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Keeping laptop alive during a long plane trip

T

TitanDiddly

Guest
I have an IBM Thinkpad 600, and the battery doesn't last very long. I'd like to use it during a upcoming trip on a plane, totally about 7 hours flight time. The seats I am booked in do not have AC power. I was thinking of making a simple circuit to take 18v from three 6v gel cells and turn it into stable 16v power for my laptop. My laptop adapter is rated for 3.36a, so whatever kind of adapter I make has to be able to source as least that much as a peak value. Does anyone know how feasable this is? I'm not exactly sure how many amps it pulls during normal operation. I'm going to guess 2A as a nice round value. Assuming, say, 85% efficeiently on my voltage converter(I confess. I have no idea what the proper term is), and 7 hours total operation, I'm going to need 14AH for the trip. That's possible to do for carry-on, no?

Also, I know the laptop is expecting very clean power. Can this be accomplished with just a simple array of a few voltage regulators and some big capacitors? I've made some very simple voltage regulators for RC equipment that just takes a higher voltage (12v) and makes clean 5v with it. That's a fairly low amperage situation, though. Is this possible for a fairly novice engineer-to-be? Is it feasable at all? Even if not for carry-on luggage, let's say I want to do it for long car trips and my cigarette lighter plug is broken, or whatever.

One big problem I can think of is voltage drop in the batteries as they drain. I'm going to need either a very low dropout regulator, or use 24v of batteries.

Anyone care to chime in with some knowledge?
 
I don't intend this as a thread-crap at all, but as a serious point. I'd be very careful about choosing what sort of home-brewed electronic device you try to bring through airport security. It'd be a miracle if you were able to convince security that what you have is in fact NOT a bomb if it's got wires sticking out all over the place and isn't labeled with a retail stamp of some sort.
That said, are you incapable of buying a 2nd battery for your laptop? Even a 3rd, depending on what your battery life is? Personally, I'd rather spend $60 bucks on new batteries than endure some of the more aggressive airport security measures...
 
Originally posted by: nardvark
I don't intend this as a thread-crap at all, but as a serious point. I'd be very careful about choosing what sort of home-brewed electronic device you try to bring through airport security. It'd be a miracle if you were able to convince security that what you have is in fact NOT a bomb if it's got wires sticking out all over the place and isn't labeled with a retail stamp of some sort.
That said, are you incapable of buying a 2nd battery for your laptop? Even a 3rd, depending on what your battery life is? Personally, I'd rather spend $60 bucks on new batteries than endure some of the more aggressive airport security measures...
Click to expand...

I just called the airline, and the CSR seemed pretty understanding. It sounded like as long as the batteries are sealed, it won't be a definately out, but in the end it's all up to the local airport. She sounded fairly optimistic.
 
My main concern would be getting the batteries onto the plane.

Apart from the potential security issues, there is also the problem of determining whether your particular batteries are safe on aircraft. Traditional 'sealed' lead-acid batteries are not acceptable (the problem is that they aren't actually sealed). However, most gel cell lead-acid should be OK because they are fully sealed. As you might guess, lead shows up crystal clear on X-ray, so you WILL have to take your batteries out and explain yourself to the security staff.

If you must build your own battery I'd rather do it with NiCd or NiMH - you also get finer control of voltage and a flatter voltage-discharge curve.

You should be able to get 16V from an 18V supply - LDOs are not specialist devices. The only issue is that the currents you are using will require a modest amount of heatsinking
 
Yeah buying an additional battery will be better. Are you planning on using the standard run of the mill voltage regulators? Not a good idea to use them in an array in parallel, the current will flow mostly through the regulator it "sees" with the lowest resistance. Also, basic voltage regulators dissipate whatever energy is unused by the device as heat instead of going to your laptop, so it's not going to be efficient especially if you end up using 24v batteries, in which in this case the regulator(s) will be dissipating more than 16 watts. A DC-DC converter or other switching converter of some sort would be best.
 
You don't need to worry much about how clean the power is because batteries are the power source. All you really need is a good quality regulator. This LM1084 regulator should work fine. The dropout on that regulator is 1.3v.
 
After some help in OT, I realized that it would be a lot easier just to get a generic autopmotive laptop supply on ebay or otherwise, and just hack off the cigarette lighter plug. I talked toa CSR at the airline, and she told me that sealed batteries are most likely fine, but everything is at the final discretion of the gate manager. The batteries I have a military surplus, MIL spec helicopter batteries. No flight problems here. You can cut them in half with a saw and they won't leak.
 
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