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    Kirt Blattenberger,


RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

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Charging w/ inverters - bad for laptops ? - RF Cafe Forums

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Post subject: Charging w/ inverters - bad for laptops ? Posted: Tue Dec 30, 2008 2:03 pm


Joined: Tue Dec 30, 2008 1:53 pm
Posts: 4
hope this isn't too dumb a question for this forum . . .

I'm thinking of getting an inexpensive inverter for the car, to charge my Lenovo Thinkpad T61 laptop from the 12v source.

After doing a bit of research I found a few posts out there that implied that using an inexpensive inverter with a modified sine-wave (as most of them are) might damage a laptop.

But many of the brand names in laptop devices sell these things, and laptops are listed as devices that can be charged.

For example :
Xantrex XPower Inverter 175 Plus
Kensington Ultra Portable Power Inverter 150

I can't seem to get the definitive answer on this.
I know a pure sine-wave inverter would be the best (and more expensive), but is it ok to use the modified sine-wave types?



Post subject: Re: Charging w/ inverters - bad for laptops ?Posted: Tue Apr 21, 2009 4:08 pm


Joined: Mon Apr 20, 2009 2:04 pm
Posts: 14

I've done quite a bit with power supplies, and I don't think you have anything to worry about.

Almost every computer power supply built for the US market doesn't have power factor correction, or anything elese that would worry about input waveshape. They simply rectify what comes in, filter it with high voltage electrolytics, and then run it through a switching supply.

As for the "modified AC" wave form, it's simply flips polarity on the output with a little dead time (open output) between. That helps loads which have induction motors by eliminating the third harmonic from the output. The upper harmonics are as strong as ever, but the leakage inductance of the motor deals with them...



Post subject: Re: Charging w/ inverters - bad for laptops ?Posted: Sat Apr 25, 2009 12:04 am


Joined: Tue Dec 30, 2008 1:53 pm
Posts: 4
Thanks very much for your reply.
I had posted on a few forums but this is the first reply from someone who seems to know what they're talking about.
I bought one in the meantime - haven't used it but a few times - but I won't worry now.

Thanks !


Post subject: Re: Charging w/ inverters - bad for laptops ?Posted: Sat Apr 25, 2009 5:29 pm


Joined: Mon Apr 20, 2009 2:04 pm
Posts: 14
You're certainly welcome.

Back in the day, I powered my PC while on the road using 150 volts DC, which I got from a supply I built. Using DC is generally not a good idea (It requires special fuses at higher voltages.), but a lot of the old power supplies didn't even care whether it was DC or AC.

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