I have been watching Ebay the past couple days for an NEC MobilePro 900 palmtop computer.
I would like to be able to recharge it in my car. They sell this http://inktomi-cnet.com.com/Lind_NE1...-+car&tag=feed
adaptor but its $50-60! It's 12V in and 12V out. Wouldn't it just be a 12V regulator and maybe some filtering components? I really doubt its worth $50, but it seems to be the only car charger available specifically for the 900 and they felt the need to jack up the price.

Opinions? Should I try and build my own regulated 12V car apadtor?
~Mike

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All Electronic components run on smoke. Let the smoke out and it no longer works.
~Tim Baker (Electronics Instructor at John A. Logan College)

 

Your car's voltage isn't 12V. It varies from about 9V when starting up to 14.4V when charging.

An ordinary 12V regulator IC like a 7812 needs an input voltage of at least 15V to regulate properly, and would not be able to supply enough current anyway.

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Uncle $crooge

 

I'm pretty sure spending $50 on a car adapter is worth it.

Like audioguru said, your car's voltage varies greatly. When the alternator kicks in, you should get very close to 14.4V. If it's lower than that, your alternator is old and slowly dying. When your ignition is off, the battery should output around 11.5-12.5V. If it's lower, your battery is old and slowly dying. Getting a constant 12V from that isn't as easy as it seems.

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Time is nature\'s way of keeping everything from happening at once.
http://membres.lycos.fr/jrainville/

 

maybe there is some sort of special charging method used to prevent damage to the battery? Chances are that the charging strategy is optimized to give you the most life out of the battery.

Unfortunitly its probably best to just buy the charger (I know what its like to want to do something like that on your own). Even if you do come up with a charger, you could be damaging the battery by using it.

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Jeff Zimmerman
To the optimist, the glass is half full.
To the pessimist, the glass is half empty.
To the engineer, the glass is twice as big as it needs to be.

 

If the battery is Li-Ion or Li-Po, then overcharging it will make it catch on fire. Lithium burns very hot like magnesium. Bye, bye palmtop. Bye, bye car. Bye, bye you.

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Uncle $crooge

 

OK, thanks for the info. The batteries are Lithium Ion but the charging circuit is in the MP900. I joined a forum for people with these computers and another guy says he bought a car adaptor and wall wart from radio shack and they both work fine. I will ask around more though to make sure noone has had bad experiences using them.
~Mike

__________________
All Electronic components run on smoke. Let the smoke out and it no longer works.
~Tim Baker (Electronics Instructor at John A. Logan College)

 

The Li-ion battery in my son's laptop has a million electronic parts inside. They are probalbly used to monitor its temperature, current and voltage when charging, to tell the charger what to do safely.
If you make your own charger then you must interface it to all that stuff.

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Uncle $crooge