Is cadence magnet necessary when installing SRM power meter?

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clm2206
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Joined: Wed Oct 24, 2007 6:56 pm

by clm2206

Not tried yet, but here is my question. I'm using a Garmin 510 with cadence/speed sensor, and have bought a second hand SRM power meter crankset, which will arrive in a week or so with no cadence magnet. For the sake of simplicity, is it possible to get rid of the cadence magnet and install only the SRM crankset? Taking cadence reading of the Garmin sensor is ok for me, but I suspect that in the absence of the magnet nothing will trigger the crankset to send data. Does the SRM crankset trigger itself with just the power begins to be applied to the crankset? Any thoughts?

by Weenie


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ghisallo2003
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Joined: Mon Jan 02, 2006 7:10 pm

by ghisallo2003

Simple no.

The SRM chain catcher in particular is super-simple though so it is not a big deal.

sungod
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Joined: Fri Dec 24, 2010 9:37 pm

by sungod

the magnet is needed, otherwise the power meter will not wake up when the cranks rotate

according to srm...

Q Where does the cadence magnet need to be positioned?
A The PowerMeter will not transmit data to your display unit without the cadence magnet or wiring harness being properly installed underneath your bottom bracket or on the chain-stay of your frame.

if you do not have the srm one it's no big deal, you can fit a small rare earth magnet in position with tape or glue and it will be fine

clm2206
Posts: 213
Joined: Wed Oct 24, 2007 6:56 pm

by clm2206

Thanks for your reply. Which size should be the smallest rare earth magnet that would trigger the SRM Campagnolo crankset? Rounded coin type 5 mm diam x 2 mm height would be enough?

Geoff
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Location: Canada

by Geoff

I agree with sungod. The SRM PowerMeter has a reed switch that needs the magnet to operate. I do not use the SRM magnet on any of my systems. I have not seen a SRM magnet on a Team bike in many years, either.

The best place to glue the magnet is on the drive-side chainstay. I recommend not trying to save a gram and use an effective size. I use the half-inch circular ones from Lee Valley Hardware, which are, like, a Loonie. This is them: http://www.leevalley.com/en/wood/page.aspx?p=32065

clm2206
Posts: 213
Joined: Wed Oct 24, 2007 6:56 pm

by clm2206

Geoff wrote:I agree with sungod. The SRM PowerMeter has a reed switch that needs the magnet to operate. I do not use the SRM magnet on any of my systems. I have not seen a SRM magnet on a Team bike in many years, either.

The best place to glue the magnet is on the drive-side chainstay. I recommend not trying to save a gram and use an effective size. I use the half-inch circular ones from Lee Valley Hardware, which are, like, a Loonie. This is them: http://www.leevalley.com/en/wood/page.aspx?p=32065


Thanks for the advice and the link.

ghisallo2003
Posts: 742
Joined: Mon Jan 02, 2006 7:10 pm

by ghisallo2003

I use the SRM Chaincatcher from K-edge. Very simple to fit - no messing around with positioning / glue.

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Calnago
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by Calnago

+1 on the K-Edge SRM unit. Works perfectly, and you get a great chaincatcher. Gluing a magnet to the frame somewhere would work but placement wasn't ideal on my frames. Really happy with the K-edge SRM mount.
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dunbar42
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Joined: Tue Jan 07, 2014 9:20 am

by dunbar42

sungod wrote:the magnet is needed, otherwise the power meter will not wake up when the cranks rotate


Cadence is a requirement to calculate power depending on the design of the PM it comes from a candence magnet or accelerometers. Otherwise you would just be measuring torque.

clm2206
Posts: 213
Joined: Wed Oct 24, 2007 6:56 pm

by clm2206

dunbar42 wrote:
sungod wrote:the magnet is needed, otherwise the power meter will not wake up when the cranks rotate


Cadence is a requirement to calculate power depending on the design of the PM it comes from a candence magnet or accelerometers. Otherwise you would just be measuring torque.


Very good point, cadence introduces time into the power calculation.

goodboyr
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Joined: Wed Jan 10, 2007 10:56 pm
Location: Canada

by goodboyr

Geoff wrote:I agree with sungod. The SRM PowerMeter has a reed switch that needs the magnet to operate. I do not use the SRM magnet on any of my systems. I have not seen a SRM magnet on a Team bike in many years, either.

The best place to glue the magnet is on the drive-side chainstay. I recommend not trying to save a gram and use an effective size. I use the half-inch circular ones from Lee Valley Hardware, which are, like, a Loonie. This is them: http://www.leevalley.com/en/wood/page.aspx?p=32065


Ha. "Like a Loonie". You just lost all the Americans.......

ninjanoir78
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Joined: Sat Jul 19, 2008 8:14 pm

by ninjanoir78

What kind of glue you Re using for the magnet?
Ninja

topflightpro
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Joined: Tue Jan 13, 2009 2:35 am

by topflightpro

I used a hot glue gun to attach my magnet.

I cleaned the DS stay with alcohol first, and lightly roughed up the magnet with some sandpaper. I then stuck the magnet to a piece of painting tape - which gave me something to hold instead of the magnet - then put the glue on the magnet and mashed it on to the frame.

I put the glue on the magnet so that I can concentrate the glue in the center of the magnet so it doesn't ooze out too much when attached to the frame. And I used the tape because the magnet will transfer the heat from the glue to your fingers.

The nice thing about using the hot glue gun is that I can pop the magnet off pretty easily and cleanly if I need to. Yes, it requires getting a blade behind the magnet, but it doesn't leave any residue on the magnet or the frame when I get it off.

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ms6073
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Location: Houston, Texas

by ms6073

I have been thinking that the Pioneer sgy-mg910p cadence magnet supplied with the Pioneer Powermeter would be a good alternative:

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by Weenie


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ninjanoir78
Posts: 168
Joined: Sat Jul 19, 2008 8:14 pm

by ninjanoir78

Epoxy should be enough?
Ninja

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