Joined

·
262 Posts

I checked its utility meter before, during, and after my ~ 20 minute charge session, during which I (as always) was the only one present.

Apparently the utility meter had just been read - my session was the first since the monthly cycle began. How do I know that? Demand reading.

The meter has a 120x multipler - all readings must be multiplied by 120 to know actual kW / kWh, so there is some loss of precision compared to a home or small biz meter.

Initial demand reading = 0.02 = 2.4 kW. On that basis, I conclude mine was the first charging session of the monthly cycle since no DCFC, even a De-de-de-de rated EA would stoop so low at 2.4 kW.

During the next 15 minutes, during which my Bolt drew an average of 42 kW, the demand reading slowly but steadily increased to 0.42 kW = 50.4 actual kW. After 15 minutes had passed, no further increase indicated since that's the nature of demand metering

What do I derive from the figure of 50.4 kW? That, coupled with the initial demand reading gives some insight into both standby power and conversion loss:

My initial demand reading of 0.02 suggests a standby loss of 1800-3000 Watts (range owing to loss of precision inherent in 120x multiplier) That's power used by station when no one is charging.

Net power while charging: 50.4 - 2.4 = 48 kW. That suggests a charging (480V 3 phase AC to ~360 Vdc) conversion efficiency of 87.5% (42kW / 48 kW)

Another observation - kWh reading remained unchanged at "15" throughout my session. That's reasonable, since it only increments every 120 kWh, and I only took 15, maybe 18 with conversion loss.

Final fun fact - The station hasn't seen much use...it's almost kinda "mine" for the time being. It has been up (more or less) since late August. If we call it 45 days or about 1000 hours, most of its 1800 kWh used that whole time (less than my house, BTW) has gone toward keeping its lights on, not charging cars.

Other than my own (admittedly incessant) updates on Plugshare, there are exactly two other checkins.

1800 kWh costs about $150 at local rates, but 50 kW costs an additional $500 in demand billing, every month as long as there is just one 15 minute 42 kW charging event per month. That is a painfully high cost of powering a poorly utilized DCFC station...What if a couple TayCans charged at the same time for 15 minutes?!?!