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For what it is worth, here are the last two home charges and respective efficiency.
31.5 kw consumed since last charge 42.8 kilowatts used to charge to 90%. Efficiency of charge 0.7360
45.8 kw consumed since last charge 63.4 kilowatts used to charge to 90%. Efficiency of charge 0.7224
This seems rather low efficiency converting AC to DC but perhaps within range experienced by others?
31.5 kw consumed since last charge 42.8 kilowatts used to charge to 90%. Efficiency of charge 0.7360
45.8 kw consumed since last charge 63.4 kilowatts used to charge to 90%. Efficiency of charge 0.7224
This seems rather low efficiency converting AC to DC but perhaps within range experienced by others?
ZeroDarkSilver
HEPA cleaning your atmosphere, you're welcome
My charger is limited to 28A at 208V (~6kW), and I see a ratio of 0.85 on average vs the kWh reported by the trip computer.
What amperage and voltage are you charging at?
ZeroDarkSilver
HEPA cleaning your atmosphere, you're welcome
Yeah wondering if I'm getting higher efficiency because I'm charging at lower power.
ZDS
Three phase power may be more efficient? Are you measuring AC power consumption with a CT at the chargers power lead and separate meter?
I also thought I read somewhere that efficiency is higher as you approach the upper end of either the chargers or inverters limit.
Three phase power may be more efficient? Are you measuring AC power consumption with a CT at the chargers power lead and separate meter?
I also thought I read somewhere that efficiency is higher as you approach the upper end of either the chargers or inverters limit.
You reported higher efficiency initially, around 80%, but with less kWh consumed before charging. How long do you go between charges? Remember that any vampire losses from the car just sitting there do not show up as kWh used on the trip meter, and that will bring your calculated efficiency down.
Interesting, Thank you for clarifying that kilowatts "lost" are not being measured by the trip meter.. The one time I got 79% was charging only 24 hours apart and only about 15 kW. Lately I've been waiting between three and six days between charges.
I assume that the idle battery loss is fairly consistent day to day. Does this mean the actual charging efficiency is also relatively consistent but the calculations are somewhat skewed by charging less often?
I assume that the idle battery loss is fairly consistent day to day. Does this mean the actual charging efficiency is also relatively consistent but the calculations are somewhat skewed by charging less often?
ZeroDarkSilver
HEPA cleaning your atmosphere, you're welcome
Could be that too. I am not measuring the power myself. I live in multi-unit complex so I am individually billed/metered. I'm going by the amount of energy I'm being billed for, which it's probably safe to say is not less than the energy I'm actually using.
ZDS;
If your car is separately metered with no other consumption, I agree,your consumption should be quite accurate.
At this point, unless someone knows better, probably the biggest variable in "measured or perceived" charging efficiency is the unmeasured idle time battery loss.
If your car is separately metered with no other consumption, I agree,your consumption should be quite accurate.
At this point, unless someone knows better, probably the biggest variable in "measured or perceived" charging efficiency is the unmeasured idle time battery loss.
ZeroDarkSilver
HEPA cleaning your atmosphere, you're welcome
Not sure about that. The vampire loss I see with my car parked in the garage is about 0.5% of rated range per day. So if I left my car sitting for 6 days I'd lose maybe 3% of charge. That by itself is not enough to account for the different between your calculated efficiency (low 70's) and mine (mid 80's). I think maybe the phase and power differences are still playing a role.
Only way to be sure is for you to charge your car at my spot, or vice versa.
Charging at your place or mine would be one way to do it. Hopefully others will chime in as that may be more efficient in time and electrons. Someone said they lose 1.5 kW per day when the car is idle. That could certainly explain the difference. I will start checking on battery percentage loss while idle and see if that sheds any light.
Boatguy
Active Member
Here is a suggested methodology to determine charging efficiency that removes vampire from the equation, but of course it's necessary to unambiguously know how much power has been drawn from your supplier.
1) Determine your car's Wh/RM constant (e.g., my S90D is 273 Wh/mi, very stable over 8 trips ~ 1,000mi). I believe this is a constant per each model.
a) Record rated miles on the dash
b) Reset Trip A
c) Drive 50-100mi
d) Divide the Trip A kWh consumed by the change in RM on the dash (not Trip A miles)
2) Compute charge efficiency
a) Record RM on the dash
b) Charge the car
c) Multiply the RM added by the constant from #1 above, this is total energy added to the battery.
b) Charge efficiency = 2c divided by the power consumed by the charger
1) Determine your car's Wh/RM constant (e.g., my S90D is 273 Wh/mi, very stable over 8 trips ~ 1,000mi). I believe this is a constant per each model.
a) Record rated miles on the dash
b) Reset Trip A
c) Drive 50-100mi
d) Divide the Trip A kWh consumed by the change in RM on the dash (not Trip A miles)
2) Compute charge efficiency
a) Record RM on the dash
b) Charge the car
c) Multiply the RM added by the constant from #1 above, this is total energy added to the battery.
b) Charge efficiency = 2c divided by the power consumed by the charger
I think there are a few things that can make the perceived charging efficiency vary more than it really does. Vampire loss could be one of those. If you lose about 3 miles per day due to vampire losses that is equal to about 1 kWh of charging per day. So lets use your initial example where you got 12/15.1 for 79.47 % efficiency. lf you didn't have any vampire losses, the calculation would be 12/14.1 = 85.11 %, which is a pretty good number. Now lets assume you use 12 kWh but wait 2 days to charge instead of 1 day. Then the calculation would be 12/16.1 = 74.53 % efficiency. That being said, it does seem like your recent 70% like numbers do seem a little bit low.
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Perhaps I am missing something but wouldn't driving any distance in one shot, noting the kilowatts consumed and charging immediately (noting total power consumed) accomplish the same thing?
I think you are onto something. If one considers a 1 kW loss per day then my last charge was more like 80%..
45.8 kw consumed since last charge + 6kw loss (6 days) = 51.8 kw used divided by 63.4 kilowatts used to charge to 90% = 81.7% efficiency.
That makes sense. Do you have a good idea how many miles you lose a day from vampire losses? Do you have energy savings setting on? I have energy savings on and always connected checked. I think that helps minimize the idle losses.
Boatguy
Active Member
If you're suggesting, charge, immediately drive any distance (enough to remove rounding error), and then immediately charge, then yes. My suggestion is a little less constrained on the timing and serves my own selfish interest to establish the Wh/RM for various models.
The consumption in the trip meter is WRONG WRONG WRONG. If you use it in any math, you'll also get a wrong result.
Don't shoot the messenger.
As has been mentioned in this thread and elsewhere, the trip meter does not measure total energy consumption. My guess is that if the trip meter was used only to measure consumption while in motion (as in watts per mile) it would be fairly accurate.
Once it is determined how much energy loss occurs while the car is not in use, the meter should be able to help keep track of charging efficiency should one be interested in measuring that.
Once it is determined how much energy loss occurs while the car is not in use, the meter should be able to help keep track of charging efficiency should one be interested in measuring that.
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