Wireless battery voltage monitoring?

Discussion in 'General Electronics Chat' started by JRP3, Jul 6, 2010.

  1. JRP3

    Thread Starter New Member

    Jul 6, 2010
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    Greetings all. I'm searching around for information on RFID or other similar wireless chip technologies. What I'm trying to find out is if it's possible and practical to have a wireless chip on a battery that can report voltage, temperature, and a unique ID number. These would be used on individual lithium cells in an electric vehicle so transmission distance would be short. If it's not possible to report dynamic voltage then a simple signal once a set level is reached, say 3.6V when fully charged, would be useful. Thoughts?
     
  2. retched

    AAC Fanatic!

    Dec 5, 2009
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    This would be overkill.

    You could have microcontroller read each batteries voltage and temperature, assign a unique ID and then transmit.

    That way, you only need 1 transmitter.

    If you really wanted to, you could use a uC on each battery to measure voltage and temperature, add the unique ID then use UART or another protocol to talk to the wireless transceiver (like a zigbee) that would report to the receiver elsewhere in the car.

    As for the "low-battery" RFID. If you used an active RFID (I dont even know if they exist) then used a 3.6v zener diode,
    When the battery voltage reached below 3.6v the zener would stop conducting. If you use a PNP transistor with that, It could power the RFID when the zener voltage was reached (3.6v in this case)
     
  3. JRP3

    Thread Starter New Member

    Jul 6, 2010
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    Actually I need the opposite of that. 3.6 volt is fully charged, so I'd need a signal when the cell got up to that voltage. Your concept would work for a low voltage signal.
     
  4. retched

    AAC Fanatic!

    Dec 5, 2009
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    Then you only need the zener to the RFID.

    The zener will conduct when when it reached its zener voltage.

    So you would monitor the zener, when it has voltage, you know 3.6v was achieved.

    That makes it that much easier.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    Gee, with a bunch of 3.6v Zeners you would wind up dissipating a good bit of power. Don't forget that Zeners have a fair amount of tolerance.

    Seems to me that what is needed is basically a switching regulator used as a clamp between each battery to allow a maximum of 3.6v. If the cells had unequal charge time, that would indicate that some of them needed maintenance/replacement.

    This kind of topic has come up before; a fellow had a large number of batteries in series, and wanted to monitor the voltage across each battery using the same display.

    I suggested that he use a microcontroller-driven array of Opto-MOS relays to select cells individually for testing. The Opto-MOS relays are silent, much more reliable than mechanical relays, and require little power to operate. A uC could scan such an array quite quickly. It certainly would be beneficial troubleshooting-wise in tracking down faulty cells.
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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