lap tops and inverters

Submitted: Sunday, May 29, 2005 at 18:31
ThreadID: 23404 Views:2365 Replies:6 FollowUps:1
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after reading a lot about using lap tops on inverters and gennys a lot has been said about not using gennys as the voltage is not always steady and inverters should be pure sine because lap tops are very fussy with voltage ect.
so could some one please explain to me why when my lap top 240 volt power supply stopped working yesterday i found an old lead with the same size power plug as in the back of the compter i cut the lead and conected it straight to a 12 volt car battery and as you can see it works perfectly no probs at all.
is this just a weird type of lap top or are we being ripped off by being told to buy pure sine inverters?
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Reply By: Cracka - Sunday, May 29, 2005 at 19:08

Sunday, May 29, 2005 at 19:08
Been running a laptop on a (square wave) inverter for years withoup problems. Maybe I've been lucky?

AnswerID: 113483

Follow Up By: Member - Sam (NSW) - Sunday, May 29, 2005 at 19:52

Sunday, May 29, 2005 at 19:52
Likewise. I have been running a number of laptops off a DSE 300W inverter (which i think is a square wave) and never ever had a problem.
FollowupID: 369575

Reply By: joc45 - Sunday, May 29, 2005 at 20:11

Sunday, May 29, 2005 at 20:11
Most laptops use an external power supply (which is how I understand yours is, which has now died). The output of the power supply is usually somewhere between 12 and 20v. While this DC output is regulated, there is another regulator and charger inside the laptop to ensure that the battery gets the right volts, as does the guts of the computer.
The laptop only likes pure DC being fed into it; this is what the external AC power supply does, and this is also what a car battery does. But the AC power supply, depending on the design, sometimes only likes a sine wave AC signal being fed into it, and gets upset with the waveshape of a "modified sine wave" inverter, causing it to either run errantly or to fail.
As I understand it, you have connected the DC input of your lappy straight to the 12 volts of your vehicle. It is possible that this may work, as the regulator and battery charger inside the lappy may cope with this lower-than-normal voltage. But it is not really recommended;
i. you may get the polarity wrong and fzzzzt!
ii. there is no guarantee that the DC neg input to your lappy is at the same potential as the earth frame of the lappy. So when the frame touches the vehicle earth, problems may arise.
iii. The regulator and charger inside your lappy may work at the lower voltage, but may not like it, and could fail prematurely, or they could already be feeding a less-than-ideal voltage to the electronics inside because of the lower input voltage.
iv. there is no overvoltage protection either; a spike on the 12v rail could carry out your lappy.
Not a recommended way of running your lappy. You can get DC-DC converters from the likes of Dick Smith and Jaycar which lift the 12v up to a selectable 15-20v to do the job properly.
AnswerID: 113490

Reply By: Richard Kovac - Sunday, May 29, 2005 at 20:14

Sunday, May 29, 2005 at 20:14
I've run and old NEC and a new acer laptop for four years and on some large trips, my thoughts are the the voltage AC adapter that comes with the laptop will control the input voltage to the computer as long as the input voltage is within the control margins I can't see a problem.
The old NEC battery is not much chop and some times when I start the vehicle the laptop shuts down, no problems just reboot and she's file, I'm sore there will be different view.


AnswerID: 113491

Reply By: Member - Phil G (SA) - Sunday, May 29, 2005 at 21:42

Sunday, May 29, 2005 at 21:42

I've run my old Tosh for about 4 years straight off the car battery.

The old Tosh requires 15 volts, and it has a 9.6volt battery. You're delivering between 12.6 and 14.2 straight from the vehicle which is pretty close anyway.

You may find the reduced voltage is insufficent to keep the computer battery fully charged, but it certainly will run fine when its hooked up.

My TabletPC runs off 19 volts, so I wouldn't dare try it without an inverter and its power pack.

AnswerID: 113503

Reply By: Mainey (WA) - Sunday, May 29, 2005 at 22:00

Sunday, May 29, 2005 at 22:00
As i understand it, my Toshiba satellite 2800 always runs off it's own battery, even when plugged into and being run by the 240v.

It may be that way with your comp, you are actually recharging the laptop battery while the comp is happily running from it's own battery, and yes it may also be different on your laptop? just my own thought and yes it is unfounded!

I run my AA and AAA battery charger direct off the 12v battery instead of the 240v recharger, so it may work the same way.
AnswerID: 113507

Reply By: Member - Jeff M (WA) - Monday, May 30, 2005 at 13:32

Monday, May 30, 2005 at 13:32
Most laptops run from betwee 15v to 21v DC. I would'nt be running it direct from 12v if it were me.

The problem with running laptop power supplies from square wave and modified sine wave instead of pure sine wave inverters is that the power supplies are of the "switch mode" type. They run erratically and inefficiantly from anything other than pure sine wave meaning you could potentially damage the supply but more commonly the amp your inverter will be drawing to power it will be much more than if you were using a pure sine wave inverter. Just like running 240v Fluro lights, do a search on that in google and you'll see what I mean...

Personally I'd go and spend $70 and get a laptop 12vDC power supply from Jaycar or the 12v Shop and be done with it. That's what I use and they are the most efficiant way to do it.

PS I also do have a pure sine wave inverter also but just turning on the inverter uses unessecary power, then you've got the ineffeciancies of converting 12vdc to 240vac and back to 19vdc again.... Why not just go 12 to 19 straight up!

Ever wondered why your inverter has fans on it? Because it produces heat... What does this mean? It means it's using power to produce that heat in the proccess of chaning 12vdc to 240vac (it doesn't come out of nowhere does it??) I'd rather use that power to run the fridge to keep the beer cold!!
AnswerID: 113562

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