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???
04/29/11 12:45
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 		 #182101 - Can't use designs with lots of varying series resistors
Responding to: ???'s previous message
But the thing is that you should not need a lot of series resistors. You can't make huge numbers of voltage dividers.

If you use one 10-bit ADC for a subchain of cells, you get

Save This Code
 o-----[MUX]--+
batt          |
 o-----[MUX]--+
batt          |
 o-----[MUX]--+
 .            |
 .            |
 .            |
 o-----[MUX]--+
batt          |
 o-----[MUX]--+-----[ADC]
batt                  |
 o--------------------+

So you don't have any resistors with strange stability or balance requirements. What you have is an ADC that gets the resolution divided by a number of cells, so you don't get a 10-bit reading from each cell. With 8 cells for each ADC, you get max 7-bit resolution.

With flying capacitors, you don't measure a subchain relative to a common ground but changes the reference for both sides of the capacitor, meaning you get access to the full range of the ADC but must instead have a MUX solution that can connect both + and - to suitable references.

List of 37 messages in thread
TopicAuthorDate
Measuring cell voltages of batteries            01/01/70 00:00      
   Large currents            01/01/70 00:00      
   Yes, you can use a mux...            01/01/70 00:00      
   Use a MUX            01/01/70 00:00      
      Mux            01/01/70 00:00      
         Opto's for this application suck.            01/01/70 00:00      
            current issues            01/01/70 00:00      
         Use capacitive sampling            01/01/70 00:00      
            Normalizing cells            01/01/70 00:00      
   Linear Technology...            01/01/70 00:00      
      Others too.            01/01/70 00:00      
   AOs            01/01/70 00:00      
      Cost shouldn't be too important here            01/01/70 00:00      
      "AO" ??            01/01/70 00:00      
      Mux            01/01/70 00:00      
   Linear technology ...            01/01/70 00:00      
      Cross-reference            01/01/70 00:00      
   Another methode...            01/01/70 00:00      
      Something like that...            01/01/70 00:00      
         why bother mucking with such ....            01/01/70 00:00      
            A lot of reasons...            01/01/70 00:00      
               when so ....            01/01/70 00:00      
                  Raj should come back...            01/01/70 00:00      
         What a lot of components            01/01/70 00:00      
      There are lots of ways            01/01/70 00:00      
         LT            01/01/70 00:00      
            Pitfall...            01/01/70 00:00      
               precision and stability            01/01/70 00:00      
                  Stability            01/01/70 00:00      
                     True, Andy            01/01/70 00:00      
                        Can't use designs with lots of varying series resistors            01/01/70 00:00      
                           Number of resistors, Westermark            01/01/70 00:00      
                              You don't need to handle 360V by a divider            01/01/70 00:00      
                                 have you thought of V/Fs ?            01/01/70 00:00      
                                    no            01/01/70 00:00      
                              One voltage divider handles several cells in subchain            01/01/70 00:00      
                  AARGH            01/01/70 00:00      

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