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.

http://tinyurl.com/6nfbrp

This one's 400W, but we're wondering if the extra cost is worth it.

Thanks for any info.

You seem to have a chip on your shoulder. While there is an element of
truth in many of the things that you say, things are not nearly so bleak
as you suggest.

spamme9 wrote:

> The 100W one isn't big enough.
>
> Here's the ugliness of all this.
>
> Any inverter you can afford will be a Chinese knock-off
> of a knock-off of another knock-off of a maybe-good original
> design.
> The "designer" copied the circuit (not to be confused with the design)
> and used the cheapest available
> parts and the cheapest labor. They had not a clue to the original
> design tradeoffs. They probably spent more money on the design of
> the attractive display box than the design of the inverter.
>
> It's tested to run a light-bulb in very infrequent use for as long
> as the warranty...assuming you can find the vendor.
>
> But your laptop is NOT a light bulb. It's a diode and a capacitor.
> When the fast rise of the modified sinewave slams into the cap, you
> get MUCH higher peak currents than you would with a light bulb.
> Just twice the current for half the time is still twice the heat in
> the output bridge of the inverter. And that assumes the transistors
> can reliably take twice or 4-times or more the peak current.
>
> When using a square wave or modified sinewave (not so square wave)
> converter to drive a switching power supply, you need much more
> "rated watts" than you'd think.
>
> Typing this got me thinking...
> Newer power supplies have built-in power factor correction to make
> life easier for the power companies. What happens when you try to
> run one of those from a square wave???
>
** Posted from http://www.teranews.com **

On Thu, 20 Nov 2008 09:38:30 -0800, <nospam@nospam.invalid> 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.
>
>http://tinyurl.com/6nfbrp
>
>This one's 400W, but we're wondering if the extra cost is worth it.
>
>Thanks for any info.
>
>
For another option... Radio shack (and probably others) sells a power
supply for laptop computers that plugs directly into the 12v outlet in
your auto, and produces whater voltage your laptop requires
(adjustable). It comes with a set of tips so that it is adaptable to
just about any laptop.

--
Charlie Hoffpauir
http://freepages.genealogy.rootsweb.com/~charlieh/

Charlie Hoffpauir wrote:
> On Thu, 20 Nov 2008 09:38:30 -0800, <nospam@nospam.invalid> 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?

I'd go with at least 150 watts. 400 is overkill for just a single laptop.

>>
> For another option... Radio (S)hack-and probably others-sell a power
> supply for laptop computers that plugs directly into the 12v outlet in
> your auto, and produces whatever voltage your laptop requires
> (adjustable). It comes with a set of tips so that it is adaptable to
> just about any laptop.

Assuming first that "just about any laptop" includes the original
poster's particular Compaq, I still consider this option to be
inadvisable. What are the chances that any of the power supply's tips
will both fit and provide the proper polarity for the laptop he or she
will buy to replace this one a few years hence? Granted, a power
inverter is not as efficient, but it'll almost certainly be a lot
cheaper than any specialized DC power supply-and it'll also work with
anything that runs on house current, now and in the future.

You seem to have a chip on your shoulder. While there is an element of
truth in many of the things that you say, things are not nearly so bleak
as you suggest.

spamme9 wrote:

> The 100W one isn't big enough.
>
> Here's the ugliness of all this.
>
> Any inverter you can afford will be a Chinese knock-off
> of a knock-off of another knock-off of a maybe-good original
> design.
> The "designer" copied the circuit (not to be confused with the design)
> and used the cheapest available
> parts and the cheapest labor. They had not a clue to the original
> design tradeoffs. They probably spent more money on the design of
> the attractive display box than the design of the inverter.
>
> It's tested to run a light-bulb in very infrequent use for as long
> as the warranty...assuming you can find the vendor.
>
> But your laptop is NOT a light bulb. It's a diode and a capacitor.
> When the fast rise of the modified sinewave slams into the cap, you
> get MUCH higher peak currents than you would with a light bulb.
> Just twice the current for half the time is still twice the heat in
> the output bridge of the inverter. And that assumes the transistors
> can reliably take twice or 4-times or more the peak current.
>
> When using a square wave or modified sinewave (not so square wave)
> converter to drive a switching power supply, you need much more
> "rated watts" than you'd think.
>
> Typing this got me thinking...
> Newer power supplies have built-in power factor correction to make
> life easier for the power companies. What happens when you try to
> run one of those from a square wave???
>
** Posted from http://www.teranews.com **

100 watts is not large enough. If a laptop uses 90 watts, and if it's
own AC adapter is 60% efficient, you will need an inverter with an
OUTPUT of 150 watts (60% of 150 is 90). Some laptops need over 100
watts. The efficiency of the AC adapter isn't easily determined (60% is
probably low, but better to be low than high for this purpose).

I'd buy at least a 300 to 500 watt inverter. You don't need that much
FOR A LAPTOP, and, really, about 350 watts is the most you can get using
a cigarette lighter plug anyway (and sometimes not that much), but
inverters come in handy at times for applications other than those for
which they were originally bought, and there probably won't be very much
of a price difference between a 150 watt inverter (a size which you
NEED) and a 300 to 500 watt model.

There is no downside, within this range, to having the larger unit (now
if you were talking about a 1000 watt or larger unit, that would not be
the case, however).


nospam@nospam.invalid 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.
>
> http://tinyurl.com/6nfbrp
>
> This one's 400W, but we're wondering if the extra cost is worth it.
>
> Thanks for any info.
>
>
>
>
** Posted from http://www.teranews.com **