Help me not fry my new laptop

January 22, 2010 10:29 AM

For the sake of convenience, I'd like to have a second power cord for my laptop. Can I safely use the power cord from my old laptop with my new laptop?

My old laptop, a Gateway, died. The hard-drive failed.

My new (refurbished) laptop is a Dell Latitude D505.

I've checked the labels on the power cords. I'm assuming that it's the Input/Output and polarity info that's important. They are close but not exactly the same.

Power cord from old dead Gateway laptop says:

Input: 100-240v ~ 2000mA 50-60Hz
Output: 19V --- 4740mA
Polarity: + ---o)--- -

Power cord from new Dell laptop says:

Input: AC 100-240V ~ 1.5A
Output: DC 19.5V 4.62A
Polarity: - ---(o--- +

(On both of them, the open side of the polarity symbol is connected to the plus sign, it's just that the order of the symbols is reversed. But, they're both center positive, right?)

Are they close enough on the input/output or should they match exactly?

Is there any other info I'm not providing that's important to figuring this out?

It would be great to have a second cord to use, but I don't want to fry my new machine.

Thanks!

posted by marsha56 to Computers & Internet (21 answers total)

Nope. The voltages are different. The Dell requires 19.5 volts. The gateway adeapter only pushes 19. It probably won't fry it, but it also probably won't work very well.
posted by Netzapper at 10:32 AM on January 22, 2010

Meh, my professional opinion is that I would have no qualms using the old adapter for the new laptop. Half a volt and 100mA is close enough, given engineering tolerances and such.
posted by muddgirl at 10:35 AM on January 22, 2010

Unprofessional opinion, although I am a sort of professional. Just not in power adapters.
posted by muddgirl at 10:36 AM on January 22, 2010

Best answer: It's only half a volt difference. It'll work, as long as the tips are the same size.
posted by zsazsa at 10:42 AM on January 22, 2010 [1 favorite]

You also don't know that the Dell requires 19.5v just because that's what it's getting.
posted by thejoshu at 10:43 AM on January 22, 2010

Agree with muddgirl. It should work fine. It may not charge your battery as fast but it should let you work with it plugged in no problem. Since the old one has less potential than the new one, it won't fry your machine so all you have to do now is plug it in and find out.
posted by postergeist at 10:44 AM on January 22, 2010

I would feel very comfortable using either power cord in either laptop.
posted by Daddy-O at 10:52 AM on January 22, 2010

I advise you in the strongest possible terms not to dick around with this kind of thing. The voltages don't match, and using a bad power supply will _dramatically_ shorten the life of your electronics, assuming that it doesn't kill them outright.

Just pony up for a second power supply.
posted by mhoye at 11:09 AM on January 22, 2010

I agree with mhoye. A power cord looks like it's in the neighborhood of $20. It wouldn't be worth it to me to risk the laptop to save that money.
posted by cali59 at 11:13 AM on January 22, 2010

I don't think you have anything to worry about. It's not like you'll be affecting the voltage supplied to any internal components. Everything in your laptop runs on 12V, 5V, 3.3V or even less, and the power supply already has to cope with a much wider range of voltages as the battery charges and discharges. The power from your AC adapter will be heavily regulated before it gets near anything sensitive.

Also, I wouldn't be surprised if a 2% variation in voltage was well within the manufacturing tolerances for those adapters in the first place. Lots of electronic equipment runs fine on cheap 12V adapters that can easily be 5-10% off.
posted by teraflop at 11:31 AM on January 22, 2010

It's not a power cord, it's a power supply just to be picky. The old one will work fine, the differences in specs are minuscule (said with an background in electronics).
posted by Ferrari328 at 11:32 AM on January 22, 2010

Yeah, that should be fine. The worst that might happen is that it won't charge as quickly.
posted by kindall at 11:47 AM on January 22, 2010

As teraflop says, the internal components will use a set of voltages that go no higher than 12V. The way these things generally work is that the laptop has a bunch of voltage regulators which take your 19V or 19.5V and bring it down to the necessary working voltages for the different components. It's actually quite likely that these regulators will happily take 20V or even 30V and still work, although they will put out more heat when the voltage drop is bigger, and so I wouldn't necessarily advise using a 25V supply, for instance. But going from a 19.5V supply to a 19V one should be no issue at all.
posted by le morte de bea arthur at 11:57 AM on January 22, 2010

Should be fine. Highly unlikely to cause damage even if it doesn't work. It might not work if you had a smart power supply of some kind but that would require more than 2 contacts and it doesn't sound like that's what you have.
posted by chairface at 12:20 PM on January 22, 2010

I'd risk it.
posted by jannw at 12:30 PM on January 22, 2010

Best answer: Are the tips physically the same on both?

.5v will make NO difference, and the current rating is simply what it _can_ supply.

This will work just fine.
posted by MonsieurBon at 2:41 PM on January 22, 2010 [1 favorite]

Best answer: Undervolting is not going to cause you issues - over-volting would be the problem.

The biggest issue will be to ensure that that the tip is identical - otherwise you will do immediate, dramatic and non-fixable damage to your laptop.
posted by jkaczor at 2:54 PM on January 22, 2010 [1 favorite]

Response by poster: Oh crap, I hadn't looked closely at the tips before. I just had assumed they were the same.

No, they are definitely different. The old Gateway tip is maybe 2/3rds the size of the new Dell.

So, I guess I won't be using the old one.

I've looked at power supplies (not power cords, thanks Ferrari328) on Amazon. They are available from between $15 to $25 or $30 or so, but a lot of the reviews aren't very encouraging. Plus since a lot of them ship from individual companies, not from Amazon, so they don't all qualify for free shipping when I add enough to the order to get it up to $25. Sigh...

I was previously leaning to trying it out since about 75% here are saying it's okay. But with what I now see as the difference in the tips, I won't be doing that.

Thanks to EVERYBODY who contributed here. Everybody's viewpoint was helpful, especially for future reference. Given what I now know, I'll be giving best answers to the users who told me to check the tips.
posted by marsha56 at 4:39 PM on January 22, 2010

Laptops are like diesel engines in that they can run with practically any voltage you supply them (within reasonable limits) because they all have dc-dc switching converters to step down the input voltage to the appropriate charging voltage of the battery (3 cell Li-ion = 10.8 V, 4 cell = 14.4 V). You could probably supply 30 volts and it would be just fine.
posted by Rhomboid at 12:17 AM on January 23, 2010

(er, those are the nominal voltages, the changing voltages will be a little higher; 3.7 -> 4.2 per cell)
posted by Rhomboid at 12:22 AM on January 23, 2010

On top of all of these technical facts, I will add my personal experience, which is total voodoo, and as a scientist, it really annoyed the crap out of me.

I had a laptop (Dell), and the cord frayed on the power adapter. I decided to replace it. I looked online, and saw the Dell replacement for $50, and the Amazon ship-from-China replacement for $20. I bought 2 cheap ones, for the convenience of having one at work and one at home. Awesome! 2 months later, power port (on the internal board) died, diagnosis "over-voltage". So, despite the fact that I was buying the generic brand adapter designed specifically for my model of laptop, apparently it did not actually deliver what it said on the box that it delivered.

My take-away message is, however ridiculous and expensive, I'll be buying the OEM power cords for my laptops now, and would never, even if the tips matched, use one meant for a different computer, especially if the numbers weren't absolutely identical, and maybe not even then. And then, I feel totally stupid and sheeplike, one of the suckers born every minute.
posted by aimedwander at 10:46 AM on January 23, 2010