how to lower voltage on laptop PS

[CaptEvo]

Hi,
I found an old Hitachi laptop PS, the reading show 18V 4A for output.
How can I lower the voltage down so that I can use it to charge my Polycharge which requires 11VDC-15 VDC input?
Thanks,

[lazy-b]

Just install a voltage regulator, you may use LM396 (10 AMPS), LM338 (5AMPs), LM350 (3 AMPS), LM317 (1.5 AMP)....this is actually an adjustable Voltage regulator..check the google for pin configuration......make sure you put an heat sink for high current....or for more simple just use a series of DIODE, each diode will drop a 0.7 Volts, say to drop 18 Volts to 15 Volts thats (18-15)/0.7= 4.28, try using 4 pcs.

been using a LAPTOP POWER ADAPTOR to power my Supernova Charger. cause its small/light.....I was thinking you might want to use it for charger, some charger can accept a wide voltage input range from 12Volts to 24 Volts, for this application a 18 Volts is OK.

Ellion

[CaptEvo]

Thanks, Ellion.
is there a specific one I should be looking for?
which one of these (http://www.radioshack.com/search.asp?find=diode&hp=search&image1.x=0&image1.y=0&image1=submit&SRC=1) should I get?

I'm clueless about this stuff.
Thanks

[Pete P]

I wish I had that adaptor :-P I've been looking for a 12v 4 A one for my friend's LCD. I wish I had thought about a variable VReg :-P I'll have to wait May's 3rd sunday now :-P

[IanS]

The third one looks right for you (RS #276-1661). Just ask them if these diodes are "schottky" as you DO NOT need this kind for your application.
Solder all four in series and make sure you are soldering the side with a "band" to the side without a "band". Disconnect the laptop PS from the mains and after this you can solder the remaining side of the chain without a "band" to the positive side of your laptop PS and the other end (the one with a "band") you can solder (or use an alligator clip) to connect to the positive input (probably red color wire) of the Polycharge charger.
Use an electrical tape to isolate well all the soldering joints.
Connect the negative side of the laptopPS to the negative input (probably black color wire) of the Polycharge and go charge....

IanS

[lazy-b]

Captevo, IanS just say it all.......Yes, make sure its just a regular Silicon Diode,....I Thinks a Schottky has a lower voltage drop I thinks its 0.2 Volts.....sometimes I use Schottky diode if I need a lower Voltage drop.

Pete P, you may visit an electronics surplus store, I just got lucky, I was able to get an 12 Volts 4 Amps HP power supply.

Ellion

[Pete P]

I use the MIT Swap meet :-P I paid $2 for the 13v 4A ac one... I wish I had read more carefully :-P But I did get a pIII 550MHz for $5!! Works great!