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Topic: my first big project - BMS - is it possible? (Read 10 times) previous topic - next topic

CrossRoads

Or set the arduino up as a floating  meter and measure across each individually.
We  had a huge thread going on this in the old forum.
My suggestion was  a series of relays for 100% isolation, arduino ground becomes - of battery being measured, Analog-in connects to battery+ (which is battery- of next in line, but so what?) Work it just like a multimeter with a relay multiplexer in front of it.


Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

Graynomad

Yep I remember that thread, what a marathon.

I think the relay idea works as long as the Arduino is floating and not sitting on the battery bank GND. This probably means an isolated PSU for the Arduino.

Can turok afford 104 relays :)

______
Rob
Rob Gray aka the GRAYnomad www.robgray.com

CrossRoads

Sure, he's been saving on gas money for 3+ years, driving around on inexpensive electricity  :D, or something like that 8)

http://be.farnell.com/panasonic-ew/tq2-l-5v/relay-dpdt-5vdc/dp/1448361

I don't know what this page says, I think  selected Nederlands for language.
Can search for similar - 5V, 250ohm coil (20mA to turn on), 30V, 1A.
Maybe look around for similar spec part but at lower cost.
Need a relay per battery.
NO side of relay connects to battery. Call that pins 4  to B+s & 7 to B-s.

Then all pin 3s get connected together and go to Analog in.
All pin 8s get connected together and to arduino Gnd.

Then the multplex circuitry turns on 1 relay at a time, connecting B+ and B- to Analog In & Gnd.
Make the measurement, turn off the relay, on to the next device.

http://www.farnell.com/datasheets/22540.pdf
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

Graynomad

#8
Jul 23, 2011, 04:29 am Last Edit: Jul 23, 2011, 04:30 am by Graynomad Reason: 1
I think it would be very important to use proper hardware decoder chips (74xx138/74xx154 style) so there is absolutely no chance that two relays can be turned on at the same time.

This would need 8 154s enabled by a single 138.

______
Rob
Rob Gray aka the GRAYnomad www.robgray.com

CrossRoads

Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

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