Replacing an SRM battery... at home :o)

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

by sungod

according to their respective datasheets, they both have the same rated capacity, battery technology and casing, so it's down to manufacturing quality and batch variation

assuming both are competently manufactured, i doubt there will be any significant difference in operating lifetime

however, this is weightweenies, the ep has a claimed weight of 6.8g, while the eve is 8g, that's over 17% heavier!

the correct choice has to be the ep version

advisory: this posting may contain less than 100% of serious

zakyma
Posts: 9
Joined: Sun Apr 27, 2014 12:22 pm

by zakyma

Hi guys,

Thanks for the valuable post, I already replaced my SRM DA 7900 battery with two 3.5v 750mah. I also remove the chain rings and that was not required but that's what was done. Offset changed from 587 to 505.

After putting everything back, the battery and chainrings offset still the same between 493 in the begining and yesterday indoors at 505. Now do I need to worry about the offset change. Please note that slope is still the same.

Please note that I tested the offset at 3, 6, 9, 12 angles and all reported within 1 to 3 units difference. I use Garmin edge 510.

Thank you.

by Weenie


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Geoff
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Joined: Sat Dec 13, 2003 2:25 am
Location: Canada

by Geoff

Should be fine. I am a bit suprised to see that the Slope is the same. Typically, when you open-up the PowerMeter, the Slope will change, even a little. Did you test it?

zakyma
Posts: 9
Joined: Sun Apr 27, 2014 12:22 pm

by zakyma

I didn't recalibrate the powermeter with weights but found after pairing it with new batteries that the slope is the same as what it was stored before battery change 26.1.

Also I think that there is no need for recalibarion as the chainrings are the same.

Thank you

Geoff
Posts: 5395
Joined: Sat Dec 13, 2003 2:25 am
Location: Canada

by Geoff

Unfortunately, that will not work.

The SRM is pretty durable and resistant to changes to Slope based upon normal usage (even the changing of rings, assuming that they are reinstalled using the same torque settings), but as soon as you open the case and change the batteries, all bets are off.

The reporting of the Slope by the PowerMeter utilising the 'automatic' system is not indicative of the true Slope of the SRM, rather it is only indicative of the Slope of the SRM when it was tested at the time of original manufacture (or at the time of the last service at SRM). Unfortunately, it is not possible for you to change the 'Automatic' Slope reported by the PowerMeter (which is why I always recommend that people set their PowerController to select Slope using the 'Manual' option).

As an aside, the average SRM PowerMeter battery (assuming no system issue causing an unusual battery drain) lasts so long now that I think it would be impossible to get through an entire battery without having to recheck the Slope. Personally, I would recommend confirming the Slope by recalibrating the PowerMeter at least at the beginning of every training season.

The calibration of the SRM is pretty simple and there are a lot of different instructions on-line that will show you how. The key is to make sure that you have a known weight to start with, so accuracy counts here. There are lab weights available, but they are expensive. Rather, I recommend using Ivanko Calibrated plates, which are certified to within 10g. I use two yellow 15kg plates on an old spindle. If you need more, please feel free to PM me.

dual
Posts: 142
Joined: Thu Dec 20, 2007 8:55 pm

by dual

Geoff wrote:Unfortunately, it is not possible for you to change the 'Automatic' Slope reported by the PowerMeter...


That is true unless you happen to have SRM's little proggie that can change the slope stored in the crank... :D

Geoff
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Location: Canada

by Geoff

@dual, what are you saying? Do you have some information on a work-around? That would be interesting...

Chiva
Posts: 328
Joined: Sat Apr 03, 2010 11:05 pm

by Chiva

dual wrote:
Geoff wrote:Unfortunately, it is not possible for you to change the 'Automatic' Slope reported by the PowerMeter...


That is true unless you happen to have SRM's little proggie that can change the slope stored in the crank... :D


Do tell!

dual
Posts: 142
Joined: Thu Dec 20, 2007 8:55 pm

by dual

@Geoff, Chiva: PM.

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micky
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by micky

Would you kindly send me a PM as well?
Interested...

dual
Posts: 142
Joined: Thu Dec 20, 2007 8:55 pm

by dual

Don-e. :)

FredBloggs
Posts: 91
Joined: Wed Jan 28, 2009 11:33 pm

by FredBloggs

dual wrote:
Geoff wrote:Unfortunately, it is not possible for you to change the 'Automatic' Slope reported by the PowerMeter...


That is true unless you happen to have SRM's little proggie that can change the slope stored in the crank... :D


Or just use a Garmin. It allows you to send a new slope value down to the SRM, but you already knew that :lol:

Geoff
Posts: 5395
Joined: Sat Dec 13, 2003 2:25 am
Location: Canada

by Geoff

PC7 user, though. The simple 'solution' is just using the 'Manual' Slope setting on your PowerController.

dual
Posts: 142
Joined: Thu Dec 20, 2007 8:55 pm

by dual

FredBloggs wrote:...but you already knew that :lol:


You bet! :D

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ms6073
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by ms6073

dual wrote:That is true unless you happen to have SRM's little proggie that can change the slope stored in the crank... :D
PM sent!
- Michael
"People should stop expecting normal from me... seriously, we all know it's never going to happen"

by Weenie


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