anne nonomus

Hi
Found a sigma wireless odometer for a couple bucks with cadence counter at a second hand store. It's missing the main mileage magnet. I went to order a replacement on Amazon, and found one, but it states that it's for "wired" only, and instructs to order a "power magnet" for wireless models. I'm confused. I thought the sensors are what's "powered" , (and the actual computer, thus the battery requirements in them), Aren't the magnets just...um...magnets? What am I missing?

Steve B.

The magnets are just that, a magnet in a package that attaches to a spoke. The most common type is the round metal thing that’s split to mount on a spoke, with an attachment screw.

You are correct (in my experience) that it’s the sensor mounted on the fork that’s either wired and has no battery, or is wireless and has a battery.

Litespud

i don’t think you’re missing anything. I’ve used the same magnet for wired and wireless sensors. I guess it’s possible that one type of sensor might require a more powerful magnet, but in my experience, the key factor is distance between the magnet and sensor

Wilfred Laurier

Yeah, you rotate through multiple wheels with all sorts of different magnets and they will all work with the same computer (if the magnet is in the right place).

njkayaker

That's common. People lose them all the time. Pretty much, any magnet will work.

I have no idea what a "powered" magnet is. It would be interesting to see that link.

alcjphil

I cannot for the life of me figure out what the heck a "power magnet" is. I have owned wired computers and wireless computers and have never given any thought whatsoever about whether the magnet on one of my wheels might not work with the wired or wireless sensor. The mechanism is very simple, as the magnet passes the sensor it operates a switch in the sensor sending a signal. With a wired sensor, it is a simple off/on/off and the computer interprets the frequency. A wireless setup involves a sensor that sends the signal to the computer via some sort of wireless protocol. As long as the sensor and the head unit can communicate with each other, the signal gets through. All that the magnet does is magnetically close the switch in the sensor as it passes by

Steve B.

Only powered sensor I can think of is wheel speed sensors used by GPS units to get a better speed data. These are powered by button batteries but are not magnets. They do sense the earths magnetic field to determine speed. That’s magic to me.

alcjphil

The OP was not asking about powered sensors. The question was about "power magnets" Stay on topic

Cyclist0108

They might be suggesting a rare earth magnet, which will be stronger than an iron magnet of similar size.

Troul 

Maybe the "power" magnet that is being referenced are used in the hub mounted types that act as a sensor & as a detector for wireless units. Such units like the Wahoo RPM, Speed, & Cadence Sensor used for bluetooth/ANT+ computers. As those types have trigger lights that give the capability to notify of output data being transmitted.

njkayaker

Wireless sensors don't need any special magnet. It would be nonsensical way to specify a rare-earth magnet anyway.

The hub mounted sensors aren't magnets. You wouldn't be looking for a magnet if you had one of these either. "Power" magnet doesn't seem to make any sense.

Seems pointless to guess at what they might be trying to say.

njkayaker

Ah, maybe this is it.

It's a marketing term.

"Sigma 2016 Power Spoke Magnet"

https://www.amazon.com/Sigma-2016-Po...XMXEP7RY5SFKE9

This is wider than the usual spoke magnets, which might mean there's less fussiness about positioning it.

In any case, it's not just for wireless.

UniChris

While I don't think it's what was originally mentioned I might have to improvise something like that.

Second to last ride my computer quit... between the time when I got on the train and slipped it off the bars, and between when I got off the train at the trailhead and put it back on. Wasted several minutes inserting and removing it, trying to clean contacts, etc.

A few days later bumped into the wheel at home and noticed the computer woke up, but only once. I've had many issues with the sensors or wires in the past so went and got a fridge magnet to tease it with. That seemed to work. And the spoke magnet was correctly oriented and within the plastic frame of the sensor, but not reading reliably...

But then it hit me to try moving the magnet vertically on the spoke. And that did it! It's possible it got bumped out of place, but I half wonder if the reed switch moved within its housing - both the old and new positions are within the footprint of the plastic base.

I keep meaning to make my own system from scratch anyway with extra features I want, then forgetting and heading out to ride with the $12 bell either working or not...

philbob57

Another version is: https://www.amazon.com/CatEye-Cycle-...SIN=B000OYFENU.

If you can't place it close enough to get reliable readings ( a problem I had with Sigma's magnets), I recommend going with something like the Cateye supplemented by something like this: https://www.homedepot.com/p/Master-M...45HD/202526363.

Steve B.

He stated this “order a "power magnet" for wireless models. I'm confused. I thought the sensors are what's "powered" , (and the actual computer, thus the battery requirements in them)”. The OP was questioning what could be powered, thus my post is somewhat relevant.

And note that people get testy when others try to tell them what to do,

njkayaker

What the OP relayed doesn't make sense. It doesn't seem useful to try to devine meaning from it. He should provide more information (like the link to what he's talking about).

Is some random dude on the intertubes, who you don't know, really able to tell you or anybody what to do?

You could get testy or you could ignore him. Your choice!

Cyclist0108

1. Anne (the OP) might not be a he.
2. The OP (Anne, who might be a she) was asking because she/he/they/it thought it didn't sound right.
3. Some people use the word "power" to describe magnetic field strength, when they really should be speaking in terms of Teslas or Gauss, not Watts.
4. Some of the rest of us were making our best attempt to guess what might have been the actual meaning of the question, given that it might have been formulated or relayed in an ambiguous manner.
5. The suggestions make sense. They might not be correct, but they were hardly nonsense. If I had suggested the OP purchase a box of magnetic monopoles, your assessment would perhaps be more justified.

Kedosto

The way you guys are posting it’s like none of you have ever spent any time reading Amazon product descriptions. So many of them are so comically bad it’s a wonder they sell anything. I guess the only thing that keeps some of those knuckleheads in business is that the buyers aren’t bothered to read the descriptions.

To the OP, you just need a magnet positioned near the sensor so that as it passes the sensor with each wheel rotation the sensor can detect it passed by. Philbob57 posted a link to a Cateye magnet which is designed for spoke mounting. Position it less than about ¼ inch away from the sensor (there will be an alignment mark) and you’ll be good to go.


-Kedosto

woodcraft

Any reasonably strong magnet will work.

A tiny rare earth one held onto the spoke with a bit of glue & some tape works great. I've used 3/16"

TheDudeIsHere

Maybe he means the speed magnet on the spokes.

Vs the magnet on the cranks that count cadence on old computer types.

njkayaker

1. Not enough information.

2. Lots of guesses based on a lack of information.

3. The suggestion to get a simple standard magnet makes sense (I didn't say otherwise).

4. The other stuff is weird speculative nonsense based on not enough information. None of which is likely relevant to the odometer mentioned.

njkayaker

And there's a lot of wild speculation what the odd description (which no one has even seen) might mean.

UniChris

Well, here's a simple idea. Test it with some magnet from around the house before buying anything. Just take something off the refrigerator (preferably a real magnet not the rubberized joke in kids spelling letters) and wave it back and forth at a rate of about a second so that it's passing the sensor twice a second. If that registers, then great, all that's needed is a common spoke magnet.

If not, then the test magnet isn't strong enough, or as likely something else is wrong - dead battery, broken, etc.

Also while it wouldn't be true for a solid state hall sensor, most computers seem to use reed switches, and in a quiet place if you get your ear close enough you can actually hear a faint click as magnet closes them.

That and the magnet waving test are probably even better done before mounting on the fork.

Steve B.

Both good points

BlazingPedals

If you have a wireless computer, it needs a powered send unit to work. The send unit senses the (unpowered) magnet on the spoke and transmits data to the head unit - the computer. In the case of a computer with cadence, the send unit is usually a one-piece that goes on the rear chainstay so that it can sense both a magnet on the rear wheel (speed/distance) and one on the crank arm (cadence.)