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I feel like a freaking genius. But only because I just accomplished something that others have already accomplished with more flair and infinitely more precision. However, I did it with commonly available parts, regular household tools — and no soldering gun. I created a snap-together replacement Newton eMate battery pack that required no special skills to assemble. I reveal all the lovely details after the jump:

This is the story: My old Newton eMate’s battery pack finally and completely died. Replacements don’t exist any more. I found two excellent explanations on the web describing how to build your own replacement battery pack. Here are the links — if you’re interested, you should read them, because the visual explanations are much better than what I’m about to tell you.

http://www.pda-soft.de/body_emate_battery_pack.html
http://www.felesmagus.com/newton/otheremate.html

I wanted to follow these already-published instructions — particularly the 2nd one, because it used a battery tray to simplify the construction, which allows you to use standard AA NiMH batteries, and not the hard-to-locate kind of AA cell with soldering tabs on the ends. But the problem was, I simply could not find a suitable 4-AA battery tray to hold the batteries. I did find a variety of trays at Radio Shack, but none in the right configuration. I thought I could take two 2-AA battery holders and wire them together to accomplish the same thing, but the extra plastic on the ends made the two combined holders too long to fit in the battery well, particularly once you ad in the snap-on connector tops for the wiring.
My brainstorm was to eliminate the snap-on connectors by taking the two 2-AA battery holders with 9-volt connectors on the top, and snapping the connector tops to each other! Then I was able to run wires from the positive and negative terminals of one end (formerly the bottom of one of the holders), splice them onto the existing wiring harness that I salvaged from the dead battery pack, and hold everything together with plain old electrical tape. And again, I have to repeat myself, with no soldering required!

If you try this — and it’s easy enough to do — the critical thing to remember is that by snapping the two battery packs together, you are creating a closed circuit, which instantly shorts the batteries and can result in a messy meltdown and chemical fire. So you need to cut the connection between the + and - terminals on the end of one of the trays. (Marked A on the attached photo.) And don’t just cut it — thoroughly remove any cross-connecting metal or wire bits, to prevent a tiny short from occurring later on. Use this newly “cut” end to attach your positive and negative wires. Hint #1: The red wire attaches to the positive terminal, the black attaches to the negative terminal. Hint #2: Be sure to attach the thermal sensor from the old salvaged wire harness to the surface of one of your batteries (Marked B on the attached photo.) Hint #3: You may have to reset your eMate before it will turn on again. I thought I had damaged my eMate or wired the harness wrong, because it would not start up after I finished this geek surgery, but a reset cured it. Hint #4: use only NiMH AA batteries. The eMate charging circuit won’t know how to handle LiON batteries, and if a LiON battery overheats, it can literally explode and burn. Dell and Sony found this out the hard way and had to issue very expensive laptop battery recalls.

And one last note: in my haste to finish the project, I did not incorporate the thermal switch (described in the two links above) that acts as a safety valve in the battery pack during charging. I’d have to disassemble one of the battery packs and insert the switch in the end. Maybe one day I will take this apart, install the salvaged switch, and actually solder the wire connections where they are currently only taped at the moment (Marked C on the attached photo). But not tonight. For now, I’ll just take care to supervise the eMate while it is charging, and to never leave it plugged in while the batteries are full.

This entry was posted on Sunday, September 3rd, 2006 at 12:16 am and is filed under Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.