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240v Electrical Question

cybergates

Member
Feb 14, 2017
554
240
So Cal
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.

i'm doing the same thing essentially. The 10-30 relocated to the garage converted to 14-30 as the ground wire was actually there just never hooked up and tested ok with a multimeter. I have that same extension just 15 feet as that what I needed - its really well built and I went w 14-50 so I can use it anywhere such as an RV park if ever needed with adapters on either end. You can actually cut the neutral prong so the 14-30 tesla adapter plug will fit into the 14-50 cord which is what I did yet the tesla branded adapter keeps the Amps at 24 Amps which is safe (search for others posting about that here if you wish, o/w I had adapters on both ends now just this one: https://www.amazon.com/gp/product/B00STD8CXC/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
 

xav-

Active Member
May 26, 2016
1,187
982
Orange County CA
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.
Thanks for the details. By the way my numbers are not just my numbers they are also on teslas website. So 27 percent waste is a very big deal and charging using a standard outlet should be used only when there isn’t any alternative IMO
 

xav-

Active Member
May 26, 2016
1,187
982
Orange County CA
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
It’s like $90 on Amazon for 25 foot (Nema 10-30 or Nema 14-30)
 
Haven't seen this mentioned yet, but I think there is a box you can get that plugs into the dryer outlet and gives you two outlets with one given priority. So if you give the dryer the priority outlet (assuming you have an electrical dryer), the EV won't get any power whenever the dryer is running. This avoids tripping the breaker, but allows you to keep everything connected all the time. I think it's called Dryer Buddy??

I have no personal experience with one but imagine it would solve problems for a few people here.
 

diamond.g

Active Member
Nov 5, 2015
2,492
1,438
Moyock, NC
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.
Are you leaving the extension cord at the vacation house? I wonder if it would be better to get the 10-30 adapter from Tesla and a 10-30 extension cord, that way you (or anyone else driving and charging in that location) don't have to worry about turning down the Amps when plugging in.
 
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dhrivnak

Active Member
Jan 8, 2011
4,531
3,962
NE Tennessee
48E4ECBE-6363-4E05-8DAF-34EF9EE6535A.png
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.
Well my test is not as clear as I get 5 miles/hr on 120v and 11 with 240v at 12 amps and 22 miles/hr at 24 amps. So I am not seeing much difference and if that 5 were really 5.5 miles per hour there is no difference.
11DA136B-84A0-437A-99E4-5BCF56010CE2.png5872376F-2395-4A28-9079-16497D9F3D19.png
 

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mongo

Well-Known Member
May 3, 2017
13,991
45,463
Michigan
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PoitNarf

My dog's breath smells like dog food
Jun 7, 2016
2,870
4,322
NJ
Are you leaving the extension cord at the vacation house? I wonder if it would be better to get the 10-30 adapter from Tesla and a 10-30 extension cord, that way you (or anyone else driving and charging in that location) don't have to worry about turning down the Amps when plugging in.

Nope, keeping the cord with me. That’s why I’m getting a 14-50 cord with an adapter so I have more options to use it in other locations if necessary. It’s my father’s house so I’d need to clear it with him first, but I would love to install a NEMA 14-50 in the garage at some point.
 

deonb

Active Member
Mar 4, 2013
4,061
4,361
Redmond, WA
Thanks for the details. By the way my numbers are not just my numbers they are also on teslas website. So 27 percent waste is a very big deal and charging using a standard outlet should be used only when there isn’t any alternative IMO

It really isn't such a big deal. If 120V is sufficient for your driving, you can't really waste enough electricity for it to be a big deal.

Let's say you charge at 120V 12A = 1.44kW. And you charge 12 hours per day weekdays/20 hours per day weekends - so you charge 100 hours per week.

100 hours per week x 1.44kW x 52 weeks @ 10c / kWh = $748 per year total in electrical charges. Take 27% of that as waste = $200/year.


If it would cost $3k to install a 240V outlet like it was quoted for fluxemag - it would take your 15 years to recover that - and... do you even know if you're going to be in the same place in 15 years?

Even if installation is only $1000, but you're in an apartment, it's only really worth installing if you know that you'll still be there in 5 years.
 
What is the max amps the three can take? I'm about to get 240v put in the garage. Trying to figure out if I should go 60 or 80amps. I plan on having two EV's in the future and will put in chargers for both to split the line

I think I should be good with 60 (25amps a piece) but why not go 80 if I can. Thoughts?
 

RayK

Active Member
Apr 5, 2016
2,308
2,319
San Jose, CA
According to the horse's mouth, 48 amps is the minimum required to get the maximum charge rate. That means a 60 amp breaker.

Home Charging Installation

Not sure if you can install two separate 60 amp breakers and expect both of them to be active (and pulling max amps) at the same time. You better have at least a 200 amp service panel and the wiring from the curb/pole to handle that.
 

xav-

Active Member
May 26, 2016
1,187
982
Orange County CA
View attachment 296431
Well my test is not as clear as I get 5 miles/hr on 120v and 11 with 240v at 12 amps and 22 miles/hr at 24 amps. So I am not seeing much difference and if that 5 were really 5.5 miles per hour there is no difference.
View attachment 296412View attachment 296413
Interesting! My numbers matched teslas numbers so I thought they were realistic. I should also add that I used a 25 foot extension cord with 240v but no extension cord with 120v

The other interesting figure is that you pull 249 volts but I pull 234 volts. Yet we both get 22 miles of range.
 

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