Safely power 5V 2.0A device with 5V 2.1A adapter?
October 21, 2006 8:19 AM   Subscribe

Can I safely use a 5V 2.1A power adapter for a device (Linksys WET11 Wireless Ethernet Bridge) that expects 5V 2.0A?

I have read this previous Ask MeFi entry Why So Many AC Adapters? and found it helpful. I did note that it says polarity is a very important thing to match, and the adapter I want to use has a polarity symbol on it (minus in the left circle, plus in the right), but I can't find a polarity symbol anywhere on the device.

My hunch is that 2.1A is close enough to 2.0A to power the device successfully (experts, please correct me if this seems wrong to you!), but without knowing how to match polarities, I'm hesitant to try it out.

Does anyone have the original power adapter for one of these devices and could check for a polarity symbol on it? Or is there some other way I can figure out this polarity question?
posted by SomePerlGeek to Technology (3 answers total)
The ampere rating on the power supply is a maximum. It will happily provide just 2 amps.

But do check the polarities.
posted by TheOnlyCoolTim at 8:23 AM on October 21, 2006

2.1 vs 2.0 amp is fine; the amperage rating merely reflects how much power the adapter can provide, not how much it always puts out. As far as polarity, it's crucial to match, so someone else will have to verify this for you. AFAIK, there's a way you can determine polarity with a multimeter, but I'm not sure how.
posted by fvox13 at 8:24 AM on October 21, 2006

Best answer: Polarity

To read the polarity symbol you are looking at, follow the line that leads away from the left and right circles. One of them will connect to a fat dot, which indicates the centre pin. The other will connect to a C shape enclosing the dot, which indicates the outside contact. Here is a page with examples:

(I'm pretty sure that you can see this symbol reversed left to right, for a total of four possibilities)

There may be different polarity symbols on different devices. They may even simply write it out in text, like "+ve centre pin", or whatever.

If you just can't find the information, you could open it up and look for circuit components that can tell you. You will probably need a multimeter to do that, and a lot more pointers from the hive mind..


There is a 99+% chance it will be fine, but..

Is it a light smallish box, or a heavy largish box? If it is the former it is a regulated switching power supply, and the output voltage will be more or less fixed at the rated level.

If it is the larger heavier type it is an unregulated line frequency transformer. Unloaded the output voltage will be about 2x the rated voltage. If the device drew much less than the rated current, the output voltage would be substantially higher than it should be.

Since you are talking about only a 5% difference, you are bound to be okay anyway. The qualification on that is, you never know whether everybody is doing their job right, and DC adapters are a frequent source of enormous frustration.


I've played around with several brands of consumer hubs/switches/routers, and I find that they are pretty robust to my non-standard choices for power supplies. If it was life and death stuff, I'd be more careful, but as it is I'd be pretty happy to just plug'er in and find out.
posted by Chuckles at 9:57 AM on October 21, 2006

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