Battery Monitoring

[Martin Jackson <mjackson@vcn.bc.ca>]

Subject: Battery SOC

  This topic is my central interest given the cost of killing a pack.
  It's been a while since Rich carried on a conversation about the Mark 
  II Regs, but that philosophy shouldn't be left out of this discussion.

  Don't go offline with the bulk of this conversation since thoughts can 
  come from anyone. However, don't post material sent to you off list. 
  There are perfectly reasonable sounding things that conveyed off list 
  are not ment for the world to hear.

  My applicable background (as an M.E.) is using a PC to collect and 
  interpret data from aircraft engines or e-meters. In the future, I 
  hope to add to the perspective on batteries from real data. Obtaining
  the data and displaying it is first priority. In the meantime, some 
  comments.
  
  stevenr@flash.net wrote:

"Lee, Darrell and others have made many good points about our battery
monitoring system.  But it seems to me we first have to define what we
want to accomplish.  Do you want to just measure battery voltages or do
you want to measure battery voltages and also have the ability to charge
a low battery."

  First priority is to know when a battery is overloaded and overtemp 
  and which one it is. An ability to upgrade to individual charging is
  better than bypassing current around strong batteries. The BatBridge 
  warns of a weakling after which manual intervention can find the 
  problem. Post temperatures are an obvious advantage.
  
  Op.Isolation is good from the electrical ground/shock and interference
  point of view. I resist having multiple voltage references due to the
  difficulty of having them all calibrate the same. An advantage is that
  the individual battery micro-monitor can be triggered to record 
  battery voltages simultaneously and transmit sequentially. The value
  of this is that transient data provides the best 'load test' 
  comparison information. My limited experience indicates dynamic 
  resistance is erratic. Simultaneous readings are needed.

  Starting with the BatBridge light indicator, the next most important
  priority is knowing relative battery condition. Everything else can be 
  handled manually wet or dry. There is no reasonable way to get away 
  from stringing at least one line through all the batteries for 
  improving condition feedback.

  The e-meter tells SoC with accumulated Amphours using the corrected
  numerical values. I'm convinced this is accurate to within 5% if the
  settings are correct and you have no business going past 20% anyway.
  The information needed is detection/alarm of weaker and less charged
  batteries with bad battery shown on the dashboard and additionally, to
  be able to know the condition of all batteries. Doing the automatic 
  ballancing is icing on the cake, "Mark II".

  A 4 cyl., 4 valve ICE has 20 parts whose leakage can be detected with 
  a vacuum guage. These parts are expected to go 100,000 miles before
  causing a problem. A 120 V pack has 60 cells expected to last 30,000
  miles, but one cell Will crap out earlier than the rest.

  It's unrealistic to say that voltage + Amp hours is not sufficient for
  charge control. It has to be. But, more important, the condition of 
  fully charged & equalized batteries is best evaluated during each 
  acceleration using simultaneous voltage (drop) readings. Temperature
  may have a secondary importance, but any micro being discussed can get
  the data and pass it on fairly cheaply (4 A/Ds available). 
  Fortunately, the Amperage through all the batteries is the same. 

L.H. "Voltage is also affected by temperature, recent charge-discharge
history, water level, battery age and construction, and other factors."

  All of which defects are detectable with comparitive Voltage readings.
  The actual behaviour is not relavant; only the objective relative 
  performance is important if maintenance is being properly performed.
  Rest voltages taken manually after dinner (before charging) should, in 
  fact, tell you enough about the state of individuals. Few people will 
  do this consistantly. The monitor should get any problem early.    ÚÄ¿
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