How interchangeable are laptop power supplies?

December 20, 2007 3:04 PM

How interchangeable are laptop power supplies?

The power supply for my Toshiba Satellite laptop just got fried - there was a kink in the cord which finally caused a wire to fray, and now the thing is dead. I have an older power supply (also for a Toshiba laptop, albeit a much older one). Can I use the old power supply?

The dead power supply has an output labeled "15V - 5A", while the older one has an output labeled "15V - 3A". Will it work?

posted by JeffL to computers & internet (9 answers total)

Duh, I'm actually referring to the brick-like "AC Adaptor", (the thing between the electrical outlet and the computer, not the internal power supply). Sorry.
posted by JeffL at 3:07 PM on December 20, 2007

No, it won't work, because the old power supply isn't rated to supply 5 Amps of current, which your new computer requires. It might work for a while and then get really hot and melty when your laptop starts to draw a lot of power, or it might work because it actually can handle more than 3A, but this isn't something you should experiment with.
posted by ssg at 3:20 PM on December 20, 2007

the smaller supply will probably let you either use the computer OR charge the battery, but not both at the same time.

it shouldn't melt down unless there is a serious problem inside the computer itself.

you're probably safe using it until you can replace or repair the correct one.
posted by KenManiac at 3:50 PM on December 20, 2007

The amperage rating isn't sufficient (as noted) and it isn't necessarily the same polarity either. You can possibly check if there is a polarity diagram on the adapters. In general, laptop power supplies are not interchangeable. So "probably safe" and "unlikely to catch fire" is about the best advice you'll get.
posted by chairface at 4:47 PM on December 20, 2007

Thanks; I think I'll just wait and get a new replacement adapter tomorrow - just to be safe.
posted by JeffL at 5:37 PM on December 20, 2007

If you have a little electrical/electronics experience, and you backup appropriately, I'd say it is exactly the sort of thing you should experiment with. However, strange things do happen; the discussion in Am I Using the Wrong Power Adapter is a great example of that..

I also wonder if the adapter is really fried, because it might just be a short in the line. I'd cut the cord before the kink, and test with a voltmeter.
posted by Chuckles at 6:20 PM on December 20, 2007

Match voltage exactly.
Match amperage closely. A little too low and you don't get much charge while you work. A little too high should in theory be fine, but if it is not well regulated then it might provide too much voltage. Not worth the risk on such expensive equipment, although not a likely outcome.
Match plug size and polarity exactly. Obviously if the size is wrong it won't fit, but if the polarity is wrong the computer might get fried.
posted by caddis at 6:34 PM on December 20, 2007

It doesn't matter what the label on the old power supply said. It does matter how much voltage the laptop actually expects, and how many amps it can draw.
posted by b1tr0t at 6:44 PM on December 20, 2007

Hmmm. I've been using my old Dell power bricks with my new IBM for the last 10 weeks. It seems like it's going fine....
posted by 26.2 at 7:24 PM on December 20, 2007