Srm power meter

I did a quick search, didn't find anything in here, but search function sucks yadda yadda.
I've been playing with zwift the last few weeks and enjoying the power aspect of it. I've really enjoyed messing around the Garmin stuff, and generally think the bike fitness tech stuff is fun. So, I started thinking about when it warms up, how will I ride my road bike with a power meter. I came across a dude selling a used dura ace 7800 crank and srm power meter. What model? Guy doesn't know, thinks batteries are dead, guy I got it from says it worked fine. Ok. Fine. $50. It's mine.
I couldn't get it to wake up by waving a magnet around the circle, so I popped it open and tried again, still no dice. I did find out it is a power meter 7, rev 1. Deader than a door nail. Ok, check battery voltages, removed the batteries and only got .3v and .45v or something. Should be 3.6v for each battery. So I fired up the soldering iron and the power supply and tested it. Made a small wiring harness to wire the two plugs in parallel, set the power supply to 3.5v, and voila! Thing sprang to life! Garmin 530 picked it up immediately and gave a readout on the details of the meter.
Guess I'll order some batters and clean up the crank arms. Anyway, fun in the cold after work.

Anybody using one of these things?

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I had one back when racing triathlons in the early 2010’s. It was a game changer, both in training and racing. Mentally, you might feel off, but physically you are still producing the wattage. Coming in Kona the last 12 miles of the bike, I remember the headwind and feeling like I sucked but then you would look down and see the watts are right where you need to be. Today, the races are done by numbers and less by heart. Have fun.


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I'm not racing at all. I'm old and slow. I have however thoroughly enjoyed heart rate sensors and getting on the Garmin train. I'm a bit of a data geek at work. This seems like a fun new gizmo.

i just like the project and getting it fired up. nice work. finding myself tinkering and trying to learn different stuff like this more and more.

^^^ that's pretty much what it is for me, a winter time garage shenanigans endeavor. When the batteries arrive tonight, I'll get it installed. The magnet for the cadence sensor arrives tomorrow.

I'd like a meter for my outdoor bike. I use Zwift in the winter and really like the data from Power and indoor rides. I'm sure there are other programs out there, but I use the paid version of Strava to measure performance improvement and geek out on that part. Fitness improvement, freshness/tiredness, etc. If you like the data part, I'll suggest tracking down something to graph your power improvements.

I can't currently remember the other program names, other will chime in. TrainingPeaks.com still do this?

Yeah, I use the paid version of Strava as well, I do like the data analysis stuff, and I love the mapping functions and seeing where people ride. For the same reason I love the Garmin stuff. Playing with maps, building tracks, etc. it's fun.
What would be cool would be to take the power output line and have it display on like a pretty vacuum fluorescent display.

Good work resurrecting that thing.

You shouldn’t need a cadence sensor if you have a power meter, it should just do that? At least my Rotor InPower does. Maybe your unit is different though.

Power is fun and useful. I only have it on the roady which spends most of its life on the trainer with only sporadic use. Still a good measure of where I’m at. Nice that my Rotor unit just takes a AA battery. It stopped working after a few years and they replaced it no questions asked. I do know the crew over there but still nice.

I had one of those, too!

I even still have some spare batteries. If these are the ones you need, they're yours. 2 of them are at 3.73V.

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Originally Posted by beaterdit

Good work resurrecting that thing.

You shouldn’t need a cadence sensor if you have a power meter, it should just do that? At least my Rotor InPower does. Maybe your unit is different though.

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The SRM needs a magnet to operate. The crank won’t wake up unless it passes a magnet. One of the cleanest options is to glue/epoxy the magnet the frame, it does not need to be an expensive bike branded sensor, any neo-magnet will work if placed correctly.
The cleanest option is the K-Edge Chain catcher with the built in power meter magnet.

https://k-edge.com/shop/chain-catche...-power-magnet/

Most modern power meters have been developed with proximity sensors and angle sensors, so they wake up on movement, and measure crank rotation based on arm angle, but magnets are still used on a few models.

Edit: if going the glue/epoxy route, make sure the magnet is securely attached.
I’ve seen a magnet come off, stick to the metal chain, travel into the rear derailleur, pulling the the lower derailleur up and into the cassette and tearing it all apart.
Ask one of my former employee techs on how he knows…..
3 hrs before bike check in at an Ironman….
that they flew 2000 miles to come to…..

Those are the batteries. I got 2 from Amazon, the eve branded ones. Popped em in there, and for testing a I zipped tied a snapped off plastic leg from a little tripod with a magnet tin the bottom. It worked, so I ordered up the correct SRM magnet that bolts under the cable guide on the bottom of the bottom bracket. Couple rides on it now, and it pairs up to the Garmin immediately, one quick zero out, and it works perfectly.

Yep, it needs the magnet, both to "wake up" and measure cadence. A separate cadence sensor is not needed. The couple of rides I've done since I've run the zwift power from the Garmin tacx power meter, and the Garmin 530 power from the SRM. They seem to measure power very closely to each other.

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Nice score for $50. Been tracking power data for the last decade on all types of riding. Good training tool if you can regularly test FTP, and fun to look at, regardless.

If the OP doesn't need or want the batteries I could use them, mine has been non functioning for a while and I refuse to seen to SRM for new batteries at their prices.

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Originally Posted by helldriven

If the OP doesn't need or want the batteries I could use them, mine has been non functioning for a while and I refuse to seen to SRM for new batteries at their prices.

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Sure, send me a PM and we'll work it out.

Nice! Yeah, I don't need em. Amazon surprisingly had them ready for prime next day delivery.