Electronics, Lighting, & Gadgets - Planet Bike Protege computer spike magnet stops working
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05-16-12, 09:05 AM
I have two different kinds of Planet Bike Protege computers. Both use the same spoke magnet. I also purchased a third mounting kit, which came with a third magnet. Over time, two of the magnets have stopped working. I know that sounds silly, but for some reason those two magnets can no longer be detected by the sensor that mounts on the fork. They still have at least some magnetism, because they'll stick to metal objects, but apparently they have lost just enough of their magnetism. I know the problem lies with those two magnets, because when I replace them with the one remaining magnet that still works, the computer works just fine.
What the heck is going on? Can a magnet really lose its magnetism like this? Is it just a Planet Bike problem? And can I get a replacement magnet? I have been unable to find just the magnet for sale anywhere, and it's not listed as a part on Planet Bike's web site. I tried a smaller magnet that I had from a previous computer, but evidently it's too small. I guess I need a nice big one like the original Planet Bike one.
05-16-12, 09:09 AM
Try adjusting your magnet toward the top or bottom area of the wheel sensor.
They sometimes don't work if they are centered on the pick up unit.
05-16-12, 12:16 PM
I don't know about the magnets losing their magnetism. They shouldn't but there may be things that can cause it.
The sensor and magnet should be as close as possible to the hub, NOT out near the rim. At the rim the magnet will be moving very fast and the sensor will be less able to detect it moving past. Also at the rim the magnet will unbalance the wheel more.
When I had a really cheap magnet give up on me I've just glued a nice strong neodynium magnet to the existing (usually a cheap ceramic) magnet, that works too. But the first step is to get the sensor close to the hub.
05-17-12, 05:19 PM
For the longest time I kept thinking how finicky my bike computer was. I could never get the alignment between the magnet and the sensor correctly. But the cadence sensor on the crank worked fine even when not aligned very well. It finally dawned on me that the contacts on the removable mount of my computer was bad. I got a new mount, problem solved. Check your whole system, not just the alignment of the magnet and sensor.
05-17-12, 07:10 PM
A permanent magnet can and will lose its magnetism for good if heated up to certain temperature. This temperature is known as Curie point (http://en.wikipedia.org/wiki/Curie_point). However, in everyday life wheel sensor magnets don't even come close to their Curie point, even though rare-earth magnets typically have lower Curie points than "ordinary" magnets.
So, unless you somehow expose your magnets to extraordinary temperatures (hundreds of degrees Celsius), they should not lose their properties.
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