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240v Electrical Question

lupend88

Member
Jul 7, 2017
340
415
Portland
Hi everyone,

I’ll try to keep this short. I’m renting a house without 240v power in the garage, yet it has 110v. It costs too much to instal 240v to the garage (I’ll spare the details about why it costs more than most houses).

The garage is detached from the house, by about 6 feet. I only drive 25 miles a day so the 110v in the garage should work 95% of my days.

My question for you all is, for those rare days in which I want to charge it faster (let’s say I’m coming back from a roadtrip), can I run an extension cord from my washer/dryer outlet from the inside of the house to the garage? Are there any potential issues that could damage my electrical system or the car itself?

Thanks for your help!
 

buddhra

Member
Dec 29, 2017
235
307
San Luis Obispo
It can be done safely if you do it right. You're not going to damage the electrical system or the car, but you could damage the extension cord (and potentially start a fire) if you exceed it's amperage rating.

Another potential option is to make or buy a box that will let you plug into two 120V outlets at the same time.
 

xav-

Active Member
May 26, 2016
1,187
823
Orange County CA
Hi everyone,

I’ll try to keep this short. I’m renting a house without 240v power in the garage, yet it has 110v. It costs too much to instal 240v to the garage (I’ll spare the details about why it costs more than most houses).

The garage is detached from the house, by about 6 feet. I only drive 25 miles a day so the 110v in the garage should work 95% of my days.

My question for you all is, for those rare days in which I want to charge it faster (let’s say I’m coming back from a roadtrip), can I run an extension cord from my washer/dryer outlet from the inside of the house to the garage? Are there any potential issues that could damage my electrical system or the car itself?

Thanks for your help!
I posted a similar thread as you a month ago.. I was planning a complicated setup of alternating 120V and 240V.

I ended up charging a couple times a week using 240V and forgetting 120V altogether.

Trust me 120V is so terrible. It’s not just slow as hell (4 miles per hour), it is also terribly inefficient. I forgot what the numbers are but I believe 30 percent of the electricity is wasted. Then you have to also account that with 120V being so slow, you would likely end up having to charge also out of the off peak hours.

I know you are planning to drive the car 25 miles a day but trust me with the vampire drain issues right now and the car being so fun I doubt any model 3 owner use 25 miles of range a day currently.

So my setup:
- NEMA 10-30 gen 2 adapter from Tesla
- 25 feet 30AMP extension cord that use the same plug as my dryer outlet (NEMA 10-30)
- I leave the extension cord always plugged in (dryer outlets are not designed to be plugged/unplugged constantly) but I only switch the breaker on when I charge.

I recommend the same setup. I would switch off the breaker when you are not charging (is no hot cable hanging around) I would keep any dogs/kids out when you are charging.

I would order the adapter from tesla ASAP as it takes a week to arrive.

Finally numbers: at 24 amps /240 v I get 22 miles of charge per hour. I basically add 220 miles of range during off peak hours at 12 cents per kWh. $7.
 
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deonb

Active Member
Mar 4, 2013
4,060
4,215
Redmond, WA
Trust me 120V is so terrible. It’s not just slow as hell (4 miles per hour), it is also terribly inefficient. I forgot what the numbers are but I believe 30 percent of the electricity is wasted. Then you have to also account that with 120V being so slow, you would likely end up having to charge also out of the off peak hours.

I have both a J1772 and a 240V NEMA outlet available but charged my Model S for years on 120v instead.

I used the J1772 for a Nissan Leaf initially but it doesn’t open the Model S or Model 3 charge port doors automatically so I never use it for Teslas. And I sometimes plug my RV into the 240V outlet and I’m too lazy to switch it... because honestly 120V works just fine for 25 miles per day.

It’s 120V / 20A if that helps...
 
Last edited:

PoitNarf

My dog's breath smells like dog food
Jun 7, 2016
2,870
4,011
NJ
When I will be driving up to my family’s vacation house next month I will also be charging off of an electric dryer outlet. Luckily the dryer at the house has been changed to a gas dryer, but the old NEMA 10-30 outlet is still there. Rather than get a NEMA 10-30 extension cord I’m going to get a NEMA 14-50 extension cord instead along with a NEMA 10-30 to 14-50 adapter. I’d rather have a 14-50 extension cord and just purchase adapters for it as necessary.

Here’s the extension cord I’m getting: https://www.amazon.com/dp/B0024ECIP0/ref=cm_sw_r_cp_api_WGB3AbM491SS3

And here’s the adapter:
https://www.amazon.com/dp/B06VWGVQDF/ref=cm_sw_r_cp_api_6IB3AbXM1AS62

If you go the same route as me then double check the dryer outlet to make sure you get the correct kind of adapter. Also since my solution will utilize the 14-50 plug that comes with the mobile connector you absolutely need to make sure you decrease the amp draw on your Model 3. Since the 14-50 plug will be in my mobile connector my Model 3 will assume it can charge at the full 32 amps that the mobile connector is capable of. Because I will actually be plugging into a NEMA 10-30 outlet the most I’ll be able to have the Model 3 draw is 24 amps. Even at just 24 amps that should allow me to charge at a rate of 22 miles per hour.
 
Last edited:

dhrivnak

Active Member
Jan 8, 2011
4,490
3,756
NE Tennessee
I posted a similar thread as you a month ago.. I was planning a complicated setup of alternating 120V and 240V.

I ended up charging a couple times a week using 240V and forgetting 120V altogether.

Trust me 120V is so terrible. It’s not just slow as hell (4 miles per hour), it is also terribly inefficient. I forgot what the numbers are but I believe 30 percent of the electricity is wasted. Then you have to also account that with 120V being so slow, you would likely end up having to charge also out of the off peak hours.

I know you are planning to drive the car 25 miles a day but trust me with the vampire drain issues right now and the car being so fun I doubt any model 3 owner use 25 miles of range a day currently.

So my setup:
- NEMA 10-30 gen 2 adapter from Tesla
- 25 feet 30AMP extension cord that use the same plug as my dryer outlet (NEMA 10-30)
- I leave the extension cord always plugged in (dryer outlets are not designed to be plugged/unplugged constantly) but I only switch the breaker on when I charge.

I recommend the same setup. I would switch off the breaker when you are not charging (is no hot cable hanging around) I would keep any dogs/kids out when you are charging.

I would order the adapter from tesla ASAP as it takes a week to arrive.

Finally numbers: at 24 amps /240 v I get 22 miles of charge per hour. I basically add 220 miles of range during off peak hours at 12 cents per kWh. $7.
It depends on where you live. In Tennessee there are no peak or off peak rates. And I have seen very little vampire drain in my 3, at most 2 miles a day. So assuming you are home for 10 hours you can get 38 miles a night. And I have no idea where you are getting 120v is 30% less efficient than 220v. If you wiring is good there should be little difference. This is from an engineer who has been plugging in for over 12 years now. About half of that time on 120v.
 

brkaus

Well-Known Member
Jul 8, 2014
8,021
6,507
Austin, TX
It depends on where you live. In Tennessee there are no peak or off peak rates. And I have seen very little vampire drain in my 3, at most 2 miles a day. So assuming you are home for 10 hours you can get 38 miles a night. And I have no idea where you are getting 120v is 30% less efficient than 220v. If you wiring is good there should be little difference. This is from an engineer who has been plugging in for over 12 years now. About half of that time on 120v.
The efficiency difference is basically due to overhead in the car. It takes a fixed X Watts (I think somewhere around 400) when charging. The slower charge rate consumes the 400 watts longer.
 
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iluvmacs

Member
Jan 27, 2014
489
810
Madison, WI
- I leave the extension cord always plugged in (dryer outlets are not designed to be plugged/unplugged constantly) but I only switch the breaker on when I charge.
Good on ya for not unplugging every time, but you're likely to wear out that breaker instead! Circuit breakers are not designed to be cycled regularly the way a normal switch is. At least on the upside, the failure mode will likely just be that it can't switch on (rather than the failure mode of a worn-out receptacle being a bad connection).

I know you are planning to drive the car 25 miles a day but trust me with the vampire drain issues right now and the car being so fun I doubt any model 3 owner use 25 miles of range a day currently.
Ha! I only drive 10 miles R/T to work, and that's only when I don't ride my bike. Vampire drain is 5 miles/day. I last charged my 3 eight days ago, and it hasn't even gotten down to 50% yet (That's ~16 miles/day average). Now that biking season is upon us, it will go down even more. Funny having the best car in the world and then not drive it because you're biking instead :rolleyes:.
 

gtmotor

Member
Apr 8, 2018
218
328
Arizona
Good on ya for not unplugging every time, but you're likely to wear out that breaker instead! Circuit breakers are not designed to be cycled regularly the way a normal switch is. At least on the upside, the failure mode will likely just be that it can't switch on (rather than the failure mode of a worn-out receptacle being a bad connection).


Ha! I only drive 10 miles R/T to work, and that's only when I don't ride my bike. Vampire drain is 5 miles/day. I last charged my 3 eight days ago, and it hasn't even gotten down to 50% yet (That's ~16 miles/day average). Now that biking season is upon us, it will go down even more. Funny having the best car in the world and then not drive it because you're biking instead :rolleyes:.

Lol I started driving my 3 to the gym 0.4 miles away instead of riding my bike just so I can spend a little more time with it.

Regarding the 110 outlet... I lasted 2 days using one of these before I switched to a 240. What bothered me the most is that for some reason my battery cooling pump runs continually on the 110 circuit and I didn't like that, especially since a charge session would be 10 hours or more.
 

voip-ninja

Give me some sugar baby
Mar 15, 2012
4,124
4,697
Colorado
Hi everyone,

I’ll try to keep this short. I’m renting a house without 240v power in the garage, yet it has 110v. It costs too much to instal 240v to the garage (I’ll spare the details about why it costs more than most houses).

The garage is detached from the house, by about 6 feet. I only drive 25 miles a day so the 110v in the garage should work 95% of my days.

My question for you all is, for those rare days in which I want to charge it faster (let’s say I’m coming back from a roadtrip), can I run an extension cord from my washer/dryer outlet from the inside of the house to the garage? Are there any potential issues that could damage my electrical system or the car itself?

Thanks for your help!

How long would the extension cord have to be?

Keep in mind that 220V extension cord with a dryer type outlet will be very expensive ($100+ for one about 8 feet long) and if you need one past about 20 or so feet you might have to have it custom fabricated and then it will be VERY expensive.

//edit

Looks like some Chinese fabricator makes one that's 50 foot long... at this price (about $200), it's a steal;

https://jet.com/product/Valterra-Mi...-with-Handle/1c7f12389ffe4116b8eaddf4087d5cad
 

scaesare

Well-Known Member
Mar 14, 2013
8,530
14,695
NoVA
Hi everyone,

I’ll try to keep this short. I’m renting a house without 240v power in the garage, yet it has 110v. It costs too much to instal 240v to the garage (I’ll spare the details about why it costs more than most houses).

The garage is detached from the house, by about 6 feet. I only drive 25 miles a day so the 110v in the garage should work 95% of my days.

My question for you all is, for those rare days in which I want to charge it faster (let’s say I’m coming back from a roadtrip), can I run an extension cord from my washer/dryer outlet from the inside of the house to the garage? Are there any potential issues that could damage my electrical system or the car itself?

Thanks for your help!

I've mentioned in a couple of other threads with people in similar situations that if you have a dedicated 12V circuit anywhere in the garage, you may be able to easily convert it to a 240V 6-15 or 6-20 receptacle with a little wire re-marking and breaker change. The Gen2 UMC has adapters available for both.

A Model 3 is rated to charge at either 11 or 15MPH, respectively... not a lot for a quick-turnaround requirement, but makes daily charging a little easier if you have modest daily driving requirements.
 
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brkaus

Well-Known Member
Jul 8, 2014
8,021
6,507
Austin, TX
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timk225

Active Member
Mar 24, 2016
2,050
1,063
Pittsburgh
You don't have 110 volt, you have 120 volt.

And for a Quick 220, not only do the power outlets need to be on 2 separate breakers, they need to be on two OPPOSITE breakers, one on each 120 volt leg in the breaker box.
 
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Garlan Garner

Banned
Mar 31, 2016
11,351
6,064
Chicagoland
It can be done safely if you do it right. You're not going to damage the electrical system or the car, but you could damage the extension cord (and potentially start a fire) if you exceed it's amperage rating.

Another potential option is to make or buy a box that will let you plug into two 120V outlets at the same time.

Those 120V plugs need to be 180 out of phase with one another ( each representing the opposite side of the 220V waveform ). If they are not out of phase ( normal 220V ), then you don't have 220Vac. You would just have two 120V outlets

In other words....just because you might have ten 120 volt outlets in your house....it doesn't mean you have 1,200 volts of electricity.
 

xav-

Active Member
May 26, 2016
1,187
823
Orange County CA
It depends on where you live. In Tennessee there are no peak or off peak rates. And I have seen very little vampire drain in my 3, at most 2 miles a day. So assuming you are home for 10 hours you can get 38 miles a night. And I have no idea where you are getting 120v is 30% less efficient than 220v. If you wiring is good there should be little difference. This is from an engineer who has been plugging in for over 12 years now. About half of that time on 120v.
Please other people weigh in. My understanding is that 120 volt is very inefficient. We used to have that Europe a very long time ago and it’s gone.

The math is here though:
120 volts 12 amps : 4 miles per hour
240 volts 12 amp: should be 8 miles per hour right? Well I get 11 miles per hour.
240 volts 24 amps: I get 22 miles per hour. Again if the yield was comparable to 120 volt I should get 16 miles per hour (4x)

I think that alone should prove that 120 volts is much less efficient. But I am not an electrician. Also there was somebody on a different thread who claimed loss on 120v was more than 30 percent.
 
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brkaus

Well-Known Member
Jul 8, 2014
8,021
6,507
Austin, TX
Please other people weigh in. My understanding is that 120 volt is very inefficient. We used to have that Europe a very long time ago and it’s gone.

The math is here though:
120 volts 12 amps : 4 miles per hour
240 volts 12 amp: should be 8 miles per hour right? Well I get 11 miles per hour.
240 volts 24 amps: I get 22 miles per hour. Again if the yield was comparable to 120 volt I should get 16 miles per hour (4x)

I think that alone should prove that 120 volts is much less efficient. But I am not an electrician. Also there was somebody on a different thread who claimed loss on 120v was more than 30 percent.

Your example points are valid for Tesla charging, and definitely show the point.

However, 120 is not that much more inefficient than 240 in the general case. A wire will transmit the same amount of power with 10A / 120v or 5A / 240V. So the current doubles.

100 ft of 12 ga wiring has a total resistance of 0.159 ohms.

Power = (i^2)r

So in a 120 v system... 15w is lost
In a 240v system... 3.97w is lost.

But the total power transmitted is P=VI, so 1200w.

11.03 / 1200 = 0.00919 or approx 1% per 100 ft. In the US, 120v only exists within a structure, so it isn't that much overall.

Where your calculation shows 27% loss for the Tesla charging at 120 vs 240 @ 12a.
 

fluxemag

Member
Jan 10, 2013
477
183
Portland, OR
I have the same situation with a detached garage. I put an outdoor-rated 240V 50A box and receptacle on the far corner of the house and run the UMC cable under the garage door when I need to charge. It cost me about $150 to do myself (I'm an Electrical Engineer) using flexible conduit on a 15 foot run. The electrical panel is in the basement on the wall near the driveway, so it was pretty easy. I was quoted $3k to put in a sub panel and run wire to the garage.

Another thought is that Tesla is planning to put in city Superchargers in Portland this year, which would mean you could stop by one once a week or so and not worry about charging at home.
 

buddhra

Member
Dec 29, 2017
235
307
San Luis Obispo
Those 120V plugs need to be 180 out of phase with one another ( each representing the opposite side of the 220V waveform ). If they are not out of phase ( normal 220V ), then you don't have 220Vac. You would just have two 120V outlets

In other words....just because you might have ten 120 volt outlets in your house....it doesn't mean you have 1,200 volts of electricity.

That's correct that they have to be on separate phases. When I did this at a rental house I had to swap two breakers around to get on opposite phases, but it otherwise worked great.
 

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