DIY with a SRM PCV?

Discuss light weight issues concerning road bikes & parts.
Post Reply
fankozola101
Posts: 12
Joined: Tue Jan 24, 2012 11:43 pm

by fankozola101

Hi WW folk,

I’d like to try a power meter. I’m not sure how long I’ll want to use it.

I’ve been thinking about buying a 2nd hand Cannondale (Road) SRM PCV.

I have a few questions:

Is there a SRM PCV Cannondale compact version available?

Does the SRM PCV accept the Polar wearlink T31 coded HR transmitter?

Is it difficult to change the power meter battery? (from the attached picture, it does not look difficult).

Thanks very much in advance for any advice.

Oh and many thanks for the "Calibrating Slope on SRM" Thread!

Frank

SRM-Guts.JPG
SRM Innards

aerogurl
Posts: 86
Joined: Mon Apr 27, 2009 11:06 pm
Location: SF Bay Area

by aerogurl

A few answers:

I don't think that SRM made a compact wired Cannondale Hollowgram. There are FSA, Dura Ace, and SRM Pro compacts floating around.

From about 2005 on the SRM PCV works with the Polar coding chip (and thus the T31). Generally, if the PCV has a serial number >10000 or with a "P" at the end of the number, then it will work with the polar coded strap. Serial numbers of roughly <5000 having no "P" are uncoded.

If you are remotely mechanically inclined, changing the batteries at home is not difficult with a simple soldering iron. I have never soldered anything complex but have successfully changed batteries in both the headunit and crank unit.

Wired SRMs are the best deal going if you don't need any of that newfangled GPS stuff.

by Weenie


fankozola101
Posts: 12
Joined: Tue Jan 24, 2012 11:43 pm

by fankozola101

Cheers Aerogurl,

What is involved with "opening the clam" like in the picture?
Obviously you have to be careful not to break the solder joints on the blue or green wires...

Is the white inner casing held by interference fit? Adhesive? Fasteners?

Or do the chainrings / chainring bolts hold the two casings together?

What battery is used?

Oh, and I noticed the SRM website makes some suggestion of temperature compensation methods being used..
Has anyone tested these PCV units for temperature drift?

Is the answer to all my questions in the Google Wattage Forums?

Thanks again

Frank

woz9683
Posts: 236
Joined: Sun Jul 11, 2010 6:58 pm
Location: MS, USA

by woz9683

1. Once you remove the chainrings, the white cover just pops off. You might need a flathead screwdriver to pry it open a little. It has an o-ring seal, so it's snug. Just be a little careful.

2. O-ring keeps the cover snug

3. Yes, the small chainring holds the cover on during normal use.

4. The battery is different depending on what model you get.

5. If the temperature swings are large during a ride, redoing your zero-offset mid ride would yield more accurate results. Frankly, I've never bothered. I just set it at the beginning of a ride, after the bike has acclimated to current conditions. I've checked a few times much later in the ride and it always seems very close.

6. Google wattage does have a lot of info. There are also several threads on here that have good information (step-by-step on how to change a battery, etc.)

aerogurl
Posts: 86
Joined: Mon Apr 27, 2009 11:06 pm
Location: SF Bay Area

by aerogurl

Crank Batteries:

Most modern SRMs (including the Hollowgram) use "LTC-7pn-s4".

http://www.osibatteries.com/p-742-eagle ... ttery.aspx

Post Reply