Hi

I have bought a bunch of second hand Toshiba laptops that are 15v. I have no transformers for them but do have lots of 19v laptop transformers.
What if anything can I do to reduce the voltage? I am familiar with soldering and have lots of spare components and resistors.
Is it as simple as soldering a resistor on the +ve line or not?
Any advice appriciated.

Phill.

If you put a resistor in that line, it would have to draw sufficient current to drop the voltage by 4 volts. Laptops draw more current when fans are on, CD drive is on, etc, than they do when none of these things are on. You're not going to be able to select a resistor that will drop 4 volts with all of the possible loads.

I'm afraid I can't think of any simple way to drop a DC voltage by 4 volts.

https://www.askmehelpdesk.com/electr...ml#post2073551
I doubt it would be practical to take an old PS brick apart and try to find the feedback network. Usually they are based on reference designs, but you'd have to do a bit of reverse engineering.

Although a box could be made using an LM150 (3 Amp) and LM138 (5 A) and a heatsink, it again is probably impractical. www.national.com. If you want to get your feet wet, then try your luck building using a switching regulator. Less heat disipated.

Your best overall solution is to get an adapter from Home at iGo, Inc. and use their Tip system to change the voltage of the adapter. The adapters are less likely to become obsolete and they are very reliable. You also get air, car and plane options with some. Latest design is thinner. Tips are typically <$10. The DC cord about $20.

Their system also works for cell phones. You use a smaller adapter plugged into a slave socket and set the cell/PDA etc with another tip.