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My cost to charge in a NY winter

I ran a little experiment to get an idea of how much it would cost me to charge monthly, especially during the winter. I have a LR RWD.

I drove 698 miles between 11/15/18 and 12/15/19. I started and ended the experiment with the battery charged to 80% to keep it consistent. The temperature has been in the 30s for much of the month. I also park outside, and preheat the car in the morning, although not every time (preheat for 15 min or so). I don’t charge the car everyday. My work commute is a short 9 mile round trip. Using a meter that I installed near my panel box, I consumed 432 kWh. My rate is about 14cents/kWh.

summary: total cost to charge is $60.48. Total energy usage is about 619 watts per mile. In my area fuel is about $2.65 a gallon. To equate what I paid for electricity, I would have to have a gas car that gets 30 mpg.
 

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mswlogo

Well-Known Member
Aug 27, 2018
8,408
7,951
MA, NH
Your Wh/mi is high, possibly because you take short trips. I am in Michigan, LR AWD with temperatures b/w 10F and 30F last month, 70 miles round trip, I get between 275 to 300 Wh/mi.

His true wh/mi is high because he is preheating. I keep telling folks it’s a waste of fuel. But they assume because they have more regen and doing it while plugged in they are saving fuel.

Imagine what the mpg ICE equivalent is at $0.26 / kWh. That equates to 16 mpg ICE.

Don’t preheat, unless you’re car is covered in ice. EV Cars heat up extremely quickly (way faster than ICE). So there is absolutely no need for it.
 
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His true wh/mi is high because he is preheating. I keep telling folks it’s a waste of fuel. But they assume because they have more regen and doing it while plugged in they are saving fuel.

Imagine what the mpg ICE equivalent is at $0.26 / kWh. That equates to 16 mpg ICE.

Don’t preheat, unless you’re car is covered in ice. Cars heat up extremely quickly ( way faster than ICE).

I don't preheat. But I do plan such that my charging ends right before I start driving in the morning. I park in a garage both at home and work, since OP parks outside, preheat might be needed. It did snow in the last month.
 

mswlogo

Well-Known Member
Aug 27, 2018
8,408
7,951
MA, NH
I don't preheat. But I do plan such that my charging ends right before I start driving in the morning. I park in a garage both at home and work, since OP parks outside, preheat might be needed. It did snow in the last month.

Also super wasteful. Charge when your battery is already warm from driving home. Otherwise all that heat in the battery is wasted and needs to be put back in before it can charge in the morning. Keep in mind he is measuring watts at the wall, not what the car is reporting (which would not include preheating, vampire, charging losses, or morning charging overhead (when your battery is the coldest)). I bet you are more like 500 wh/mi or more if measured at the wall. No way your car gets 275 wh/mi (at the wall) in the winter.

Effectively you are preheating the battery.
 
Preheating is definitely wasted energy, I agree. I’ll change it up for the next 30 days. I’m going to preheat very little or not at all. I’ll also try to charge after the battery is warm. Outdoor temps will be similar.

I’m seeing 300-400 wh/mi in the car but am measuring at the wall charger to get a true cost. This includes the wall charger drawing current while sitting there lit up. I have been charging at work for free and still can. However, I really wanted to know what it would be like without having that luxury.
 
Also super wasteful. Charge when your battery is already warm from driving home. Otherwise all that heat in the battery is wasted and needs to be put back in before it can charge in the morning. Keep in mind he is measuring watts at the wall, not what the car is reporting (which would not include preheating, vampire, charging losses, or morning charging overhead (when your battery is the coldest)). I bet you are more like 500 wh/mi or more if measured at the wall. No way your car gets 275 wh/mi (at the wall) in the winter.

Effectively you are preheating the battery.

(275-300) Wh/mi to > 500 Wh/mi! Highly unlikely.

(a) Preheat battery and preheat cabin are two different things. I agree that the car will always preheat the battery in winter. What I meant was I don't preheat the cabin (I should have been more clear about it).
(b) Based on my energy meter readings, I am about 80% or more efficient when charging on level 2. Even considering that, and preheat of the battery, >500 Wh/mi is a huge jump from what was observed in the car ((275-300) Wh/mi)!
(c) In my case, vampire losses are minimal, since the car sleeps both at home and at work.

I never measured any of these numbers other the readings from the car and the energy meter readings. I hope someone would chime in to provide some facts for better understanding of charging loses.
 

mswlogo

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Aug 27, 2018
8,408
7,951
MA, NH
(275-300) Wh/mi to > 500 Wh/mi! Highly unlikely.

(a) Preheat battery and preheat cabin are two different things. I agree that the car will always preheat the battery in winter. What I meant was I don't preheat the cabin (I should have been more clear about it).
(b) Based on my energy meter readings, I am about 80% or more efficient when charging on level 2. Even considering that, and preheat of the battery, >500 Wh/mi is a huge jump from what was observed in the car ((275-300) Wh/mi)!
(c) In my case, vampire losses are minimal, since the car sleeps both at home and at work.

I never measured any of these numbers other the readings from the car and the energy meter readings. I hope someone would chime in to provide some facts for better understanding of charging loses.

If your charging in the morning you are preheating the battery when it’s unnecessary. This assumes you have a long enough commute home that it warms the battery significantly (a necessary by product of driving). That heat is wasted if you don’t charge while it’s in that heated state. You Let it cool (and heat your garage a little). Then reheat at 5AM or when every it starts.

The OP did measure the full cost (with preheating the cabin). Preheating cabin for 15 minutes is way less costly than typical preheating the battery.

I have a short commute that doesn’t heat the battery much. So I charge once or twice a week, or after a longer errand, so I don’t waste energy heating the battery every day just to add 5% charge. I do 30% charges on a naturally warmed battery (when I can). Summer time I might charge daily, since it gets right to business.

Most wasteful thing is to charge a cold soaked battery every morning. Probably not great for the battery either. Thermal cycles is what age things.

How wasteful your at charging every morning depends on how much battery you use a day. If it’s a ton, it won’t make much difference. If it’s really small it won’t make much difference either, except charging less often would save. If your in the sweet spot like 50 miles a day it’s gonna be a large hit. That’s enough to warm the battery and toss that heat.
 
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I ran a little experiment to get an idea of how much it would cost me to charge monthly, especially during the winter. I have a LR RWD.

I drove 698 miles between 11/15/18 and 12/15/19. I started and ended the experiment with the battery charged to 80% to keep it consistent. The temperature has been in the 30s for much of the month. I also park outside, and preheat the car in the morning, although not every time (preheat for 15 min or so). I don’t charge the car everyday. My work commute is a short 9 mile round trip. Using a meter that I installed near my panel box, I consumed 432 kWh. My rate is about 14cents/kWh.

summary: total cost to charge is $60.48. Total energy usage is about 619 watts per mile. In my area fuel is about $2.65 a gallon. To equate what I paid for electricity, I would have to have a gas car that gets 30 mpg.
You would need to preheat the car and take short trips so you might find you would need a car at 50 mpg to actually get 30 mpg with the preheating and short trips. Remember EPA tests with no hvac.
 
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I forgot that I reset the trip meter for this time period. 256 kWh used for an avg of 367 Wh/mi

So difference between 367 Wh/mi (noted from trip meter) and 619 Wh/mi is 252 Wh/mi which includes:
  1. Batter preconditioning
  2. Cabin preheat
  3. Vampire loss
  4. Sentry mode (if not used, zero, else 10% of battery per day?)
  5. Other (may be negligible)
My question is, which of the above options is causing the majority of the Wh/mi loss?
 
Short trips destroy the efficiency for any car. An ICE car gets 50mpg (like my Prius did), would get 20 if I drove to the supermarket a few miles away during the winter.

There are variables to preconditioning.
Unheated garage: then your going to use a lot more power.

Parking in the driveway (plugged in): Even more power.

Heated garage: very little power.

Also Keep in mind in addition to sentry, smart summon might keep the car awake and using power.
 
So difference between 367 Wh/mi (noted from trip meter) and 619 Wh/mi is 252 Wh/mi which includes:
  1. Batter preconditioning
  2. Cabin preheat
  3. Vampire loss
  4. Sentry mode (if not used, zero, else 10% of battery per day?)
  5. Other (may be negligible)
My question is, which of the above options is causing the majority of the Wh/mi loss?
I barely use sentry mode, so that won’t be a huge factor. Preconditioning, preheating cabin and vampire loss are the big ones. This month I’m going to try charging when battery is warm, and will not pre heat the cabin. Will be interesting to see the results.
 
I do not think very many 3800 pound performance ICE cars would get anywhere near 30MPG driving the way it was described in the first post of this thread and premium gasoline might also be require. Measuring the power delivered to the UMC is the best way to know how much power you are using/paying for. There is also a small percentage of power wasted in the wiring as heat. I charge at nominally 240V @ 24A or 5.76KW my open circuit voltage is normally around 246V and it drops to around 240 when pulling 24A. So I am paying for 246V X 24A or 5.904Kw from the power company but at the measuring point it reads 5.76KW; therefore, the lose in the wiring is about 144W. I am using a dryer circuit for charging so I am not plugged in at all times while parked in my garage. I was not instrumented last winter so had to guess as to what was going on exactly. When it gets colder this winter, I will gather more power readings. When the temps drop below 60F, I normally try to charge for around an hour to warm the pack before departure. When the traction battery is at around 47F the motor is used to slightly warm the battery before I see the full 22MPH rate. When charging for at hour at around 47F, I believe about 300 to 500W of power is used for heating before the charge rate charges at 22MPH (not very much); however, when the pack temperature drops to around 40F, the first 20 to 30 minutes of my charging session does not add any miles. I have read the long range RWD motor draws a maximum of 3.5KW so about 1.75KW of power would be used to heat the traction battery. So the question is if I charged for hour and a half which would add about 22 miles but use around 1.75KW for heating would that be better than not charging? With charging I would have more regen and use less friction braking during the 22 mile drive but I suspect I would not recover the 1.75kw of power. If the 22 mile drive had many start/stops, charging first might use less power due so some or better regen? If I needed the range to get to a Supercharger, then I would not worry about the power usage to heat the battery/cabin before departure but I normally have plenty of range for all other times. None of what I described above is exact and there are many other factors that could be taken into account. With everything said above, 619 watts/mile still seems quite high!
 

mswlogo

Well-Known Member
Aug 27, 2018
8,408
7,951
MA, NH
I do not think very many 3800 pound performance ICE cars would get anywhere near 30MPG driving the way it was described in the first post of this thread and premium gasoline might also be require. Measuring the power delivered to the UMC is the best way to know how much power you are using/paying for. There is also a small percentage of power wasted in the wiring as heat. I charge at nominally 240V @ 24A or 5.76KW my open circuit voltage is normally around 246V and it drops to around 240 when pulling 24A. So I am paying for 246V X 24A or 5.904Kw from the power company but at the measuring point it reads 5.76KW; therefore, the lose in the wiring is about 144W. I am using a dryer circuit for charging so I am not plugged in at all times while parked in my garage. I was not instrumented last winter so had to guess as to what was going on exactly. When it gets colder this winter, I will gather more power readings. When the temps drop below 60F, I normally try to charge for around an hour to warm the pack before departure. When the traction battery is at around 47F the motor is used to slightly warm the battery before I see the full 22MPH rate. When charging for at hour at around 47F, I believe about 300 to 500W of power is used for heating before the charge rate charges at 22MPH (not very much); however, when the pack temperature drops to around 40F, the first 20 to 30 minutes of my charging session does not add any miles. I have read the long range RWD motor draws a maximum of 3.5KW so about 1.75KW of power would be used to heat the traction battery. So the question is if I charged for hour and a half which would add about 22 miles but use around 1.75KW for heating would that be better than not charging? With charging I would have more regen and use less friction braking during the 22 mile drive but I suspect I would not recover the 1.75kw of power. If the 22 mile drive had many start/stops, charging first might use less power due so some or better regen? If I needed the range to get to a Supercharger, then I would not worry about the power usage to heat the battery/cabin before departure but I normally have plenty of range for all other times. None of what I described above is exact and there are many other factors that could be taken into account. With everything said above, 619 watts/mile still seems quite high!

I think you got that right, you won't recover the energy heating that you put into the battery to have better regen. Even if it was a longer trip your car would naturally heat the battery any way. Preheating battery only helps the front end of your longer trip. The only practical time it makes sense to preheat is, you need the extra range or you need to melt some ice. In the case you need more range you are probably doing a lot of highway and regen doesn't add that much to efficiency when cruising on the highway.

Even though wh/mi looks worse on the car display without preheating, it will improve wh/mi measured at your house meter.
 

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