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Charging was at 238/40A for 60 minutes then dropped down to 32A

Discussion in 'Model S: Battery & Charging' started by andrewket, May 21, 2013.

  1. andrewket

    andrewket 2014 S P85DL, 2016 X P90DL (soon 100)

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    I started charging when I got home from work today at 238/40A. I always wait to see it ramp up before walking away, and it was definitely 40A. Just now I noticed the MS is charging at 32A (indicates 236V 32/32). I have power monitoring in place, and sure enough I can see the MS charged at 40A for about 60 minutes, and then dropped down to 32A by itself. What would cause this? Voltage sag, so the MS dropped the amperage to get the voltage back up? Heat? The car is the garage and it was a hot day. Anyone know?
     
  2. djp

    djp Roadster 2.0 VIN939

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    The current ramps down as the battery approaches a full charge, kind of like easing up on a gas pump to top off the tank. What was the % charge when the current dropped?
     
  3. andrewket

    andrewket 2014 S P85DL, 2016 X P90DL (soon 100)

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    Hm, from what I've seen it ramps down just at the very end. It was probably at about 195 rated miles when it dropped down.
     
  4. cinergi

    cinergi Active Member

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    I've never seen it ramp down for a standard-mode charge -- only a range-mode charge. I consistently consume 40 amps right up until charging is over and it cuts off immediately. Were you doing a standard mode or a range mode charge?
     
  5. andrewket

    andrewket 2014 S P85DL, 2016 X P90DL (soon 100)

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    Standard. And you're right, according to my consumption graphs on every other charge it was pulling 40a right to the end. Here is the graph:

    e4udetug.jpg
     
  6. scaesare

    scaesare Active Member

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    Given that the voltage was down to 236 even with the reduced current, it could be that at 40A the sag was even worse, and the car did indeed throttle back. (I don't know what those thresholds are... anybody?)

    Are you using the UMC? Given the several threads reporting overheating/melting problems, any chance it's causing the problem? It's been postulated that he stress on the pins from the design causes them to easily lose contact surface area on the connections with the adapters...
     
  7. bluetinc

    bluetinc Member

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    Hey Andrew,

    I've never seen this happen so I can't confirm what's going on with a scope but, the fact that it indicated that it was charging at 32/32 instead of 32/40 indicates to me that the EVSE decided to reduce the charge current (prob. due to high temperatures inside the EVSE) rather than the car reducing the charging current. I saw one other post a month or so ago that said they saw the same thing happen when it was hot out, but with no extra details. If you can recreate this, please let us know.

    Peter
     
  8. andrewket

    andrewket 2014 S P85DL, 2016 X P90DL (soon 100)

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    I'm charging now at 40A. We'll see if it drops down.
     
  9. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    I second the heat suggestion. It doesn't have to be the EVSE, the car can do it too. The "/32" just means this is the maximum the car thinks it can charge at (when the car does the software limiting for HPWC, for example, it shows /60 instead of 60/80).

    236V isn't significant enough voltage drop, not even if you started with 250V. Even then, the car simply stops charging and reports "extension cord" errors.
     
  10. hj-45

    hj-45 Member

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    Does anyone know the exact voltage for these "extension cord errors?" On only my second night with the car, it didn't charge last night with the message on the screen and the cord having a red light. I assume it was due to lack of load on the grid causing grid voltage to go up and out of spec for the cord, so I measured and found 237 V (5AM). Plugged the car into 115 and it charged fine. 45 minutes later before I left for work in another car, I measured 230V and is currently charging fine. I am using the UMC with NEMA 14-50.
     
  11. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    I don't think enough data is there to be able to determine it precisely. It's not an absolute voltage, but rather a measure of the voltage drop, and it may only be considered on 125V or below. I haven't heard of anyone getting the extension cord error with the 240V adapters.
     

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