View Full Version : Minimal-cost Power Supply Strategy - Repurpose Laptop Power Supplies

25-01-2012, 08:29 PM
Most owner-built CNC machines use "chopper" type motor controllers because they can enable higher motor speeds, improved position definition accuracy and better torque curves. But to deliver the same average current as non time-chopping controllers, chopper type controllers need higher voltage to chop. Typically, at least double rated motor voltage is suggested as the chopper controller's input, and three times higher input voltage can work even better if the controller's voltage handling limits are not too closely approached.

Higher voltage than commonly-found 24-volt high-efficiency switching power supplies are often desired and beneficial. But reviewing commonly offered higher voltage DC power supplies with enough current capacity to never "sag under load" when all axes are simultaneously moved (rare but possible), tend to be budget busters to minimal-cost do-it-yourself builders.

I reviewed many new and used potential power supplies. I think I have found a "hole in the market." Specifically, used 18-20 volt rated DC laptop computer power supplies appear to be really promising candidates. Consider how much used Dell 135-watt 19-volt 6.7-amp power supplies command. Join two in series with a pair of reverse-current protecting diodes, and you'd have a 38-volt 6.7-amp switching power supply with about 86% efficiency and proven durability. If you're concerned about keeping them cool, add a little fan, which could be heat triggered if you like.

Or for an even lower-priced 38-volt power supply, I'm seeing Dell 19-volt 2.67-amp power supplies offered for $5 and under each on eBay. Series a pair of them the same way.

Laptops die more often than their power supplies, so there seems to be a continuous flow of used low-priced units offered in used markets. I have not tried this yet, but I just ordered some and will report back with results after some trials. Has anyone else tried this general strategy?