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Determine Amperage

Discussion in 'Model 3: Battery & Charging' started by giantshark18, Jan 2, 2020.

  1. giantshark18

    giantshark18 Member

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    Hello my Tesla technical experts. :)

    I received my Model 3 on 12/31 and am able to charge for free at work. The problem is work is 38 miles from my house, so I need a solution to charge at home besides the super slow 120v option.

    I want to leverage my dryer outlet but am confused by how the circuit breakers are set up in my breaker box. I show that two 30 amp breakers (not double-pole) are assigned to the dryer. A similar setup on my AC and Range circuit breakers. I assume max amps is based on each breaker, not the combined total of both?

    Either way, I know I need to stay at 70% of max amperage, but I am not sure what that max amperage is. I will probably reach out to an electrician, but since I am so naive on this, they could tell me I need an entirely new breaker box and wouldn't know if it's true.
     
  2. brkaus

    brkaus Well-Known Member

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    those are called two pole breakers. They are still 30a. They just protect both sides in case of a short.

    in normal use, 30a is flowing out one wire and back the other.

    you are allowed 24a charging on a 30a outlet (properly wired). Using the correct Tesla adapter will properly enforce this limit b
     
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  3. mongo

    mongo Well-Known Member

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    A 240 load like a dryer should have a dual pole breaker and not be using a two single pole (non-linked) breakers.
    30 Amp is the circuit limit (power flows through both breakers in series), charging is considered a continuous load, so you are limited to 80% or 24 Amps in this case.

    Feel free to post pic of your breaker box.
     
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  4. giantshark18

    giantshark18 Member

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    Thanks for the offer. Here are a couple of pics. Dryer is the green breaker. Pardon the terrible labeling... Purchases the house from my parents and this sort of thing is not my Dad's expertise.
     

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  5. mongo

    mongo Well-Known Member

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    Yeah, it looks like the 20 Amp black breaker is the only real 240 breaker. I think you can get handle ties for the dryer, range, and air conditioner to make it better.
    It appears to be a Zinsco Gte Sylvania Style.
     
  6. ewoodrick

    ewoodrick Well-Known Member

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    The dryer plug would be a 30A circuit. You can get the Tesla adapter for it.

    But, I'm not sure why you don't think that 120V charging at home would be sufficient if you charge at work. No, I'll always recommend having a charger at home, so go for it, but I'm not sure why you feel such a big need.

    At 76 miles round trip, any of the cars would be able to do at least two full commutes before needing charging. So you really don't need any charging at home, except for maybe some weekends, but even then, you should have some Superchargers available if you need more than 120V.
    Don't underestimate 120V charging, It can easily fill your 38 mile commute overnight.
     
  7. mongo

    mongo Well-Known Member

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    At 300 Wh/mile, 76 miles is 22.8 kW. A 120V 12 Amp source is 1.44 kW gross, so time is > 16 hours per day without work charging. The plug can top off coming home when the car was fully charged at work, but nice not to rely on that.
     
  8. ewoodrick

    ewoodrick Well-Known Member

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    Did you hear me say "Without work charging?" I was saying quite the opposite. I was saying "Without home charging"

    But indeed, if you look at 12 hours of home charging, you get 60 miles per day, sure, not enough. But let's extrapolate a little further than a single day. It gets you 300 miles in 5 days. So you end the week down 80 miles. Plenty of time to catch up on the weekends and still do some weekend driving.

    Isn't that's what weekends are for? Rest and recovery?
     
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  9. AlanSubie4Life

    AlanSubie4Life Efficiency Obsessed Member

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    The OP's in California, home to the highest electricity rates. Speaking specifically to home charging, without work charging, since you are suggesting it is workable: Having your car burn 250W overhead for an extra 12 hours each day is 3kW per day. Obviously it depends on their solar situation, rate plan, etc. However, for example, if they end up in Tier 2 (which they would), in rate plan E-1, it would be about 30 cents per kWh.

    That's an extra $1 per day for sticking with 120V charging. You simply would not have that use with proper home Level 2 charging. That's a lot of money! As an added bonus you have to make sure that you've got enough charge at all times and think about it, and you can't even think about time-of-use rates if that makes sense for you, since there's no way to cram your charging into that window.
     
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  10. giantshark18

    giantshark18 Member

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    I should have noted that the main reason why I thought I might need more charging capability at home is that I tend to work from home Mondays and Fridays, so I have to get through four days of having access to only 120v or local superchargers (closest is 6 miles away).
     
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  11. AlanSubie4Life

    AlanSubie4Life Efficiency Obsessed Member

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    To me it looks like these (but not the red one) are already tied together with a metal clip device that bridges to the other handle (never seen that method before), but obviously being there in person would make it easier to tell...

    I have no idea. These breakers would each tap into opposite phases of the bus bar as is, so wouldn't they have 240V across them (?)... at least with the breaker boxes I am used to.

    Screen Shot 2020-01-02 at 2.09.23 PM.png
     
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  12. mongo

    mongo Well-Known Member

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    I do believe you are correct, your ability to enhance exceeded mine. Red appears to individual loads.
     
  13. ZOMGVTEK

    ZOMGVTEK Member

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    Those are handle ties, and totally legit. Anything with a handle tie appears to be connecting opposite sides of tandem breakers. This is either going to be if they have a shared neutral, or more likely they are 240V circuits. That panel is honestly beyond capacity at the moment and likely beyond the acceptable service life. I'd say most sparks would recommend replacement and I tend to agree in this case. It looks like there is a stab behind that lower KO, so you could technically get a duplex in place of that single 20 and shift everything up. That would get you one space for a tandem with a handle tie to an adjacent breaker. If you ran a 20A circuit and a NEMA 6-20 I wouldn't be too concerned. But personally, i'd gut that and drop in an Eaton CH panel.
     
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  14. AlanSubie4Life

    AlanSubie4Life Efficiency Obsessed Member

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    Easy enough for the OP to determine - just flip one of the greens and see whether the other one comes with it...he did say it wasn't double-pole so I really have no idea.

    Anyway, looks like most likely can just use the dryer outlet. Just be safe...
     
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  15. ZOMGVTEK

    ZOMGVTEK Member

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    A little pin comes out the side of those brass ties that goes into the side of the handle for the adjacent breaker. They are mechanically tied. That's how some panels used to do it, and its still done for shared neutrals if people actually follow code.
     
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  16. DickBlonov

    DickBlonov Member

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    Sure looks like it. Easy way to make sure, flip one off. The other one should follow.

    Phil
     
  17. AlanSubie4Life

    AlanSubie4Life Efficiency Obsessed Member

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    Yeah, that's what I thought. The summary is that this dryer breaker is good for EV charging, he just needs the adapter, right? And the OP should know all the stuff about buying the adapter, not plugging and unplugging very often at all, possibility of Dryer Buddy if his dryer is not a gas dryer, checking that the dryer outlet is in good condition to start with, etc, etc.
     
  18. ZOMGVTEK

    ZOMGVTEK Member

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    Yeah, you'd be fine charging off the dryer plug at 24A, so long as the receptacle is in good shape. Dryers run near enough the same power as the EV would consume from that plug for a reasonably long duration.

    Of course, how practical this is depends on where the dryer plug is located and where you park the car. But if you're OK with that, go right ahead. That panel would be a breeze to replace depending on what permits you'd need to pull in your area. Maybe $300 in cost if you don't need permits and the POCO lets you pull the meter yourself in that area. But this may translate into a few thousand if its CA, i'm not sure. Presumably its a main lug panel and there is a disconnect somewhere?
     
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  19. giantshark18

    giantshark18 Member

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    Thanks again. I am learning quite a bit from you all. I can confirm that the two 30 breakers are tied together with a pin and move together. Same for the 40 amp breakers.

    This is the original box from when the house was built in 1980. It is located in the garage, about ten feet from the dryer outlet. I would replace if the cost is under 1K, but would want to wait if its in the thousands of dollars. That is unless someone sees something of concern from a safety standpoint.

    How can one tell if it is in good shape? Plugs stay in well and feel secure (pic below). Also, would the dryer buddy make sense beyond the benefit of not having to continually plug and unplug from the outlet?
     

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  20. mongo

    mongo Well-Known Member

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    Cool that the breakers are correct! Panel seems ok, it would be >$1k to replace.

    Easiest things: When you first start using it, watch the voltage on the in car display to see if there is abnormal drop. Also check to see if the outlets gets overly warm. Does anyone you know have an IR camera?

    The less plug-unplug cycles the outlet goes through the better.
     
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