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Charging 120v vs 240v efficiency

You can’t exclude the overhead from your power bill! ;)
From what I understand from the explanation, the overhead is the same whether you are charging at 120 or 240. So if you are charging for a fixed period of time the "overhead" is still the same and still the same cost.

You could theoretically charge X amount in one hour at 120V and if the charging efficiency was the same, charge the same X amount in 30 minutes at 240V. The extra half hour spent at 120V you have to still “pay to keep the lights on” (car fixed overhead).
I think the only real cost difference really comes into play is that charging at 120V will take longer for the same amount of power so you are paying for the overhead for a longer period of time. Otherwise, the cost of charging is exactly the same because you pay by kw not time.

For a quick example you can take a peek at my Google Sheet. (please correct me if I did something wrong in the calcs) If I did it right it is 30% MORE expensive to charge via 120v vs 240v. You can use that number to determine at what point it makes sense to "upgrade" to 240V. At 10,000 miles per year it would cost an EXTRA $192 (I assumed 0.20 per kw since electricity is expensive here) per year to charge at 120V vs 240V. Would take a while to justify the electrician upgrade and the wall charger cost, but if you are in it for the long haul it is certainly worth the investment to pay less and charge quicker.

Dave
Model 3 Performance
 
I don't really disagree, but just how much $$ does it matter. 2kWh @ $0.10/kWh is only 20 cents.

I think the amount is larger than you think (or I recently did all my calculations wrong).

Where I live costs are about 0.20/kWh. For 10K miles per year that equates to roughly $192 EXTRA to charge via 120V. If you bump that up to 0.47/kWh that was mentioned in this thread that is about $452 EXTRA per year to charge via 120V. It just helps an EV owner make a more informed decision. For my charging trends I'm going to put off the upgrade to 240V because right now it is not worth the cost for installation and supplies. But if we get a second EV soon I would likely jump at the upgrade because of the time and money savings.
 
I think the amount is larger than you think (or I recently did all my calculations wrong).

Where I live costs are about 0.20/kWh. For 10K miles per year that equates to roughly $192 EXTRA to charge via 120V. If you bump that up to 0.47/kWh that was mentioned in this thread that is about $452 EXTRA per year to charge via 120V. It just helps an EV owner make a more informed decision. For my charging trends I'm going to put off the upgrade to 240V because right now it is not worth the cost for installation and supplies. But if we get a second EV soon I would likely jump at the upgrade because of the time and money savings.
I went $300 all in to get a 240V installation here. I had two estimates, the same.
 

darth_vad3r

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May 6, 2019
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I think the amount is larger than you think (or I recently did all my calculations wrong).

Where I live costs are about 0.20/kWh. For 10K miles per year that equates to roughly $192 EXTRA to charge via 120V. If you bump that up to 0.47/kWh that was mentioned in this thread that is about $452 EXTRA per year to charge via 120V. It just helps an EV owner make a more informed decision. For my charging trends I'm going to put off the upgrade to 240V because right now it is not worth the cost for installation and supplies. But if we get a second EV soon I would likely jump at the upgrade because of the time and money savings.

Ya, depending on circumstance the payoff could be a year, or a decade or two. It really varies.
 

darth_vad3r

Well-Known Sith
May 6, 2019
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I just posted an updated chart using power as the x-axis in this other thread here: Better to charger higher or run battery lower?

Since this thread is about 120V vs 240V I thought I'd tack 120V onto that existing chart into this super noisy chart :)

The theoretical model used here is described in the above-mentioned thread, and is 5% inherent loss from the AC-to-DC charger and then a range of 250 to 350 W loss from fixed overhead from the car being 'on'. Based on this model, it doesn't matter what the voltage is, the efficiency is tied to power, if you can get 32A at 120V, you'd get the same efficiency as 16A at 240V (this is shown by orange 120V triangles overlapping with red 208V circles, and purple 120V triangles overlapping with blue 208V circles).

Screenshot from 2019-08-21 21-55-16.png


NOTE: The only actual measured numbers on this chart are the black circles, and the set of 3 pairs of green circles and red stars.
Everything else is theoretical, but... it looks like a decent model.

When I get the chance I plan to add real 120V data to the chart, and hopefully also figure out how to make it look less like crap.
 

ewoodrick

Well-Known Member
Apr 13, 2018
5,285
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Buford, GA
I don't know that is what happens, but it's a possibility.

Have you been here, though?! (sarcasm) ;) This is an enthusiast forum. People aren't having any of that if you just tell them, "Don't worry about it." I've seen that, and they will not accept that answer, because they say they know it's not completely vital, but they want to find out what is best, what is ideal, even if it makes very little difference. And I would agree for myself, that I would want to know the ideal, but it's up to me how close I want to try to get to that and if it's worth the effort.

So I try to stick with what is informative, but not scary. I tell people that best is staying nearer to the middle state of charge, but each person has to balance that with having enough range for their own comfort level to have the car be practical and usable. That way, each person gets to know it's a balanced preference decision and doesn't feel like they are breaking a rule if someone says some exact number but their circumstances mean they need to go a little outside that.

Yes, I've been here and yes they do listen. And then they listen to advice like yours and get totally confused. Because in your attempt to clarify, you created complete mud.

People want simple answers

Set max to 80-90%
Plug in as it fits your needs
Don't got really low (<10%) unless you need to
Charge to 100% once a quarter
Charging to 100% is absolutely safe and will not harm the battery
Feel free charge to 100% before leaving on trips
 

ewoodrick

Well-Known Member
Apr 13, 2018
5,285
4,291
Buford, GA
I think the amount is larger than you think (or I recently did all my calculations wrong).

Where I live costs are about 0.20/kWh. For 10K miles per year that equates to roughly $192 EXTRA to charge via 120V. If you bump that up to 0.47/kWh that was mentioned in this thread that is about $452 EXTRA per year to charge via 120V. It just helps an EV owner make a more informed decision. For my charging trends I'm going to put off the upgrade to 240V because right now it is not worth the cost for installation and supplies. But if we get a second EV soon I would likely jump at the upgrade because of the time and money savings.

But $0.47/kWh isn't a representative cost. AFAIK, $0.20 is higher than the average cost across the country. A lot of places have summer and winter rates with winter being significantly cheaper. My winter rate, for 8 months of the year is less than $0.05. (less than $40/yr then)
By the way, how long would have taken you to pay back the $192 if you were still driving your old car?

There's a lot of users for which 120V IS the RIGHT DECISION. Installing a 50A circuit into older home sometime isn't a real possibility. If you've got an older house with a 50A or 100A service, that means running new service, which is hugely expensive. In multi-family buildings, there's often not an option.

So many people assume that 120V is not an option. For many people it is a quite viable option.
 

darth_vad3r

Well-Known Sith
May 6, 2019
1,574
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Canada
From what I understand from the explanation, the overhead is the same whether you are charging at 120 or 240. So if you are charging for a fixed period of time the "overhead" is still the same and still the same cost.

Yabut... you need ~2x as much time to charge the same number of “miles” back into your car every night on the same amp circuit (say you are limited by the 32 A UMC) so it doesn’t make sense to compare equal time periods. You need to compare equal energy delivered to the battery.

I think the only real cost difference really comes into play is that charging at 120V will take longer for the same amount of power so you are paying for the overhead for a longer period of time.

Ya, this is the point!
[Except you mean energy, not power. kWh added to the pack.]

Otherwise, the cost of charging is exactly the same because you pay by kw not time.

LOL, that’s like saying getting gas a block away for $2/gal at a slow pump is the same cost as driving 50 miles out of your way just to get gas at “the same” $2/gal at a faster pump. It costs gas to get the other gas, somits effective price with your unnecessary detour is higher.
[also, you pay by kWh (energy), not kW (power)]

Think of it as a large supply hose, split into one small hose, and one slightly larger delivery hose.
The small one goes down the drain and is wasted. The slightly larger one fills up your gallon jug.

When you increase the total power delivered you increase the size of the supply hose and the delivery hose, but the waste hose stays the same, increasing the efficiency of your water-filling system that bills you per gallon supplied.
 
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AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
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But $0.47/kWh isn't a representative cost.

It is for some people, though usually they can change to a different plan and get somewhat lower overall costs.

My winter rate, for 8 months of the year is less than $0.05. (less than $40/yr then)

My low winter rate is about 2 cents MORE per kWh than it is in the summer. ~19 cents in winter, ~17 cents in summer.

There's a lot of users for which 120V IS the RIGHT DECISION.

No one said it wasn't.

So many people assume that 120V is not an option. For many people it is a quite viable option.

No one here said it was not an option. It's a perfectly fine option for many people.

We're just presenting the numbers as accurately (and as simply, though that can be difficult) as we can, so people can understand the tradeoffs. Remember, everyone's situation is different, so there is not a one-size-fits-all approach.

The original question was: Is charging at 120V less efficient? The answer is yes, it is, and approximate data is provided in the plot above. This does not mean that 120V charging is inappropriate.
 
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But $0.47/kWh isn't a representative cost. AFAIK, $0.20 is higher than the average cost across the country. A lot of places have summer and winter rates with winter being significantly cheaper. My winter rate, for 8 months of the year is less than $0.05. (less than $40/yr then)

So many people assume that 120V is not an option. For many people it is a quite viable option.

I wish I could get my costs that low. One of the drawbacks of living on Long Island. For now I'm sticking with the 120V for now. The cost is still way less than the ICE car I had before so I can live with it. I'll hit the nearby Supercharger if I need a big charge, but the cost for my 50amp circuit to the garage was well over $1k because there is no easy path to my detached garage. Maybe my next house...
 

jsrawa

Active Member
Apr 11, 2016
1,094
841
Colorado
Reviving an old thread but wanted some opinions. We are building a new house and have a Model 3 but will likely get a Y in the next year. I requested one 240v outlet in the garage instead of two thinking that the car that needed a faster charge could use it as needed while the other uses a 120v, I received a free HPWC through referrals and will install that at the 240v. I’ve used a 120v so far and been ok but winter is tough when it gets very cold. They charge $550 for a 240v, 60amp. Is it worth it to pay for two to future proof or is it just overkill, right now we drive less that 30 miles a day unless we make a trip. I just can’t make up my mind if the second is necessary or overkill. I realize there is some cost savings with 240v and I went 60amp even though I can’t utilize it all to try and future proof.
 

AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
11,946
15,478
San Diego
Reviving an old thread but wanted some opinions. We are building a new house and have a Model 3 but will likely get a Y in the next year. I requested one 240v outlet in the garage instead of two thinking that the car that needed a faster charge could use it as needed while the other uses a 120v, I received a free HPWC through referrals and will install that at the 240v. I’ve used a 120v so far and been ok but winter is tough when it gets very cold. They charge $550 for a 240v, 60amp. Is it worth it to pay for two to future proof or is it just overkill, right now we drive less that 30 miles a day unless we make a trip. I just can’t make up my mind if the second is necessary or overkill. I realize there is some cost savings with 240v and I went 60amp even though I can’t utilize it all to try and future proof.

To me it seems like a terrible inconvenience to have to juggle cars around and a potential disturbance to marital or civil union bliss, so I'd just get two 240V circuits, and ensure that they are optimally located and can easily be switched over to Wall Connectors, if desired. This is assuming panel loading, etc., etc. are not an issue. But mostly I'd just push very hard to have two decent charging options. Just takes out a requirement to think and plan in daily life and simplifies it. I like daily life to be simple though; I can't even be troubled to turn on light switches most of the time these days.
 
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Ask the electrician how big a second EV circuit you can add before it jacks the cost for a larger service line or breaker box.

If it is just $500 for a 14-50, that is a no-brainer when rolling it into the cost of the house. If he says $3k because it triggers a bunch of other upgrades then maybe not.

Remember there are a lot of options on charging amperage when using a wall connector, and a fair number of options between 5-15 and 14-50 with outlet adapters maybe one of those options gives you a better than 5-15 without having to make other big upgrades if that is a concern.
 
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Rocky_H

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Feb 19, 2015
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Since you already have the one 60A circuit run to the garage, it would be relatively cheap to have an electrician interrupt that line there in the garage with a small small sub-panel and split it to two 30A circuits on each side of your garage, or maybe 40A and 20A if you think one car will need more charging than the other most of the time.
 
Reviving an old thread but wanted some opinions. We are building a new house and have a Model 3 but will likely get a Y in the next year. I requested one 240v outlet in the garage instead of two thinking that the car that needed a faster charge could use it as needed while the other uses a 120v, I received a free HPWC through referrals and will install that at the 240v. I’ve used a 120v so far and been ok but winter is tough when it gets very cold. They charge $550 for a 240v, 60amp. Is it worth it to pay for two to future proof or is it just overkill, right now we drive less that 30 miles a day unless we make a trip. I just can’t make up my mind if the second is necessary or overkill. I realize there is some cost savings with 240v and I went 60amp even though I can’t utilize it all to try and future proof.

I'm of the personal opinion that [email protected] is quite sufficient for each vehicle (this could fully recharge, 0-100%, even a Long Range Model 3 overnight). So with that...

If it were me, I'd ask about how to best be able to provide 2x30A circuits on that breaker, if that's even a thing (or how you could design for that instead). In the future, you or another owner of the house may want two J-1772 charger stations installed that can load-share between them (or, say, two Tesla Wall Connectors that load-share). You may also want these circuits to individually be able to draw the 60A.

Location of course matters with this idea, basically just run it to a box where it would hopefully be useful one day.
 
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Rocky_H

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Feb 19, 2015
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Can't you put two Tesla wall connectors on the same circuit and they will share power draw? Then you can have either car charging at max rate, depending on need, and not have to install a whole secondary line and breaker, etc.

Load Sharing - TESLA Wall Connector
Well, you USED to be able to do that with the version2 wall connectors. Tesla made the boneheaded, idiotic, moronic, short-sighted, infuriating, pathetic decision to replace the version2 with the version3 that does not have this most used feature!!!!!! They say that they plan to implement that at some unknown point in the future with a software update!

Well guess what? IT WASN'T READY TO RELEASE THEN! They should have waited on switching over to the version3 until they had that feature ready to go in the initial release of that product since that functionality is so vital.

(And no, they still haven't implemented it.)
 
Well, you USED to be able to do that with the version2 wall connectors. Tesla made the boneheaded, idiotic, moronic, short-sighted, infuriating, pathetic decision to replace the version2 with the version3 that does not have this most used feature!!!!!! They say that they plan to implement that at some unknown point in the future with a software update!

Well guess what? IT WASN'T READY TO RELEASE THEN! They should have waited on switching over to the version3 until they had that feature ready to go in the initial release of that product since that functionality is so vital.

(And no, they still haven't implemented it.)
Hahahahahahahahahahaha! Really!? Brilliant.

I take back my post. I now only recommend installing a pair of J-1772 chargers that has way more features and load sharing as well as being compatible with any other EV.

Shame about having to use the adapter though.
 
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