There seems to be a lot of confusing information out there.
I use a "Juice" universal supply, $90 new (cheaper for a used one on e-bay, I suppose).
It does DC-DC voltage conversion from 6V to 24V. I've used it successfully with two
Dell laptops and a Compaq. It also charges my cell phone, and powers my digital camera.
There's nothing unique or unusual about the Dells, other than that your adapter must be able to
step up the 12V to the higher Dell voltage, which all the latest "universals" do (and do automatically,
with no switching of switches required). DC-DC conversion is significantly more efficient than
running an AC inverter off a 12V battery (more on that below) and then using the standard AC power
brick for your laptop, where you're wasting tons of battery power in conversions.
So-called "12V" batteries don't charge at 12V. The voltage has to be higher than the battery's voltage
or it won't charge. That's why your car's DC system puts out between 13.8-14V, otherwise your battery
would never charge. That's why my solar charger puts out 14V (it has the direction-control diode built in,
by the way, and at 0.25 amps is considered a trickle charger and so doesn't need current regulation).
Finally, no laptops that I know of have the charging control circuits (current regulation ,etc.) in the "brick" that plugs into AC power. That circuitry is on the laptop's mother board. The brick is just a AC-DC converter that supplies the proper voltage and has overload protection, nothing more. As long as you
supply the proper voltage to the laptop's DC input, the batteries will charge just fine.
Paul
-----Original Message-----
From: sf-bay-tac-bounces@seds.org on behalf of John R Pierce
Sent: Mon 4/26/2004 10:32 AM
To: The Astronomy Connection
Cc:
Subject: Re: [TAC] Solar Battery Charger == Some Questions
>> Please note that direct DC adapters will not work with some laptops, Dell
>> in particular, AFAIK.
>
> Likely that you cant just stick 12v in most laptops. (Most I've seen,
> dell, fujitsu, ibm, are 16v.)
>
> However virtually every laptop mfr has been for some time
> making 12v adapters, ie "car-auto" power adapters.
indeed. the AC 'brick' is also the power regulation for the battery charger
on most laptops. With Li-Ion batteries, charge regulation is critical.
I'd be very leery of any aftermarket 'universal' power solutions if they
aren't designed for the specific laptop family.