Electrical Power for Laptops

Alan French wrote:
"Alan French" wrote in message
...
I just revived an old non-working laptop that we were given. What options
are available to get some added work hours out of it when away from the
house?

We have an inverter/drive corrector, and could plug that into one of our
17AH 12volt batteries, and then plug the laptop's AC adapter into the
inverter. That seems inefficient, and maybe there is a good reason not to
power the laptop this way.

Would it be reasonable to make an adapter to plug the laptop directly into
the 17AH battery, or is there some reason this would be bad for the
laptop?

Rod, Pat, and William,

Thanks for your advice. I appreciate it.

For some reason I had assumed that laptops used 12v, but I see that the one
here uses 15v.

That's like mine--gotta find an inverter, of enough capacity to power
you laptop (check the current rating of the laptop's transformer).

--
Pat O'Connell
[note munged EMail address]
Take nothing but pictures, Leave nothing but footprints,
Kill nothing but vandals...

A 17AH 12V battery with an inverter is a good solution, but I think the 17
AH battery will be empty too soon. My laptop is 0.37 Ampere DC. It can be
easily calculated that it will run 2.2 hours max. with a 17AH battery. When
temperature is 0 Celsius, it will only run 1.4 hours max (capacity of
battery 63%). Energy loss in my inverter is 10%. I use a 70Ah battery.

--
Jan
http://home.wanadoo.nl/jhm.vangastel/Astronomy/


"Alan French" schreef in bericht
...
I just revived an old non-working laptop that we were given. What options
are available to get some added work hours out of it when away from the
house?

We have an inverter/drive corrector, and could plug that into one of our
17AH 12volt batteries, and then plug the laptop's AC adapter into the
inverter. That seems inefficient, and maybe there is a good reason not to
power the laptop this way.

Would it be reasonable to make an adapter to plug the laptop directly into
the 17AH battery, or is there some reason this would be bad for the
laptop?

Thanks.

Clear skies, Alan

A 17AH 12V battery with an inverter is a good solution, but I think the 17
AH battery will be empty too soon. My laptop is 0.37 Ampere DC.

I think you meant to write AC and 220 volt at that.

It can be
easily calculated that it will run 2.2 hours max. with a 17AH

I am curious if you have actually measured this or if this is just a calculated
number.

The stated current draw of the transformer is a maximum value and I suspect
that it is only that high when the laptops own battery is being charged. The
operational needs are likely much less.

Something to consider...

Most laptop batteries are around 4000ma-hr and something around 10-12 volts and
will power the laptop for 2 hours or so. I would seem that if one could get
the DC from the battery directly to the lap top rather than going through the
DC-AC-DC conversions that there would be more than enough to run the laptop for
many hours.

It is also difficult to believe that the DC-AC-DC conversion is so inefficient
that a 17 amp-hour battery will only run the laptop for the same amount of time
that its own 4000ma-hr would.

Something else to consider for Alan if he is brave and knowledgeable...

If one is handy with wires and meters and such...

If they laptop is essentially disposable, the 15 volt requirement is actually
close enough to the 12.6 volts that a 12 volt battery produces that you might
get away with operating directly off the 12 volt battery. Some laptops though
actually operate on AC and have the rectifiers built in to the laptop.

My guess is that the 15 volts is actually there to provide a bit of headroom
for the charging regulator and that the laptop actually operates on something
signficantly less.

Another possibility if one is handy is to wire the battery external battery
directly to battery terminals of the laptop itself, replacing the battery.
This would take some investigation to see if it were possible and might require
some external circuitry.

Personally I just use an inverter plugged into the motorhome's second battery
which is 106 amp-hours or so...

But mostly I avoid such things and use my Palm with Planetarium which runs for
a month or so on two AAA cells.

jon

On 12 Apr 2004 12:21:29 GMT, (Jon Isaacs) wrote:

A 17AH 12V battery with an inverter is a good solution, but I think the 17
AH battery will be empty too soon. My laptop is 0.37 Ampere DC.

I think you meant to write AC and 220 volt at that.

It can be
easily calculated that it will run 2.2 hours max. with a 17AH

I am curious if you have actually measured this or if this is just a calculated
number.

The stated current draw of the transformer is a maximum value and I suspect
that it is only that high when the laptops own battery is being charged. The
operational needs are likely much less.

Something to consider...

Most laptop batteries are around 4000ma-hr and something around 10-12 volts and
will power the laptop for 2 hours or so. I would seem that if one could get
the DC from the battery directly to the lap top rather than going through the
DC-AC-DC conversions that there would be more than enough to run the laptop for
many hours.

FWIW, I have a 20Ah Xantrex Powerpack 400, and the manual says it can
run a laptop computer for 6 hours on a full charge.

Cheers,

-Craig

"Craig Levine" wrote in message
news
On 12 Apr 2004 12:21:29 GMT, (Jon Isaacs) wrote:

A 17AH 12V battery with an inverter is a good solution, but I think the
17
AH battery will be empty too soon. My laptop is 0.37 Ampere DC.

I think you meant to write AC and 220 volt at that.

It can be
easily calculated that it will run 2.2 hours max. with a 17AH

I am curious if you have actually measured this or if this is just a
calculated
number.

The stated current draw of the transformer is a maximum value and I
suspect
that it is only that high when the laptops own battery is being charged.
The
operational needs are likely much less.
Dead right.
Looking at a fairly 'heavy duty' (P4 with 15.5" 1800*1400screen), laptop,
the power supply specifications, are 18v at 4.2A (charging), and 18v at 1.4A
(running only). Slightly smaller laptops will draw a little less.
Most 12v to 18v boost inverters, manage better than 80% efficiencies, so the
current draw at 12v, would be (18*1.4)/(12*0.8) = 2.62Amps.
Now in general, for telescope operations, you should only look to relying on
the battery delivering about 0.6 it's rating (the rating is for the 'ten
hour' discharge rate, and falls to typically 85% - 90% at a four hour rate -
also the rating falls with temperature, and with age). So a 17Ahr battery
would run the laptop reliably for about (17*0.6)/2.62 = 3.9 hours.

Something to consider...

Most laptop batteries are around 4000ma-hr and something around 10-12
volts and
will power the laptop for 2 hours or so. I would seem that if one could
get
the DC from the battery directly to the lap top rather than going through
the
DC-AC-DC conversions that there would be more than enough to run the
laptop for
many hours.

FWIW, I have a 20Ah Xantrex Powerpack 400, and the manual says it can
run a laptop computer for 6 hours on a full charge.
This is a pretty good 'guideline' figure, and tallies closely with the
figure above, but probably assumes 'room temperature' operation, which
improves the likely run time significantly. In the cold, I'd only rely on
perhaps 5 hours.

Best Wishes

On Mon, 12 Apr 2004 14:06:27 +0100, "Roger Hamlett"
wrote:



Dead right.
Looking at a fairly 'heavy duty' (P4 with 15.5" 1800*1400screen), laptop,
the power supply specifications, are 18v at 4.2A (charging), and 18v at 1.4A
(running only). Slightly smaller laptops will draw a little less.
Most 12v to 18v boost inverters, manage better than 80% efficiencies, so the
current draw at 12v, would be (18*1.4)/(12*0.8) = 2.62Amps.
Now in general, for telescope operations, you should only look to relying on
the battery delivering about 0.6 it's rating (the rating is for the 'ten
hour' discharge rate, and falls to typically 85% - 90% at a four hour rate -
also the rating falls with temperature, and with age). So a 17Ahr battery
would run the laptop reliably for about (17*0.6)/2.62 = 3.9 hours.



Thanks for the info Roger. I figure that the battery I have is
over-kill for running the Orion SVP in DC mode and the dew-heater in
AC, but it also doubles as an emergency power source. so far this year
we were whacked dead-on by a hurricane, and a blizzard that dumped 3.2
feet of snow in 24 hours

Cheers,

- Craig

"Craig Levine" wrote in message
...
On Mon, 12 Apr 2004 14:06:27 +0100, "Roger Hamlett"
wrote:



Dead right.
Looking at a fairly 'heavy duty' (P4 with 15.5" 1800*1400screen), laptop,
the power supply specifications, are 18v at 4.2A (charging), and 18v at
1.4A
(running only). Slightly smaller laptops will draw a little less.
Most 12v to 18v boost inverters, manage better than 80% efficiencies, so
the
current draw at 12v, would be (18*1.4)/(12*0.8) = 2.62Amps.
Now in general, for telescope operations, you should only look to relying
on
the battery delivering about 0.6 it's rating (the rating is for the 'ten
hour' discharge rate, and falls to typically 85% - 90% at a four hour
rate -
also the rating falls with temperature, and with age). So a 17Ahr battery
would run the laptop reliably for about (17*0.6)/2.62 = 3.9 hours.



Thanks for the info Roger. I figure that the battery I have is
over-kill for running the Orion SVP in DC mode and the dew-heater in
AC, but it also doubles as an emergency power source. so far this year
we were whacked dead-on by a hurricane, and a blizzard that dumped 3.2
feet of snow in 24 hours
It is also worth saying that the life of lead acid cells, is better if they
are not discharged too deeply, so having a bit 'more' battery than you need,
is a good thing (this applies even to 'deep discharge' designs, but the
problem is less).
It sounds as though having a slightly 'OTT' battery is particularly
worthwhile for you... :-)

Best Wishes

"Alan French" wrote:

We have an inverter/drive corrector, and could plug that into one of our
17AH 12volt batteries, and then plug the laptop's AC adapter into the
inverter. That seems inefficient, and maybe there is a good reason not to
power the laptop this way.

Inefficiency, plus most of the cheap 12V-120VAC inverters produce
gigantic amounts of EMI (an issue for radio types and other
weak-signal stuff). I use one of these:

http://user.gru.net/n4uau/kits/Volta...e/apvb-kit.htm

The RadioCrap version of this product is as described: crap. It
doesn't have the necessary current for modern laptops (even the above
has issues in this department though), but worse, it "floats" the
laptop, which can produce exciting results when you connect something
to the laptop _and_ the battery. (Fortunately for me, the excitement
was limited to a few fuses...)

Alan French wrote:

I just revived an old non-working laptop that we were given. What options
are available to get some added work hours out of it when away from the
house?

We have an inverter/drive corrector, and could plug that into one of our
17AH 12volt batteries, and then plug the laptop's AC adapter into the
inverter. That seems inefficient, and maybe there is a good reason not to
power the laptop this way.

Most 12DC - 120AC inverters are reasonably efficient, and ~$25 should
buy a halfway decent unit. (FWIW, I've had good luck with a 'Coleman'
unit bought at Kragen/Schucks/Checker/etc. auto partz. It's typical
'made in PRC' schlock, but it provides a reasonably stable output and
hasn't caught fire, yet!) Since the current draw will be modest, you
should be able to run the whole affair off your car battery. FWIW, I've
run a P90 laptop off such a setup for well over 8 hours without needing
a push start. (You might want to monitor things with a volt meter the
first few nights. ) Most inverters have a built in low-voltage
warning beeper, and will shut down completely before discharging the
battery to damaging levels. Whether or not that level will leave enough
juice to crank the car is the 'great inquandrable'.

Would it be reasonable to make an adapter to plug the laptop directly into
the 17AH battery, or is there some reason this would be bad for the laptop?

As others have pointed out, few laptops eat 12V. (16 or 18v seem more
common.) Feeding the laptop's P.S. 12~13v might work fine. It also
just might cause a meltdown.

-Greg

Thanks everyone for all the advice. It sounds like I should invest in a
decent inverter, and pull out the old deep cycle battery from the basement,
although one of the 17AH batteries might provide reasonable service if we
travel by air. Perhaps we will give one a try on a few nights and see how
things work out.

I am sure Sue will be quite happy to be able to use Megastar out by the
scope.

Clear skies, Alan