Re: Power Inverters

Martin Slaney wrote:
nospam@xxxxxxxxxxxxxx wrote:
We're looking for a power inverter to recharge our Compaq notebook
in the car. Is it better to buy one with a larger rating (400W) rather than
a smaller one? Black & Decker has a 100W model ($13) and it gets
good reviews:

http://tinyurl.com/5fstl9

But the notebook uses something like 90W, so we'll be very close to
this inverter's capacity. The alternative is something larger, e.g.

Well you're right to "err on the side of caution" wrt the ratings of these kind of gadgets, but ....

You say you want to "charge" the laptop ... well if you mean _just_ chrage the battery, I think you'll find that takes a good deal less current than _powering_ the laptop. If you want to power the laptop (which will include simultaneously charging the battery) - then it might be wise to go for a conservative rating of inverter, but a "90W" (and lets assume that 90W rating is "ambitious") - should be absolutely fine for just charging the battery. Excercise caution though if you fire up the machine aswell.

Also - make damn sure that this inverter has effective filtering (it sure as hell should) - the 12V in cars can carry massive spikes e.g. when you turn on the ignition etc.

Well many laptops as many frequent fliers already knows... if the laptop can't get enough power to power everything. It may turn off the battery charger and may underclock the CPU to keep itself powered. We know this because many 12v outlets in airlines only supply 90 watts.

Also charging the battery works like this. Take for example this EeePC. Total watts at any time is 20. And when you charge with the laptop off, it still draws 20 watts. When running and charging, it still uses 20 watts. When the battery is charged, it drops down to 10 watts.

So the charging power takes everything that is left over. And I have noticed this from virtually all laptops I have ran across. Which explains why if you are using the laptop, it takes longer to charge the battery.

--
Bill
Asus EEE PC 8GB 1GB SoDIMM Adata 16GB
Windows XP SP2 and Xandros Linux
.

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