I have a driller that works with rechargeable batteries, which have almost failed, and I am not interested in replacing them.

I thought to replace the batteries with a circuit which will be able to supply the driller with the needed current and voltage using a transformer and a certain circuitry. What I don`t know, is how to convert the transformer output to 18V and ~5A (which was the batteries output), while using a transformer that can output less than 5A.

Hope this is clear enough. Thank you!!

 

Good luck. The motors used in cordless drills can suck down a LOT of current when not limited by the internal resistance of a battery. I've measured more than 20A from a small 12V drill hooked up to an SMPS. Switch-mode supplies will tend to cut out to protect themselves unless you substantially overspec them, and a linear supply that can handle that much current will be big and very heavy.

A better option might be to rebuild the battery packs. If they're NiCd or NiMH packs, you should be able to open them up and identify suitable replacement cells fairly easily.

 

So, you are planning on turning the cordless drill into a corded drill?

The simplest answer is a 12V lead acid battery and a charger. Chances are the 12V will provide plenty of drill power, but if you really want 18V, try three 6V batteries in series. Just don't discharge the batteries too much, or they will be permanently damaged.

 

About the only thing I'd consider worth trying is a laptop power brick. They'll supply about 19V at 5A if they're rated for 100W or so. Might work.

A linear supply (big transformer with rectifier) would just be so cumbersome that I can't imagine using it with a drill. Drill press maybe, but not something I need to tote around.

 

Nice suggestions, really. What I might try is a laptop power brick. Pretty compact, and should give me enough drill power. Thank you all!!