Using a Laptop from My Car Battery? - Page 2

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Re: Using a Laptop from My Car Battery?

Relative to what?
Relative to a resistor, it's exactly the same...100% waste.

Re: Using a Laptop from My Car Battery?

It's not waste free at all.  The voltage is dissipated in the transistor.

I repeat my original post:

THERE ARE ONLY TWO WAYS TO CHANGE ONE DC VOLTAGE TO ANOTHER:

1.  Convert it to AC, change it, and convert it back to DC.

2.  ***IF*** the input voltage is higher than the desired voltage, you
can just "waste" the excess voltage as heat.  This is VERY inefficient,
but it does work.  It's not even an option, however, if you have 12
volts and you need, say, 15 volts.

The second way is what ALL "linear regulators" and "linear power
supplies" do.  It takes a switching power supply to do it the first way,
which is actually far, far more efficient and is the only way to simply
not waste ALL of any "excess" voltage as heat.

Re: Using a Laptop from My Car Battery?

Barry Watzman wrote:

Of course. You're right Barry. I must have been having too many late
nights. My mistake.

Re: Using a Laptop from My Car Battery?

Inverters normally do not provide sine-wave output, but the inverter
output doesn't go into the laptop, it goes into the laptop's AC adapter,
which doesn't care.  There is no issue for the laptop; very rarely,
there may be an issue for the AC adapter.

W. Watson wrote:

Re: Using a Laptop from My Car Battery?

These quasi sine wave inverters got to quite a bit of trouble to produce the
quasi sine wave (and waste quite a bit of power doing it).  Better to use an
inverter that provides a DC output (after all, the first thing the laptop
power supply does is to turn the AC into DC).

They are freely available in Europe and presumably the US as well.

Re: Using a Laptop from My Car Battery?

Maybe, but more likely not.

First, you must not connect your laptop to the electrical bus of the
CAR.  The car's power bus is incredibly dirty and has huge spikes as
things cut on and off.

As to a car battery (disconnected from the car itself, or with the car
engine not running), it's a good source of 12.6 to 13.5 volts.  The
problem is that your laptop most likely runs off of 15 to 19 volts DC
from it's power supply and a car battery is probably too low.

It might be possible to jury-rig a connection to where the laptop
battery connects to the laptop, but on most laptops the battery has an
onboard microprocessor that talks to the laptop, and the laptop may not
work without this data connection; simply providing power may not be enough.

Again, don't under any circumstances try to connect the laptop to the
car's electrical system with the car running.

W. Watson wrote:

Re: Using a Laptop from My Car Battery?

Hmmm ... wonder what police, fire and every other emergency service
running with laptops in the vehicle use!

Re: Using a Laptop from My Car Battery?

They are connecting equipment that was intended to be so directly
connected ... that has power supplies inside it that are tolerant of
this environment.  It's certainly possible to design equipment to
tolerate this, all automotive electronics does it.

But a laptop computer was not designed to operate this way.  A laptop
that was intended for this application could certainly be designed, but
that's another matter.

none wrote:

Re: Using a Laptop from My Car Battery?

There still remains the question of the inconsistent frequency if one uses
an inverter to produce AC, and then plugs the laptops adpater into it. Maybe
it has no impact at all on the HD or other components.

Has anyone actually used a laptop in this way and found that after six
months the laptop is doing just fine. I talked to a sales guy at Best Buy
and he said that's exactly what he was doing, but he was not just doing it
when the motor was off. He puts his laptop in the passenger's seat and runs
it with an inverter. I guess he gets lots of music from his laptop that he
might not get. He admitted that he's only done this a handful of times, so
he hardly meets the six month requirement I posed above.

Barry Watzman wrote:

--

Web Page: <speckledwithStars.net>

Re: Using a Laptop from My Car Battery?

The frequency of an inverter in this application has no impact.  The
laptop's AC adapter/charger is a switching power supply.  The first
thing it does is take the incoming line voltage, run it through a full
wave rectifier and then crudely brute force filter it with some
capacitors to a rough, high-ripple DC.  Frequency is irrelevant.  In
fact, almost everything is irrelevant ... noise and (over a very wide
range) voltage included.

If there was any risk, it would primarily be to the laptop's AC adapter
rather than the laptop itself.

W. Watson wrote:

Re: Using a Laptop from My Car Battery?

Good. Thanks.

To just clarify for all what I was driving at (aside from frequency), what I
didn't want was:

(DC-car)]---inverter---[(AC/120)]---converter---[(DC-laptop) ]

the [ and ] are plugs/sockets. {} is the laptop itself. --- is wire.() is
the voltage type, e.g., (AC).

What I wanted was:

(DC-car)]---dc/dc---[(DC-laptop)]

I hope the figures are clear. Simply, one dc/dc adapter was what I wanted.

The reason I was concerned about a stable frequency was that several years
ago, I was concerned about protecting our household power in the event of an
outage. A simple solution was to have a big 12v/dc battery and hook up an
inverter to it, then plug a desktop into it. I read that a stable frequency
was a concern in that case.

Is there a name for the dc/dc adapter? Voltage booster?

I understand that decades ago that cross-country power used AC (Tesla), but,
in the decades that produced silicon devices, AC went into the grid only to
be converted to dc for cross-country transmission. At the other end, it was
back to AC from the DC. I suspect what you are saying is something close to
the same idea.

Barry Watzman wrote:

--

Web Page: <speckledwithStars.net>

Re: Using a Laptop from My Car Battery?

W. Watson wrote:

Perfectly clear, thanks.

There have ALREADY been several very clear replies, including one I
posted myself, if you care to read them.

In case you missed them, there are boxes that do precisely this. They
consist of  a small box. At one end you have a lead that goes into the
car's cigar lighter. On the other end you have a lead with an adapter to
go into the laptop socket.  They cost around \$30.
For technical reasons, there is an AC stage inside the box, but the
frequency is much higher than the standard mains frequency, ensuring a
higher efficiency and causes no ill effects.

Is that clear now?

The one I have here is called a MAX90W. I paid 15 euros (about \$20) for
it and it works fine. The output can be set to any voltage between 15
and 24 volts and it comes with a range of connectors to fit most laptops.

Re: Using a Laptop from My Car Battery?

In the US, most air/auto power adapters with ratings of 90 watts and
above (or even 60 watts and above) are quite a bit more than US \$30.
Some of them are more than \$100.

Re: Using a Laptop from My Car Battery?

Barry Watzman wrote:

I should have mentioned that it was a low cost (and possibly low
reliability, but I have been OK so far) model and I got it from ebay.
But it was new and boxed and the price was for immediate purchase; the

Our friend would well be happy with a \$100 model if it suits his purpose.

I've just taken a look at the US ebay site and found this
http://cgi.ebay.com/DELL-laptop-Car-Charger-New-Most-Models_W0QQitemZ260126148453QQihZ016QQcategoryZ31512QQrdZ1QQcmdZViewItem

Its for Dell, costs \$31.

Re: Using a Laptop from My Car Battery?

Just from the physical size of that unit I would guess that it's output
is 60 watts or less (it's actual power output, without regard to any
claims that may be made).  You can charge a battery with that, but you
may not be able to run a laptop.

http://cgi.ebay.com/DELL-laptop-Car-Charger-New-Most-Models_W0QQitemZ260126148453QQihZ016QQcategoryZ31512QQrdZ1QQcmdZViewItem

Re: Using a Laptop from My Car Battery?

Barry Watzman wrote:

It was only supposed to be an EXAMPLE of the kind of things he can find
if he looks. I wasn't recommending that he buy this particular box. Nor
was I saying that this box can do everything.

I was saying that boxes exist that can convert from 12 v to voltages
suitable for laptops (whatever the electronics inside the box) and that
they can be had for a reasonable price.
Just what a "reasonable" price is can vary.

In formal logic, an EXAMPLE proves existence.

Now he knows they do indeed exist, the original poster can go and look
for a box that suits his particular purpose and wallet.

Re: Using a Laptop from My Car Battery?

Thanks. I read and understood several posts above.
I see the next post mentions wattage. Mine is 90w. I'll be trying out later
today. I'm leaving on my trip Saturday. If it doesn't work, I'll return it.
My choices at this point are limited to it. Whatever way it goes, I can deal
with it. Without it, it'll be a little less convenient.

--

Web Page: <speckledwithStars.net>

Re: Using a Laptop from My Car Battery?

From an aesthetic perspective, wanting to avoid two devices (inverter
and laptop AC power supply) and their associated cords is
understandable; but both solutions will normally work equally well
(having two devices is also less efficient from an energy perspective,
but that is usually not a consideration).

Re: "The reason I was concerned about a stable frequency was that
several years ago, I was concerned about protecting our household power
in the event of an outage. A simple solution was to have a big 12v/dc
battery and hook up an inverter to it, then plug a desktop into it. I
read that a stable frequency was a concern in that case."

It's not an issue for a computer; it may be a minor issue for a CRT
monitor (you may get some bars through the picture), but even there
nothing that would usually keep the display from working.

All commercial power distribution is AC.  You won't find DC anywhere.

W. Watson wrote:

Re: Using a Laptop from My Car Battery? -- OT

Barry Watzman wrote:
*/---------- snip -----------

Barry,

I think he was referring to long-haul
transmission.  On the West Coast, we use DC
transmission on one of the newer lines from
the Pacific-Northwest to Southern California.
The earlier lines were 3-phase AC.

--
pj

Re: Using a Laptop from My Car Battery? -- OT

I find that hard to believe, for ANY power transmission application.  At
some point, you need to step it down, and you can't do that with DC.
Further, there is no inherent transmission advantage to DC vs. AC, and
on top of that DC is hard to generate from a mechanical generator.

PJ wrote: