Charge Time and Energy Consumption

[OC Dan]

Admittedly, I am not an electrical engineer. So, I'm wondering.....if charging at 110v takes 10-14 hrs based on my consumption, which often rolls me into higher electric company rate tiers, would it be less expensive to install a 220v charger so that all charging would been taken care of during off peak times? Also, if I'm able to charge in say 2 hours @220v, instead of 10 hrs at 110v, am I using less energy. I assume energy consumption is exactly the same, just being done in a much shorter time frame, but again I didn't graduate from MIT.

 

[campfamily]

Admittedly, I am not an electrical engineer. So, I'm wondering.....if charging at 110v takes 10-14 hrs based on my consumption, which often rolls me into higher electric company rate tiers, would it be less expensive to install a 220v charger so that all charging would been taken care of during off peak times? Also, if I'm able to charge in say 2 hours @220v, instead of 10 hrs at 110v, am I using less energy. I assume energy consumption is exactly the same, just being done in a much shorter time frame, but again I didn't graduate from MIT.

Think of the electrical charger as a water hose. The 110v charger gives you water at a much slower rate than the 220v charger. But, the total amount of water is just the same.

Now, the 220v charger may be a bit more efficient than the 110v charger; somebody else here would need to comment on that.

BTW, you don't need to be an MIT grad to understand how these things work. They are actually rather simple, far simpler than an ICE.

Keith

 

[WattsUp]

Admittedly, I am not an electrical engineer. So, I'm wondering.....if charging at 110v takes 10-14 hrs based on my consumption, which often rolls me into higher electric company rate tiers, would it be less expensive to install a 220v charger so that all charging would been taken care of during off peak times? Also, if I'm able to charge in say 2 hours @220v, instead of 10 hrs at 110v, am I using less energy. I assume energy consumption is exactly the same, just being done in a much shorter time frame, but again I didn't graduate from MIT.

Charging at 110V or 220V will consume the SAME amount of electricity, just at different "speeds". (Technically, there may be a slight difference in efficiency, but for the sake of this discussion it is negligible.)

Anyway, if your electricity company bills you based ONLY on consumption, then there should be no difference in cost charging at 110V or 220V.

However, if your electric company bills you based both on consumption AND the time-of-day that consumption occurs, the longer duration required to charge at the slower 110V speed might end up costing you more (e.g., if the time required for your charge is longer than the low-rate period lasts). To avoid this, either schedule your charging sessions so they occur only during the low-rate periods (this is what the "Value Charge" feature is for) or use a faster EVSE (220V) so the entire charge can occur during the low-rate period.

With an EVSE that can supply 6.6 kW, the FFE can fully charge in under 3.5 hours, which should easily "fit" within most low-rate periods offered by electric companies (typically, several hours overnight).

 

[OC Dan]

Thanks guys. Kind of what I was thinking. I'm starting to stretch the legs of the FFE a little more as it is becoming one of the the most fun cars I have ever owned. The 110V gets me through the week, but the weekend consumption blows my "Value Charge" out the window since it needs much more than the 10 hour window to top off. $1,200.00 for the 220v install is still a heck of a lot of 110v kw hours though!

 

[WattsUp]

$1,200.00 for the 220v install is still a heck of a lot of 110v kw hours though!

I use the ClipperCreek LCS-25, which costs $469 right now (which is about $100 less than what I paid about 2 years ago). The LCS-25 outputs 4.8 kW, which charges the FFE in 5 hours. CC also offers higher (and lower) power models.

I added a plug to my LCS myself and just plug it into my 240V outlet when I want to charge -- no "installation" required -- and can also take it with me when needed. It is even easier these days, because you can now buy EVSEs with various plugs already attached directly from CC.

 

[v_traveller]

I'm starting to stretch the legs of the FFE a little more as it is becoming one of the the most fun cars I have ever owned. The 110V gets me through the week, but the weekend consumption blows my "Value Charge" out the window since it needs much more than the 10 hour window to top off. $1,200.00 for the 220v install is still a heck of a lot of 110v kw hours though!

Assuming you're in OC and your "value charge" is 10 hours, is it safe to assume you are with So Cal Edison, either TOU-D-A or TOU-D-B? If so, If you're on A, then I understand your concern with blowing past the 10-hour super-off-peak window since the off-peak rate is over twice the super-off-peak rate. In that case, I suggest you look into switching to plan B; currently with winter rates in effect the difference between super off-peak and off-peak is only 4 cents/KWh. (12c vs 16c). During the summer season the difference is slightly higher at 6c.

I have TOU-D-B... Since the off-peak isn't significantly higher than super-off-peak, I have yet to make the switch to Level 2 charging. Sometimes charge periods start before 10pm or end after 8am, but the penalty is minimal.

If you are already on TOU-D-B, I'd say don't worry about any charging you have to do outside of the weekday 2pm-8pm on-peak period. Still pretty cheap compared to your projected $1200 cost of installing L2.

 

[hybridbear]

The 110V gets me through the week, but the weekend consumption blows my "Value Charge" out the window since it needs much more than the 10 hour window to top off. $1,200.00 for the 220v install is still a heck of a lot of 110v kw hours though!

Your utility doesn't offer the cheap rate all the time on the weekend?

 

[OC Dan]

I am with SoCal Edison. I didn't switch anything with my plan since buying the car. I did call, and they said the plan I'm on would probably be the most beneficial as long as I keep charge times between 10p-6a which are the off peak rates. The gal I spoke to went on and on about the differences and I was a little confused in the end. May have to look in to plan "B", as she did mention super off peak rate of 6c per KWh. I think she said regular off peak is 11c per KWh. To get the super off peak rate she went into something about the rate times shifting around, and that's when I started losing her.

I don't believe we get any weekend rate differences. It is all based on time of day as far as I know.

 

[v_traveller]

The rate tables for the different SCE time-of-use plans are here, updated for 2016. It's not as complicated as it sounds over the phone:

https://www.sce.com/wps/portal/home/residential/rates/Time-Of-Use-Residential-Rate-Plans

I'd suggest checking your bill to confirm which one you currently have. If not TOU-D-B and you consume 700KWh or more per month on average, I would strongly suggest switching.

About a year ago I did a write up on the new SCE TOU plans, maybe this will help too, scroll to the last comment for a link to a spreadsheet you can play with:

http://ev-vin.blogspot.com/2015/02/new-sce-time-of-use-rate-structure.html

On the subject of weekend rates: I often charge midday on weekends and holidays since there is no peak period... off-peak goes from 8am to 10pm, and 10pm-8am remain super-off-peak.

 

[scottt]

Thanks guys. Kind of what I was thinking. I'm starting to stretch the legs of the FFE a little more as it is becoming one of the the most fun cars I have ever owned. The 110V gets me through the week, but the weekend consumption blows my "Value Charge" out the window since it needs much more than the 10 hour window to top off. $1,200.00 for the 220v install is still a heck of a lot of 110v kw hours though!

I installed the GE charger ($400 for the charger, $80 for wiring) myself. As others have mentioned here, Clipper Creek is another good alternative. Definitely do NOT spend $1200 to have one installed.

 

[OC Dan]

Great info guys. I really apprecite it!

Also, back to 110v vs 220v, I understand the water hose analogy, and that make perfect sense. What I don't get is why does it take around 18hrs to charge a flat battery at 110v, and only 3.5hrs on 220v? Around 5 times longer for 110v seems odd based on 220v charge time.

 

[coulomb_carl]

Most 240V circuits are designed for higher currents than 120V circuits (think oven, dryer, range, water heater, AC unit.) Usually a 120V circuit is breakered at 15A while a 240V circuit is usually at least 20A but more commonly 30A, 40A, 50A etc.

 

[WattsUp]

Great info guys. I really apprecite it!

Also, back to 110v vs 220v, I understand the water hose analogy, and that make perfect sense. What I don't get is why does it take around 18hrs to charge a flat battery at 110v, and only 3.5hrs on 220v? Around 5 times longer for 110v seems odd based on 220v charge time.

The reason for the shorter charge times is that 220V EVSEs typically output many times more power than 110V EVSEs. More power means faster charging.

The voltage is only half of the equation -- the other is the amperage. Voltage and amperage taken together measure power, and the power output of your EVSE is what governs to time it takes to restore energy (stored power) to your battery.

The calculation for power expressed as watts is simple:

watts = volts * amps

Thus, the basic calculation to estimate time-to-charge for any given power level is:

watts-hours needed (to charge battery) / watts supplied (by EVSE) = hours (needed to charge)

110V EVSEs usually operate at about 12 amps, so the power output is:

110 volts * 12 amps = 1320 watts

Thus, the time needed to fully charge the FFE using 1320 watts is:

24000 watt-hours / 1320 watts = 18.2 hours

(Why 24000 watt-hours needed to charge the battery when the usable capacity of the FFE is only about 19000 watt-hours? The answer is that charging is not 100% efficient. Turns out, 24000 watt-hours must be delivered by the EVSE to reach charge of 19000 watt-hours stored in the battery, since the overall charging process is only about 80% efficient. In other words, it takes somewhat more power to charge the battery than actually ends up stored in it. This is true for all battery charging.)

220V EVSEs, on the other hand, typically operate around 30 amps, with a power output of:

220 volts * 30 amps = 6600 watts

(You can already see that 6600 watts is much more power than 1320 watts.)

Accordingly, the time needed to fully charge the FFE using 6600 watts is:

24000 watt-hours / 6600 watts = 3.6 hours

----

So, to complete the "hose" analogy...

Voltage is analogous to the diameter of the hose. Amperage is analogous to the speed of the water running through it. Change either aspect of the hose and the "water power" (how much water the hose can supply) will change proportionally. Conversely, if somebody were to give you just the hose diameter or just the water speed, you would not know the water power. You need both measurements.

 

[NightHawk]

A typical 220V,30A EVSE charges at 6600Watts (220*30) compared to
a 120V,12A EVSE at 1440Watts (120*12)

6600/1440 = ~5 times the charging power and the charge time is proportional to that
Also the 240V EVSE is also more efficient (less losses) so its actually even higher, so I typically get about 6x faster charge time on my 220V EVSE compared to the 120V EVSE.

 

[OC Dan]

Wow....excellent explanation! Thank you guys for taking the time to educate me. I'm very handy, but electricity has never been my strong suit.

 

[triangles]

One more thing I don't think has been quite touched on is why 240V (L2) charging is more efficient. To simplify things I'm going to ignore the whole AC/DC conversion the charger does. The charger must also convert the supply voltage to the battery voltage which is somewhere near 360V. Your supply voltage is 120V or 240V (L1 or L2). The greater you have to increase the voltage, the greater the conversion loss will be. As is obvious 120V to 360V is a much larger jump than 240V to 360V. I don't know what the exact efficiencies of the two voltage conversions but I suspect the it would be difficult to see much real world difference in energy usage between the two. In other words yes L2 is more efficient but the difference is probably negligible.

Another way to think about why L1 is so much slower. First, if you're not already aware the FFE charges at 12A while on L1 charging and just under 30A while on L2. Note: some L2 stations can't supply the full ~30A and some L2 stations are as low as 208V but we'll ignore that for this example and assume L2 means 240V @ 30A. L1 charging is equivalent to L2 charging at 6A. They are both the same kW charge rate (240x6=1440kW; 120x12=1440kW). When you look at it this way it is more clear why L1 is 5 times slower (30A/6A=5).