[RESOLVED] Notebook Computer AC Adapter Intechangeability

[Muddy]

My notebook came with an AC adapter with an output of 19 vdc (center positive) ... 3.16 amps ... (which works out to 60 Watts)

I lost the orginal adapter and am in a remote location where the only replacement I could find was a universal AC adapter (APC TravelPower) which I configured for 19 vdc (center positive) ... 3.7 amps ... rated for 75 Watts even though the math at my settings indicate that it is working at closer to 70 Watts. The voltage is the only thing variable, of course, so I am stuck with the 3.7 amps.

I plugged this in and it has been working fine with my laptop for a day now. My assumption is that the Notebook will only draw as much amps as it needs.

The APC adapter documentation doesnt list my notebook as compatible which is no surprise since it is an OEM brand (Compal), so the APC tech support line and manuals are no help to me.

Am I taking any risks using this adapter? If so are they short term or long term risks?

Thanks in advance for any help!

[-TPM-]

Well most things have a built in tolerance, so the small amp increase may not be a huge problem. Although I'd rather go with a power supply that lists your laptop just in case. Kingston have a very good one (that's what I use). It's all auto as well so you don't have to select pin's and voltages etc.

[DaveBo]

My assumption is that the Notebook will only draw as much amps as it needs.

Your assumption is correct.

[Muddy]

I spoke to a technical person (through our computer supplier). He says that I'm OK in my situation .... but probably if I tried using an adapter closer to 90 Watts on my 60 Watt notebook I might have a problem no matter what the voltage.

I feel much better now ...

[Muddy]

Well most things have a built in tolerance, so the small amp increase may not be a huge problem. Although I'd rather go with a power supply that lists your laptop just in case. Kingston have a very good one (that's what I use). It's all auto as well so you don't have to select pin's and voltages etc.

I cant find a Kingston AC Adapter anywhere searching the net. Do you have a webpage?

Thanks for the info, BTW!

[-TPM-]

Ooops I'm sorry it's Kensington, not kingston. Here a link too it on their site: http://us.kensington.com/html/6368.html I got mine from Costco for ~$80 and it came with a few exctra tips. I also forgot too say it's also a car and plane adapter, which can be pretty handy.

You can find out if it'll work with your laptop etc here: http://us.kensington.com/compApp/ktg...=2&pageId=9162

[DaveBo]

but probably if I tried using an adapter closer to 90 Watts on my 60 Watt notebook I might have a problem no matter what the voltage.

The rated voltage is critical, along with the polarity, i.e. +- orientation of the connector tip. These have to be precise.

As far as current (milliamps) and power (watts) as long as the adaptor can, at a minimum, supply your systems needs there is no upper limit.
i.e. if the adaptor can supply a megawatt, it doesn't matter, your system will only use what it needs.

e.g. you car's battery supplies 12V
- at 500amps to your starter motor
- or 0.5amps to the tiny bulb in the domelight
quiet happily as needed.
(Note, my current numbers above are not exact, don't quote me.)

[Muddy]

-TPM- Thanks for the link!

Davebo: One person I talked to explained that laptop AC adapters swing the voltage depending on how many amps are being drawn in order to regulate the Watts. So the lower amp draw would cause the voltage to swing up to keep the watts constant.

I have no firsthand knowledge, though.

I was going to try to measure the AC adapter output voltage while plugged into my laptop, but could not see a way to do it without stripping insulation from wires :-) ...

[DaveBo]

One person I talked to explained that laptop AC adapters swing the voltage depending on how many amps are being drawn in order to regulate the Watts. So the lower amp draw would cause the voltage to swing up to keep the watts constant.

That's somewhat true, but not by design.

In simpler (cheaper) adaptors the voltage will drop slightly below the rated voltage as current demand goes up. An analogy is, the more you open a water faucet (more current) the lower will be the pressure (voltage) in the system. This is an inherent weakness in the system, not a designed-in feature.

A good power supply will be regulated to try to maintain a fairly constant voltage. i.e. you want to regulate (keep constant) voltage, not current or power (watts).

Sorry I'm not explaining this very well.
But, take my word for it, voltage must be correctly chosen for the application, i.e. if it calls for 19volts, don't use 12 or 24.
You can probably get away with +/- 5%.

Polarity is usually non-negotiable if the adator is outputting DC!

Current and power are demand driven and as long as the supply can handle the unit's demands at a minimum you're OK. If the supply/adaptor can provide a 1000 times your power needs - that's OK too.

Think of the AC outlets in your home. You don't want to plug a 110V unit into a 220V outlet unless you're a pyromaniac.
But, you normally don't care about the power you're using unless it's going to exceed your wiring and circuit breakers max limits.

FYI, I was an electronics tech in the US Navy (ETN2) and in the private sector for many years. Also worked for a computer power supply co.
It, AMPSCO, along with all its customers, Digital, Prime, Incoterm ... have all gone out of business. The ship I was on has been decommissioned, the company I work for now is closing soon ...
forget everything I've said and have a Merry Christmas!