Introduction: Alternate Power for the Sigma BC 2006 Cyclometer

Picture of Alternate Power for the Sigma BC 2006 Cyclometer

This is the Sigma BC 2006 cyclometer. The wheel sensor is wireless. The main unit, the wheel sensor, and the heart monitor strap each use a CR2032 battery. The power in the main unit shuts down automatically when not in use, but the wheel sensor broadcasts a digital signal 24 hours a day, 7 days a week. Battery life in the wheel sensor is disappointingly short. The batteries are relatively expensive. I wanted a way to control the battery drain from the sensor and provide a less expensive source of power.

Step 1: An Alternative to the CR2032 Battery

Picture of An Alternative to the CR2032 Battery

Pictured is the battery my digital camera uses. It is a CRV3 lithium photo battery rated at 3.0 volts. It actually produces a bit more than that. When it will no longer power my camera, it still has more than enough power and voltage left to power the wheel sensor on my SIgma cyclometer.

Step 2: The Original Battery Holder

Picture of The Original Battery Holder

This is the waterproof cover and battery holder for the wheel sensor. A metal tip built into the battery holder makes contact between the positive (+) edge of the battery and brass strip on the wheel sensor's circuit board. The exposed surface of the battery is the negative (-) terminal of the battery and it makes contact with a raised spring terminal on the wheel sensor circuit board.

Step 3: Battery Terminals on the Wheel Sensor Circuit Board

Picture of Battery Terminals on the Wheel Sensor Circuit Board

I had my battery modification to the wheel sensonr done before I decided to make it an Instructable. This graphic was done in Google Sketch Up with modifications in MS Paint. The yellow arrow shows the negative (-) battery terminal on the circuit board. I soldered a black wire to the center raised tip of this terminal. The red arrow points to the positive (+) terminal on the circuit board. I soldered a red wire to it near the arrowhead. If you look closely, you can see a darker arc at the other end of the brass strip to indicate the contact area where the metal tip on the battery cover rubs against this brass strip on the circuit board. I wanted to avoid that area with my soldering, lest I would need to undo my modification. I also waited until my warranty had expired before attempting this modification.

Step 4: Seal the Opening for Moisture

Picture of Seal the Opening for Moisture

I considered drilling holes into the battery cover or the case of the wheel sensor for the wires. But, I decided to fill the opening with hot glue. When cooled it provides protection from damage due to movement of the wires and holds the wires in place. The hot glue also seals to protect against moisture. There is plenty of clearance for the magnet mounted on a wheel spoke. If I need to undo my modification I can dig out the hot glue fairly easily.

Step 5: Battery and Switch

Picture of Battery and Switch

I plan to make a holder for the battery. Currently the black and red wires are soldered to it and the battery is taped to the bicycle frame's top tube with plastic electrical tape. I added a sliding switch so I can disconnect the power to the wheel sensor when I am not riding. Later I will make a more permanent mount for the switch, too.

I could bypass the switch and run wires to power the main unit of the cyclometer, too. But, that battery lasts quite well.

On my inaugural ride with my used camera battery powering the wheel sensor my Sigma BC 2006 performed very nicely. I am pleased.

Comments

rimar2000 (author)2009-06-23

Good work, Phil, and it is environmentally friendly.

Phil B (author)rimar20002009-06-23

Thank you, Rimar. Eventually the battery will no longer be useful and will still need to be discarded. Recycling centers in the US once accepted old alkaline batteries, but no more. I have a shoebox half full of old batteries.

ll.13 (author)2009-06-23

A good project! Although it is a shame the battery is "open" to vandals (or looking unsightly)

Phil B (author)ll.132009-06-23

Your point about vandals is well-taken. My bike is virtually never parked anyplace other than in my garage. If I left it locked to a bike stand out of my site, that would be a problem. The Sigma BC 2006 main unit does twist off of its mount so I can take it with me to foil thieves. Thanks for the comment.

qupada (author)2009-06-23

Couple of questions;

Did you consider disassembling a 2032 battery to make a dummy battery? Cleaning the electrolyte gunk out of batteries may not be the most appealing task, but if you were lucky would have reduced the necessary modifications to drilling a hole in the centre of the battery cap to pass the wires out, and would make swapping between the big external battery and the regular CR2032 easier.

Have you tried the cheap direct-from-China option? http://www.dealextreme.com/details.dx/sku.751 at USD$3.66 (shipped!) for 20 CR2032's, hard to go wrong (aside from not being the exactly environmentally friendly solution). I've paid that price for a single battery at local stores before.

Saying that, the CR-V3 is a very good solution to the problem, probably one of the more reasonable ratios of price to capacity among the 3V primary lithiums, though maybe a little harder to come by than the extremely common CR123A.

Phil B (author)qupada2009-06-23

I thought long and hard about opening a 2032 battery to make a dummy, but could not conceive a way of removing all of the electrolyte while still keeping enough of the battery's case intact to make it work. I really wanted to avoid drilling a hole in the case or the cover. One reason is that I might one day want to remove my modification so I can sell this cyclometer to someone, even though that is not likely. I had not checked the Internet for 2032 batteries and had not considered "The China Solution." (That phrase has an eery history from the days just before the fall of the wall in East Germany.) Thanks for the information. Again, I used the CRV3 because it is what I have as a leftover item from my digital camera.

About This Instructable

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Bio: I miss the days when magazines like Popular Mechanics had all sorts of DIY projects for making and repairing just about everything. I am enjoying ... More »
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