PowerTap SL Problem/Question



bing82

New Member
Mar 14, 2006
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Hi all,

I have a PowerTap SL 2.21, about four months old. For the first time last night, after riding about four minutes, the computer display of watts and speed suddenly dropped to zero for both values while riding rollers. The transmission icon remained on solid, and the HR and cadence displays continued to work fine. I removed the remounted the computer from the cradle, and it worked fine again for about 20 seconds, then watts and speed dropped to zero again. I seem to be able to repeat this process.

The troubleshooting section in the manual covers only conditions where the transmission icon is not displayed or is blinking. It appears the computer is getting transmission from the hub, but the hub is not transmitting correct data.

I wiped what road grime there was (from two outdoor rides so far this year) off the hub, zeroed torque, ran self test procedures on the computer, wiggled cables, cleaned the contacts, made sure the receiver was mounted properly, etc. with no success. The computer display seems strong with no battery warnings, and I've had the unit only since the beginning of December and haven't ridden that many hours on it, so I assume the batteries are fine. The ride outdoors before this problem occurred was on damp roads, and the bike picked up some dirt from the road, but it wasn't raining and I would hope that amount of dampness wouldn't cause a problem.

Any idea what could be wrong? Any tips would be much appreciated!

Thanks,
Tim
 
bing82 said:
I have a PowerTap SL 2.21, about four months old. For the first time last night, after riding about four minutes, the computer display of watts and speed suddenly dropped to zero for both values while riding rollers. The transmission icon remained on solid, and the HR and cadence displays continued to work fine.
I assume you mean the display showed zeros and not dashes, right? What's your setup for cadence data -- hub, pedal or hub/pedal?
 
Yes, the display showed zeros for watts and speed. The cadence is set to pedal. Thanks.
 
bing82 said:
Yes, the display showed zeros for watts and speed. The cadence is set to pedal. Thanks.
So, the only thing you're getting from the hub is the transmission icon. If you were getting dashes and no hub icon, one candidate would be frame vibration but that's a different set of symptoms. One leading candidate would be the hub batteries. There might be enough juice to send the hub icon but not enough to send the strain gauge data. Normally, the hub icon begins flashing before the hub batteries fail completely, but I don't know that it does so every time. Changing the hub batteries is quick and cheap, so you might want to rule that out before going much further with diagnostics. You can get the batteries at most places that sell small batteries (e.g., CVS, Walgreens, Radio Shack). I think they cost less than $10 for two. I always keep a backup set on hand.
 
Thanks for the suggestions. I installed new batteries in both the hub and the computer just to be sure. I left the battery cover off over a 24-hour period to let it dry out, but there was no moisture at all to be seen when I pulled it off.

Typically, the system will work okay for about five minutes or so, then it will start dropping the watts and speed data, or displaying highly variable data, jumping all around between 0 and the current actual wattage, despite maintaining the same cadence in the same gear on the rollers. I have zeroed the torque and checked the settings on the computer and it appears normal. Last night, it worked fine for a few minutes, started jumping around, then dropped the data completely for so long that the computer went to sleep, despite the fact that the transmission icon was still on solid. A few minutes later, I turned it back on and it worked fine for about ten minutes, then went bad again.

I have a second receiver and wiring harness I bought for my TT bike. I plan to install that on the TT bike and try it out tonight to eliminate the wiring as a problem. If it's still failing, I'll try to find someone in my club who also has a PowerTap to borrow their hub/computer for a little while to see what works and what doesn't. Failing that, it looks like I'll have to send the entire thing back to Saris. I'm not pleased that something so expensive can go bad after 600 miles of riding (500 indoors), and am not looking forward to sending it back due to reports on the web about them taking *forever* to get it repaired and returned.

Regards,
Tim
 
Update: I just reviewed the raw data from my ride last night. During times when the wattage was displaying incorrectly, the torque recorded was consistent and appeared accurate. I assume the computer calculates watts based on torque and wheel speed. So... I think that means torque is okay but the wheel speed is not being measured correctly. Not sure if that helps solve the problem though.

Tim
 
bing82 said:
Typically, the system will work okay for about five minutes or so, then it will start dropping the watts and speed data, or displaying highly variable data, jumping all around between 0 and the current actual wattage, despite maintaining the same cadence in the same gear on the rollers. I have zeroed the torque and checked the settings on the computer and it appears normal. Last night, it worked fine for a few minutes, started jumping around, then dropped the data completely for so long that the computer went to sleep, despite the fact that the transmission icon was still on solid. A few minutes later, I turned it back on and it worked fine for about ten minutes, then went bad again.

I have a second receiver and wiring harness I bought for my TT bike. I plan to install that on the TT bike and try it out tonight to eliminate the wiring as a problem. If it's still failing, I'll try to find someone in my club who also has a PowerTap to borrow their hub/computer for a little while to see what works and what doesn't. Failing that, it looks like I'll have to send the entire thing back to Saris.
Those symptoms are consistent with a receiver going bad, so your current plan (testing with the new receiver) is spot on.

bing82 said:
I'm not pleased that something so expensive can go bad after 600 miles of riding (500 indoors), and am not looking forward to sending it back due to reports on the web about them taking *forever* to get it repaired and returned.
That has never been my experience, and I've been using power taps since 2001. I've always been pleased with their customer service & turnaround time.

Also, if you have a bad receiver that's less than a year old, I would expect them to just ship you a new one ASAP free of charge. They recently did that for me.
 
bing82 said:
I have a second receiver and wiring harness I bought for my TT bike. I plan to install that on the TT bike and try it out tonight to eliminate the wiring as a problem.
You don't need to actually "install" the receiver and wiring harness to the bike if you're testing it on a trainer. You can just "hang it" from the chain stay (flat part toward the hub, of course) and attach the computer mount to the handlebar. This is how I diagnosed and eventually eliminated my hub dropout problem caused by frame vibration. I was able to determine that firmly mounting the receiver to the stay caused dropouts whereas hanging the receiver from the stay resulted in no dropouts.
 
RapDaddyo said:
So, the only thing you're getting from the hub is the transmission icon. If you were getting dashes and no hub icon, one candidate would be frame vibration but that's a different set of symptoms.
RapDaddyO, it seems you have some good suggestions for different kind of PT problemes. I looked around a bit on the forum, but I can't find a description of the symptoms/problems I'm experiencing (although I'm sure the answer is in here somewhere).

I have a brand new PT 2.21 (only used for 10-15 hours). I'm getting the cadence and HR, but a few times toady on my indoor trainer, the watt and speed readings only showed dashes (not zeros) for a few seconds before the normal readings popped back up. The transmission icon was on all the time, no blinking.

Could this be the vibration problem you have mentioned earlier?

Any other ideas?

Thanks!

_________
CycleFast
 
I mounted another receiver/wiring harness on my TT bike and got the same problems with the other bike. I tried the receiver in many different positions all with the same results. Some positions didn't work at all.

I tried a friend's computer with my hub and got the intermittently incorrect speed and watts, and verified that my computer seemed to work fine on his bike with his hub.

Based on those tests, I'm concluding that my SL hub has gone bad after about three months and 650 miles (only two rides outdoors - sigh) and will be sending it back to Saris next week. They have told me their normal turnaround time is ten days. We'll see how it goes and I'll post the results here. I have a training camp in three weeks and I really want to use the PowerTap there. I hope I get it back in time.

Tim
 
CycleFast said:
RapDaddyO, it seems you have some good suggestions for different kind of PT problemes. I looked around a bit on the forum, but I can't find a description of the symptoms/problems I'm experiencing (although I'm sure the answer is in here somewhere).

I have a brand new PT 2.21 (only used for 10-15 hours). I'm getting the cadence and HR, but a few times toady on my indoor trainer, the watt and speed readings only showed dashes (not zeros) for a few seconds before the normal readings popped back up. The transmission icon was on all the time, no blinking.

Could this be the vibration problem you have mentioned earlier?

Any other ideas?

Thanks!

_________
CycleFast
The vibration problem was very tricky for me to solve because originally I was trying to solve the problem by finding the right sort of spongy material to put between the stay and the receiver. The problem is that it's not only affected by what material you use but also how tight you tighten the cable ties. Since the cable ties aren't tightened with any precision (e.g., torqued), it's a real ****-shoot to get the right solution. Then, one week I got a bad cold or flu virus and didn't feel like riding at all. So, I decided to strip my bike completely and give it a top to bottom cleaning. Once I had clipped all the cable ties, I decided to solve the vibration drop-out problem once and for all. So, I put it on a trainer and tried a whole bunch of solutions. That's when I hit upon the idea of "hanging" the receiver from the chain stay rather than cinching it to a stay with cable ties. I used to get dropouts regularly when freewheeling. It didn't bother me much because (obviously) when I am freewheeling I am making zero watts and I rarely care about my speed or any other data at that point in the ride. But, still, it was an irritation to see the dropouts. Ever since I went to the "hanging" installation, I have not had one single hub transmission dropout.

The one thing you said that makes me wonder if you have the dropped hub transmission problem caused by vibration is that you said the transmission icon remains on throughout. If you have the vibration problem, you should be getting no transmission icon when you are getting dashes for watts and speed. You might have a hub battery problem. Anyway, the vibration problem is testable on a trainer. Just get the wheel spinning and then freewheel it (or even reverse pedal to get it really screaming). That should cause the hub transmission dropout if your installation has that problem.
 
RapDaddyo said:
The one thing you said that makes me wonder if you have the dropped hub transmission problem caused by vibration is that you said the transmission icon remains on throughout. If you have the vibration problem, you should be getting no transmission icon when you are getting dashes for watts and speed. You might have a hub battery problem. Anyway, the vibration problem is testable on a trainer. Just get the wheel spinning and then freewheel it (or even reverse pedal to get it really screaming). That should cause the hub transmission dropout if your installation has that problem.
Thanks for your tips! I'll look into it.

Do you (or somebody else) know how CyclingPeaks handles dropout (--) readings when it calculates AP, NP, etc? Do the dropout values decrease my averages, or does the program somehow compensate for dropouts?

_________
CycleFast
 
CycleFast said:
Thanks for your tips! I'll look into it.

Do you (or somebody else) know how CyclingPeaks handles dropout (--) readings when it calculates AP, NP, etc? Do the dropout values decrease my averages, or does the program somehow compensate for dropouts?

_________
CycleFast
If I'm not mistaken, the computer records no data when there is no data from the hub (i.e., dropped hub transmission). I don't think the computer records only cadence and/or HR when there is no power and speed data from the hub. But, I can't recall actually looking for such instances. If the computer is in fact recording watts and speed as zeros during dropouts, this will affect the computations for NP, AP, etc. This is also testable. If you can replicate the dropouts on the trainer, do a 5sec on/5sec off test (pedal for 5secs, freewheel for 5secs to get the dropouts, then repeat, etc.) for ~1min and then download the ride file. If it is recording zeros during the dropout segments, it will be very evident in the ride file.
 
RapDaddyo said:
If I'm not mistaken, the computer records no data when there is no data from the hub (i.e., dropped hub transmission). I don't think the computer records only cadence and/or HR when there is no power and speed data from the hub. But, I can't recall actually looking for such instances. If the computer is in fact recording watts and speed as zeros during dropouts, this will affect the computations for NP, AP, etc. This is also testable. If you can replicate the dropouts on the trainer, do a 5sec on/5sec off test (pedal for 5secs, freewheel for 5secs to get the dropouts, then repeat, etc.) for ~1min and then download the ride file. If it is recording zeros during the dropout segments, it will be very evident in the ride file.
What you say sounds right to me. To see if zeros or nulls are being recorded, you can also simply look at the raw data or export to a csv file and look at that. Zeros will affect computations, but blanks will not.

In my experience, with the problem I am having, when the computer displayed "0" for speed and watts, it actually recorded blanks (nulls?) in those fields. Torque, time, HR, and cadence from the pedal are all recorded properly. But with my case, torque was still being transmitted and the transmission icon stayed on. Only speed was missing. My hub/wheel went back to Saris today. Hopefully I'll see a new or fixed one come back soon. Their customer phone support has been helpful so far.
 
bing82 said:
What you say sounds right to me. To see if zeros or nulls are being recorded, you can also simply look at the raw data or export to a csv file and look at that. Zeros will affect computations, but blanks will not.
Watch out for data conversions. You've got one if not two data conversions going on here. Some apps get a little loose in their treatment of zeros and nulls and blanks. It seems that only a few of us care about the differences.:D
 
RapDaddyo said:
If I'm not mistaken, the computer records no data when there is no data from the hub (i.e., dropped hub transmission). I don't think the computer records only cadence and/or HR when there is no power and speed data from the hub. But, I can't recall actually looking for such instances. If the computer is in fact recording watts and speed as zeros during dropouts, this will affect the computations for NP, AP, etc. This is also testable. If you can replicate the dropouts on the trainer, do a 5sec on/5sec off test (pedal for 5secs, freewheel for 5secs to get the dropouts, then repeat, etc.) for ~1min and then download the ride file. If it is recording zeros during the dropout segments, it will be very evident in the ride file.
I have moved the receiver closer to the hub and added some sponge. It worked fine today during my 20 minute test ride. Hope the problem is solved, I'm having a long ride tomorrow and I'll see if it happens again then. Thanks for your contributions.


By the way, the values in CyclingPeaks shows dashes for watts and N-m when the dropouts occur.

For example, I have several readings that look something like:

+2:00:18, 80.39km, ---watts, 144bpm, 91rpm, 0kph, ---N-m

But it's hard to tell if the recorded --- values are counted as zeros or not counted at all when calculating AP, NP, etc.

_________
CycleFast
 
CycleFast said:
I have moved the receiver closer to the hub and added some sponge. It worked fine today during my 20 minute test ride. Hope the problem is solved, I'm having a long ride tomorrow and I'll see if it happens again then. Thanks for your contributions.
I hope that solves the problem.


CycleFast said:
By the way, the values in CyclingPeaks shows dashes for watts and N-m when the dropouts occur.

For example, I have several readings that look something like:

+2:00:18, 80.39km, ---watts, 144bpm, 91rpm, 0kph, ---N-m

But it's hard to tell if the recorded --- values are counted as zeros or not counted at all when calculating AP, NP, etc.
You can test that. Output a segment of the file that has the dashes for watts and speed (as a PT CSV file) and then manually create columns for NP, AP and average speed, etc. in Excel. Then, when you select the segment in CP, the CP averages should agree with your computed values in Excel. If they don't agree, try changing the denominator for the averaging routine to count only the rows without dashes. If it then agrees with CP, you know CP is not counting the dashes as zeros. BTW, you'll have to convert the speed and torque data to English before you do the calculations in Excel because the export file is European (metric).
 
Just wanted to close this thread by saying that Saris/PowerTap was very helpful and quick in getting my bad hub fixed and back to me. I mailed the wheel out 2-day on a Monday, and I had it back on Thursday of the next week. They verified that the hub was reporting speed incorrectly, and replaced the "torque tube" and all the other guts in the hub, tested it, and sent it back to me 2-day shipment. I popped it on the bike last night and everything works like a champ.