External DC Voltage Range

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Level 1

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External DC Voltage Range

Hello -

I'm interested in running my Powerbook 15 inch Titanium 867 MHz from a nominal 24 volt solar battery system. If run the laptop directly from this external battery system, it would be exposed to a potential voltage range of 22 - 28 volts. The PB power adapter supplies 24.5 volts, but does anyone know if the PB requires a tightly regulated power supply at 24.5 volts, or can I directly supply filtered but unregulated DC of 22 - 28 volts? In other words, does anyone know what the acceptable input voltage range is, or where I could get that information?

It would be easy enough to use a 24 volt linear regulator to keep the computer from being exposed to higher voltages from the external battery, but the intrinsic voltage drop across the regulator and the lower voltage limit of the battery system would not keep the computer from being exposed to the lower voltages between 22 - 24 volts. Using a DC-DC boost converter to bring the battery voltage before running it through the 24 volt regulator would be a more painful solution that I'd like to avoid if possible. Any information would be helpful.

Thanks very much.

Posted on Sep 1, 2007 10:36 AM

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Answer 1

Dan White

Level 6

9,446 points

Sep 1, 2007 8:16 PM in response to Michael95

A bit of Googling found this:

http://www.globalsolar.com/dmdocuments/FAQs-1.pdf

How do I charge my laptop with the portable, folding solar panel?
Laptops are tricky to charge. We recommend using a portable external battery to connect to the laptop and connect our solar panel to the portable external battery for charging.You can try charging your laptop directly using the laptop manufacturer's car charger adapter connecting one end to the laptop and the other end into the car charger receptacle cable made for our solar panel, but the odds are this won't provide enough current for the laptop. See our brochure called Laptop Options under the Instructions section of our web site for more information.

Good luck.

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Answer 2

Michael95 Author

Level 1

0 points

Sep 2, 2007 6:10 AM in response to Dan White

Thanks Dan - that's the way my system would be set up, with solar panels charging the external 24 volt battery system, and then the PowerBook taking it's power from this external battery. Problem is, the 24 volt lead-acid external battery has a voltage range from 28 volts fully charged, down to 22 volts as it discharges. The PowerBook brick adapter provides 24.5 volts, right in the middle of this range, but more tightly regulated so that there isn't much fluctuation up or down. What I don't know is whether the PowerBook can tolerate the wider range of voltage input that the external battery system would provide. Again, it would be easy enough to just regulate the external battery voltage input to the PowerBook down to a steady 24 volts when the battery voltage is greater than 24 volts, but it's more difficult to boost it up to 24 volts when the battery is below 24 volts...

Anyone else have any insight?

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Answer 3

Dan White

Level 6

9,446 points

Sep 2, 2007 7:38 AM in response to Michael95

My Googling found a few commercially made units that claim to be able to charge/run a laptop. Why not buy one of those instead of building it yourself ? Those folks should have worked all this out already.

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Answer 4

Rod Hagen

Level 7

32,000 points

Sep 3, 2007 7:29 AM in response to Michael95

Hi Michael,

I doubt that you will have a problem with low voltage in the range you mention. Some of the third party auto adaptors for this model actually cite outputs in the 18-20 V range. I know that by the time you get down to 16.5V you are beyond working range (hence the fact that MacBook's 16v output power packs won't work with the PB's), but if you can keep the output in the 20 to 24 V range (I'd certainly be worried about letting it go higher) then I think you will be fine.

The developer note at http://developer.apple.com/qa/qa2001/qa1266.html has some interesting information that might help you design an appropriate set-up, too, though it was written for the alu G4's.

http://blogs.experience.com/Patrick/2007/01/portable-solar-power-for-1_116769220 143696495.html also has some useful tidbits, but bear in mind the guy is using a MacBook with lower voltage/ higher amperage requirements.

Another option might be to use something to drop the voltage down to the 12 to 15 / 16 V auto and airline levels and then use an adaptor like the Kensington one - http://us.kensington.com/compApp/ktgUSPower.jsp?pageId=9162 - to handle regulation of power to the PB?

Cheers

Rod

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Answer 5

Michael95 Author

Level 1

0 points

Sep 5, 2007 7:08 PM in response to Rod Hagen

Rod -

Thanks much for the very useful information and links. One of the issues I was trying to avoid was the problem of serial conversion inefficiencies eating into my relatively expensive solar power budget; ie converting from 22 - 28 volts down to 12 volts and then back up to 24 volts. The information you provided suggests that occasionally dropping down to the 22 volt range on the input side to the PB shouldn't be much of a problem. At the other extreme I was assuming that I would need to cap the voltage on the high side to keep it from rising above 24 volts.

Incidentally, spent some time in your country about a year ago and totally fell in love with it; truly amazing part of the planet. Again, thanks very much for the information -

Michael

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