I have my MS set to charge at 12am to take advantage of the lowest electricity rates. And when looking at my electrical usage, I notice my car using a lot more electricity than it expended that day. For example, the day before yesterday (starting with a full charge) I used 14.1kwh of energy based on what the MS trip meter said. In charging (after deducting baseline draw the rest of my house uses) it used 19.6kwh. If my math is correct, that's about 40% extra energy being used. Is this amount of loss typical? I'm charging with a Nema 14-50 outlet.
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The car reports energy usage from the battery, so it doesn't report energy lost due to inefficiencies during charging which is typically at most 90% efficient with 85% being typical.
In addition, vampire losses may not be factored in as well: Power drain while idle (Vampire Load)
So if you take 19.6 kWh, 85% of that is 16.7 kWh. That leaves another 2.6 kWh for vampire loss which seems to be in the ball park.
Although if you don't have a dedicated measuring device, I would be doubtful of the accuracy of your 19.6 kWh reading - are you sure you got an accurate baseline draw for the rest of the house?
Thanks for posting this data though - I've often wondered what the actual efficiency of the Model S is over time including charging and vampire losses and would love to see more data. How many miles did you drive in between charges?
In addition, vampire losses may not be factored in as well: Power drain while idle (Vampire Load)
So if you take 19.6 kWh, 85% of that is 16.7 kWh. That leaves another 2.6 kWh for vampire loss which seems to be in the ball park.
Although if you don't have a dedicated measuring device, I would be doubtful of the accuracy of your 19.6 kWh reading - are you sure you got an accurate baseline draw for the rest of the house?
Thanks for posting this data though - I've often wondered what the actual efficiency of the Model S is over time including charging and vampire losses and would love to see more data. How many miles did you drive in between charges?
ToddRLockwood
Active Member
Vampire load should be greatly reduced when Sleep Mode arrives in the next firmware version.
You might want to install a wireless circuit monitor inside your panel, just to be sure your only measuring that 14-50 outlet. Another potential issue is the length and gauge of the wire between your panel and the outlet. If the wires are getting warm, there could be some loss there, too.
You might want to install a wireless circuit monitor inside your panel, just to be sure your only measuring that 14-50 outlet. Another potential issue is the length and gauge of the wire between your panel and the outlet. If the wires are getting warm, there could be some loss there, too.
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Know of any good ones that aren't too expensive and are accurate?
If you're losing more than a couple percent in your wiring you've got bigger issues...
When you charge in the middle of the night and every other nighttime hour has exactly the same usage, I would say the extra usage during the hours of charging is pretty definitely the car charging. Do you really have power usage that goes up and down during the night in your house? In my house the nighttime usage excluding car charging is never more than 300 watts, so the 10kW car charging is pretty distinct.
ToddRLockwood
Active Member
I don't have one, but I remember a thread on TMC dealing with it last year. The one I recall reading about was quite easy to install—simply an inductive clamp that picks up the wire right at the breaker. The unit used wifi to get the data to your computer.
You might try starting a new thread asking about it... "Single circuit load monitor"
Good point - mine does fluctuate at night (fridge cycling on/off), but not that much and as you say - 300W is the upper limit and is lost in the noise when the car is pulling 10kW. for 2 hours.
I am already on firmware 5.0 (took delivery of my car 2 weeks ago), so vampire drain should already be lower shouldn't it? And yes I can be very confident in my estimation of my home's baseline draw because during the wee hours of the night (12am-6am) it fluctuates only .01 to .02 per hour. I drove 40 miles between charges. Thanks for pointing out the car's own charging efficiency loss, I hadn't factored that in.
I am already on firmware 5.0 (took delivery of my car 2 weeks ago), so vampire drain should already be lower right? And yes I can be very confident in my estimation of my home's baseline draw because during the wee hours of the night (12am-6am) it fluctuates only .01 to .02 per hour. I drove 40 miles between charges. And thanks for pointing out the car's own efficiency loss when charging, I hadn't thought of that.
ThosEM
Space Weatherman
Quick charging efficiency assessment
Someone please critique this very simple method of assessing charging efficiency:
1. Note the initial and final charging states using app notifications, to get charging time and rated distance increase.
2. Note the charging rate from volts and amps reported by the car at the connector, to get Watts.
3. energy put into the battery is rated consumption (189 Wh/km or 302 Wh/mi) times range gained in charging.
4. energy from the wall is charging rate in W times the duration of the charging in hours.
5. Divide 3. By 4.
Notifications made me realize this is easy to do and I'm getting over 90% efficiency at 9.6 kW charging in my garage. If I put in numbers from supercharging (as reported early in a session with low initial SOC), I get even higher values around 95%. Clearly this does not assess losses in the line leading to the charging port. In supercharging the losses of the onboard rectifier are moved to the external rectifier, which perhaps accounts for the higher apparent efficiency. Perhaps we can conclude that the rectifier and battery losses are each about 5% at these levels of charging? Lower rates at 120 V may suffer in comparison. I haven't tried that yet.
How about you?
Someone please critique this very simple method of assessing charging efficiency:
1. Note the initial and final charging states using app notifications, to get charging time and rated distance increase.
2. Note the charging rate from volts and amps reported by the car at the connector, to get Watts.
3. energy put into the battery is rated consumption (189 Wh/km or 302 Wh/mi) times range gained in charging.
4. energy from the wall is charging rate in W times the duration of the charging in hours.
5. Divide 3. By 4.
Notifications made me realize this is easy to do and I'm getting over 90% efficiency at 9.6 kW charging in my garage. If I put in numbers from supercharging (as reported early in a session with low initial SOC), I get even higher values around 95%. Clearly this does not assess losses in the line leading to the charging port. In supercharging the losses of the onboard rectifier are moved to the external rectifier, which perhaps accounts for the higher apparent efficiency. Perhaps we can conclude that the rectifier and battery losses are each about 5% at these levels of charging? Lower rates at 120 V may suffer in comparison. I haven't tried that yet.
How about you?
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ThosEM
Space Weatherman
That was actually two data points, one from L2 charging and one from L3 supercharging.
But my routine charging rate from the wall is 46 kph of a total of 416 km "capacity." From the energy app, I make the rated consumption as 189 wH/km, meaning that my 416 km rated range corresponds to 78.6 kWh, so that's 46 km/h / 416 km * 78.6 kWh = 8.7 kW into the battery from a nominal load on the connector of 9.6 kW, which is a routine efficiency of 90.5%.
If the car is giving me accurate voltage and current, that is really not bad! Much of the time my voltage sags to 235-237 V, but I always get the 46 km/h so that would make the efficiency of the rectifier 92.5%. I can substantiate the reported 46 km/h charging rate by noting how much rated range I get and the time to get it from the app notifications, which gives a true 46-47 km/h.
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