Off grid cell high/low volt alarm

Discussion in 'The Projects Forum' started by doovalacky, Jul 18, 2013.

  1. doovalacky

    Thread Starter New Member

    Jul 18, 2013
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    Hi guys,
    Did post this on another forum related to batteries and did not get much response.

    Basically I have 16 ~3.2V LiFeYPO4 cells in a 48V arrangement. Primary aim is high and low cell alarm as its unattended. While the global battery high/low should work I have found they can drift and one or more cells hit the limit early. Outputs of the alarms will go into a picaxe I already have operating to kill load or solar regulator.

    The AQV252V SSR is intended to duplicate the balance function that typical lithium battery management systems have but suited to the high current I can get from solar system.

    Not all the crash hot with electronics so feel free to shoot holes in the JPG schematic attached. Or suggest a better method.
    Obviously I have only drawn 2 cells monitors currently, rest will duplicate after tweaking. As an example to a cheaper SSR with the same pinout.
     
  2. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Your concept seems to be OK. I'm working on correcting some errors in the details.

    Stand by.
     
  3. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    OK, here's my corrections.
     
  4. doovalacky

    Thread Starter New Member

    Jul 18, 2013
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    Thanks Ron. Much appreciated I would have been happy just to be told my mistakes.
    On phone atm but can see 1 major correction and the additional resistors. Will look at it closer when get home from work.
     
  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I had an additional description that I forgot to post.
    The 7665 has active low, open drain outputs. Accordingly, I drove the cathodes of the opto switch LEDs, through current limiting resistors. The anodes connect to +v.
    I did not attempt to analyze your 7665 resistor programming.
    Also, you had left the wipers of your pots floating.
     
  6. doovalacky

    Thread Starter New Member

    Jul 18, 2013
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    Ron,
    Understand what you have drawn thanks. Should have picked up on both the drain output and requirement for current limit.

    I think I have the resistor programming right but little unsure if allowing enough current across them for it to operate. Only identified a maximum amount as limit in spec as 0.5mA.
    Unless "The operating currents of the bandgap reference and the comparators are around 100nA each" means what it has to draw on those inputs.
     
  7. doovalacky

    Thread Starter New Member

    Jul 18, 2013
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    Sorry but a little confused on the current limiting resistor compared to values shown. Aiming at about min 1.5V and 7.5-15mA for both?

    Allowing for some range operation would this be correct?
    low alarm
    2.6V = 1.1V x 120 Ohm = 9mA
    3V = 1.5V x 120 Ohm = 12.5mA

    High
    3.5V = 2V x 240 Ohm = 8.3mA
    4.2V = 2.7V x 240 Ohm = 11mA ( = magic smoke being released from batteries!)
     
  8. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I have concluded that the 7665 OUT1 can't drive two LEDs reliably.
    I have added a PNP in the attached schematic. See also the middle attachment.

    300Ω should provide about 7mA each with typical specs, and at least 5mA, even at worst case Vfwd on the LEDs and 200mV Vce(sat) on the PNP.
    I don't know your lower threshold (for OUT). You may want to adjust the value of R8 down a bit. Be aware that OUT2 has more sinking capability than OUT1. See middle attachment.

    Regarding resistor programming, see the right hand attachment, copied from the datasheet.
     
  9. doovalacky

    Thread Starter New Member

    Jul 18, 2013
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    Still playing around with this. Had a "voucher" credit card that was about to expire so ordered a few parts to test with to use it up. Freight from site I was originally looking at ended up huge so ended up making some changes.
    Different Opto, and I found a low current SSR (2mA).
    Learning how to use Eagle so have drawn it up while I wait for stuff even though it may still undergo revision.

    On another note some asshole nicked my Fluke 289 at work which is going to put a crimp in plans.
     
  10. doovalacky

    Thread Starter New Member

    Jul 18, 2013
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