What is the level 2 charger really doing?

Discussion in 'Prime Plug-in Charging' started by labumm, Mar 13, 2017.

  1. labumm

    labumm Junior Member

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    I am beginning to read about L2 charger in anticipation of replacing my 2004 Prius, which I have been driving since Dec 2003 (original battery!).

    My understanding is the battery charging control is in the Prius Prime and the EVSE is more of a safety device to make sure the 240 V is not live unless it is connected to and communicating with the car. And the ground is good. If that is correct, the EVSE is a very expensive contactor.

    Can anyone direct me to a technical article this? Everything I am finding is about installation and wiring.
     
  2. bhtooefr

    bhtooefr Senior Member

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    It also tells the car how much power is available, so it adapts to what the charger can supply. But, yes, it fundamentally is a safety device.
     
  3. I'mJp

    I'mJp Senior Member

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    The evse must communicate the capability of the wire connecting the car, so that it is not overloaded.
     
  4. mmmodem

    mmmodem Taste Tester

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    Yup, it's a very expensive extension cord. I think of it this way. If one single person gets electrocuted in the slightest way, even if it's a slight buzz that made hair stand up, the EV business would be over. There is enough FUD on exploding battery fires and EMF radiation. An electrocution would spell the end.
     
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  5. bwilson4web

    bwilson4web i3 and Prime

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    Each car has an AC-to-DC charger that has a hard current limit. My BMW i3-REx is 31-32A and our Prime is 16A.

    In the USA, these voltages are commonly available:
    • 120VAC (home)
    • 211VAC (commercial)
    • 240VAC (home)
    Typically each circuit has a current limit, a circuit breaker, and the standard is no more than 80% load.

    Do you have an electric dryer circuit? These are typically 30A, 240VAC. This is more than enough to charge a Prime at the max rate but not run the dryer at the same time.

    Bob Wilson
     
  6. Lee Jay

    Lee Jay Senior Member

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    This one is 208VAC - 120V * sqrt(3).

    Basically, it's the line-to-line voltage when the line-to-neutral voltage is 120V. That's the same reason why the lights in my building run on 277V - it's the line-to-neutral voltage when the line-to-line voltage is 480V (480V / sqrt(3)).
     
  7. fotomoto

    fotomoto Senior Member

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    Agreed and to add one more thing, they're UL certified which costs but more importantly it means one's home insurance will cover any damage caused by one unlike a DIY kit.
     
  8. bisco

    bisco cookie crumbler

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    just the j plug and cord alone are quite expensive, but the prices keep dropping with increased volume. now the chinese have jumped in with low cost units.
     
  9. Trollbait

    Trollbait It's a D&D thing

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    Copper isn't steel or aluminum cheap. A 10ft replacement cord for an electric dryer will cost $20 or more. Most cables from the EVSE to the car are 25ft.
     
  10. labumm

    labumm Junior Member

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    Thanks for the information. From Bob Wilson's reply, the charging is limited to 16A . Is that 16 A in the battery? My understanding is that the charging power is 3.3 kW with 120 VAC and 6.6 kW with the 240 VAC level 2, which are both 27.5 A.

    I am assuming the charge controller is some type of switch-mode AC to DC design. In principle these are not very sensitive to input voltage, but you'd need the 240 VAC input to get the full charging power.
     
  11. bisco

    bisco cookie crumbler

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    the 16a limit is in the charger controls. toy doesn't want you filling the battery any faster, to prolong longevity.
     
  12. labumm

    labumm Junior Member

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    What I'm getting at is that 16 A is 6.6 kW if it is at 412.5 V. If that is the max charge current in a 412.5 V battery, this all makes sense.
     
  13. Lee Jay

    Lee Jay Senior Member

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    I don't think that's entirely true. The 16A limit is the current capability of the in-car charger, and it corresponds to about 3.3kW of battery charge rate. However, the battery can be charged at about 9kW with charge mode, and apparently at something more like 15kW with CHAdeMO in Japan. This indicates the battery isn't the limit, but the charger itself is.

    No, 16A is the AC demand capability of the charger, not the DC output capability.
     
    #13 Lee Jay, Mar 14, 2017
    Last edited by a moderator: Mar 15, 2017
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  14. PT Guy

    PT Guy Active Member

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    Let's back up a bit. The charger is inside each electric car. The EVSE or charging station is outside the car. Level 2 works at 240 volts AC. Level 1 works at 120 volts AC. The EVSE or charging station includes a smart control device, the cord, and the SAE J1772 plug that connects to the car.

    Toyota includes a Level 1 EVSE that plugs into a 120 volt home circuit rated at 15 amps or more. (If you think your house has 110 volt power, we'll forgive you--I usually measure 117 and a fraction volts.) It draws about 12 amperes of current when charging. You can buy a Level 2 EVSE that is connected to a 240 volt circuit rated at 20 amps or more. It actually draws 16 amperes, all the Prime can accept.

    Electrical power is measured in watts or watts/1000 (kilowatts). Volts x amp = watts. (With complications for AC circuits that we'll ignore.)
    120 x 12 = 1440 watts of power for the Level 1 station.
    240 x 16 = 3840 watts of power for the Level 2 station.
    3840 / 1440 = 2.66 times as fast to recharge the Prime when using the Level 2 charging station. (More complications that we'll ignore.)

    That is what the Level 2 charging station is really doing. (I do not see any payback in the purchase and installation cost of an L2 EVSE. It'll save, what, 1 or 2 cups of gasoline if I don't have time for a full recharge with my L1 station. There is no electrical cost saving using 240 volts vs. 120 volts.)
     
  15. bisco

    bisco cookie crumbler

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    why does everything come down to payback?
     
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  16. bhtooefr

    bhtooefr Senior Member

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    There actually is an electrical cost savings, though.

    Most EVs tend to have a fixed power draw during the charging phase for the computers and the cooling system. Faster charging means that this fixed draw runs less.
     
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  17. kevinwhite

    kevinwhite Active Member

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    This is a description of the J1772 system and operation. SAE J1772 - Wikipedia

    The EVSE advertises its current capability by the PWM duty cycle - it is up to the charger in the car to honour that value or less.

    One thing that got left out of the standard is that there is no way for the car to tell the EVSE that it has finished charging.

    kevin
     
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  18. bisco

    bisco cookie crumbler

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    so what makes it shut off?
     
  19. bhtooefr

    bhtooefr Senior Member

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    The car stops pulling current. And, a smarter EVSE can detect this and know that the car stopped charging.
     
  20. bisco

    bisco cookie crumbler

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    the digital display on my L2 has 3 colors. yellow when unplugged, blue when plugged in and charging, green when charging has finished, but still plugged in.
     
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