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Power readings drop to zero
Posted: Thu Jun 04, 2015 10:19 am
by blp
During a ride, usually after an hour or so, the power reading will occasionally display zero, even if I am putting significant force on the pedals. When the power does start to display, it rises slowly. This has been going on for a while.
During my last ride, I powered up a short hill, (2H:03:49) and the power displayed was zero. Should have been in the 500W range.
Isaac recorded Power=159W; Sp=31.6 km/h; Wind=29.1 km/h; Slope=4.7%; Gear ratio=2.64 (50/19) Total weight of bike and myself is 78Kg.
I have Newton 5 and Powerstroke. Fast recording is "On", and I have the display interval set to 2 seconds (was 5).
Re: Power readings drop to zero
Posted: Thu Jun 04, 2015 3:40 pm
by Velocomp
Maybe the wrong ride was posted, but on the ride file I looked at, around the 2 hr 3 minute mark you appear to cross a street, starting from zero speed. Watts jump to around 500W, due to zero starting speed, then settle down. I don't see any evidence of high slope on the route at this point.
Re: Power readings drop to zero
Posted: Thu Jun 04, 2015 4:35 pm
by blp
Just south of that Google Earth capture is the rise, 4% average for a few meters. (A pinpoint selection in Isaac read 7%.)
My point really, is no power was displayed.
Re: Power readings drop to zero
Posted: Thu Jun 04, 2015 4:38 pm
by blp
Follow-up.
I didn't see all the GE trace, my bad.
You can see after I went around the corner, power dropped then picked up again..
I didn't stop hard pedaling until the top of the ride. That flat part of the power trace should not be flat.
Re: Power readings drop to zero
Posted: Thu Jun 04, 2015 5:07 pm
by Velocomp
I just noticed that your CdA for this ride is 0.171
Based on a rider weight of 70KG, your height would have to be 96CM to have a CdA this low!
This is definitely a problem...
Are you riding a TT bike or road bike? What is your actual height?
Re: Power readings drop to zero
Posted: Thu Jun 04, 2015 9:11 pm
by blp
I am actually 173 cm, 67 - 68 Kg.
Road bike, usually on hoods.
Re: Power readings drop to zero
Posted: Fri Jun 05, 2015 7:07 am
by Velocomp
OK, now it all makes sense.
Your CdA should be .34, not .17. In the place you were concerned about, you were on the flats so your watts were way too low.
Your corrected ride file and profile are attached. You'll find your watts on the flats are about 200W, comparable to what you do on the hills.
Load this profile into your Newton and all will be well.
Re: Power readings drop to zero
Posted: Fri Jun 05, 2015 9:55 am
by blp
Thanks John.
You're right, this now makes sense.
Re: Power readings drop to zero
Posted: Sun Jun 07, 2015 5:01 pm
by blp
An embarrassing confession...
My Garmin speed / cadence sensor had been knock just enough for the crankarm magnet to be marginally within range.
Re: Power readings drop to zero
Posted: Wed Jun 17, 2015 10:12 am
by blp
After installing a new battery in the Garmin GCS-10, that power is still dropping to zero.
I did notice that I still has speed indicated. If the Newton is provided a known speed, shouldn't the power be calculated and displayed?
Re: Power readings drop to zero
Posted: Thu Jun 18, 2015 9:30 pm
by lorduintah
If the cadence is not getting registered by the Newton, it thinks you are not pedaling - hence no power.
Run the checks on the GSC-10 = punch the button and swing the magnet around on the crank past the sensor - no light == no sensing. (Review the Garmin trouble shooting.)
You may have to do this in a low light room - easier to see if you do get flashes as the mag passes the sensor.