Charging advice for a weekend-only car

[STS-134]

TLDR if you drive little enough that 120V charging is practical, then 240V charging isn't worth it financially (for the efficiency gains).

Assuming 120V charging is 20% less efficient (I think that number is high, but not sure) and electricity costs about 10 cents per kilowatt hours, then you're losing 2 cents per kilowatt hour.

If the 240V charging install costs $500 it'll take 20,000 kWh to break even, or about 60,000 miles. So not entirely unreasonable to invest in 240V charging purely on financial grounds if you drive a lot - however, if OP only drives 100 miles per weekend they the payoff period would be over 10 years.

Assuming the panel is close to (or in) the garage, the materials costs are only a breaker, some wiring, and a receptacle. I'm unsure about whether you include the NEMA 14-50 adapter for the Mobile Connector in there. Plus, we're at over 30¢/kWh here.

(plus if you do drive a lot you probably need faster charging anyway)

I think the big benefits (besides not paying extra money to the utility) are in keeping average SoC low for minimizing degradation which is the OP's primary concern.

 

[Tofuprince]

Mobile Connector vs Wall Connector has been discussed at length. My personal preference is for the Wall Connector due to fewer points of failure (hard wired vs plugged in). You may prefer to use the Mobile Connector in order to have a portable device for trips, or to have a 50 amp receptacle available for other purposes like a welder or an RV.

As for charging, many here will recommend that you keep the car plugged in all the time. I don’t really subscribe to that philosophy, and in your situation, would probably plug in on Friday night, charge to 80% or 90% for the weekend, then let it sit all week, unplugged, at around 40% state of charge. This will keep your average state of charge around 50% and you should have excellent long term battery life.

Prepare for a bunch of different opinions. At the end of the day, it doesn’t make that much of a difference, so do what works best for your situation.

Thank you for this advice! Let's say I get home on a Sunday night, and the charge is at 35% or so. Do you recommend charging it to 50%, unplug it (I probably want to keep it unplugged due to the thunderstorms), and charging it on Thursday night for the weekend?

 

[STS-134]

Thank you for this advice! Let's say I get home on a Sunday night, and the charge is at 35% or so. Do you recommend charging it to 50%, unplug it (I probably want to keep it unplugged due to the thunderstorms), and charging it on Thursday night for the weekend?

If you want to preserve your battery, use Scheduled Departure to charge it. And you should charge on Thursday night if your weekend begins on Friday.

 

[Spinkick]

Doesnt the car unplug itself when its parked? I assume thats what the loud clicking sound is when the contactors are disengaged . People are overthinking it. It even says in the manual to keep the car plugged in at all times, its the best thing you can do to the battery.

get ready for a religious discussion when people recomment X charging state. Just read the manual and keep the charge under 90 percent, unless you are taking a trip. Enjoy!

 

[jcanoe]

Doesnt the car unplug itself when its parked? I assume thats what the loud clicking sound is when the contactors are disengaged . People are overthinking it. It even says in the manual to keep the car plugged in at all times, its the best thing you can do to the battery.

get ready for a religious discussion when people recomment X charging state. Just read the manual and keep the charge under 90 percent, unless you are taking a trip. Enjoy!

The high voltage battery contactors can disconnect the battery from the Tesla Model Y. The Model Y, when plugged in, would still be connected to the power grid. Voltage spikes from lightning can easily damage electrical equipment. More direct lightning strikes can split trees, melt wiring and receptacles. Lightning voltage potential can exceed several million volts. Lightning can jump from utility pole to pole or to another structure.

Although unlikely to happen lightning can irreparably damage electric vehicles and other plug-in vehicles while the vehicle is plugged in. Lightning could easily jump across the high voltage contactors inside the Tesla Model Y. At that point there would probably already be severe damage to the Tesla vehicle's electrical system; so many electrical system components affected and so much wiring damaged that the vehicle could be declared a total loss.

 

[STS-134]

Whole house surge suppressor on main panel to protect against lightning.

 

[jcanoe]

Whole house surge protectors can run $500 or more installed. The most common way that lightning enters a home is through the home's wiring, next would be the copper water pipes.

As a radio engineer and ham radio operator once told me, if you want to protect any piece of electronic equipment during an electrical storm then whenever possible unplug the equipment.

You can't unplug your HVAC compressor, easily unplug the refrigerator or the freezer but you can unplug your expensive flat screen television(s), game consoles and computer and even the router. Your Tesla automobile is probably many times more expensive than all of your other electronics combined. It takes almost no time or effort to unplug the vehicle until the storm(s) have past through.

 

[Jimboy435]

Hi Guys,

I am getting a MYP delivered next week and wanted your advice on the charger and battery percentage. I work from home, so driving the car on weekdays is unnecessary. I will use the car on weekends to take the family out and probably use about 50-60 miles per day on Saturdays and Sundays.

I plan to charge the car in the garage, so the cost-effective option seems to be installing a NEMA 14-50 plug and using the mobile charger. We got a quote to install the NEMA 14-50 at $350 + the charger for $230 = $580. The quote for installing the TWC is $425 + the charger for $425 = $850.

Here are my questions.

• Other than charging speed, are there any differences in using the TWC vs the mobile connector?
• What state of charge should I set the MYP to if I only drive on the weekends? (Battery degeneration is my biggest concern as I plan to keep the car for a while.)
• We sometimes get thunderstorms here in Dallas, do I really need to unplug the car even with the 50amp breaker?

Thank you for the help in advance!

Best of luck driving on the weekends only. Once you have it and don’t need to worry high cost of gas..you will try to find excuses to drive the EV..this car is addicting..

 

[jcanoe]

Lightning strike damages three vehicles; 2 trucks and 1 Tesla Model 3 (the Tesla was plugged in).

https://www.reddit.com/r/TeslaLounge/comments/12c0uo8

 

[JKennedy442]

I've gotten away with Level 1 charging for 5+ years. If my state (NY) had incentives to install a Level 2 charger only then would I consider it. I drive about 10-12K a year so it's always plenty enough for me. Maybe once a year it will be not fast enough, and then I either supercharge or use my wife's Mustang. My advice to anyone that doesn't put a ton of miles on their EV is to just give it a go with Level 1. If you find it's a nuisance, then have a Level 2 installed.

 

[johnny_cakes]

At 120V/12A (NEMA 5-15), this overhead is about 10-20%. At 240V/48A, this overhead is only about 1-3%.

Assuming 120V charging is 20% less efficient (I think that number is high, but not sure) and electricity costs about 10 cents per kilowatt hours, then you're losing 2 cents per kilowatt hour.

I switched from 120v to 240v charger in February, and here's my before and after comparison:

 

[johnny_cakes]

Saturday it has to go 120 to anotherr state, putx around for 40, and back 120. I'm not making it on one charge, so I'm not going to try. I'll charge to 85% before launch and destination charge back up to 75% for the return, then back to the "on arrival home recharge to 50%" automated (Tessie) routine it goes.

How do you automate the charge limit reset through Tessie?

 

[dafish]

Johnny, I use the automation “on arrival” to set to 50% and start charging. At 11:45pm use an automation schedule to stop charging, and then on Sunday night through Thursday night I set a 11:50 schedule to increase charge to 63%. The tesla departure charge takes it from there for m-f mornings

 

[johnny_cakes]

Johnny, I use the automation “on arrival” to set to 50% and start charging. At 11:45pm use an automation schedule to stop charging, and then on Sunday night through Thursday night I set a 11:50 schedule to increase charge to 63%. The tesla departure charge takes it from there for m-f mornings

Clever, thanks!

 

[mark02115]

Clever, thanks!

Really good process - Thanks

 

[D.E.]

Hi Guys,

I am getting a MYP delivered next week and wanted your advice on the charger and battery percentage. I work from home, so driving the car on weekdays is unnecessary. I will use the car on weekends to take the family out and probably use about 50-60 miles per day on Saturdays and Sundays.

I plan to charge the car in the garage, so the cost-effective option seems to be installing a NEMA 14-50 plug and using the mobile charger. We got a quote to install the NEMA 14-50 at $350 + the charger for $230 = $580. The quote for installing the TWC is $425 + the charger for $425 = $850.

Here are my questions.

• Other than charging speed, are there any differences in using the TWC vs the mobile connector?
• What state of charge should I set the MYP to if I only drive on the weekends? (Battery degeneration is my biggest concern as I plan to keep the car for a while.)
• We sometimes get thunderstorms here in Dallas, do I really need to unplug the car even with the 50amp breaker?

Thank you for the help in advance!

Charge to ~80%, use the car. 60 miles or so won’t require full charging. Charge slowly, only charge rapidly if you need to, but if you need to don’t worry. I use 14-50 plug for mine, 240V. I get about 23 miles of range for each hour of charge. I leave it plugged in when in the garage.

You can get a whole house surge suppressor, we just put one in. It protects everything you have. It isn’t a buy once and forget, they do need to be replaced at 3-5 year intervals (if I remember correctly). Anyway do that and it’ll protect the Tesla as well. I think the Tesla is well protected on its own, I’ve never heard of one done in by a surge. But if you own your house, you probably could use the house surge protector.

We had a neighbor who’s house was struck by lightning. I’ll attach a picture of his surge protector. The unit was welded to the carpet, but the TV attached to it was fine.

 

[briank9]

Mobile Connector vs Wall Connector has been discussed at length. My personal preference is for the Wall Connector due to fewer points of failure (hard wired vs plugged in). You may prefer to use the Mobile Connector in order to have a portable device for trips, or to have a 50 amp receptacle available for other purposes like a welder or an RV.

As for charging, many here will recommend that you keep the car plugged in all the time. I don’t really subscribe to that philosophy, and in your situation, would probably plug in on Friday night, charge to 80% or 90% for the weekend, then let it sit all week, unplugged, at around 40% state of charge. This will keep your average state of charge around 50% and you should have excellent long term battery life.

Prepare for a bunch of different opinions. At the end of the day, it doesn’t make that much of a difference, so do what works best for your situation.

I mean why cant you leave it plugged in and set a limit to 50%, thats what I do when im on vacation or away

 

[Big Earl]

I mean why cant you leave it plugged in and set a limit to 50%, thats what I do when im on vacation or away

I never said you can't.

 

[Pianewman]

I don't subscribe to the "plug in while away/vacation" philosophy either. Left alone, fully asleep, there's virtually zero parasitic draw on the HV battery, so no need to keep plugged in..

Where I live (Fort Worth, TX) the risk of issues with lightning, inconsistent power (surges?), etc. creates an iffy energy delivery to my home. I'd rather not risk compounding the issue with a $60k vehicle attached to the electric grid!

 

[Art84]

This is what a Wall Connector manual says:

You don't need to worry about power surges. Wall connectors has a protection agains this.

Or in the worst case scenario, you have a car insurance, and "comprehensive" coverage covers stuff like this.