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Thread: HPWC vs. NEMA 14-50

  1. #1
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    HPWC vs. NEMA 14-50

    Ok, I don't understand something.

    When they are available, I will install an HPWC in my garage and it will be on the same circuit as the drop (240v circuit breaker) from my garage sub panel as the NEMA 14-50.

    The same voltage AND the same current is available to both the socket and device.

    What is it that the HPWC does that makes the car charge faster? (With twin chargers in same car.)

    I simply don't understand the difference between plugging into one vs. the other.

    You can invert voltage (step it up) but you cannot "increase" amperage.

    Is it intelligence within the HPWC that "enables" the second charger? Why the need?

    Having used a Leaf L2 wall "charger" for a while, I understand there is communications between the two (compared to L1) ... but I don't see the logic or need for the HPWC?

    I am sure this has been answered before but I cannot find it.

  2. #2
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    A NEMA 14-5 receptacle is limited to 50 amps. I believe the twin charging takes advantage of circuits 60 amps or greater. The HPWC will support a circuit up to 100 amps (at 80% draw) to maximize charging. At maximum, the HPWC will draw 19,300 kWh and that would get you a maximum of 68 miles of charge/hour (if your driving gives you maximum range).

    If the panel you are running the circuit out of does not have the capacity for a breaker bigger than 50 amps, then there would be no difference.
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  3. #3
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    Quote Originally Posted by dailydriver View Post
    A NEMA 14-5 receptacle is limited to 50 amps. I believe the twin charging takes advantage of circuits 60 amps or greater. The HPWC will support a circuit up to 100 amps (at 80% draw) to maximize charging. At maximum, the HPWC will draw 19,300 kWh and that would get you a maximum of 68 miles of charge/hour (if your driving gives you maximum range).

    If the panel you are running the circuit out of does not have the capacity for a breaker bigger than 50 amps, then there would be no difference.
    Ah, hah!

    So the picture on the Tesla web site where they show a NEMA socket below the HPWC is misleading.

    And I'd need a 100 amp sub panel in my garage, and a separate circuit to the NEMA vs. HPWC to make this fully operational.

    Makes me wonder if the twin chargers are worth it ... (rhetorical question) ... see you Saturday ...

  4. #4
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    Singel charger = 10 kW
    Twin chargers = 20 kW

    50A at 240 V = 12kW BUT continous load allowed is only 80% of that, 40A, which gives 40 * 240 = 9.6kW.

    If your wiring and breaker to the NEMA 14-5 plug is limited to 50A (40A continous load) which is what the plug it self is limited to, then putting the HPWC on this circuit will not allow you to charge faster (or to take advantage of the twin charger). The HPWC allows you to do this if you hook it up to a circuit (breaker, wiring) that allows more than 50A continous load, as said above up to 100A.
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    Quote Originally Posted by dailydriver View Post
    A NEMA 14-5 receptacle is limited to 50 amps. I believe the twin charging takes advantage of circuits 60 amps or greater. The HPWC will support a circuit up to 100 amps (at 80% draw) to maximize charging. At maximum, the HPWC will draw 19,300 kWh and that would get you a maximum of 68 miles of charge/hour (if your driving gives you maximum range).

    If the panel you are running the circuit out of does not have the capacity for a breaker bigger than 50 amps, then there would be no difference.
    If you cannot wire your HPWC to a 100 amp circuit breaker with #4 wire, you can't gain any advantage. The twin chargers are helpful only when on the road using an HPWC in the wild, or a Roadster HPC with adapter.

    As you normally would charge at night in your garage, a 14-50 outlet would do a full charge in 9 hours or so. There is rarely need for faster charging, and most people can do without the HPWC. If you have serious need for faster charging, you need to make sure your wiring is able to handle the HPWC. Since many garage sub panels are only 100 amp, a 100 amp breaker would overload the panel if almost anything else was on while you were charging.

    If your panel serves both house and garage (like an attached garage), a 100 amp circuit with 80 amp load on a 200 amp panel would probably be OK, especially at night with few other things working. But here again, having a 50 amp circuit with a 40 amp load would be less apt to cause any overloads.

    Besides, the car likes to charge slowly. It is possible that the 40 amp charge is better for the battery.

    Obviously, I opted to save the money and use an existing 50 amp circuit. I am still able to use supercharging, but even on vacation to Canada, I only charged at 14-50 outlets most of the time.

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    You don't have to have 100A to benefit from the HPWC. It can be set with any limit up to 100. So 60A would still provide a benefit over a Nema 14-50, but it would be marginal and it's up to you whether or not it would be worth it.
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    Quote Originally Posted by roblab View Post
    If you cannot wire your HPWC to a 100 amp circuit breaker with #4 wire, you can't gain any advantage. The twin chargers are helpful only when on the road using an HPWC in the wild, or a Roadster HPC with adapter.

    As you normally would charge at night in your garage, a 14-50 outlet would do a full charge in 9 hours or so. There is rarely need for faster charging, and most people can do without the HPWC. If you have serious need for faster charging, you need to make sure your wiring is able to handle the HPWC. Since many garage sub panels are only 100 amp, a 100 amp breaker would overload the panel if almost anything else was on while you were charging.

    If your panel serves both house and garage (like an attached garage), a 100 amp circuit with 80 amp load on a 200 amp panel would probably be OK, especially at night with few other things working. But here again, having a 50 amp circuit with a 40 amp load would be less apt to cause any overloads.

    Besides, the car likes to charge slowly. It is possible that the 40 amp charge is better for the battery.

    Obviously, I opted to save the money and use an existing 50 amp circuit. I am still able to use supercharging, but even on vacation to Canada, I only charged at 14-50 outlets most of the time.
    My house has attached garage. 200 amp main panel, some 30 feet from garage. 50 amp drop with aforementioned Leaf charger.

    So upgrade to #4 wire (if conduit can handle!) ... would be required but would be concerned in summer with A/C on overnight AND car charging.

    Sounds to me like not worth it. Do NOT want to go back to Tesla again to revise paperwork so I'll take twin chargers for wild use or "resale value".

    I'll just add a NEMA outlet to existing circuit.

    Cheers!

  8. #8
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    Be careful quoting wire sizes/gauges without lots of context. There are many cases where 4AWG wire would not meet electrical codes if asked to carry 80-100A of current. Make sure you involve a competent electrician (or be ready to read LOTS of NEC codebook...) before deciding on a wiring plan for something that uses this much juice.

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    Quote Originally Posted by Johan View Post
    Twin chargers = 20 kW

    50A at 240 V = 12kW BUT continous load allowed is only 80% of that, 40A, which gives 40 * 240 = 9.6kW.
    I suspect the 10kW advertised rating is based on 250v / 40a (I think the charger is spec'd to max 264v).

    250 * 40 = 10kW for a 50 amp breaker (80% * 50 = 40 amps)

    250 * 80 = 20kW for a 100 amp breaker (80% * 100 = 80 amps)

    Obviously, in Japan, that would only be 200 volts, and in commercial areas of the USA, only 208 volts. Residential in the USA/Canada is 240 volt split phase. Most of the rest of the world, 220 or 230 volts.

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    Quote Originally Posted by roblab View Post
    If you cannot wire your HPWC to a 100 amp circuit breaker with #4 wire, you can't gain any advantage. The twin chargers are helpful only when on the road using an HPWC in the wild, or a Roadster HPC with adapter.
    AWG 4 is only good to 95 amps when used in dry applications (THHN) or 85 in wet (THWN).

    Since many garage sub panels are only 100 amp, a 100 amp breaker would overload the panel if almost anything else was on while you were charging.
    It's usually ok, because you're only using 80A on an HPWC and rarely do you have significant loads in a garage. You'll have to be careful if you run space heaters, or have a freezer or two, or so... When I'm asked today how to prepare, I generally recommend a #2 feeder to a 125A subpanel in the garage, from which you can run an HPWC or 70A EVSE, a 14-50, and even 1-2 receptacles (have to plug in the buffer, right?)

    (In fact, I know a lot of electricians who generally don't use #3 because the price difference is very small, and #2 will allow for 125A expansion later.)

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    Quote Originally Posted by ljwobker View Post
    Be careful quoting wire sizes/gauges without lots of context. There are many cases where 4AWG wire would not meet electrical codes if asked to carry 80-100A of current. Make sure you involve a competent electrician (or be ready to read LOTS of NEC codebook...) before deciding on a wiring plan for something that uses this much juice.
    The only case where a #4 would be permitted to carry the HPWC's load at full power is if all devices were rated for 100% duty cycle / continuous load -- breakers, wire, junction boxes, etc. -- which you won't find easily and it will be extremely expensive compared to using #3.

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