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Messure temperature on ALL cells

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Joined: 05/11/2012
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Points: 45

Hej.

Started thinking of some kind of solution for monitoring cell temperature on all the cells instead of just a few.

Found the cheap digital 1-wire sensor (that need two or three wires) DS18B20.
ds18b20.jpg

DS18B20 seems to be the cheapest digital sensors on Ebay, about $1 each, and enables really simple wiring. Maybe this is not even necessary because of the lower charge-current I plan to use form the IMAX-chargers ( http://visforvoltage.org/forum/12347-use-imax-b8-rc-chargers-instead-built-one-possible ) and the cell-monitoring “activity” soon to be posted. Still it would be a nerdy-fun to log temperatures on all 102 cells.

Looks like a laptop with digitemp would be able to read all 102 sensors.
http://www.digitemp.com/

http://web-tech.ga-usa.com/2012/04/reading-ds18b20-temperature-sensors-with-digitemp/

Interface:

http://martybugs.net/electronics/tempsensor/hardware.cgi

Serial / USB-converter:

Ebay search “CP2102”
usb.jpg

To automate temp-logging in an efficient low cost way maybe a tiny NAS-server could be used. (Search Ebay: “652 nas”).
nas.jpg

Temp connections to one port, and a USB-flash-drive to collect data in the remaining port.
This might be the optimal solution since all the logic is already built in to the Snake-OS Linux. So it will require nothing extra to talk to a network or write to a USB-thumb-drive, or dump data to a laptop etc.

http://code.google.com/p/snake-os/

http://groups.google.com/group/dealextreme-nas-/browse_thread/thread/356058655ba31c19/d25c6bae08bf371f?fwc=1&pli=1

Initiative to read two ANALOGUE (not DS18B20) sensors:
https://groups.google.com/forum/#!topic/dealextreme-nas-/_WauM292r3g

Or maybe use a Arduino solution.
http://pottier.emmanuel.free.fr/TemperatureMonitor_ArduinoNAS.pdf

Search Ebay “2004 LCD Display USB”. And for the CP2102.

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Joined: 10/08/2008
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Points: 341
Re: Messure temperature on ALL cells

And then what? Let's say you find, as I would assume temperatures to vary by 10 degrees. How will you help your battery. Knowledge is one thing, but if you can't do anything to help the uneven heating of the battery that's another thing. The Lairds software has the fan running all the time, that helps.

Mik
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Joined: 12/11/2007
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Points: 3710
Re: Messure temperature on ALL cells

HarryS wrote:

And then what? Let's say you find, as I would assume temperatures to vary by 10 degrees. How will you help your battery. Knowledge is one thing, but if you can't do anything to help the uneven heating of the battery that's another thing. The Lairds software has the fan running all the time, that helps.

I can see a few potential benefits, although I have no idea how practical the use of the suggested sensors would be.

You could for example stop charging (or riding) if any cell temperature is reported as >50degC, or more than 20degC higher than the lowest temperature.

The fans could of course run all the time, anyway.

If you could log the temperatures, then you would know exactly which cells to replace when you eventually need to take the battery apart again. The differential temp rise should be closely corresponding with differences in internal resistance. It would also be an indirect measure of cell SOC and cell capacity, because the IR rises steeply when the cell is nearing empty. The temp rise could possibly be detected before cell reversal occurs, therefore allowing to limit damage from deep discharging of the weakest cells.

Would all the 102 sensors be connected in series with a single cable?

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