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Power Fluctuation

Discussion in 'Model S: Battery & Charging' started by Pete90D, Aug 27, 2015.

  1. Pete90D

    Pete90D Fan of Red Lights

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    #1 Pete90D, Aug 27, 2015
    Last edited by a moderator: Mar 13, 2016
    Has anyone seen this before?

    I was doing a range charge and when I got back in I saw this going crazy. I turned off the A/C and it kept going, but when I turned the A/C back on it leveled out to 12A. The dash was actually showing the numbers fluctuate even faster.

     
  2. spaceballs

    spaceballs Member

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    #2 spaceballs, Aug 27, 2015
    Last edited by a moderator: Mar 13, 2016
    Likely normal, you taper the current near the end of a charge. I.e. same when you fill a glass up with a pitcher and want to fill it to the brim but not spill over.
     
  3. Pete90D

    Pete90D Fan of Red Lights

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    I don't mean the decrease in amperage I mean the crazy fluctuation. I've seen it taper down to 1A before, but not jump around between the numbers like that and then once I turn my A/C back on go to a constant amperage
     
  4. snort

    snort Member

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    The batteries are built with many cells in series. They're only charging the ones on the end and those are charging their neighbors. Each cell has a voltage limit (which the battery management system in the car knows and tells the charger about) so they charge the cells on the end right up to the limit, then wait for the voltage to drop a little, meaning the electrons are finding their way to interior cells, and then do it again.

    many sophisticated battery chargers do something like this when trying to get the absolute maximum charge--even for Lead Acid and NiCds. the iterations aren't usually so fast but it's the same thing. I guess everything is faster in a supercharger...
     
  5. Pete90D

    Pete90D Fan of Red Lights

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    Interesting. I just hadn't seen it before. I've done several range charges with a few Teslas and it was always pretty constant with maybe a 1A fluctuation as the amperage decreased.

    Thanks for the info
     
  6. kennybobby

    kennybobby Member

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    It appears that the 90 is charging at slightly higher voltages too, 404 = 4.208 vpc, 405 = 4.218 vpc. Maybe part of making it a 90 pack is to charge an extra 40 mV at the top up to 4.2. Does your pack label say 400 VDC?

    As for the current fluctuations, some of the charging patents describe methods to detect SOC level based upon open circuit voltage and dV/dt. i read that to mean the current is momentarily turned off and measurements are quickly taken, the calculations and control decisions made, and the current back on again--all done much faster than the update/averaging rate of the current display shown on the monitor.
     
  7. physicsfita

    physicsfita Member

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    I hate to disagree, but batteries charging in series don't work the way you envision. First off, a battery doesn't hold extra electrons -- I tell my students that a "charged" battery is like a "charged" fire extinguisher. If there are the right chemicals available in the cell, the battery will move electrons through the circuit -- it doesn't create any (think of a conveyor belt here). A "discharged" battery is one where the chemical reactants have gone to products. When charging, an external potential (the DC charging unit) effectively runs the "conveyor belt" backwards -- this provides the energy to run the chemical reactions in reverse, thus "charging" the battery (you could have done this by pouring in more chemicals, just like my old sump pump battery). At all times, the battery is electrically neutral.

    Secondly, the way this "conveyor belt" works is by creating an electric field that goes through the entire series of batteries. This field acts on all the batteries in the series at once. Thus, the reversed chemical reactions are occurring in each cell in the series simultaneously. (I'm neglecting what happens during the billionth of a second or so right after the charger is connected/disconnected, but that all averages out, anyway.)
     
  8. snort

    snort Member

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    yes, my description was intentionally simplistic. most of the readers here are not physicists or electronic engineers.

    the chain of cells is a gigantic and fairly complex RLC (resistance, inductance and capacitance) circuit. it takes some time for the charge "field" to propagate through it. I have found that the electrons as marbles analogy helps explain this.

    --Snortybartfast
     
  9. snort

    snort Member

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    I should mention that the "taper" is there to smooth out the cycling between high and low charge rates near the end of charge. It serves essentially the same purpose, to let the charge seep through the chain of cells, which takes several seconds. my guess is that they haven't quite got the rate tuned perfectly yet for 90kwh batteries.
     
  10. Zextraterrestrial

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    #10 Zextraterrestrial, Aug 28, 2015
    Last edited: Aug 28, 2015
    I think this has been added in the firmware quite a while ago and I am only guessing that it was actually something added/changed based on some Tesla patent I read a long time ago. The amperage pulses when getting near complete which may help to allow a slower/longer charge taper somehow.

    ..and I could be totally off, looking for that patent... lot of others I haven't seen(Model X stuff + others...Metal air hybrid for the X??? 'working' on it since 2012)
    hmm not sure what I thought I saw. the final stage charge I found only describes constant current but it is based on a few parameters that may fluctuate enough to see the waving at the final charge stage
     
  11. scottm

    scottm Active Member

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    Those damn 90 packs, just can't trust 'em.
     
  12. Daniellane

    Daniellane Member

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    000.jpg
    I have a 2017 90D MS w/ 72amp onboard Charger . Had a similar issue on my HPWC on 100a Circuit. Has anyone else witnessed anything like this?
    After plugging charger display alternated 0..1...0...1...amps. Then a message saying ⚠️ unable to charge would briefly appear, then it ramped all the way up to the full 72 amps with no problem. If I stopped charging I could not duplicate the issue inlets I waited several hours. Had an appointment at the service center & they found no issue. Logs indicated power source was unstable. They had given me a 75D MX loaner. Same issue on my HPWC. Next day I tried using the mobile charger on the loaner on my backup 240 50a receptacle on the same sub-panel. Same message. Service center compared logs on both cars. Same error. I discovered that if I delayed plugging it in several seconds after the green indicator light appeared the error did not occur. All this was happening during a record breaking heat wave (100 degrees in Portland). So A/Cs were working overtime. The working theory from the charging tech support group @ Tesla was either my power or my power company's power was unstable as a result.
    Left town for Palm Desert for 2 weeks.
    After digging around online, I found a reference to unstable power issues resulting from bad A/C start capacitors. I recalled that after having my A/C serviced, I was told that the capacitor was just under what it should be and it would probably need to be replaced next time. I called my HVAC guy last week and had him come by & replace the capacitor. Returned home today. Problem seems like it's gone. Not sure what caused it since temps are back in the 60s.
     
  13. scottm

    scottm Active Member

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    Never seen that on my 85 pack at a supercharger, but then again, I don't supercharge much. And seldom to 100%

    If 90 packs are just 85 packs with 5 more bolted on, maybe this is the behavior of topping up the last 5?
     
  14. TexasEV

    TexasEV Well-Known Member

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    They're not. There's something different about their chemistry. Search 90 packs for details.
     
  15. scottm

    scottm Active Member

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    You means issues for the whole house, but only Tesla chargers are sensitive enough to have issue, and nothing else in your house reacts to HVAC motor capacitor problem? Is there a link or reference you can offer that talked about that problem?
     
  16. Daniellane

    Daniellane Member

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    Here's where I found it:

     
  17. Daniellane

    Daniellane Member

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    No nothing else really seems to react to the A/C.
     
  18. Daniellane

    Daniellane Member

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    Well it looks like the problem is not gone. I was just able to re-create the message this morning by immediately inserting the plug into the port with no delay. I assumed that the AC capacitor was actually replaced. Tomorrow, I will need to confirm that my HVAC guy did actually replace i'm a start up capacitor. Last I talked to him, he was heading to my house to do the repair.
    I suppose it's possible that he didn't have the part he needed and ordered it but never let me know. In any case, Going to do some testing on panels & incoming power....
    I will post any pertinent information that results from the testing.
     
  19. AmpedRealtor

    AmpedRealtor Well-Known Member

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    I've been having intermittent charging problems the last couple of months, also since it has gotten hotter here in Arizona. Tesla said it recorded voltage spikes on the line and said it was probably dirty power, ACs coming on, etc. Coincidentally, one of my AC capacitors went out a couple of days ago and I needed to have it replaced. I wonder if that was causing the problems?
     
  20. Daniellane

    Daniellane Member

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    I just got off the phone with my HVAC guy and he said that he did replace the capacitor last week while I was out of town.
    So, the problem was not the capacitor.
    The weather here in Southwest Washington is very mild, so I can't really blame it on the spikes due to air conditioning's in general. A buddy of mine with a great deal of experience and electrical issuesI checked all the connections to the subpanel in the main panel and even the wall charger. All were perfect and now even a little tighter. Next step, having an electrician come over and give and give me a favor check out my panels a for a check up check up.
    Yeah they use the term dirty power with me too.
    Didn't help my research online on the subject any.
    Dirty power is generally considered power coming from sources like cool, where as clean power is Hydro electric, wind, solar etc.
     

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