[XCSSA] Sine of the times?

[X-otic Computer Systems of San Antonio]

On Friday 04 April 2008 15:20, X-otic Computer Systems of San Antonio wrote:
> I've got one of the $29 inverters in my car to power my phone charger
> and HP tablet.  Despite being rated at 300 Watts, it cannot run my
> Dell laptop with an 80W power brick.  I can plug in the brick and the
> laptop will charge, but as soon as I turn on the laptop the inverter
> squeals and powers down.

It should be obvious that even 300Watts is unrealistic, as most cigarette 
lighter fuses are 12V 20A fuses.. which will only get you 240watts max 
(12*20).  My guess is that they're measuring "peak power" (at the top of the 
sine wave), which would be = (RMS*(1/0.707)... or in other words.. 

Real Power = RMS power = Peak Power * 0.707

In the case of the listed 300Watts, that would be 212 Watts.  

But even still.. one would think that it should at least power your laptop's 
80 watts.  There may also be a real vs reactive power rating component to 
think about too.  Especially when dealing with switching power supplies.  The 
thinking there goes that the output of a power inverter does not like feeding 
a purely inductive load (like in a laptop power supply) IIRC.  

Charles?

Tweeks


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