Can someone please tell me where I have gone wrong? I have a battery powered impact screwdriver, the battery is rated at 12vdc 2amp. The battery was exhausted so I built a power supply for it. I used a ring transformer with an output of 12v and 50va. The output was fed into a bridge rated at 400v and 4 amperes. Across the dc output I connected a 3500mfd 35vdc electrolytic capacitor. When the drill was connected across the capacitor output it worked fine in both directions. However when I tried to screw a screw into a plastic wallplug the screw would only go in about halfway - it was also difficult to unscrew it. Can anyone give me an explanation and how, if possible I can correct it?