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Old 21-05-2010, 02:44   #1
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Running a Laptop Efficiently

Wow my lap top is sucking the juice!

Right now I can plug it into a 500W inverter which is on the verge of overloading requiring the dimming of my screen just stop the inverter shutting down. Now including the losses in the inverter this must be drawing a huge current on the order of 50A, or about 600W from the batteries. The power pack says 240V AC @ 2A.

The thing is, on the DC side of the power pack laptop lead, the current draw is 3.16A @ 19V DC which is 60 watts, or about 10 times less than the power it is drawing from the house batteries when you include all the wasted power in the voltage conversions.

How accurate does the 19V DC supply to the lap top have to be?

Is there a common way of gaining efficiency here?

DC - DC converter for 12 - 19V?

What about 2 x 24v batteries in series regulated down to 19V?

Should I just get a lap top that requires 24 or 12v? (if there are any)

Should I be buy a specific laptop for this application?

Cheers, Dennis.
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Old 21-05-2010, 03:07   #2
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I just got a cheap car charger thing for it off ebay for $17. It has a input rating of 11-14V and a range of outputs and plugs.

See how it goes I hope its efficient.
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Old 21-05-2010, 03:10   #3
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There are a multitude of cheap adaptors available for running your laptop from a 12VDC power supply, either in your car or on your boat. Should be much more efficient than converting to AC and back down again. Here's a link to one - or just google "car laptop power supply"

Low Cost Auto to Laptop DC/DC Power Adapter Cord

EDIT: you beat me to it, and the one you bought is even cheaper! All the best.
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Old 21-05-2010, 03:28   #4
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I will try to take a current reading off it to see how efficient it is.
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Old 21-05-2010, 05:52   #5
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Google SDR-70W, it's an auto DC power regulated adaptor with DC outputs from 15 to 24 volts and multiple connection tips. Be VERY VERY careful when connecting the connection tips. Use a multi-meter to determine which side is TIP or positve. Hooking them up reversed can fry your equipment.

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Old 21-05-2010, 06:03   #6
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Could the problem be the inverter-laptop power supply interface? I've seen poorly designed inverters have a problem with other electronics. Is the inverter a true sine wave, quasi-sine wave, or square wave model? Have you tried a different power supply or device on the inverter?
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Old 21-05-2010, 06:41   #7
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This is the one I got Universal Notebook Laptop HP ACER TOSHIBA Car Charger - eBay, AC Adaptors, Laptop Accessories, Computers. (end time 27-May-10 00:03:43 AEST)

I'm not sure what the inverter is. Probably a cheap square wave. In either case, using any inverter is going to waste a massive amount of power since there is a huge power loss in the laptop lead AC to DC power pack anyway. The power pack input is 240AC @ 2A which is up to 480 watts. Where the output is 19V @ 3.16A which 60w. Its no wonder the 500w inverter was struggling with 480w on it.
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Old 21-05-2010, 15:35   #8
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You don't need a pure sine wave inverter for charging a computer.
Mind you, you don't need an inverter at all for the computer.

The 12v to 19V converter you have bought will work well for you

For all our inverter needs... recharging batteries, shaver, etc we use a 150 watt inverter, modified sine wave.
unless you are using a microwave or eletric kettle its all you need.
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Old 21-05-2010, 16:05   #9
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DC to DC converters are more efficient than using an inverter, but the gains are usually about 20% to 30%. If your inverter is drawing 600w to power the laptop something is wrong. I would stop using it until you find the cause of the problem. This is not normal.
Your system is consuming about 500w more than it should, this will be dissipated as heat somewhere, thatís a lot of energy and can easily start a fire.
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Old 21-05-2010, 18:35   #10
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Inverters need a load to operate. Inverters like loads with a power factor as close to 1 as possible [ Power factor - Wikipedia, the free encyclopedia ]. I've seen inverters do very strange things to loads that are electronic, not transformer or motor, so I offered the suggestion.

The car charger should be more efficient as it has the simple job of converting DC to a higher voltage DC (that probably means some kind of electronic switching circuit inside the power supply). If the computer runs fine from the car adapter, I'd stick with that (and buy a spare). There will be some losses in the voltage up-conversion but it shouldn't be more than 20-30%.
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Old 24-05-2010, 03:37   #11
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Cheers. Yeah something must be wrong in that inverter. Thing is it also struggles on a 300W inverter I tried with several laptops. I guess that this could be because the inverters are both pretty old and cant handle electronic switching circuits as loads. I would expect a power factor close to unity with a electronic power supply, it it has been designed right. But the sharp shapes of the power curve might cause a few probs. I am going to measure the current draw on the 240v side at home to see if there is any difference when its plugged in the inverter.
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Old 24-05-2010, 16:13   #12
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On another note, once you get all of that sorted out, there are a few ways to get your laptop running efficiently.

Run linux. If you insist on your normal OS, minimize flashy graphics in the OS settings. Don't watch movies. Don't listen to music. Turn the brightness down on the display. Use an external antenna for your wireless transmission. Keep the computer cool. These will dramatically decrease current draw.

I think the max for a laptop is around 100w right?
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Old 24-05-2010, 21:12   #13
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I am trying the 300w inverter. Its square wave. This is the first time I have used my new laptop on this inverter.

I have actually measured current draw from the 12v battery supplying the inverter this time.

With no laptop battery it draws on average about 3A or 35W from the house battery. Thats a small load!

However when I plug the lap top battery in (its 96% charged) its using 5A and this is enough to trouble the inverter. Any current spikes over 6A will bring the overload buzzer on the inverter on. I have seen 8A and it would have shut off it had not only been for a second. Once the battery was 100% charged it didn't seem to draw anymore than with no battery in. I expect that with a 100% flat battery the current would go off the scale. That is probably why the laptop power supply is rated for many more watts than the laptop and I expect charging it would overload many small inverters.

So the question is why does a 300W or 500W inverter start crying enough when clearly there is never more than 100W going through it? I wrongly assumed the inverters were actually overloading because the loads were high, but they are not.

I guess its because the inverters are old square wave? Or just crap? And cant really handle switch mode power supplies
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Old 24-05-2010, 22:51   #14
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lap top power

that seems pretty high , mine a toshiba uses a 19 volt at 3.6 amp stays cool. I have a program that shuts off the hard drive too and use the dim screen ap. My invertor is a 350 watt and works great. the meter says its pulling 160 watts with bright screen and 125 with low bright screen To charge the battery during the day I have two 40 watt panels. There is something you need to check on. Some invertors that use the mod-sinewave are not efficent and will cause the unit to excessively pull extra amps and over heat. more power needed to do the same job. I have an Exceltech stackable set up - 120/240 volts

Quote:
Originally Posted by dennisail View Post
Wow my lap top is sucking the juice!

Right now I can plug it into a 500W inverter which is on the verge of overloading requiring the dimming of my screen just stop the inverter shutting down. Now including the losses in the inverter this must be drawing a huge current on the order of 50A, or about 600W from the batteries. The power pack says 240V AC @ 2A.

The thing is, on the DC side of the power pack laptop lead, the current draw is 3.16A @ 19V DC which is 60 watts, or about 10 times less than the power it is drawing from the house batteries when you include all the wasted power in the voltage conversions.

How accurate does the 19V DC supply to the lap top have to be?

Is there a common way of gaining efficiency here?

DC - DC converter for 12 - 19V?

What about 2 x 24v batteries in series regulated down to 19V?

Should I just get a lap top that requires 24 or 12v? (if there are any)

Should I be buy a specific laptop for this application?

Cheers, Dennis.
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Old 24-05-2010, 22:56   #15
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Weird, all our laptops run fine off a 150W MSW inverter...
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