AC adapter - Basic Electronics Question

DaSilva · 11-09-2008 10:20PM #1

Hey, I'm trying to understand some electronic stuff. My laptop AC adapter packed in, and a replacement is pretty pricey, €60 upwards which is annoying as it's a pretty old laptop.

Anyway, the power supply output specs are 19.5V, 6.7A .
I understand the Voltage output figure, but what does the Amperage figure mean? Is 6.7A the most current that can be drawn from the adapter? Reason is I can find power supplies with close 19-20V but nearly all the adapters, even specifically designed adapters for laptops generally have much lower Amperage output figure. Is the Amperage very important? If I use an adapter with the same voltage but lower amperage will it overheat?

Thanks

kelly1 · 13-09-2008 12:32AM

DaSilva wrote: »

Hey, I'm trying to understand some electronic stuff. My laptop AC adapter packed in, and a replacement is pretty pricey, €60 upwards which is annoying as it's a pretty old laptop.

Anyway, the power supply output specs are 19.5V, 6.7A .
I understand the Voltage output figure, but what does the Amperage figure mean? Is 6.7A the most current that can be drawn from the adapter? Reason is I can find power supplies with close 19-20V but nearly all the adapters, even specifically designed adapters for laptops generally have much lower Amperage output figure. Is the Amperage very important? If I use an adapter with the same voltage but lower amperage will it overheat?

Thanks

Hello DaSilva, the output power sounds high 19.5 x 6.7 = ~130W. The PSU for my laptop is 65W. 6.7A would be the max output current so I wouldn't suggest using anything less. I would imagine the current drawn by the laptop would be fairly constant so unless it way overspec'd, you'd need something around the 130W mark.

Noel.

mawk · 15-09-2008 02:17PM

while kelly is largely correct, i dont think going a little lower will do any great harm. a 20v 4a DC transformer (ish) should have plenty or grunt to charge it even from flat. it wont charge as fast and possibly not quite as full. but it should work fine. lots of chargers are under spec to save cost. i misplace chargers all the time and charge stuff with my big bench power supply. i often notice the batteries charge happily at over what the OEM charger outputs.

Jonathan · 15-09-2008 04:48PM

DaSilva wrote: »

Hey, I'm trying to understand some electronic stuff. My laptop AC adapter packed in, and a replacement is pretty pricey, €60 upwards which is annoying as it's a pretty old laptop.

Anyway, the power supply output specs are 19.5V, 6.7A .
I understand the Voltage output figure, but what does the Amperage figure mean? Is 6.7A the most current that can be drawn from the adapter? Reason is I can find power supplies with close 19-20V but nearly all the adapters, even specifically designed adapters for laptops generally have much lower Amperage output figure. Is the Amperage very important? If I use an adapter with the same voltage but lower amperage will it overheat?

Thanks

Take a multimeter to the laptop an see what amps it is consuming when you have the cpu maxed out. I bet it wont be near 130w.

Turbulent Bill · 18-09-2008 02:20PM

jmccrohan wrote: »

Take a multimeter to the laptop an see what amps it is consuming when you have the cpu maxed out. I bet it wont be near 130w.

Do not do this! Considering the OP has no concept of current (the amp specification), messing about with a multimeter which is potentially connected to the mains is a very bad idea. Get a matching power supply, or ask someone who knows what they're doing.

mawk · 18-09-2008 02:49PM

Turbulent Bill wrote: »

Do not do this! Considering the OP has no concept of current (the amp specification), messing about with a multimeter which is potentially connected to the mains is a very bad idea. Get a matching power supply, or ask someone who knows what they're doing.

pfft, if he doesn't shock himself a few times and break some appliances in the process.. how is he supposed to learn?

AC adapter - Basic Electronics Question

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