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Wahoo speed sensor battery change problem

Old 09-30-20, 07:52 AM
  #1  
pdlamb
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Wahoo speed sensor battery change problem

Ran the battery down on my Wahoo speed sensor, so I replaced it. (And it looks like the people who designed this were the ones who designed the barely user replaceable battery on the Garmin HRM, but that's another grumble.)

Just like the directions said, after replacing the battery, the sensor's LED flashed several times. So, put it back on the wheel. But now the sensor apparently isn't transmitting anything; I can't pair it with a phone, GPS, or power meter. None of them even registers another sensor in the neighborhood.

Any ideas on what to do next?

FWIW, a web search found how to replace the Wahoo battery, and a couple links to how to fix the same problem on a Garmin sensor. But I think the Wahoo battery contact has to be working to make the Wahoo's LED flash.
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Old 09-30-20, 08:21 AM
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Yep.

Go into your Wahoo and forget the sensor
Go into your phone and forget the sensor under Bluetooth
Re-Start your phone
Re-Pair your sensor
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Old 09-30-20, 08:54 AM
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Take the battery out of the sensor and put it backwards for 10 seconds. This resets the sensor. Then put the battery in the correct way.
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Old 10-13-20, 11:10 AM
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Originally Posted by texbiker View Post
Take the battery out of the sensor and put it backwards for 10 seconds. This resets the sensor. Then put the battery in the correct way.
Mmmmmm. I wouldn't do that. My experience with electronic devices is that if the designer didn't include a reverse polarity protection diode it lets all the magic smoke out. If there is a reverse polarity diode, then reversing the polarity does nothing.

Last edited by DangerousDanR; 10-13-20 at 11:11 AM. Reason: cleanup
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Old 10-13-20, 03:27 PM
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Originally Posted by DangerousDanR View Post
Mmmmmm. I wouldn't do that. My experience with electronic devices is that if the designer didn't include a reverse polarity protection diode it lets all the magic smoke out. If there is a reverse polarity diode, then reversing the polarity does nothing.
Reversing the battery is the method advised by wahoo. Won’t hurt anything.
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Old 10-13-20, 03:43 PM
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Originally Posted by DangerousDanR View Post
Mmmmmm. I wouldn't do that. My experience with electronic devices is that if the designer didn't include a reverse polarity protection diode it lets all the magic smoke out. If there is a reverse polarity diode, then reversing the polarity does nothing.
There is no reverse polarity going on.

If you look at how the battery compartment for a coin battery is designed, you should realize that if put in backwards, there will only be one side of the battery completing the circuit. I would think about all this is doing is letting some capacitance in the circuitry be relieved.

Not certain if capacitance is the right thing or even correct word to use. But till someone that knows comes along, I'm sticking with that.
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Old 10-13-20, 05:17 PM
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So it is a do nothing. I have not been very impressed with Wahoo's support, and if they recommend doing that, particularly in light of Iride01's claim that the battery will not make contact, I have even less.

Iride01's claim sounds like it is probably true. Many of those coin cell contacts grip the side and contact the top. On a coin cell like the ones in the Wahoo, if they don't contact top and bottom reversing the battery is a do nothing. Note that I just had my car's fob apart to change the coin cell, and it has side grippers along with top and bottom contacts. I am sure that fob costs quite a bit more to build than a Wahoo sensor and, since mine tends to go through the washing machine every couple of months, it is a more rugged design.

Yes, capacitance is close enough for government work, The charge stored in capacitors needs to dissipate to completely shut down the electronics. I was involved in developing a product that kept enough charge in a capacitor to keep a real time clock running for a week, so that we could loose the battery and when it was replaced, we would know the date and time.

As a side note, here is an article which describes a simple reverse polarity protection circuit: https://components101.com/articles/d...ity-protection
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Old 10-13-20, 05:31 PM
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Originally Posted by DangerousDanR View Post
So it is a do nothing. I have not been very impressed with Wahoo's support, and if they recommend doing that, particularly in light of Iride01's claim that the battery will not make contact, I have even less.

Iride01's claim sounds like it is probably true. Many of those coin cell contacts grip the side and contact the top. On a coin cell like the ones in the Wahoo, if they don't contact top and bottom reversing the battery is a do nothing. Note that I just had my car's fob apart to change the coin cell, and it has side grippers along with top and bottom contacts. I am sure that fob costs quite a bit more to build than a Wahoo sensor and, since mine tends to go through the washing machine every couple of months, it is a more rugged design.

Yes, capacitance is close enough for government work, The charge stored in capacitors needs to dissipate to completely shut down the electronics. I was involved in developing a product that kept enough charge in a capacitor to keep a real time clock running for a week, so that we could loose the battery and when it was replaced, we would know the date and time.

As a side note, here is an article which describes a simple reverse polarity protection circuit: https://components101.com/articles/d...ity-protection
It's not a do nothing. It essentially completes a circuit by bridging the two contacts with a conductor. You could use a wire a real coin or anything else that conducts electricity well. What this does other than discharge some capacitors is not in my knowledge. But doing this has seemed to resolve issues with other devices that use coin batteries.

I will admit, AFAIK, it's anecdotal that it actually helps. Garmin says you can also just leave the battery out for a few minutes.

If you don't think something is going on, well then you need to be glad cathode ray tube TV's went by the wayside. You could unplug them, then reach in there and get a 125,0000 volts run through you as capacitor for the high voltage side discharged.

Thankfully modern electronics don't require such high voltage.
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Old 10-14-20, 07:04 AM
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Originally Posted by DangerousDanR View Post
So it is a do nothing. I have not been very impressed with Wahoo's support, and if they recommend doing that, particularly in light of Iride01's claim that the battery will not make contact, I have even less.
It seems almost certain that you know less about it than Wahoo does.

==========================

Wahoo says to flip the battery around to reset the sensor. (It's a fairly common feature generally; not just for wahoo devices.)

https://support.wahoofitness.com/hc/...What-Can-I-Do-

What it does is short the contacts. It doesn't reverse the polarity.

The batteries are designed to work this way. That is, they are designed so that installing them backwards in certain sockets (like the one Wahoo is using) won't reverse the polarity.​​​​​

The negative contact is the bottom. The positive contact includes both the top and the side. The top is one piece, like a bottle cap. The bottom is flat.

For these devices, the positive contact is usually made on the side (the door is just a piece of plastic).
​​​​
​​​
Originally Posted by DangerousDanR View Post
Many of those coin cell contacts grip the side and contact the top. On a coin cell like the ones in the Wahoo, if they don't contact top and bottom reversing the battery is a do nothing.
???

The battery case is two pieces of metal. The top (positive) is like a bottle cap. The bottom is flat. The two are separated by an insulator. Look at one.

There needs to be contact with the bottom. The positive contact can be made anywhere on the top cap (including just the side).

​​​​​​

Last edited by njkayaker; 10-14-20 at 07:26 AM.
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Old 10-14-20, 08:17 AM
  #10  
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Originally Posted by jadocs View Post
Yep.

Go into your Wahoo and forget the sensor
Go into your phone and forget the sensor under Bluetooth
Re-Start your phone
Re-Pair your sensor
This will fix 99.9999999% of these issues.
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