Electricity/electronics question (super easy for EEs!)

[Bobmuhthol]

I have a Linksys 5-port switch that I want to use, but I can't find the power adapter for it. It's rated at 7.5 V, 700 mA DC, and I briefly tried using another power adapter I have with 9 V, 1.5 A DC output. It turned on and seemingly functioned (didn't actually test it with a network yet) but I did not leave it on in case this is not a good combination. Will this work or is it going to kill the switch and everything in its path?

[Gan]

I'm surprised that it fit into the power connector in the back of the switch. Usually the connectors are sized by voltage rating.

I'm no EE, but I wouldnt use it because of the overload of the voltage and current.

[Drew2]

One google search, 10 seconds later...

http://www.10stripe.com/articles/replacing-device-power-adapter.php#involt


For a laptop, the laptop will have some voltage regulation hardware of its own onboard, and so can probably cope with a slightly higher voltage (0.1 V should be fine; 0.5 V is riskier but not a bad bet; 1 V is pushing your luck). However, it will mean that the voltage regulation hardware produces a bit more heat, which will make the laptop hotter. Lower-than-expected voltages may be dicier; there you are putting your faith in not just the laptop designers (who designed in some margin in the voltage their laptop can accept) but also the power supply maker (who designed in some margin in what their supply can output, knowing it would sag some under load).

For other devices, you may or may not have as much freedom. You really don't want to stray more than around 0.1 V from the original device (with one little exception noted in the next section). Luckily for you, such devices normally use one of a limited set of common voltages, so finding a replacement that matches closely should not be too hard.


I'm disappointed in you, Alex.

[Bobmuhthol]

Yeah, I can Google it too, but that doesn't answer my question. I'm using very specific ratings on a very specific device, and if I listened to that article I wouldn't have been using the switch last night at all.

As far as fitting, the connector is actually a little loose but it says in fine.

Edit: I used it after I posted last night, for probably 15 minutes, and it was working properly. I just don't know if leaving it plugged in constantly, which would be necessary if I do use it, is feasible.

[septus]

If you pump in more voltage than it's specced at, then you have a great chance of blowing it up/burning up a part. Of course this should happen fairly soon. The parts inside might be rated at more than it says on the box, but who knows. I'm guessing you're shortening the life of the device at the very least. Amps don't matter, as the device will only pull in as many amps as it needs. I'm surprised you didn't release the magic smoke.


Of course, I'm not an EE either. But I work for a semiconductor company so I'm around them all day.

[Bothra]

If it works and the thing is $20-$40 to replace then I would just run it till it burns up. I don't think a switch should cost that much. There will be some linear regulator somewhere in there that will step down that 7V input probably to a 3.3 or 5 V digital line for the microprocessor. The farther you get away from the 7V input on that part the hotter it will get and shorten the product life. But it will probably perform normally till you let the smoke out. The relationship is probably nearly linear in temperature for a 20% increase or so (7 -> 9V) but the relationship between reliability and temperature is likely exponential. Of course these things are derated some too so your air conditioned room probably buys you something.

All this is just conjecture since I don't have a schematic, but if it were me I'd run it till it explodes my house.

[Bobmuhthol]

It's a $22 replacement, but I might as well buy a power adapter if we're going to expect a failure sooner than normal. Thanks guys, and on that note, where would a good place be to buy adapters as cheaply as possible?

[Bothra]

Not sure, but dude, just run that shit into the ground. When you get the new switch it will come with a supply. There's a chance the thing will outlive you.

[Back]

Thanks guys, and on that note, where would a good place be to buy adapters as cheaply as possible?

Radio Shak.