Charging efficiency from UMC + 240vac/40amp NMEA 14-50 to Battery

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#1
There is much discussion of WHrs/mile (or kWHrs/100miles) that M3 owners are experiencing, but these are all based on power measurements downstream of the M3's built-in charger. One anecdotal report said that reported only ~80% of the power that was supplied to the UMC as measured using a Kill-a-Watt meter connected to a 120vac/15amp wall outlet. Surely the M3's built-in charger will operate at higher efficiency from a standard, 240vac, NMEA 14-50 outlet on a 50amp circuit drawing 40 amps continuous. Right?

So, do you measure the kWHrs of utility power supplied to the UMC from your home NMEA 14-50 outlet?

If so, what values are you finding for the ratio: kWHrs supplied to the UMC (measured ahead of the 14-50) / kWHrs added to the battery (reported by your M3)?

Also, what rate of charge have you specified? The full 40amps available or something less? And how are you measuring the power supplied by your 14-50 outlet?
 

96s46p

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#2
Yes 240v has better efficiency. Umc gen2 is limited to 32a, good for those of us with a 14-50 outlet on a 40a breaker. Usually I only charge at 20-24a because it is fast enough.
 
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#3
Yes 240v has better efficiency. Umc gen2 is limited to 32a, good for those of us with a 14-50 outlet on a 40a breaker. Usually I only charge at 20-24a because it is fast enough.
Thanks for reminding me that the gen2 UMC limits us to 32amps - I don't have my M3D yet.

I share your optimism that charging at 240vac must be more efficient than charging at 120vac, but I'd really like to quantify the difference between energy pulled from the electric utility and energy delivered to the battery. To that end I have included a watt-hour meter in the circuit for the NMEA 14-50 outlet that I have installed - now I just need an M3 to measure.:(

I'm sure others are metering the power input to their charger and would like to to hear from them - please?
 
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#4
I use an Eyedro sensor on my 14-50 line (using the UMC) and have taken measurements at various currents. Nitty-griity: My line voltage runs about 245V with only about 7 ft of 6/3 between the sensor and 14-50 outlet.

I don't see any significant difference between 24 and 32 amps and believe that I'm getting around 91% efficiency. I ran a couple of tests at 15 amps; probably seeing a couple percent lower efficiency (no clue why). Out of curiosity I also checked out 12 amps @120V using a kill-a-watt type device and measured about 82%.

btw- The M3 doesn't report kWh's added (might report at superchargers- can't remember). You have make a calculation based on % added (using an assumption of what 100% equates to). Personally, I've settled on using 73 kWh=100% until I see a more definitive number.
 

garsh

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#5
I'm getting around 91% efficiency. I ran a couple of tests at 15 amps; probably seeing a couple percent lower efficiency (no clue why). Out of curiosity I also checked out 12 amps @120V using a kill-a-watt type device and measured about 82%.
That matches other data I've found.
I wasn't able to find numbers for a Tesla, but I found several reports about the charging overheads for the Nissan Leaf.

Level 1 (120v, 12 amps): 78% efficient
Level 2 (240v, 16 amps): 91% efficient
Level 2 (208v, 30 amps): 91% efficient
CHAdeMO (500v DC, ~100 amps): 93% efficient

So it looks like there may be some minimum level of charge rate required to overcome the majority of overhead losses, then other factors become more important in calculating charging losses. Hopefully we can dig up similar reports for a Tesla.

Sources:
http://www.mynissanleaf.com/viewtopic.php?t=8583
https://avt.inl.gov/sites/default/files/pdf/fsev/SteadyStateLoadCharacterization2015Leaf.pdf
https://www.researchgate.net/profil...ency-of-quick-DC-vehicle-battery-charging.pdf
 

96s46p

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#6
From the Tesla specified umc rate table you get 0.92mi/amp at 240v and 0.25mi/amp at 120v. So if 240v is 92% efficient 120v is only 50%.
 
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#7
Besides rounding errors (the table you're referring to has 1 digit precision), it appears that Tesla is understating the numbers on 120v circuits for one reason or another. My Model 3 reports 5 mph charging rate when using the 5-15 adapter - not the 3 mph shown in the table. Note that my line voltage runs close to 123v so I wouldn't be surprised if many owners see 4 mph.