polar s720i power unit

keep the feedback coming. I've been thinking about one for a while.

Does it look like you can change the battery yourself? Heard that you had to send it in.

When you talk about all of the wires, can you get a wired model, or is it all wireless?

the power unit is wired all the way, unlike the wireless speedometer & cadence device you buy for the s720i unit. in other words, when you buy the power unit, you must remove the wireless devices you may have installed to use with your s720i, and replace them with the wired power/speed/cadence device.

the battery for the power unit appears to be easy to replace. i have not looked at how hard it would be to replace the battery for the s720i HRM (the "watch" & brains).

i am very happy with the unit which i've been using since january '04. i also like the software & infrared downloading tool. i'll report back in after a few weeks of using the power unit.

an update after 3 rides with the power unit.

just so you know, unlike the wireless speedo & cadence connections of the s720I, once you install the power unit, you are "wired" for these functions. the watch is strapped to a handlebar mount which has 2 small metal tabs that mate with 2 tabs on the watchback. this connection brings the readings from the cadence magnet, rear wheel speedo magnet, and chain/frame mounted wattage sensor.

shortly after leaving on my 2nd ride, i found that the wattage & speedo functions were very intermittent. the display would flash to zero, indicating that connections had been lost.

i had read somewhere that the watch, which is strapped to a handlebar mount, could be finicky. so as i was pedalling, i would tap it, and the readings would begin again. unfortunately, this kept happening every 30 seconds. so after a few minutes of this, i pulled over and looked at how the watch was mounted.

sure enough, i did not get a good connection between the mating tabs, therefore every bump would interrupt the signal. i carefully remounted it, then was off. i was able to get continuous readings, but was a bit puzzled with some of the readings i was getting as i moved through the gears.

more later...........

the greater the distance between the chain and the chain sensor, the more suspect the reading. so after 30 minutes of riding, i stopped at a red light and moved the sensor approx. 1/8" to center it better along the axis of the chain. that seemed to do the trick. i started getting more sensible readings regardless of what gear i was in.

on my 3rd ride, i had the same problem with the watch mount. knowing what to look for, i was able to remount the watch and get good readings. so, the lesson so far seems to be that extreme care must be taken to correctly mount the watch prior to starting.

i've looked at the wattage readings using polar's software (downloaded via an infrared device from the watch). they appear to be consistent, and correlate to when i am exerting greater effort (e.g., heavy mashing up inclines) or less effort (e.g., cruising downhill). i am not an expert on wattage, so i can't attest to the accuracy of the readings. but intuitively, they seem to make sense.

i just started qualitatively reviewing my 3 rides and it is very interesting to see the times when HR coincides with wattage, and also when it does not. i think i am beginning to appreciate the added bonus wattage can make in training. i certainly have a better appreciation for the posts regarding sustaining [censored] watts for xx minutes.

i hope this helps folks who may be contemplating purchasing a wattage device.

The polar power manual does not tell you how to set up correctly. You need to use a piece of foam under the power sensor to raise it up to get consistent readings, i have been using one for 2 years and get very consistent results form all sensors.

The sensor has to be almost touching the chain whn on the smallest chainring and smallest rear cog. You will get some odd reading whn climbing in the lower gears but for time trialing i have no problems

The battery is dead easy to change, its the same as a camera battery and changes in the handlebar mount

The watch has to be sent to LSI in Southam, Warks.

Let me know if you want a piccy of the set up, happy to advise. I have used the bike on a turbo with powercranks and get very close results.