Question Dell achieving high performance with lower wattage charger?

robo731

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Jul 14, 2012
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I have a Dell N7110 with a 48 WHr 6 -cell battery. I believe it's supposed to use a 90 Watt AC adapter to charge, however the charger I have is 65 Watts.

When I boot the laptop it gives a warning that it will adjust performance to match the lower watt power adapter.

I'm wondering if this really has an effect on the performance? If the two chargers deliver the same current then it should not affect the performance of the laptop, only the charging speed, right? Is there a way to override this performance adjustment if there is one?
 

velocityg4

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It might have some effect. How much I couldn't say. As CPU/GPU frequency tends to effect power draw on a curve. Not linearly. So it may just be a few tenths of a Ghz or disabling turbo boost. The only way you'd know is to benchmark the differences between a 90W and 65W AC adapter.

It has to do this as the CPU, GPU and other parts may draw too much current for the 65W AC adapter at full load. Which would risk damaging the AC adapter or causing a fire. If the AC adapter doesn't have some mechanism to cut or limit power when the draw is too high.

The chargers don't deliver the same current. Current is amps. Both are 19.5V one is rated for ~3.3A the other ~4.6A. If you wanted. You could use a 130W AC adapter to no ill effect or even higher. The problems arise when it is too low a wattage (watts = volts x amps). There is no upper threshold for amps. You can have an adapter which is capable of delivering way more amps than a device needs. As long as the plug, voltage and plug polarity are the same. Those three must be the same.

The AC adapter is just an external PSU. It's no different than trying to use too weak a PSU in a desktop. The only difference is that Dell made their laptop recognize when it is on too weak an AC adapter. Adjusting the speed settings accordingly. While a desktop will keep chugging along until the PSU suddenly cuts power or blows out. In the case of cheap units.

If you could override these settings. There are a few possible outcomes. I couldn't say which is true.
  • The AC adapter overloads and burns out. Possibly starting a fire.
  • The AC adapter overloads and cuts power to protect itself when it overheats. Which a UL listed device is supposed to do.
  • The AC adapter limits its draw when overloaded and your battery has to make up the difference. Until the battery is drained. Then the computer crashes.
  • Your uses of the machine don't cause an overload or Dell overestimated the draw and the machine operates within 65W under full load.
Edit: By the way. Don't be tempted by cheap replacement units. Only use an OEM unit or at least a well reputed third party brand which undergoes all appropriate safety testing and certification. A lot of the cheap no name brands use substandard parts. Which may not undergo any UL testing. Sometimes they just slap on fake UL markings.
 
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robo731

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Thanks for the detailed explanation!

No worries, it is an OEM adapter.

Interestingly the dell manual for this laptop lists a 65W, 90W, and 130W adapters on page 89. Perhaps it's my particular configuration that requires atleast a 90W one.

Anyway, the 65W is the only charger I have right now, so hopefully the performance will be sufficient for my purposes.

Though the battery alone, fully charged, should be able to deliver enough power for maximal performance atleast until it runs out, right?
 
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