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So far I have only had it charging when I'm asleep so I guess I missed that.
Is the charge constant at 29mph or does it slow down as the battery charge level increases?
If you're not range charging to max, it should stay constant. It doesn't taper like the super charger will because charging at 40 amps is like a trickle. I charge at 80 and it does 64 mph right up until the time it cuts off. Not sure what it would do if charging to 100% as I've never done that.
Actual charging rate will depend on line voltage (total Watts=V*A). I regularly see faster advertised rate since I'm close to the sub station and get about 245V@40A to the car through the HPWC (single inverter in the car). The power factor (efficiency) on this should be high but if the inverter or battery can't maintain ideal temperature (packed in a tight, hot & humid garage with little air flow) it will reduce. At just 40A as long as the inverter can stay cooled it should be constant rate, even dual charger at 20KWh is nothing compared to the Superchargers. I was charging yesterday in Connecticut and the cooling fans sounded like something between a turbo fan and a SciFi space saucer taking off due to the humidity. 300A@370V=111KWh DC to the battery, charge rate was showing over 480MPH! at the start and I unplugged when it dropped to around 190 after adding 200 miles of range).
Not really important to the topic, but you twice mention humidity in relation to cooling of chargers. Humidity has very little effect on cooling of hard surfaces. It makes you uncomfortable because it reduces evaporative cooling from your skin, but the devices don't feel that.
swaltner
Active Member
The math is very easy. The units all line up perfectly. How much power is going into the battery?
40 amps * 240 volts = 9,600 volt amps = 9,600 Watts = 9.6 kW (call it 10 kW)
How long to deliver a full charge at that rate?
85 kWh / 10 kW = 8.5 h (h stands for hours)
So, call it 9 hours for a full 0% to 100% charge. For your specific question:
85 kWh / 10 kW * 45% = 3.8 hours
For your specific question, call it 4 hours. Granted, there's actual line voltages, charger inefficiencies, charging tapers, battery/ambient temperatures and many other things that can change the actual time, but this lets will let you quickly GUESSTIMATE the charge time on a specific outlet.
40 amps * 240 volts = 9,600 volt amps = 9,600 Watts = 9.6 kW (call it 10 kW)
How long to deliver a full charge at that rate?
85 kWh / 10 kW = 8.5 h (h stands for hours)
So, call it 9 hours for a full 0% to 100% charge. For your specific question:
85 kWh / 10 kW * 45% = 3.8 hours
For your specific question, call it 4 hours. Granted, there's actual line voltages, charger inefficiencies, charging tapers, battery/ambient temperatures and many other things that can change the actual time, but this lets will let you quickly GUESSTIMATE the charge time on a specific outlet.
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Cottonwood
Roadster#433, Model S#S37
Your results are good, but you have interesting, canceling errors. The AC->DC conversion in the Model S is about 90% efficient, so about 90% of the power from the wall ends up in the battery, the rest is shed as heat. The actual, usable energy in the Model S battery is about 90% of the advertised number. Those two 90% factors cancel and your results are right on.
An easy, approximate rule-of-thumb is that you get 3 rated miles per hour for each kW of AC charging power, and 3.33 rated miles per hour for each DC kW of charging power; 80 Amps at 240 Volts on an HPWC is 19.2 kW AC or about 58 rated mph. 333 Amps at 360 Volts, near 0% SoC on an 85, is 120 kW DC or about 400 rated mph.
Direct air cooling of electronics, yes I wasn't recalling the details, it does decrease but the effect is negligible. Thanks for the refresher.
