# Power Factor Correction laptops and modified sine wave UPS?

Discussion in 'Dell' started by Ron Hardin, Aug 1, 2011.

1. ### Ron HardinGuest

Do any Dell laptops find themselves unable to power from a modified sine
wave UPS?

No use springing for a sinewave UPS unless necessary.

So far I haven't noticed laptops failing but I suppose one might secretly
be on its own battery power and I didn't realize it.

Ron Hardin, Aug 1, 2011

2. ### RnRGuest

If I recall correctly, this has already been discussed here and no
need for special UPSs (anyone pls correct me if I'm wrong). Aside
from this, I still don't understand what a PowerFactor is and I recall
having a part of a lecture one day in an Electrical Engineering
college class going over it (I'm not an EE). I've also read about it
in a usenet newsgroup and still didn't quite get it but I also gather
it doesn't get used much my EEs (tho I could be wrong). No need to
explain it since I'm sure I can Google it if I really need to learn.

RnR, Aug 1, 2011

3. ### NickGuest

It depends on the power supply in the computer being hooked up to the UPS.

As I found out the hard way a year and a half ago, my XPS 9000/435T does
need a UPS with a sine wave output. Plugged into a UPS with a non-sine wave
output, my computer shuts down instantaneously when the UPS switches to
battery backup power.

No idea if any other models (desktop or laptop) are the same way.
Power factor is the phase angle between current and voltage in an AC
circuit.

In a pure resistive circuit, it's zero because the current and voltage are
exactly in phase. If there's unbalanced inductance or capacitance in the
circuit, then the power factor won't be zero because the voltage and current
won't be in phase.

Nick, Aug 1, 2011
4. ### RnRGuest

Thanks Nick for correcting me. Great explanation too !!

RnR, Aug 1, 2011
5. ### Ron HardinGuest

The apparent trouble is that the modified sine wave confuses the circuits in
PFC power supplies and they decide to shut down rather than deal with it.

The trouble is not in the modified sine wave itself but in faulty design of the
PFC supply.

The question is whether these supplies (that shut down) are used on laptops.

Some dell adapters claim to be PFC supplies but I don't know that they shut
down with a modified sine wave.

Ron Hardin, Aug 1, 2011
6. ### RnRGuest

Funny Ron, as I was writing the last post, I was wondering about
laptops too. I haven't heard of it but that doesn't mean anything. I
will let someone else more qualified answer this question. Also I
wonder besides Dell, if this question affects other brands too??

RnR, Aug 1, 2011
7. ### DaddyGuest

Is there something about a laptop that makes it different from a desktop
w/r/t a sine wave UPS? If so, apologies in advance and ignore the rest
of this post.

I had a similar question when I purchased my desktop (Studio XPS 8100),
which also has a power factor correcting power supply. The problem was
that a pure sine wave UPS would have set me back roughly half the cost
of my computer.

I had deep suspicions about the need for a pure sw UPS, but I won't
repeat the long back-and-forth discussions I had about this topic.
Suffice it to say that, on paper, you need a pure sw UPS...but the real
world is much different. Try this test before you spend the next two
months eating sandwiches:

Pull the UPS' plug from the wall socket. Does your equipment still run?
Are you getting error messages? If the answers are yes and no,
respectively, then you're good to go without an expensive new UPS.

If you're using your laptop for some very critical purpose, you want to
spend the extra money, but then you're talking about a completely
different situation from the norm.

Daddy

Daddy, Aug 1, 2011

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