Agonizingly slow charging at 120 volts

[PhilBa]

Just because we haven't invented a use for a unit doesn't make it not exist...

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"Grins / supercharge minute" anyone?

How about Furlongs/GigaWatt?

 

[Galve2000]

1.44kw * 85% efficiency = roughly 1.2kW / hr.
24hrs *1.2 = 28.8kw
vampire losses = -5kw per 24hrs
daily gain 23.8kw in optimal conditions, if it's too hot or too cold, the numbers can get even lower if the car has to heat the pack or run the cooling pumps, etc.

+1

This is about the most accurate explanation I have seen regarding 120 V charging..

for the sake of simplicity, I always assume a 120 V outlet will provide 2 miles of range per hour. anything more than that is "cake" and should not be counted upon...

The Model S vampire loss does put quite a dent in the calculation tho.. it's rather scary...

 

[Longhorn92]

The miles per hour based on 120 or 240 line of thinking needs to change. I switched my displays to indicate +KW instead of miles. You need to understand your average kW/mi figure and then know how many kilowatts are going back into your pack.

Sadly, I know many won't go through the trouble to do the calculations, but it is the most reliable way of understanding how long of a charge you'll need.

120v * 12amps = 1.44KW (maximum) per hour charge. Recalculate based on the actual voltage displayed onscreen (this number can fluctuate downward during peak hours during the day). I found that 120v has lower efficiency in charging than 240v due to some overhead, so I'll use 85% charging efficiency.

1.44kw * 85% efficiency = roughly 1.2kW / hr.
24hrs *1.2 = 28.8kw
vampire losses = -5kw per 24hrs
daily gain 23.8kw in optimal conditions, if it's too hot or too cold, the numbers can get even lower if the car has to heat the pack or run the cooling pumps, etc.

Just to clean up power/energy units for the calculations listed above:

Regular outlet power: 120V * 12A = 1.44kW
Adjusted for efficiency: 1.44kW * 85% efficiency = roughly 1.2kW
Amount of energy in a day: 24hrs * 1.2kW = 28.8kWh
Vampire losses in a day = -5kWh per day
Daily gain of approx. 23.8kWh in optimal conditions - if it's too hot or too cold, the numbers can get even lower if the car has to heat the pack or run the cooling pumps, etc.

So you get the following optimal results per day of charging (based on your average Wh/mi of usage):
300 Wh/mi = 79 miles (or 3.31 mi/hr of charging)
325 Wh/mi = 73 miles (or 3.03 mi/hr of charging)
350 Wh/mi = 68 miles (or 2.83 mi/hr of charging)

Again, these are optimal assuming a full 120V and 12A with 85% efficiency and 5kWh of vampire losses per day.

 

[Klaus]

Just to clean up power/energy units for the calculations listed above:

Regular outlet power: 120V * 12A = 1.44kW
Adjusted for efficiency: 1.44kW * 85% efficiency = roughly 1.2kW
Amount of energy in a day: 24hrs * 1.2kW = 28.8kWh
Vampire losses in a day = -5kWh per day
Daily gain of approx. 23.8kWh in optimal conditions - if it's too hot or too cold, the numbers can get even lower if the car has to heat the pack or run the cooling pumps, etc.

So you get the following optimal results per day of charging (based on your average Wh/mi of usage):
300 Wh/mi = 79 miles (or 3.31 mi/hr of charging)
325 Wh/mi = 73 miles (or 3.03 mi/hr of charging)
350 Wh/mi = 68 miles (or 2.83 mi/hr of charging)

Again, these are optimal assuming a full 120V and 12A with 85% efficiency and 5kWh of vampire losses per day.

Very nice, thank you!

 

[Jack]

Maybe this is a silly question... Is leaving your S overnight in a public charging spot "safe"? Can anyone remove the plug? Wouldn't someone get annoyed with me if I leave my car there for 12 hours overNight while sleeping, taking up the spot for another user?

i get my 40 in 2 weeks and most of my driving is around the DC area. I can easily take our hybrid SUV on big family trips.

But, my family lives 65 miles away. I had assumed I could easily get there and back on one charge, but, to be safe, I would charge a little there while I was visiting for a few hours.
Likewise, I have friends about 115 miles from home who would like to see the car. I had assumed I could charge there overnight.

But both of these homes only have 110 V outlets on their exterior. They both have dryers, but wouldn't I need a really long extension cord?
It sounds like a 110 V plug won't really gain anything for me at either location so I'd need another plan.

It seems a little funny to me to arrive at a friend's house and have to ask them for a ride to leave my nice new car in some random location to charge for an afternoon or overnight. A dryer outlet at the home seems more convenient if I can access it!

A simple and cost effective solution is to acquire a NEMA 10-30 (i ordered from the Telsa Store) and use the dryer outlet. This works great in my Cape Cod home - i had a quote for $500 for an external outlet, but it's easy enough to use the dryer outlet (presuming you're not using the dryer), and get level 2 charging. My dryer is close the the driveway - but a 25" extention cord is $20 and works fine.

I have an HPWC in my main home and am delighted with it, even at 60a per the 4.4 limitation.

 

[EarlyAdopter]

There's some more data on charging at 120V on a thread I started here:

Charging rates, current draw, and efficiency data for 120V charging

 

[Longhorn92]

Just for another point of reference (as well as one odd occurance at the end of charging)... this last weekend I tested my 120V outlet in the garage to see what kind of charging rates I would get. The end result was that over a 12-hour period (to full charge), I got an average of about 3.42 rated mi/hr.

Background info: "40" kWh car, garage was about 60 degrees, software v4.5 (1.33.44)

I started with 103 rated miles (it was actually 102 when I plugged in, but within about a minute it already changed to 103, so I'm starting with that). After an hour, it was at 108 rated miles (so roughly 5 rated mi/hr). Over the first three hours, it averaged 4 rated mi/hr, then the average started to slowly decrease over time to end at about 3.42 rated mi/hr over the entire 12-hour period. In the end, I had 144 rated miles (*see odd occurance below) which is normal when "fully" charged with the 40 kWh cars. The charging was always in the 110-116V range, and I never saw it pulling anything other than 12A the entire time.

The odd thing that happened was at the end of charging; the rated miles immediately dropped by two miles at the end of charging. At the 12-hour point (a few minutes before the car was fully charged), the car displayed 146 rated miles. This struck me as odd and I noted it because I normally only see 144 rated miles when the car finishes charging from my NEMA 14-50 outlet. However, a few minutes later when the charging actually ended, the car only displayed 144 rated miles. I assume that this may happen with the 14-50 outlet as well, I have just never paid attention at the end of charging.

 

[FlasherZ]

The odd thing that happened was at the end of charging; the rated miles immediately dropped by two miles at the end of charging. At the 12-hour point (a few minutes before the car was fully charged), the car displayed 146 rated miles. This struck me as odd and I noted it because I normally only see 144 rated miles when the car finishes charging from my NEMA 14-50 outlet. However, a few minutes later when the charging actually ended, the car only displayed 144 rated miles. I assume that this may happen with the 14-50 outlet as well, I have just never paid attention at the end of charging.

This happens with 4.5, and happens with any power source. It seems they changed the way they calculated rated miles. When AC mains power is supplied (the HPWC or UMC turns "on" and delivers power to the car), the miles will jump up by 3-5 miles of range; 10 seconds after AC mains power is disconnected (the contactor shuts off), it will drop. I've seen the car charge up to 238 miles or so, shut the mains off, then it shows 235 after 10 seconds.

I asked Tesla about this behavior, and they said it would require a little bit more work.