electronics can take a pretty wide ranging voltage input as well. IE, it's not a problem to plug it into 240v in europe and 110v in the states.
posted by paanta at 7:11 AM on November 13, 2008

For checking the polarity, look for a symbol that looks like this (only less ascii!)
- ---( --- +
the - symbol with a half circle indicates the outside part of the connector is negative and the + going to a dot in the center indicates the center is positive.

This symbol should be on the outside of the equipment and also on the power supply - beware of power supplies that have changeable tips. As long as they match you are good to go. Here's a web page with some handy symbols including the polarity.

Here's my mental checklist I use when plugging in random power adaptors:
  • Are they both DC ? (some psu's are e.g. 12V AC)
  • Are they both centre positive
  • Is the PSU within 0.5v of the target voltage
  • Is the PSU rated to the number of amps the device needs (e.g. device needs 2A, any psu that can supply 2A or more will be fine).

  • posted by samj at 7:23 AM on November 13, 2008 [1 favorite]

    If you can't find the polarity symbol on the power adapter, or the polarity is switchable and you're not sure you got it right, then pick yourself up a multitester at a hardware or electronics store. The cheapest one will do fine for basic stuff like this. I think I paid a whopping $15 for mine. Every toolbox should have one. Here's one if you have a Fry's in your area.
    posted by kindall at 11:54 AM on November 13, 2008

    i do not think power supplies are standardized. I have one of those multi brand ,car,and airplane notebook power adaptiers and their are two diff voltage settings and tons of diff tips.
    posted by majortom1981 at 3:19 PM on November 13, 2008

    Response by poster: OK, had to just gamble on the polarity thing. I couldn't find the symbol on the adapter (though i did find it on the laptop, in the battery bay). A polarity tester would be beyond my understanding, even if I had easy access to a place where I could get one. I'm in Eastern Europe, not speaking the language, so my options are limited.

    But I've dialed up the right voltage, found the appropriate tip, and the laptop's been chugging away on the new adapter all day, so it's all good, or at least it looks that way. :o)

    Thanks for the help all!
    posted by leticia at 10:04 AM on November 14, 2008

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