AC adapter question (for the electronic/electrical engineer types)

[icarus]

Hi guys,

If I use a Dell AC adapter with output of 19.5V 4.62A with my Toshiba laptop (whose factory-supplied AC adapter before it blew up had an output of 19V 4.74A), will anything bad happen?

I'm not thinking permanently, just long enough to, say, watch a hockey game?

[HelloHockeyFans]

IIRC, the voltage level is what can blow your device up. The higher current levels mean shorter charge periods. Can any other engineers confirm this?

EDIT: Don't blame me either please. b

[photon]

That's pretty close, probably within tolerance of the AC adapter ratings itself; most AC adapters are fairly cheaply made and their outputs can vary by quite a bit. The laptop itself would likely have circuits in it to deal with slight overages and stuff. It's only half a volt more (2.5%).

My only concern would be the max current of the Toshiba adapter is higher than the Dell one.. not by a whole heck of a lot mind you, and my gut tells me that a) the max current draw is probably never reached and b) even if it did it would likely just make the Dell adapter hotter than normal, but probably not enough to start a fire.

The biggest thing would be the connector, and the polarity of the connector; some connectors have the positive in the centre, others have it on the outside, plus the shape might be different enough that it doesn't make a good connection, introduces noisy power, and that can be very hard on components.

My gut tells me it should be ok, but I'm 14 years removed from my degree.

How badly do you want to buy a new laptop?

[Phanuthier]

My guess is you'll be ok. I'm sure your laptop is protected to voltage surges and as photon said, you are within tolarance.

This is the non-application side of me, but if you split the cables, you could make a voltage divider out of the adaptor. Knowing your load and input power, you could make a little circuit to give you your desired input voltage to your laptop.

Don't blame me if something goes wrong though

Oh, and check your laptop to see if it gets warm. If it does get warm, then you might want to unplug it.

[photon]

Originally Posted by HelloHockeyFans

IIRC, the voltage level is what can blow your device up. The higher current levels mean shorter charge periods. Can any other engineers confirm this?

The current rating of an adapter isn't what it provides, it's more what it can provide maximum. The current drawn will depend on the voltage and the resistance that the laptop shows to the adapter..

So in this case, let's assume the old adapter was running at max. V = IR, so for 19V and 4.74A that's a resistance of 4.008 Ohms.

If we take that resistance and put the new adapter's 19.5V across it, that's 4.86A, while the adapter is only rated for 4.62A.

That's simplistic though, since the resistance (and thus the current draw) will change depending on what's being used. And there's usually circuitry to regulate the voltage (though in a laptop I wonder if they offload ALL that to the AC adapter).

And keep in mind the AC adapter will be rated for full power operation of the laptop AND charging the battery at the same time. So to keep the current draw down the battery could be left out of the laptop, or keep it off while charging.

[icarus]

Originally Posted by photon

And keep in mind the AC adapter will be rated for full power operation of the laptop AND charging the battery at the same time. So to keep the current draw down the battery could be left out of the laptop, or keep it off while charging.

So I should not charge and use the laptop at the same time?

I do have a cheap replacement AC adapter on order from Hong Kong, but I am pretty sure it won't arrive before the playoffs!

[Phanuthier]

Whichever the case, the computers not gonna blow once you power it in (at least I doubt it) and if your circuit components are gonna burn, you'll probably feel the computer get warm. So, watch the heat of the computer.