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Question on power distribution using dual chargers at >40 amps charging current.

Discussion in 'Model S: Battery & Charging' started by rainman50, Jun 12, 2014.

  1. rainman50

    rainman50 Member

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    I have read here that someone stated that if you have dual chargers and charge greater then 40 amps that it will distribute it equally amongst the 2 chargers instead of just the incremental amount over 40 amps going to the 2nd charger (secondary).

    Is that true?
     
  2. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    Absolutely!

    I have dual chargers and an 80-Amp HPWC. I normally set the current to 56 Amps to get half the resistive heating of the full 80 Amps. When I do this, you can see the current ramp up to 28 Amps, pause, then ramp up to the full 56 Amps. If you do this at 80 Amps, the pause is at 40 Amps, etc. The assumption is that the charging system makes sure that all is OK with the master charger before ramping up the slave charger. The nice part about this split is that the 1/2 power resistive heating applies to the chargers also, and electronic failure rate goes down exponentially with reduced temperature. This is a real exponential equation, not just a phrase. :wink:

    Dual chargers are nice for home charging, but where they really help is on the road, when you find High Amp L2 (HAL2) chargers in the wild! It happens more often than you would think, which is why I strongly recommend them to new buyers placing their orders.
     
  3. tga

    tga Active Member

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    What happens at less than 40 amps? Do both chargers run, or is one idle?
     
  4. rainman50

    rainman50 Member

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    Thanks for the verification.


    - - - Updated - - -

    I'd like to know this as well.


     
  5. apacheguy

    apacheguy Sig 255, VIN 320

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    IIRC, one charger handles the full load. But I wonder why? If what cottonwood says is true, then it would only make sense to split the load 20/20 between the chargers (or 50%/50%).

    But the chargers are liquid cooled, which mitigates the resistive heating so it shouldn't be a big deal.
     
  6. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    My assumption would be that up to 40 kW it's more efficient to just use one charger. Over 40 kW both have to be used anyway so splitting the load is the right thing to do.
     
  7. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    Even with liquid cooling, more power to dissipate makes the electronics get hotter. Less power means less temperature rise means higher reliability.


    I think you mean 40 Amps (I would love 40 kW charging...)

    Efficiency is definitely an issue. As the chargers go much below 1/2 power, I am sure that the overall efficiency degrades. Also simplifying the software is nice. The way they have it is pretty simple: up to 40 Amps, use the master, above 40 Amps, split equally between master and slave until you hit 80 Amps total.
     
  8. Andyw2100

    Andyw2100 Well-Known Member

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    I must have read this the first time long before my car came and decided then to charge at 56 amps most of the time, unless I have a need to charge faster. It sounded good, and made sense to me.

    I just thought I'd check back now to make sure that since this was written about eight months ago, and since things change pretty quickly in the world of all things Tesla, that nothing has changed with respect to the internals of the car, the HPWC, or the software that would make a setting other than 56 amps a better setting to use.

    Thanks!
     
  9. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    You are welcome. Nothing has changed that I know about. I still do normal charging at 56 Amps and use 80 when I need a quick top up.
     
  10. Andyw2100

    Andyw2100 Well-Known Member

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    Excellent! Thanks again for your insightful post. I have no need to charge at 80 amps very often at all, but were it not for having read your post months ago I'd probably be doing that routinely and putting unnecessary extra strain on the various components of the system.
     

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