: Does charging at 240 volts cost less than at 120?



Bill R.
12-15-2010, 02:54 AM
:confused:

My electrician says that charging at 240 volts (Level 2) is more efficient (less electricity used) than at 120 volts, thus offsetting the cost of the higher voltage charging equipment. I know it is much faster but had not heard that economic argument before. Does this make any sense?

Rusty
12-15-2010, 03:17 AM
My electrician says that charging at 240 volts (Level 2) is more efficient (less electricity used) than at 120 volts, thus offsetting the cost of the higher voltage charging equipment. I know it is much faster but had not heard that economic argument before. Does this make any sense?

Barely yes, and I can't imagine it offsets the cost if you have the time, but there probably is some efficiency benefit to charging at 240. If your electrician knows what it is (if I understand things correctly, I may not) that would astound me.

There's a fixed cost for conditioning the battery. It's the same number of watts at 120V and 240V, but it's a lower percentage of the total watts available at 240V. So 240V will spend less time charging, and hence less watt-hours conditioning the battery during the charge. At least, I think that's how it'll work. I've not heard a definitive answer.

Will that justify the cost of a $2000 SPX install? Ummm.... I don't think so, not very quickly at least. Now maybe the charge circuit in the car operates more efficiently at 240V, but I've not heard anyone claim such. Most of the explanations I've heard about the roughly 4 hours charge at 240V vs. the 8-10 hours charge at 120 involve the amount of energy spent on the TMS.

And the amount of energy you spend on the TMS during charge depends on where you live. Fargo in the winter or Arizona in the summer? Probably a lot. San Diego (guess where I live :-) most of the year? Not so much.

Now if you drive a lot and need to do two-a-day (or three-a-day) charging to avoid burning gas? Yeah, 120 won't do that. I'm taking a wait and see approach, and will convert to 240 not for cost, but for convenience.

airjim22
12-15-2010, 03:24 AM
my 2 cents says. yes the 240 is a little more efficient but very minimal. Spas could be heated with 120v or 240v some argued while you waited for the water to heat, you would lose some heat waiting for the rest of the water to heat up. Wiring does have some power heat loss as electrons travel down the line. The 240v gives those electrons a cleaner easier path to the battery, but again very little. I see a 25 foot cord vs a 10ft cord having a bigger impact than the 120vs240 debate.

Marty
12-15-2010, 03:52 AM
Another, very minor in most cases, advantage is that the losses in the wiring are related to current and not voltage (I^2R) so that for the same wire length and gauge the losses would be half for 240 than 120. In a well-designed home electrical system the difference would be minimal.

There are lots of other variables that might come into play. such as ambient temperature. In slightly cold climates the waste heat from a 120-volt charge would be generated for a longer time, possibly negating the need for resistance heat overnight if the battery is charged at 240 and then cools. Way too many nits to pick, and likely not a whale of a lot of difference. A kilowatt-hour is for all practical purposes a kilowatt-hour.

volt11
12-15-2010, 10:15 AM
So with no significant difference in efficiency, I'm wondering how many people getting 240V chargers feel they need it for faster charging, and how many are getting one just to have it? Even if it only runs you $500, that would have bought somewhere between 3500 and 6000 extra gas-powered miles (depending on where gas prices are likely to go in the next few years) for those times when you ran out of time to fully charge your Volt.

(Personally, assuming I buy one, it honestly will be more in the "just to have it" category.)

barry252
12-15-2010, 10:58 AM
So with no significant difference in efficiency, I'm wondering how many people getting 240V chargers feel they need it for faster charging, and how many are getting one just to have it? Even if it only runs you $500, that would have bought somewhere between 3500 and 6000 extra gas-powered miles (depending on where gas prices are likely to go in the next few years) for those times when you ran out of time to fully charge your Volt.

(Personally, assuming I buy one, it honestly will be more in the "just to have it" category.)

I bought one to have the faster charge time. I know my feeble mind will forget to plug it in at night and I could get a quick boost in the morning to get me to work. Even though I have 110 in my garage, it's not a dedicated line, so it may have needed rewiring anyway. So, might as well get the tax credit and the 240V charger installed. I have the charger and it's getting installed on Friday, 12/17.

VIN63 is on the road; I hope to pick it up soon!

scottf200
12-15-2010, 11:06 AM
So with no significant difference in efficiency, I'm wondering how many people getting 240V chargers feel they need it for faster charging, and how many are getting one just to have it? Even if it only runs you $500, that would have bought somewhere between 3500 and 6000 extra gas-powered miles (depending on where gas prices are likely to go in the next few years) for those times when you ran out of time to fully charge your Volt.
(Personally, assuming I buy one, it honestly will be more in the "just to have it" category.)

I like the 120v idea because 8-10 hours would easily work overnight. I would like to be able to tell folks that it is that simple to own a Volt as well. Remember most electric only cars will not have that option. Leaf, for example, takes over 20 hours to charge on 120v per their FAQ.

I am considering the 240v because occasionally (weekly) I come home after work and need to go do something else a couple/three hours later. I could then charge twice that day and use little to no gas.

volt11
12-15-2010, 01:39 PM
I like the 120v idea because 8-10 hours would easily work overnight. I would like to be able to tell folks that it is that simple to own a Volt as well. Remember most electric only cars will not have that option. Leaf, for example, takes over 20 hours to charge on 120v per their FAQ.

I am considering the 240v because occasionally (weekly) I come home after work and need to go do something else a couple/three hours later. I could then charge twice that day and use little to no gas.

I think we're on exactly the same page. Most people will have overnight to do a full "commute" charge, but it's the ability to get more juice in before, say, going out to dinner later, that seems to be the best reason for the 240V option. Even in one hour at 240V you should be able to add 8-10 miles on electric.

therfman
12-15-2010, 02:37 PM
(Puts on electrical engineer hat)

There may be more to this than simple resistive losses. I haven't done a ton of work with high-power electronics, but in many cases, AC/DC converters run more efficiently at higher voltages. This is often the case for computer power supplies, whose efficiency is higher on European voltages than North American. The difference varies depending on load, and can reach 10% depending on design (better designs often have lower variance)

The numbers that we already know (for battery capacity and current usage at the 120V plug) point to charging system efficiency in the low 80% range on 120V. Getting a 10% efficiency gain at 240V may be difficult, but 5% is probably possible. That would save about 0.6 kWh per charge. For me, that's about 5.5 cents.

Unless you charge the Volt three times a day or will use the charger for 30 years (if it's truly standard, that may be possible), there is no economic sense to go to 240V despite the efficiency gain. If the goal is to use the least amount of energy possible, then some gains can be squeezed by going to 220V.

Cheers,

Luc

maynard
12-15-2010, 02:42 PM
I just ordered, and paid for, a $490.00 Voltec charger for 2 reasons. The US Govt. will give me a tax refund equal to 50% of the purchase price only until 12/30/2010. Our electric supplier will install a dedicated meter free and the electricity is much cheaper at night. So, I will plug in in the evening but the Volt won't charge until the lower rate times. That would be impossible usng 120VAC. So, yes, 240VAC saves money. I filled out the Edison form with my estimated driving time and miles, and when we would charge. Their estimate is that we will save $195.00 per year doing the charge this way. Not too bad. Now, if we could just get Volts here in Michigan.

Rusty
12-15-2010, 04:23 PM
Our electric supplier will install a dedicated meter free and the electricity is much cheaper at night.

A second TOU meter is what would drive us to 240V as well. Our panel is maxed (in fact, we already have some load distribution issues). So when we fix that we'll add a subpanel. At that point we'll have a TOU meter wired in (once the local utility figures out its options, it's still working on that).

The extra cost of a 240V EVSE will be down in the noise compared to the rest of the project. But going TOU (either 120V or 240V) will save money, and there's no significant cost going to 240V for us.

scottf200
12-15-2010, 09:28 PM
I just ordered, and paid for, a $490.00 Voltec charger for 2 reasons. The US Govt. will give me a tax refund equal to 50% of the purchase price only until 12/30/2010. Our electric supplier will install a dedicated meter free and the electricity is much cheaper at night. So, I will plug in in the evening but the Volt won't charge until the lower rate times. That would be impossible usng 120VAC. So, yes, 240VAC saves money. I filled out the Edison form with my estimated driving time and miles, and when we would charge. Their estimate is that we will save $195.00 per year doing the charge this way. Not too bad. Now, if we could just get Volts here in Michigan.

It is not clear to me and others if the 50% tax refund is available if you just buy it and install it "yourself".

See last entries in: http://gm-volt.com/forum/showthread.php?5832-SPX-accepted-my-Voltec-order-today!/page6

If we did get the 50% tax refund then I would buy it since I was going to get an extra 120v cord anyway[so I wouldn't have to remove mine from the car everyday] which has a price to be determined still as far as I know.

Marty
12-15-2010, 10:16 PM
So with no significant difference in efficiency, I'm wondering how many people getting 240V chargers feel they need it for faster charging, and how many are getting one just to have it?

Three reasons for me.

1. Faster charging. There are plenty of times when I'll come home from work and then go out in the evening after an hour or two. Dinner, a movie, work callout (I'm a network guy), etc. I'll be able to do my regular commute all-electric but being able to "top off" when I get home is appealing. There are some potential financial costs based on TOU metering to do this, so it may not be every day but the ability to do so if I know I'm heading out in the evening is nice.

2. Convenience. The cord is right there on the wall. Open the door, plug in the car, done. I don't need to get the 120V cord out of the trunk, uncoil it, plug it in to the wall, etc.

3. Protection against my own laziness and stupidity. The 120V cord stays in the trunk. If I used it for my primary charger I would need to remember to unplug it from the wall and stow it in the trunk every time I might want to charge on the road or go out of town. This way it stays with the car all the time.

My cost for the Voltec delivered was $557 plus about another $120 in electrical supplies to install it. That's a net of less than $350 after the tax rebate. No word yet on availability or cost of spare 120-volt charge cords but I bet they'll be $300-plus for the next few months (then drop like a rock for generic ones).

PatsVolt
08-16-2011, 10:32 AM
The one time charge for the cost of the 240V Charging interface is a wash to me. Then again, I did not have to have it installed as I had a 70 amp subpanel available to me in my garage and that saved me a bunch. Biggest thing about the 240 SPX is that it improves turn around time. You will appriciate that on weekends, when you may have lots of errands to do. I plug in every time I get home and the car is ready for another local trip in an hour or two and I don't have to worry about how much air conditioning or heat I use and I use sport mode just for the fun of it. These are the things that make the higher efficiency of the 240V Charger interface worth the one time cost.

hamchief
08-16-2011, 10:57 AM
As far as what the electrician said, running a 2000 watt load on 240V rather than 120V is better because the current drawn at 240V would be half that at 120V and the I^2R losses would therefore be less. However, the charge rate for the 240V charger is double that of the 120V cord...therefore, the AC current is about the same and line loss would also be the same. The only electricity savings would be that the line losses would only exist for half the time. If your line losses are that significant, it's time to run a new line.
For my situation, I can't justify the expense of a 240V charger - if I have to use a few drops of gas once in a great while, so be it.

Now another issue: those of us who are familiar with battery technology know that when you increase the charge rate of a battery, its operational lifetime is decreased. A lead-acid battery, for example, can be charged overnight or very quickly at high charge current. We know that the life of the battery is decreased like this.
I wonder if there has been any research showing the Volt battery life if it's charged at 120V vs 240V every time?

detroitsongbird
08-16-2011, 11:13 AM
For the difference between 240v and 120v is always having a full charge in the morning vs. once or twice a week having a full charge in the morning. Plus, as already pointed out, gaining another 12-15 miles of charge between getting home from work and heading out in the evening. With 120v it's almost not worth the effort to plug it in for one hour. With 240v it is definitely worth the effort. And, giving the flakiness of the 120v charger and hot days in the late afternoon, too many times the 120v charger overheated during that attempt to charge.

solar_dave
08-16-2011, 11:14 AM
Actually Flooded Lead Acid batteries like a substantial charge rate of 10-13%. The minimum rate should be at least 5%. This promotes adequate stirring of the electrolyte. Go below 5% and you are likely to get sulfation shortening the life of the battery substantially. They also like to have a discharge rather than leaving them in float all the time.

Not sure on the Lithium batteries.

RScott
08-16-2011, 12:08 PM
I wonder if there has been any research showing the Volt battery life if it's charged at 120V vs 240V every time?

That would be very useful to know. I'd also be interested in knowing if the 'reduced level' charging (8A vs 12A) makes much of a difference (presumably slightly less efficient, but what about battery life?).

Rusty
08-16-2011, 12:21 PM
Nominal charge rate for a typical Li-Ion battery is 1C, which in the Volt's case is 16 kW. At 240V that would be a 72A+ draw at 220V. As far as the Volt's battery is concerned, 3.3 kW (.2C) and 1.44 kW (.09C) are both nearly trickle chargers. There should be negligible if any degradation of battery life between the use of the two.

Bert
08-30-2011, 05:58 PM
That's probably correct.
Some day I am also going to measure what is the maximum current absorption the pack can take during regenerative braking, probably a few C. Just for the sport I'd like to avoid using the legacy brakes (and ultimately using utility energy to heat metal discs).

If the electrochemically recommended charge and discharge rates are in a 2 to 1 relationship, you would end up at a possible ~50kW charge rate (since the batteries are obviously able to feed the >100kW motor during hard acceleration)

Also, the motor is probably 98%-ish efficient and a power drive circuit shouldn't have much loss either in 2011, leaving only the battery with significant dissipation opportunity.

About 240 vs 120V charging efficiency - the line losses are identical, and assuming no battery conditioning is going on I guess there is probably only a minimal thermal effect that results into potentially slightly higher losses at 3.3kW (ie. 240V vs. 120V) charging - since resistive dissipation in a battery is not entirely linear. Meaning here that it could be so that there is proportionally slightly more than double the dissipation at 240V charging then at 120V.

In any cases, common sense would suggest that the delta must be negligible.

PS I charge at 240V too - 3h turnaround time is already slow enough.

Revoltron
12-11-2012, 12:42 AM
I wanted to revive this thread to see if anyone has any more current data to add to the discussion.

I just purchased a GE Wattstation 240V charger that I expect to using before weeks end. If it performs as promised I will be fully charging my Volt in 4 hours. This versus the 10 to 11 hours it presently takes to charge using the 120V system. It would seem just from a straight mathematical standpoint that 4 hours at 240V will consume less electricity than 10 hours at 120V.

For me the main purpose for upgrading to 240V was to be able to comfortably charge in the semi-limited window of a TOU second meter. Lower rates go into effect at 9pm and I need a full charge by 7:00am. Where I live, I typically pay 33˘ per kilowatt hour. Under the TOU plan, I will only pay 12˘.

Unfortunately, I am finding Southern California Edison less than helpful in getting the second meter implemented. Anyone been able to get such a project through?

silvercorvette
12-11-2012, 03:02 AM
So with no significant difference in efficiency, I'm wondering how many people getting 240V chargers feel they need it for faster charging, and how many are getting one just to have it? Even if it only runs you $500, that would have bought somewhere between 3500 and 6000 extra gas-powered miles (depending on where gas prices are likely to go in the next few years) for those times when you ran out of time to fully charge your Volt.

(Personally, assuming I buy one, it honestly will be more in the "just to have it" category.)
My free (for 2 years) charger with free installation was a no brainer. Duke Energy installed the charger at zero cost, if after 2 years I decide I want to keep it I pay them less than $250 (I forget the exact amount. I have had to charger for 11 months and love it because I can run some errands in the morning, stop home for lunch and have the car charged and ready to go by the time I finish lunch. With the 240 volt charger I have occasionally driven more than 120 electric miles in one day. Errands in the morning, recharge while I have lunch, visit my mother in the nursing home have supper while I recharge and drive over to my cousin for a visit in the evening.

When you consider that an installed charger would cost $1,000 to $1500 installed I would be crazy to not keep it after the 2 year trail period.

silvercorvette
12-11-2012, 03:17 AM
The one time charge for the cost of the 240V Charging interface is a wash to me. Then again, I did not have to have it installed as I had a 70 amp subpanel available to me in my garage and that saved me a bunch. Biggest thing about the 240 SPX is that it improves turn around time. You will appriciate that on weekends, when you may have lots of errands to do. I plug in every time I get home and the car is ready for another local trip in an hour or two and I don't have to worry about how much air conditioning or heat I use and I use sport mode just for the fun of it. These are the things that make the higher efficiency of the 240V Charger interface worth the one time cost.
Another good point I forgot to mention, Not only am I able to not worry about using the heat, pre-conditioning the car a 240 also works better. Before I got the 240 volt charger I would warm up the car on grid but with 120 volts the battery would loose some of it's charge. 120 volts isn't enough juice to warm the car and keep a full charge.

silvercorvette
12-11-2012, 03:26 AM
I wanted to revive this thread to see if anyone has any more current data to add to the discussion.

I just purchased a GE Wattstation 240V charger that I expect to using before weeks end. If it performs as promised I will be fully charging my Volt in 4 hours. This versus the 10 to 11 hours it presently takes to charge using the 120V system. It would seem just from a straight mathematical standpoint that 4 hours at 240V will consume less electricity than 10 hours at 120V.

For me the main purpose for upgrading to 240V was to be able to comfortably charge in the semi-limited window of a TOU second meter. Lower rates go into effect at 9pm and I need a full charge by 7:00am. Where I live, I typically pay 33˘ per kilowatt hour. Under the TOU plan, I will only pay 12˘.

Unfortunately, I am finding Southern California Edison less than helpful in getting the second meter implemented. Anyone been able to get such a project through?
WOW that is a lot, I forget what I pay but it is somewhere between 10 and 11 cents regardless of what time of day it is. I am so glad I moved from NY back there it is about 25 cents

Ron C
12-11-2012, 10:13 AM
I wanted to revive this thread to see if anyone has any more current data to add to the discussion.

I just purchased a GE Wattstation 240V charger that I expect to using before weeks end. If it performs as promised I will be fully charging my Volt in 4 hours. This versus the 10 to 11 hours it presently takes to charge using the 120V system. It would seem just from a straight mathematical standpoint that 4 hours at 240V will consume less electricity than 10 hours at 120V.


Only if your math is broken.

4 hours at 240V = 960VH, while 10 hours at 120V = 1200VH. Clearly 960VH < 1200VH.

But that's irrelevant. You missed 2 important parts of the word problem of "which is cheaper?" -

You pay for KWh, not VH
W = V * I


You left out the current portion of the equation. Charging at 240V is at 15A, while charging at 120V is 12A. Now the situation looks more like:
4 hours @ 240V, 15A = 14400WH (or 14.4KWh), while 10 hours @ 120V, 12A = 14400WH (or 14.4KWh).

This is nominal charging times - current SOC varies, as well as the input voltages. However, there is a slight improvement in efficiency within the onboard charger (the AC->DC and DC->DC conversions) where 240V comes out ahead.

If it costs you $500.00 for the L2 EVSE and you pay $0.10/KWh, it will take you approximately 5000 hours of reduced charging due to the efficiency to recoup that charge. Unfortunately, you only save about 12 minutes due to that efficiency per full recharge cycle, so that implies you'll need 25000 charge cycles to break even. I charge at home once per day on average. That's 68+ years, but for me it's actually worse. My average price per KWh is $0.07 or less, so it's going to be longer.

I have a L2 for 3 reasons: a) time reduction, b) preconditioning, and c) naiveté. I'm pleased with mine, largely because I can come home from work (with near 0% SOC) and hang out for an hour then go to dinner with TLW (like we did last night - Monday night date night) and use none or only a small amount of gas. I wouldn't be able to do that with L1.

Michvolt
12-11-2012, 04:12 PM
I recently had the 240 charger installed and I love it. I got it because there was an incentive program through our electric company for the first 2500 customers who had the TOU meter installed. I got the line ran, new meter and charger for $147 plus we get 40% off the TOU rates. The biggest selling freature was the lower rates but honestly, now that I have it I absolutely love charging it so quickly. On the weekends I always get up early to run errands on Saturday morning, by the time I get home my EV charge is gone. Before the 240 chargers I would have to wait til the next day to run on 240 again. Now I can do a few things around the house and have a full charge to run around in the afternoon. It really is so nice!

I got my car on 10/12/12 and started the paperwork to have the 240 charger installed right away. It took about a month to get them out for the estimate. Once we got the estimate they came out within a week to install charger. Then the city had to inspect, which happened about a week ago. Now the electric company has to finish the meter installation, which will happen tomorrow and then we are switched to TOU rates. I have been able to use the charger since it was installed (so for about 2-3 weeks) and I will say it again...I love it!!

Crys
2013 Silver Ice Metallic

BCNeuman
12-12-2012, 08:03 PM
I do not have a 240 charger, since my typical driving is not such that I need a full charge each night. But in SCE territory, the super off peak time of use period lasts from midnight to 6AM. Thus with a level one charger, one can not do a full charger entirely in the super-off-peak period. A level two charger allows one to do that full charge at super-off-peak rates. (yes, "super-off-peak" is what SCE calls the period).

Ron C
12-12-2012, 10:33 PM
Only if your math is broken.

4 hours at 240V = 960VH, while 10 hours at 120V = 1200VH. Clearly 960VH < 1200VH.

But that's irrelevant. You missed 2 important parts of the word problem of "which is cheaper?" -

You pay for KWh, not VH
W = V * I


You left out the current portion of the equation. Charging at 240V is at 15A, while charging at 120V is 12A. Now the situation looks more like:
4 hours @ 240V, 15A = 14400WH (or 14.4KWh), while 10 hours @ 120V, 12A = 14400WH (or 14.4KWh).

This is nominal charging times - current SOC varies, as well as the input voltages. However, there is a slight improvement in efficiency within the onboard charger (the AC->DC and DC->DC conversions) where 240V comes out ahead.

If it costs you $500.00 for the L2 EVSE and you pay $0.10/KWh, it will take you approximately 5000 hours of reduced charging due to the efficiency to recoup that charge. Unfortunately, you only save about 12 minutes due to that efficiency per full recharge cycle, so that implies you'll need 25000 charge cycles to break even. I charge at home once per day on average. That's 68+ years, but for me it's actually worse. My average price per KWh is $0.07 or less, so it's going to be longer.


Lookie there - my math is broken. I conflated hours and KWh in that last calculation. Let me retry that:

You need 5000KWh of savings @ $0.10/KWh to make up the 500.00 cost of the L2 Voltec. Based on what I see, the L2 charging saves 12 minutes on a full charge, but that 12 minutes is at 3.3KWh/hour, making each L2 charge worth 0.66KWh (instead of 0.2KWh <- that's the mistake). 5000 KWh @ 0.66KWh/charge requires ~7600 charges (instead of 25000). I charge fully ~6 times a week, which means it would take around 24 years, 4 months to recoup that expense.