Homemade laptop charger

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chris414

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I need a really long battery life, but dont want to buy expensive laptop batteries. I just need to be able to run my netbook (acer aspire one) for long periods of time in a fixed location, so it doesn't matter that this solution won't be portable... anyway my plan is to just take to car batteries and connect them in series, then use a simple linear voltage regulator chip that you can buy for a few cents to step the voltage down from 24V to 19V... do you think this will endanger my laptop?*-)
 
First off, a simple voltage regulator for a few cents will most likely let out the magic smoke as soon as you flick the switch. It will most likely not be able to handle the power going through it. But while I would not do it, what you propose is most certainly possible, but make sure of a few things:
  • Regulator must have built in thermal shutdown.
  • Check the max power your current power brick can put out, and find a closest match for the regulator
  • Put in a second safety stage to make sure current and voltage going into your laptop is what it should be
But why cant you just take your power brick with, or are you going to remote locations or something similar? Knowing the situation we might be able to come up with a better solution
 
Why can't you just use the AC adapter, I guess no electricity in the area?

Maybe an inverter and the AC adapter would be better? Might need voltage regualtor for a laptop?
 
It should work... just test it first with some sort of load and a decent multimeter before hooking it up to your netbook. The AAO's charger is rated @ 19V / 1.58A. The maximum current a LM317T can supply is 1.5A, so maybe have a look at the LM338T which can go up to 5A continuous. You'll also need some heatsinks. Have a look at:

http://www.reuk.co.uk/buy-LM338T.htm

and

http://www.reuk.co.uk/LM317-Voltage-Calculator.htm

to calculate the resistor values needed.
 
I don't know how efficient this is since a lot of energy is "lost" in the form of heat. Maybe consider building a switching supply? Or buying one :D
 
Last edited:
D4N said:
I don't know how efficient this is since a lot of energy is "lost" in the form of heat. Maybe consider building a switching supply?
Click to expand...

Linear voltage regulators do put out a lot of heat, but are the simplest to use. Building your own switching power supply is no easy task. I've done it before, but I would not recommend it to someone who does not have a decent electrical background. I think the inverter idea from Techrat is the best one, but I have a suspicion that the OP is trying to find a cheap solution, which will probably rule out the inverter.
 
Archer said:
Linear voltage regulators do put out a lot of heat, but are the simplest to use. Building your own switching power supply is no easy task. I've done it before, but I would not recommend it to someone who does not have a decent electrical background. I think the inverter idea from Techrat is the best one, but I have a suspicion that the OP is trying to find a cheap solution, which will probably rule out the inverter.
Click to expand...

Yip switching supplies are indeed more difficult to build, had to build a few of them at varsity. Getting the correct output voltage and winding inductors are hard :D
 
D4N said:
Yip switching supplies are indeed more difficult to build, had to build a few of them at varsity. Getting the correct output voltage and winding inductors are hard :D
Click to expand...

Also involves some black magic...
 
+ 1 for the inverter option - it'll keep you going for a while, depending on whether you have the single (12V) or dual battery (12V or 24V) option. I use the Tedelex Intelli-Power2/4 units on my home server and PC's, and they work great. When the power goes out, I can still use my laptop and ADSL modem. Just remember that you'll need to charge the batteries, so I'm unsure how you'll do this. As this requires AC, surely you'd have this onsite, so why not use the normal laptop AC power adapter?
 
chris414 said:
... do you think this will endanger my laptop?*-)
Click to expand...
I once forgot my power supply and used one with an output voltage 1 volt lower and equal current rating. It totally screwed up the power savings setting/controls. Only came right again after reinstalling windows.
 
Thanks for the replies - I'm mainly concerned with how sensitive the netbook will be to ripple? Also if using a linear regulator the voltage can drift a little (a few tenths of a volt at most) as more current is drawn... will the laptop be able to reject ripple/"drift"?
 
chris414 said:
Thanks for the replies - I'm mainly concerned with how sensitive the netbook will be to ripple? Also if using a linear regulator the voltage can drift a little (a few tenths of a volt at most) as more current is drawn... will the laptop be able to reject ripple/"drift"?
Click to expand...

If you insist on using a linear regulator, you should definitely put in a feedback loop to keep the output voltage constant. A few tenths of a volt is way to much, I would not let it go over +- 0.1V. Anything more and you're asking for trouble. You will also need to put in a nice fat capacitor on the output to keep the output as ripple free as possible. It becomes quite a mission. IIRC a laptop does very little with the power coming into it, it relies heavily on the power brick to give it the proper voltage and current. Inverter is the way forward, it will be more expensive but you won't have to go through building and testing crazy circuitry.
 
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