Do I need a home charging station or just a 240 volt outlet? Advantages to either?

Discussion in 'General' started by jeffgamer, Oct 16, 2019.

  1. Texas22Step

    Texas22Step Active Member

    @jeffgamer -- please note that in the USA Congress just passed a last-minute extender bill that restored the EVSE federal income tax credit of 30% of the cost up to $1,000. This may or may not influence some of the EV charging decisions you are making. For more info, see and this forum thread for more info.
  2. tps5352

    tps5352 Member

    Here is an updated version of that comparative table:
    Tesla Charging Option Costs.jpg
    The estimated dollar figures are very approximate and costs can vary significantly. Each homeowner should carefully consider their specific situation and needs.

    So this is but one of many possible scenarios. Nevertheless, what stands out is that the two Tesla home charging options need not be that different in total price, even though a NEMA 14-50 receptacle is by itself much less expensive than a Tesla wall connector. The same lesson may apply to other brands of electric cars and home connection hardware.
  3. bwilson4web

    bwilson4web Well-Known Member Subscriber

    Oh, did I mention my house access had to be upgraded to 200 A service because of weathering of the original cables and the higher load of our EVs. We also needed an emergency, natural gas fired generator to handle any extended power outages like the 4 day, 6 hours from the April 2011 tornadoes. It costs more than $3k to add the EV wiring and EVSE.

    Bob Wilson
  4. Texas22Step

    Texas22Step Active Member

    Could forum members please set me straight if I am wrong (or incomplete in some important way) about this:

    U.S. utilities providing electrical power to residences almost universally provide single phase, 240V AC (alternating current) power to the home. Most modern entrance panels at residences can handle up to total loads of 200 amps AC (while this can be increased if need be, although many utility meters are limited to 300 amps of metered power delivery).

    The implications for residential "charging stations" include that the wall plug or EVSE installed at the residence will provide only AC power, so the EV itself has to have an AC/DC converter on-board to take the AC power from the wall and then charge the battery with DC. The so-called "fast" DC commercial charging stations now emerging supply DC power directly to the EV at high amperage, so your EV has to be able to accept that power via a compatible connector and internal charging mechanisms.

    Because all or nearly all residences have limited capacity of about 200 amps for everything in the home (e.g., central air / heat, electric dryers, etc.) and it is in any case AC power, it simply isn't possible at most or all residences to install a "fast" DC charger (at least using the grid) in your garage at home. This is a major reason why there are beginning to be substantial commercial networks of "fast" DC charging stations available out there.
  5. bwilson4web

    bwilson4web Well-Known Member Subscriber

    I would call it "split phase" not "single phase." The Neutral line comes from the center tap of the utility transformer. As for service to homes, my 1969 built house only had 100 A service. Modern houses will come with 200 A or more.

    The challenge of a DC power supply ties directly to the difference between AC-to-DC conversion:
    • single (or split) phase AC - the unsophisticated converters feed it to a diode and into a capacitor. This results in huge current surges when the AC voltage is above the capacitor voltage. Sophisticated converters draw current across all voltages of the AC signal but these are in effect feeding a power, switching regulator. This makes the load look more like a resistor than the diode-capacitor converter.
    • the AC effective voltage is 240 VAC - the DC voltage of my Tesla and BMW i3 batteries are in the 350-400 VDC range. So the output voltage of the switching regulator needs to be boosted up, nearly double. The built-in charger has to do this but typically at relatively low power, ~7 kW.
    • three phase AC - this allows a full-mesh, diode network to draw power across the board from which ever of the three phases has a voltage higher than the capacitor. So it has the effect of 'smoothing' the power draw and avoiding excess peaks.
    So let's assume we wanted a DC fast charger at a 200 A service, split-phase home. My approach would be:
    • 200 A * 240 VAC = 48 kW maximum draw, house is dark
    • 2 salvage, 7 kW car chargers - operating in parallel and with the ability to add more, 14 kW initially
    • master control signals and monitor - non-trivial, these need to be mastered
    For this effort, the charging time initially is cut in half. So it takes just under 6 hours to put a full charge on our Model 3. This cuts to 3 hours with two, repurposed chargers, or 2 hours with three. Good, fast, cheap: pick two.

    Bob Wilson
    tps5352 likes this.
  6. Texas22Step

    Texas22Step Active Member

    @Bob Wilson -- thanks so much for this detailed explanation. You clearly are way above my own pay grade in this whole area.

    How much do you think your suggested approach would cost (labor & materials) to implement in a typical 200 A service entrance residence?

    In my own case, I already use a 40 A breaker for a 32 A L2 EVSE for my Honda Clarity PHEV, but it sounds like I would need to move that up to at least a 60 A breaker / circuit for the higher load of the "fast" DC charger. Since we live in Texas where central a/c is really a necessity for a good part of the year (and the house would likely not be "dark" without getting a divorce), I might need to up the panel to 300 A capacity too (which I understand is the utility delivery maximum at the meter w/o a lot of additional expense on the utility side).

    To accomplish all of this, I would have to hire somebody to do the work, as my own electrical skills are pretty limited. Is this a task one could trust with a competent local (licensed) electrician?

    I am thinking about going full electric with our next vehicle, but I really don't want to pay the retail rates at the commercial chargers nor yield the time that would take -- even if they are "fast." Perhaps I should just charge "slowly" until the EVSE manufacturers put together a complete package to accomplish residential "fast" charging?

    Anyway, thanks again for the information.
  7. bwilson4web

    bwilson4web Well-Known Member Subscriber

    Your 40 A service will work fine. At night, charging speed it not a problem as you'll easily have 8-10 hours. I would avoid a home, fast DC charger as it would be overkill ... unless you're running a taxi service <grins>.

    If you are a two, plug-in family, a separate 50 A, 240 VAC into an external, weather proof NEMA 14-50 would be a good solution. But you might want to consider using scheduled charging to minimize peak draw on your utility. Charging between midnight and 9 AM works well so the EVSE doesn't run hot and the vehicle is kept cool. Never forget that 'heat is the enemy.'

    Bob Wilson
    Re-Volted likes this.
  8. tps5352

    tps5352 Member

    Just want to say how impressed I am with your posts on this and other forums. Keep up the good work! A real help to those of us just entering the world of plug-in electric cars.

    Tim Stevens (hope to be a Tesla owner in 2020)
  9. bwilson4web

    bwilson4web Well-Known Member Subscriber

    Pay close attention to any @hobbit postings. He has forgotten more than I can share:

    Bob Wilson
  10. Re-Volted

    Re-Volted New Member

    jeffgamer :
    Or someone else with the similar question. I had the same Volt, which is only capable of charging at 8 or 12 amps. That means you can plug it into any 110 outlet, and 240 isn't needed. Use the lower setting if you have a 15 amp breaker or are sharing a 20 amp breaker. Only use the 12 amp setting if you have a dedicated circuit of at least 20 amps. This will nightly recharge you completely in the summer and fall a little short in the winter using full range.

    Sent from my iPhone using Inside EVs
  11. interestedinEV

    interestedinEV Well-Known Member

    Operative word "modern". Most insurance companies need a minimum of 100 amp and many older homes are in the 100-200 category

    Second, even if the panel is rated for 200 amp, the wiring inside may not take 200 amps, you may need to do some rewiring (change the gauge of the wires)

    Now can a house be upgraded to 400 amps? I do know people who have and they many have enough capacity to add a DC charger. So I would say it is possible in some homes. The question is cost. This Delta charger below needs 100 A (after all the other household load, AC/, washer/dryer, dishwasher, water heater, lighting etc.) and will set up back about $11,500 without installation, cables, internal wiring etc and you can buy it on Amazon . So if you have 100 amps and about $25,000 to spare you can have a DC charger at home. Does it make sense if you are not going to charging often? Not to me, but if you have installed gold toilets you may as well as add a DC charger at home as a status symbol.

    Delta EV Wallbox DC Fast Charger 25kW Commercial Charging Station - Single CCS Connector (Single-Phase, 240v)
    ( )
    Last edited: Dec 27, 2019
    Texas22Step likes this.
  12. DucRider

    DucRider Well-Known Member

    Even a 25 kW DCFC unit for residential use will need much, much more than a 60A circuit. The Bosch EL-52240 ($8,995 on Amazon) requires a 165A circuit. Most Tesla's will fully utilize a 60A circuit with their 11.5 kW (48A) AC charge rate and will easily fully charge overnight. If you are driving 400+ miles a day with a return home to charge during the day, you could maybe utilize a home DCFC. But the cost will pay for a lot of public charging - which will also be many times faster than any unit that does not require three phase 480.
    Texas22Step likes this.
  13. interestedinEV

    interestedinEV Well-Known Member

    The Bosch is cheaper than the Delta ($11.5 K on Amazon) but the Delta needs 100 A as against the 165A for the Bosch. So you are paying between $9-11,500 for the unit alone plus another $5000-15,000 in other expense. I agree with you that if you are going to driving 400 miles a day (70,000-80,000) miles year, you are better off with the public charger. And it all most sounds commercial or mixed usage (if you are communting to work or normal errands 3-5 hours each way depending on traffic, it is just way too long). if you are doing so much , that you could own your own public charger and write it off as business expense.
    Texas22Step likes this.

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