I currently have a 4 peice cordless tool set from Coleman, that I always wished had an option to be run off of an outlet. The set comes with two battery packs and recently one of the packs stop taking any charge. The other pack doesn't last very long anymore so pretty soon I knew I would be out of luck. So, I decided to take apart the battery pack that didn't work and change it so that it could be plugged into the wall.
The first thing I did was take apart the battery pack and see what was inside. It is full of batteries that are about the size of "C" style batteries. There was a bunch of them in the bottom portion of the pack and two that stuck up into the part that slides inside the drill.
I decided to use one of my microwave transformers for this project because they are easy to find and free. I'm sure I could have gotten by with a smaller transformer because this one can put out a lot more wattage than would have been needed to power these tools. However, I already have a few of these around and to buy one the exact size needed would have been expensive. The only trade-off is that this transformer is a bit bigger and heavier.
Since the transformer won't fit inside the battery pack itsself, I decided that I would build a box to house the transformer, which would plug into the wall, and then I would have a long cord running from that box to the battery pack which would could be inserted into the drill, circular saw, saws-all or flashlight.
The only thing that would be housed in the battery pack is a bridge rectifier that I had purchased at radioshack for another project and never used. The bridge rectifier will convert the 18v AC comming from the transformer into 18v DC that the drill needs to operate.
Below is a drawing of how the whole system will come together.
The two batteries that fit in the top "stem" of the pack have the connections that contact the tool soldered to them. I pulled these batteries out. These connections are where I would need to connect my wires that would be hooked up to the DC side of the bridge rectifier.
Next, I soldered a couple of wires to the connections and pushed them back in place. I also taped the two batteries together and pushed them back in there just to have something to hold the connections in place. I didn't want the connections to get pushed down when the battery pack was inserted into the tool.
At this point I decided to give it a test and make sure that it all worked. I inserted the top of the battery pack into the drill and hooked up the transformer to a wall outlet. I connected the bridge rectifier on the other side of the transformer and to the battery pack and fired it up. Everything worked great.
I decided to use an old extension cord to go from the transformer to the battery pack. This way I could have a short cord going from the transformer to the wall so that the transformer could just sit by the outlet and I would be able to take the drill up to 25 feet way.
I decided to keep the ends on the extension cord so that they could be used to keep the cord from being able to be pulled out of the box. This thing will probably take a bit of a beating while being used around the house and shop so I didn't want the cords to get yanked out.
I simply cut a notch out of the top of the battery holder that I could lay the cord in. This way if the cord gets pulled on, it can't pull the end through the notch.
I hooked up the AC side of the bridge rectifier to the end from a computer power cable which was plugged into the extension cord. Then I hooked the wires I previously soldered into the battery pack to the DC side of the bridge rectifier.
I closed the box back up, gave it another test and the battery pack side of the project was complete.
The next part was to build a box around the transformer. I used wood for this becuase it is the easiest for me to use.
I used small bolts to connect the connectors from the secondary to the prongs on the extension cord.
Then, I taped them up so that they couldn't contact anything else and stuffed it into the box.
I cut notches in the side peices so that when I screwed them in place they fit over the cords comming out of the box but were too small to let the cord ends come out.
After the box was all sealed up I added some rubber feet that I salvaged from microwave ovens.
I also added a wooden handle to make the box easier to carry.
It works pretty nice and with the long cord it is still pretty conveinent to use.
I was really happy with how this turned out. It only took a couple hours to do and cost nothing.
Created 12/30/2008 - CleghornElectronicsKits.com
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