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My laptop's AC adapter went out last night and I bought a replacement today, but will not be able to test it until tonight or tomorrow.

My laptop is a Gateway P7801-U, but unfortunately Gateway does a very poor job of detailing their specs and no power requirements are given beyond the battery capacity.

The label on the old adapter says 19V @ 6.3A max. The new adapter I bought is this Lenmar 120W model with variable voltage setting. I read on the packaging that the current is only 5.5A when set at 19V though.

I'm a mechanical engineer and not an electrical engineer for a reason, and I have no idea what these numbers mean when it comes to plugging in my laptop. Could I run the system at this lower amperage? Do I want to? In other words, would I be able to turn the machine on at all, or even worse, damage it?

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2 Answers 2

up vote 3 down vote accepted

If you have the same voltage, but different amperage then the power supply could theoretically burn out faster. Basically the normal analogy is voltage is pressure. You have the same amount. Amperage is flow - the adapter isn't capable of delivering as much as the old one. This could cause the adapter to overheat as it would be running at higher percentages of its capacity versus the old one. The main issue is how much draw are you doing? Are you running the screen at full brightness, running lots of stuff off the USB ports, running heavy applications... Anything that brings your laptop up to max capacity will draw more power.

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+1. That's a very helpful, clear description of voltage/amperage. Thanks a lot. +1 for question, also. Regards, –  Xavierjazz Mar 3 '11 at 20:37
    
Yeah - that's great, thanks a lot for the analogy. The whole electrical thing just never clicked with me, but pressures and hydraulics make it much more clear. –  NoCatharsis Mar 4 '11 at 1:32

Blackbeagle raises good points about current and voltage. To check a bit further, I have had a look at what various suppliers are specifying for a third party replacement, and the current ratings I have found range from 4.9A to 5.5A - for example, this one on Amazon:

http://www.amazon.com/Replacement-Warranty-P-6831fx-P-6860fx-Computer/dp/B003E1RYWO

This is listed as:

Replacement Plug with 5 Year Warranty for Gateway Laptop Ac Adapter P-6825 P-6828h P-6829h P-6831fx P-6832 P-6836 P-6860fx P-7801 P-7801u P-7805u P-7805u Computer Power Battery Charger 90w

..and the power spec is as follows:

19V,90w ,4.74A

I found that particular model listed on various sites so I would suggest that your 120W (5.5A) unit will probably be fine.

Edit: More evidence:

http://www.batterynerds.com/Gateway-P-7801u-FX-AC-Adapter-79869?zmam=55412609&zmas=1&zmac=8&zmap=AC-LT02-G12975&shop

Compatible 90W Gateway P-7801u FX AC Adapter. Replacement 19V 4.74A laptop AC Adapter is guaranteed to meet or exceed original Gateway P-7801u FX AC Adapter specifications.

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