February 21, 2009

FAIL: Cordless Drill Battery Modification

Not every DIY project succeeds. Sometimes, there are failures. Sometimes the failures are pretty spectacular. It is ok to fail, however, so long as you learn something. This is why I am sharing these not so successful projects.

A few years ago the battery pack in my Ryobi 9.6 volt cordless drill died, I decided a replacement battery was just too expensive for the value of the drill. I had nothing to lose with the battery at that point, so after disassembling it, I determined that a bunch of NiMH AA cells could replace the existing Ni-Cad 'sub C' cells for the same voltage, but with 30-50% increased capacity (mAh).

Thomas Distributing carries tabbed NiMH cells. The tabs make it easier to solder cells together to form a battery pack. So I ordered up the right amount of cells and set to work.

Not having performed a lot of electrical tinkering at that point in my life, I foolishly used 22 gauge wire to connect the battery tabs together. It's what I had on hand, but sometimes you just have to buy the right material for the job. The battery pack went together pretty easily and it wasn't long before I had it charged up and ready to go.

Unfortunately, this is where the story goes down hill...For a project I was working on, I needed to drive four 6" screws into solid oak blocks. I got through about one and a half before the smoke started pouring out of the battery compartment. I quickly tore it apart and separated the batteries, my heart racing the entire time.

The high torque required to drive the screws into the hard oak (it nearly stalled the drill) drew so much current from the battery pack that the wires heated up to the point of melting the insulation and causing the pack to short out. Several of the batteries got so hot that they vented acid inside the enclosure.

Undaunted, I ordered more batteries and rebuilt the battery pack using heavier gauge wire.

Since I still needed to drive the remaining screws, I again used them as my test subjects. I got through the remaining screws just as the smoke started pouring out of the battery pack, again.

This time, before I could get it torn apart to stop the short, one of the cells exploded with a rather impressive bang!

That marked the end of my attempt at cordless drill battery pack re-building. I never figured out exactly what caused the second meltdown. Obviously something shorted out, but it didn't appear to be the same problem as before.

Under normal use the re-built battery pack would have worked just fine, but the extreme test conditions I put it through were too much. I would rather have an early failure, however, than to be lulled into a false sense of security. Especially considering the potential to have caused a fire.

So my recommendation is, don't try this at home. And by the way, I ended up spending more on the batteries than if I had just bought a new OEM battery pack.

February 19, 2009

TIP: Disposable Epoxy Mixing Trays

Epoxy, that universal fix for everything that duct tape can't handle (wait, duct tape can't fix everything?). Unfortunately, anything you mix it on needs to be disposable. But paper can soak through, and cardboard soaks up the epoxy and gets droopy or can contaminate the epoxy with fibers. So what is one to do?

Save the flat areas of the clear plastic packaging that is used on everything from kids toys to memory cards (I believe it is sometimes referred to as clam shell packaging). Then use it to create custom sized trays to mix the resin and hardener on. I have found this type of plastic to be just the right thickness to make a good tray. Small pieces are stiff enough to not droop, yet it is easy to cut.

In addition to the tray, you can also cut out a small 'spatula' to do the mixing and applying with. Or, whittle down a popsicle stick if you need something a little firmer.

When you are done with your repair, let the remaining epoxy dry and throw it away, no mess, no fuss.

February 18, 2009

REPAIR: Cordless Phone Battery Modification

My wife picked up a pair of cordless phones on Freecycle to replace our old phone that was dying a slow and staticy death. Unfortunately, one of the handsets didn't work when we plugged it in.

I suspected it was just a battery issue, and after swapping batteries between the two handsets was able to confirm my suspicion.

Since I had recently replaced the battery in the old phone, I figured no problem, just swap batteries. Or not, as it turns out the connectors between the two brands of phones are different.

There's nothing special about cordless phone batteries, in the end they are just 3 Ni-Cad AA's linked in series to give 3.6V at whatever capacity you want. The more milliamperes (mAh), the longer the talk time. In fact, you could easily buy your own batteries and wire them up to create your own battery pack. But, in this case I just wanted to swap connectors for a quick and dirty fix.

The swap is easy. Snip the wires on both batteries to remove the connectors. Strip a quarter inch or so of insulation from both the desired connector and new battery. The wires for both parts should be color coded red for positive and black for negative. Cross the stripped end of the red wires from the connector and battery and twist to create a connection.

If you feel motivated, the wires can be soldered together to guarantee the connection will not pull apart. I did not do this for two reasons. One, I was in a hurry to make sure the phone worked, and two, the soldered joint will be less flexible for installation in the phone. Another consideration is that the wires are not loaded once installed in the phone, so there is little to no risk of the splices being separated.

Now repeat for the black wires. When finished, wrap the wires individually in electrical tape to hold the splices together and prevent shorting. Re-install into the phone and you are done!

My phone has been operating on the modified battery for about a year now with no ill effects. In fact, we can't tell the difference between the two handsets unless the back cover is removed.

This method could easily be used to maximize the talk time for your cordless handset by utilizing a higher mAh battery pack than normal. You could also save a few bucks by picking the cheapest replacement battery available, regardless of brand and then adapting it to your phone.

February 15, 2009

Welcome to my little corner of the world!

Here are the chronicles of my tinkering. What is a tinkerer? According to Merriam-Webster:

..to work in the manner of a tinker ; especially : to repair, adjust, or work with something in an unskilled or experimental manner

While in my professional career I'm paid to do the opposite of tinker, at home it's all I do. College may have prepared me for life as a design engineer, but no one teaches you how to repair home electronics or build gadgets. It seems in fact, that in this age of mass produced junk electronics, that the art of tinkering is being lost, or more appropriately, being driven into extinction.

I grew up with my family the proprietors of a repair shop, doing metal fabrication, vehicle repair, small engine repair and whatever else could be done to make a few bucks. Time and cheap Chinese imports passed the business by years ago, but it left an indelible mark on how I approach life.

I hope that by sharing some of my exploits I can help someone save a buck or two, and find satisfaction in doing it themselves.