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Real Time Battery Voltage

Discussion in 'Model S: Battery & Charging' started by AO!, Mar 31, 2014.

  1. AO!

    AO! New Member

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    I've searched the forums but can't seem to find the answer to a fairly simple item...how do I read the battery voltage in real time from inside the vehicle?
     
  2. David99

    David99 Active Member

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    there is heaps of data from the battery that the car gets, but I think Tesla has chosen to not expose that to the end user.

    The only time you can see the voltage is when the car is charging at a Supercharger, since its directly going to the battery.
     
  3. wycolo

    wycolo Active Member

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    I should think a clamp-on voltmeter would be safe enough to install somewhere along the passenger side cable run. Never owned one so not sure if they can read thru thick insulation, etc. If you know the pack voltage you essentially know the whole story.
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  4. captain_zap

    captain_zap Electron tamer

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    I don't think such a thing exists. You can get clamp on ammeters, but to measure voltage you need some type of a connection.
    A pretty good estimate of battery voltage can be made from the state of charge. Since there are 96 cells in series, and they vary between about 3.0 and 4.15 volts per cell, this means battery voltage ranges between about 288 and 398V.
     
  5. AO!

    AO! New Member

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    Why would they not expose the data to the driver? Are they afraid that the data would expose trade secrets or maybe it would show some type of problem?
     
  6. Jason S

    Jason S Model S Sig Perf (P85)

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    Of what possible use do you have for this data? Perhaps we're being too literal when you ask for "real time voltage".

    Describe the use case, and maybe we can point you to something useful.
     
  7. Doug_G

    Doug_G Lead Moderator

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    I'd find it very useful to have a temperature readout for the battery pack. Just a single global pack temperature. Would be very useful for trip planning purposes in extreme cold conditions.
     
  8. Jason S

    Jason S Model S Sig Perf (P85)

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    How would that help you plan anything? I'd find it interesting, but I wouldn't be able to do anything useful with the data. Now if there was a way to tell it what temperature to sit at, and to use land power to warm the pack then I'd have a use.
     
  9. Doug_G

    Doug_G Lead Moderator

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    I would be able to better understand how the car is going to behave when I depart. Will it activate the pack heater? How long will I need to preheat for? What is the effect of wind on how fast it cold soaks? Things like that. Over the last two winters I've gotten something of a feel for it, based on regen limits and pack heater usage. But a simple temperature readout would be far more informative.
     
  10. Jason S

    Jason S Model S Sig Perf (P85)

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    Aha! Both informational in terms of how quickly it cold soaks and better planning in terms of how much time before it can do full acceleration and/or regen.

    I think I'd really like to have a "departure time" setting that would do whatever it takes to make the car 1) charged, 2) interior warmed/cooled, 3) battery pack optimized.

    But a temp gauge and some fiddling around could get close, I suppose.
     
  11. wycolo

    wycolo Active Member

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    > a simple temperature readout would be far more informative. [Doug_G]

    You could attach temp sensor to coolant loop as close to batt pack as possible. Then as pump starts you should get useful info.

    > to measure voltage you need some type of a connection. [captain_zap]

    Hook a 10 megohm resistor to the 400v buss and bring into cab with 600v rated 26ga wire to your digital readout velcroed to dash. Heck, its only 400vdc, not like 14kv.
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  12. Doug_G

    Doug_G Lead Moderator

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    If you're crazy enough to do something like this, use three 3.30 Megaohm resistors in series, carefully insulated. The reason for the three resistors is that even if two of them short out you've still got a high resistance connection.
     
  13. wycolo

    wycolo Active Member

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    #13 wycolo, Apr 2, 2014
    Last edited: Apr 4, 2014
    > use three 3.30 Megaohm resistors in series, carefully insulated. [Doug_G]

    Yes!! I thought that but failed to type it - the string of resistors is much safer than just one.

    I knew a NYC Subway electrician who claimed he tested for live 600v dc with fingertips (on SAME HAND!). He was a chain smoker who never seemed to drink any liquids while he was inspecting our wiring work in renovated apartments. The rest of us were inhaling drinks in the summer heat. I imagined his bloodstream was more gel than liquid. Do not try this at home!
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  14. wycolo

    wycolo Active Member

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    Think of all the endless speculation and postulating that would never have occurred had TM installed a real time (always ON) dashboard battery pack voltmeter. With a comparison CHART on the 17 in screen that could be brought up whenever needed and used to interpret the voltage reading at any given moment (S60s would have their own chart). Temperature compensation could be built into the chart if need be. And you could compare this Vb to Vsc while at a SuperCharger (to be sure the voltmeters track accurately).
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