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Level 1 charging sufficient for low daily miles?

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Right, exactly. The gains in efficiency and the fact that once charged, your car/computer will "sleep" to calibrate BMS stuff. It seems like you should really rush to get your charge filled up, or at least to a pre-set point, and then do it again in the morning to get the battery warmed for driving.

Example of what I mean: I drive 80 miles a day, which represents about 20 kWh battery usage at a 250 Watts per mile efficiency.

My preference is to set it to 70% SOC for daily routine driving. This brings me down to 50% when I arrive home in the evening. I'd like to have it charge to 60% immediately, and then go to sleep. Then, in the morning or in an hour or so before I plan on driving, start charging up to my target of 70% for the next day's usage. This gives it an opportunity to sleep, warm the pack before I drive it in the morning, and calibrate.

You'd obviously have to figure out the magic number based off your driving habits... But, a 240V@40A 14-50 outlet would provide 9.6 kW before any efficiency or overhead losses. Even if we dropped this down to 9.0 kW, that's still a lot of energy, enough to provide around 9*4=36 miles of range at a 250 Watts per mile efficiency.

Maybe in the future Tesla will give us the fine-tuning to set the daily charges to 5% increments.
 
Like others have said, it's really about what is already working. Money being no object, of course putting in faster charging is more ideal, it just comes down to personal context. Personally for my household, we really only need one HPWC, but considering this is a long term, and likely more than 2 Teslas in the future, we put in two. The way I figured it was that if I am going to do this in the future anyhow, I might as well spend the money now, and be able to enjoy the benefits. Otherwise, it's the same money, if not more in the future, to do the same, and miss out on the convenience now. There's an economic term for it, I just can't remember right now.
 
We don't have our Tesla yet but we have been driving short-range electrics for the past almost 6 years. L1 is typically under-rated in the EV world for some reason. Sure, its less efficient, sure there are plenty of us that have the skills to self-install a Nema 14-50 (including myself), but for some, L1 will work just fine. Especially during a pandemic.
 
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And the other reason is that the car will never go to sleep during charging. That in itself is in the order of 200-300W.

The slower you charge, the larger that is as a percentage of the charging power.
Assuming the car consumes at least ~200W while charging the overhead is significant:

Level 1 (120V @ 8 amps, 960W), 200/960 = 20.8% overhead before any other charging losses
Level 1 (120V @ 12 amps, 1440W), 200/1440 = 13.9% ...
Level 2 (230V @ 32 amps, 7360W), 200/7360 = 2.7% ...
 
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@jcanoe is correct, but also don't forget about other options if you're stuck on 120V:

Level 1 "NEMA 5-20" (120V @ 16A, 1920W), 10.4%
Level 1 "TT-30" (120V @ 24A, 2880W), 6.9% ----- this would require a special third-party EVSE adapter, as Tesla does not offer a genuine one. This is commonly referred to as the "120V RV port"

So, there are options if you're truly stuck on 120V but had the amperage. I have an unused "single" 120V breaker spot available. I cannot combine up to open up another to get the 240V.

But, it may be worth it for efficiency's sake to just upgrade the panel, and it would be safer as well since it would bring the house's electricity up to modern code.

Edit - Also, the TT-30 would provide you 10 miles of range per hour at a 250 Watts per Mile efficiency. Overnight, that would probably cover a short commute and any spontaneous or short travels.
 
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I am currently at an AirBnb that doesn't have 220V/NEMA-1450. So what do I need to purchase to charge from 110V (i know it will be extremely slow, but need any additional charge I can get).
Nothing beyond the Tesla Mobile Connector kit that should have been provided when your purchased the vehicle. The Mobile Connector can accept different 120V and 230/240V power plug connectors (sometimes called pigtails.) The NEMA 5-15 power plug adapter is the one that is currently included with the Tesla Mobile Connector kit that will enable you to plug into any 120V 15 amp receptacle and charge (as long as there is a proper earth ground.)
 
I bought the 14-50 adapter. But I don't see a plug to use a 110V outlet. Can someone send me a link to what I need to buy?

Gen 2 NEMA Adapters

Select the 5-15 option. But look at the outlet first - if one of the slots is the shape of a T, you can get the 5-20 adapter from that same page and charge a bit faster. New construction usually requires a 20 amp outlet in garages anyway, so you will be able to use it elsewhere. But I'd first tell your local Tesla showroom that you didn't get a 5-15 with your car and see if they give you one...
 
Does it come with the MY? I don't recall seeing this- can someone post a picture?
You should have received this Mobile Connector Bundle. Did you check underneath the hatch floor in the lower storage areas (there is a shallow storage space behind the rear seats (under the carpeted panel) and a much deeper storage area underneath the rear carpeted panel. Also check the front trunk if you don't find the Mobile Connector Bundle in the rear of your Model Y.

Gen 2 Mobile Connector Bundle
 
The 5-15 power plug adapter will work in any 5-20 receptacle, just be limited to charging at 120V and 12 amps instead of 120V and 16 amps (25% less amps, less power and slower (fewer miles of EV range per hour of charging) than if you use the 5-20 power plug adapter.
 
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If that plug is the only plug on the circuit, you should be able to upgrade it to 220V while keeping max current capacity the same (15 or 20A) without changing the wires. This way you can charge nearly 2.5x faster.

110V is doable at low daily mileage, but would be limit the flexibility of your car use and increase cost due to less efficient charging. 220V even at 15A circuit would be sufficient for most people to not having to compromise much.
 
On a 110 outlet, the model Y will roughly charge at 1% per hour. You can also expect to have more plugged in time on weekends than during the work week. So you can catch back up to your net losses that occur all week long.

If they do net metering in your area, you’re going to want to step up your charging game to take advantage of the lower rate hours at night. The 110 is just too slow to take advantage of this. It will be plugged in charging continuously in an attempt to keep up.