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laptop power consumption
By kell, Section Homebrewed Electricity Posted on Sun Oct 10, 2004 at 05:30:20 PM MST
running on external batteries

How do I get my laptop to consume less power? When I run the computer from a battery plugged into the jack on the back of the computer it thinks it's "plugged in" to line power and keeps the screen at its brightest etc, running down the battery plugged into the back. Unlike the settings for internal battery use, it does not have a reduced power setting option in the Control Panel for "plugged in". So I can't make it consume less power from the battery that I have wired in to the external jack. I have a Toshiba Satellite A15, purchased less than a year ago, running Windows XP. Surely someone else has plugged a laptop in to a battery through the jack on the back of the computer. How do you get it to cut down the power consumption?

laptop power consumption | 19 comments (19 topical)

Re: laptop power consumption (3.00 / 0) (#1)
by jimovonz on Sun Oct 10, 2004 at 05:50:25 PM MST

You can usually manually adjust the screen brightness at any time. Most often a combo of the function key and <sun up>/<sun down> keys. Other power save functions should have separate settings for battery/plugged in.

Re: laptop power consumption (3.00 / 0) (#2)
by kell on Sun Oct 10, 2004 at 07:29:25 PM MST

Thanks for the sun down key tip.

[ Parent ]

Re: laptop power consumption (3.00 / 0) (#3)
by debequechute on Sun Oct 10, 2004 at 07:56:34 PM MST

Adjust your power settings under the control panel, or display settings, screen saver tab, power button. Most laptops are set by default to increase the CPU speed (power consumption) if it's plugged in. Change this to keep it at the lower setting when plugged in. That screen brightness also helps.

Also check your task manager for background tasks that take up portions of your CPU time. Get rid of those that you don't need. The lower your CPU utilization, the lower the power consumption. If you leave it running while you're not using it, also turn off screen and hard drive after so many minutes in that same power tab.

Re: laptop power consumption (3.00 / 0) (#4)
by debequechute on Sun Oct 10, 2004 at 07:59:03 PM MST

Ah, disregard part of that I just reread the part about not having that setting. I think Toshiba has their own proprietary utility for doing that. Check their web site for that model.

[ Parent ]

Re: laptop power consumption (3.00 / 0) (#5)
by JeroenH on Mon Oct 11, 2004 at 08:39:29 AM MST

I run my Compaq laptop (old one) on 12V directly. The computer says it runs on 16V, and that's also what the AC adapter delivers, but it runs fine on 12V.

My laptop's battery does not work anymore, but the laptop keeps trying to charge it, and that consumes lots of power. I have only measured it on 240V: it consumed 50W with the battery inserted, which dropped to 30W when I removed the battery.

So do some measurements for your particular computer.

As for the computer not wanting to reduce its power when (it thinks) it's connected to line power: if your battery is dead, maybe you could disassemble it, remove the cells, and connect the 12V directly to the battery terminals. That way the computer thinks it's on battery (which is true) and you can use the power reduction options.

I have also connected some other computer equipment to 12V. My router and 10/100 switch run fine from 12V. My cable modem needs 3.3V and 7V, so I'm still figuring out how to run that from 12V. I would like to avoid the use of an inverter if possible.

Re: laptop power consumption (3.00 / 0) (#7)
by ghurd on Mon Oct 11, 2004 at 09:12:17 AM MST

3.3v and 7v can be done very easy from 12v. Voltage regulator 7800 series
Get a 7807. The 7807 can be used as is for 7v.
They make a 3.3v regulator too, but no one had it when I needed them. 7803.3? 783.3?

Can use a 7803 if you can't find the 3.3v.
The 7803 will need a resistor (1500 ohm 1/4 watt) from out to ground pin, and another resistor from ground pin to ground (you have to test it to see what value, I'd start with 50 ohms).

Use the 2 caps like the instructions say.

Piece of cake.

G-

[ Parent ]

Re: laptop power consumption (3.00 / 0) (#6)
by ghurd on Mon Oct 11, 2004 at 08:48:41 AM MST

Our Toshiba laptop only pulls a little under 3.5 amps from 12v, into a cheap inverter, into the factory power cord. Its about 4 years old, P3 (?), energy star.
The $12 50w inverter gets noticably warm after about 2 hours, no fan in it.
A group 27, 105ah should get me about 30-35 hours.
What kind / how big / how old is your battery?
What current is the laptop pulling?

I guess I'm wondering if your external battery is any good.
A not up too snuff battery could make it seem like the laptop is more power hungry than it really is. Those screens don't draw much anyway, so I wouldn't think there would be a very significant change from adjusting the settings unless the external battery is small or damaged.

G-

Re: laptop power consumption (3.00 / 0) (#13)
by kell on Mon Oct 11, 2004 at 08:15:09 PM MST

ghurd

No, I'm not worried about the condition of the battery, I just obviously want it to run as long as possible so I wanted to override the "plugged in" settings.

I can plug 12 volts in to the back and run it that way, although it won't charge the internal battery at that voltage. The power supply that came with the computer puts out 15 volts, and I imagine I would need something near that if I want the computer to charge its internal battery. The most efficient way to turn 12 volts into 15 volts is to use a step-down converter with an isolated ouput of several volts and simply stack its output on top of the battery you are running it from. That way you are only using the converter to produce a few volts at your running amperage and drawing only that, with all the rest of your power direct from the battery, instead of drawing everything through a converter as you would with a step-up. Much more efficient.

You should see if you can just get a dc plug and run your computer right off your 12 volt batteries, and skip the inverter/smps combo, which is burning up at least half your energy I'll bet.

The nice thing about my computer is that I can remove its battery and it will still run on the jack.

[ Parent ]

Re: laptop power consumption (3.00 / 0) (#15)
by ghurd on Tue Oct 12, 2004 at 08:17:08 AM MST

We use it mostly on-grid. Quite a bit in the car. Sometimes on-site for a half hour. Sometimes on my friend's T-105s. Battery drain on this is not a problem for this one.

G-

[ Parent ]

Re: laptop power consumption (3.00 / 0) (#8)
by LopeDogg on Mon Oct 11, 2004 at 01:09:42 PM MST

hi there
ghurd is correct about the 78xx regulators, and configuring the 7803 with a resistor inbetween its ground pin and ground will increase its output voltage, but its not the most stable configuration, i think its output voltage will fluctuate with load, which could be fine, you would just have to measure what ur device draws and configure it to run on a dummy load which draws the same amount.

A better method of this "hack" is to put a diode inbetween the ground pin of the regulator, and ground. just gotta use a diode with a .3V drop, i think germanian diodes have such a drop.

what i would reccomend is just to use an adjustable 3 pin regulator called LM317T
I think it puts out up to 3A, and you configure it with resistors.
make sure u test any power supplies u build with dummy loads first.

Re: laptop power consumption (3.00 / 0) (#17)
by ghurd on Tue Oct 12, 2004 at 03:39:54 PM MST

We built piles of them. They are stable if the output to ground takes 2-3ma, and if the output side cap is used. Without the output cap, sometimes they won't even turn on (I have no clue why), some work fine without it. These were all for current varying devices (ie: DC speed control with the ground pin to ground being a pot). Very suprisingly stable.

Most very less than 0.02Vdc 0.1 to max current. Better regulation than diodes.

It works. And a 5A 7805 is cheaper and eaiser to find cheap than a 5A 317.
No bypass transistors, etc.

I know what you are saying.

Disclaimer: I got most of them 'unknown surplus', so all 78xx may not act the same. But we did it with quite a few different types.

[ Parent ]

Re: laptop power consumption (3.00 / 0) (#18)
by ghurd on Tue Oct 12, 2004 at 03:59:00 PM MST

Afterthought:

How about a 7809 to a 3V zener? (pricy hi-watt diode)
OK, thats 6v. (9-3=6)

Then how about a 7810 to a 3V zener. Thats 7v. (10-3=7)

Dropout. Most 78xx list about 2v as dropout, so add 2v to the xx. A 7810 (xx=10) needs 12v in (10+2=12v) to work.

Some of our mystery 78xx's never really drop out, they just do what they can, like 6v into a 7808 still gives 5v out.

Some of the math was added for people not familiar with 7800 series stuff.

And we put potted them in cast Al boxes. A 5a 7805 running 5a from 14v can get... well... 'hot'. Some 7800's have a thermal shutdown.

Just thinking different.
Yea, OK. Cheap.

G-

[ Parent ]

Re: laptop power consumption (3.00 / 0) (#9)
by dave123 on Mon Oct 11, 2004 at 01:30:28 PM MST

Be careful about tapping into existing laptop battery packs and attaching more battery power. I have an older Compaq (7400/7800?)with the dc converter inside the computer, and tried just this thing. The battery pack for this laptop has some complex circuitry inside that communicates back and forth with the computer, advising of when/how much to charge, when to switch between battery power and ac, reports out on how much battery capacity is left, etc. On my computer, it will not even run on dc without this communication.

Here is what I tried. My computer's battery pack ran from approximately 12v "discharged" to 14.4v "charged". I ran the computer on its own battery until the voltage matched a fully charged 17 AH SLA that I had laying around, then paralleled them. The computer's battery gauge was confused. It kept dropping at a normal rate until it got to about 3%, where it hung for a considerable time, like over an hour, then the whole thing shut down and no longer would run on the battery at all; something in the battery's internal circuitry got fried.

I then tricked the computer to think it was running on ac voltage by feeding 5v to a reference line normally used by the battery to advise when its fully charged, while feeding the computer power via an SLA. This seemed to work at first, but it would also get confused and just shut off.

I got lucky and found a replacement battery for this computer that someone was recycling. It doesn't last as long as my old one, but at least it is functional.

By the way, my laptop won't run on a Vector 150w/300w inverter (screen flashed high/low in brightness along with a repeat clicking sound), even though the laptop itself pulls 45 watts max. This, along with me just hating the idea of having to convert to ac when I know the computer just converts back to dc anyways, is what drove me to this experiment.

If I ever get another laptop, I will be sure to get one that has its ac to dc converter outside of the computer.

Re: laptop power consumption (3.00 / 0) (#10)
by JeroenH on Mon Oct 11, 2004 at 02:34:00 PM MST

OK, thank you for the advice. Dismantling your battery and using it as a fancy DC power plug is not a good idea.

There's another way of running your computer on 12V DC (if your notebook doesn't like the 12V) without first converting to 240V/110V AC: I saw a DC/DC converter the other day which is available in several output voltages (16/18/20V DC). It's brand-specific, mainly due to the plug-shape, but it should be easy to cut the plug of and solder another plug on.

[ Parent ]

Re: laptop power consumption (3.00 / 0) (#19)
by ghurd on Tue Oct 12, 2004 at 04:13:55 PM MST

Most laptops now have a switching regulator on the power cord.
They are big-time efficient, and a good design shouldn't be effected by an inverter.

"I THINK" if it says something like input 100~250V in, 50~60Hz, 4 amps out (yes, out), then it is a switcher. I did a Aussie laptop (240Vac 50Hz to 110Vac 60Hz) just by changing their plug to ours (USA).

(thanks to Mister Magazine of Au. for the laptop, and the opportunity to ruin it, which didn't happen. I hear it's quite popular for 'men' in Au. Honestly, never heard of it.)

[ Parent ]

Re: laptop power consumption (3.00 / 0) (#11)
by juiced on Mon Oct 11, 2004 at 02:39:32 PM MST

Im sure many already know about batteries, but if not here is some input.

http://www.juiced.ca/phpbb/viewtopic.php?t=698

I want to mention that if the battery is Li-Ion, YOU CANNOT USE IT & Trying to use the pack as a'fancy plug' would probably not work due to the way it operates.

Canada's -Debatable- A.E./R.E Debate Site
News, discussions and debates!
www.juiced.ca

Re: laptop power consumption (3.00 / 0) (#12)
by Zero on Mon Oct 11, 2004 at 04:32:56 PM MST

Targus do a 'Universal auto air adapter' for most laptops, they use a different 'tip' depending on your make and model. runs from 11 - 16VDC.
I have a compaq 7400 and it runs it fine but you have to be carefull not to have the laptop on charge in a car when you start the engine as it blows the laptop batteries and the 'tip' which Targus will replace free of charge but not the battery:(

Zero.

Re: laptop power consumption (3.00 / 0) (#14)
by srnoth on Mon Oct 11, 2004 at 08:21:21 PM MST

Hey kell,

I have a Toshiba Satellite A15 as well, and when my power adapter shorted out and blew, I had to run my laptop off of UPS batteries for the week it took for the new adapter to arrive. The laptop runs fine off 12v, but will not charge the battery at that voltage. In order to charge the battery, I had to plug it into the car, with the engine on, so the voltage was about 13.5v.

Anyway, to reduce your power consumption, go to control panel, and click on "TOSHIBA Power Saver". In there, you can set the processor speed to low, the fan to battery optimized, and the screen to be darker.

Good luck with that,
Stephen.

Toshibas forever!!

Re: laptop power consumption (3.00 / 0) (#16)
by wiredwrong on Tue Oct 12, 2004 at 02:35:39 PM MST

I have a dell latitude P3 that will not take a charge, I currently use a 19 amp sla, and a 300W inverter made by MaxPower, I found that there are power settings in CMOS where I can adjust power consumtion, screen brightness ect. ect. I have to press F2 and go into setup for these settings also found that it will last longer by leaving the old battery out of the laptop, with this setup i have got more than 8 hours of heavy use in a night, at the time they Dell wanted about $85 for a replacement battery, and the sla cost me $15 and the Inverter I got for $7 at a garage sell. so total cost of $22 for a battery that last about 8 hours made more sense.
Randy OKC,OK

laptop power consumption | 19 comments (19 topical)

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