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Charging Speed-Converting MPH to Watts

5K views 26 replies 11 participants last post by  2928 
#1 ·
I have a Grizzl-E charger hardwired on a circuit protected with a 50 amp breaker. I set it to draw 40 amps, according to the
charger’s owner’s manual. When charging, the car reports that it’s adding 32 MPH.

According to Tom Moloughney here, 32 MPH corresponds to a 48 amp draw (at the US standard 240 volts.)

Being concerned about overloading the circuit, I lowered the Grizzl-E’s draw to what the manual claims is 32 amps. After doing so, the car reports adding 27 MPH, corresponding to Tom’s 40 amp charging experience.

All that to ask: is there a way to convert the MPH report on the car to kilowatts, so that I can figure how many amps the car is drawing? (I don’t have a strong enough ammeter; otherwise, I’d just measure it directly.)
 
#4 ·
All that to ask: is there a way to convert the MPH report on the car to kilowatts, so that I can figure how many amps the car is drawing? (I don’t have a strong enough ammeter; otherwise, I’d just measure it directly.)
Any elm327 adapter and free Car Scanner Elm Obd2 app will show the amps, volts and kW while charging or driving, plus the temperature of the battery pack.
 
#11 · (Edited)
(40 Amps X 240 V) = 9600 Watts divided by 100 divided by your 'Vehicle-->Data' screen's miles per kWh should approximately equal your Charging MPH reported. I use Long Term.
(Plug in your actual voltage at your EVSE, if you know it. During summer, 240 Volts is optimistic)

(40*240)/100/3.3=29.1

For a 48 Amp setup for ID.4:
(48*240)/100/3.3=34.9

For my 16 Amp right now, actual voltage is 219 Volts, long term 3.2 kWh/mile:
(16*219)/100/3.2= 10.95 mph
My display is showing 11 mph

I agree, there's a better way. But, this works for now.
 
#14 ·
I know this is an old thread, but rather than start a new one, I noticed something new today… am plugged into a Tesla wall connector at a supermarket using my Tesla Tap. Anyway, the car says 30mph charge speed, and when I tap the Data tab, it shows -43.2kWh. So, apparently it does read out the charging rate in watts, just not on the Charging screen! (Note: I am sitting in the car while the boss shops and an running the climate control while charging since parked in the sun.)
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#17 ·
Good point! In my head, I was thinking amps, I suppose… maybe just chalk this one up to a software glitch? Because I think in the past I’ve seen it at zero when charging…
 
#20 ·
Be reminded that the volts is multiplied by the Power Factor. Ideally unity but not always dependent on quality of transmission infrastructure (capacitor banks to help achieve, etc).
@d287 I was thinking Amps at first, too! I was scratching my head why it wasn't closer to the standard 40A or 48A rate (unheard of at most public charging locations).

@Tinman it should be 43,200 kW / 240volts = 180 amps! That's a touch on the high side.
 
#22 ·
I was trying to math out the glitch in the software that could come up with an indication that there could be 43.2 kWh of range being added to the battery per hour by a Tesla Level 2 EVSE. If it's off by a factor of 10, therefore delivering 4.32 kW net to the battery per hour with a 30 Amp/7.2 kW EVSE with the AC running in the sun, it becomes more reasonable.

I think Nai3t missed the hour divided by hour part of the kWh/h unit of measurement showing on the original screen image.

(minus 43.2 kWh/h = plus 43.2 kWh added to the battery per hour. If it's off by a factor of 10, 4.32 kW added to the battery in an hour would correlate to 4.32 kW net x the indicated 3.5 mi/kWh = about 15 mph of charging )
 
#23 ·
kWh/h has been used as unnecessary long hand to indicate capacity gained per hour, ie rate, when in fact the h's cancel and it just becomes kW, which is also rate.

So in this example from the photo 43 kWh/h would fill the ID.4's 77 kWh battery back in 1h50m and 43 kW is just the instantaneous power which, left running for an hour, would result in 43 kWh of charge stored.

And when I run the numbers for a decimal error, I still come up with an oddball non-standard amperage around 20 which is possible, but it would more likely be 24 to match up with a commonly available 30 amp breaker.
 
#24 ·
So, it definitely wasn’t getting 43 kW into the battery. I was connected for half an hour and added 6% to the battery :) And it was a Tesla wall connector so I don’t know it’s rating, but users on PlugShare with Teslas reported getting around 10kW, which would be around 43 amps…
 
#25 ·
That gets back to my original thought in that (a) it's common to have 40A or 48A due to common 50A and 60A circuit ratings, so 43 would be a total oddball amperage rating, but (b) that amps don't mean much without voltage and so could either be 5.2 kW (120v), 8.9kW (208v), or 10.3 kW (240v). I guess let's see what this does after the software update, if it is really just an miscalculated indicator?
 
#26 ·
I’m not sure what was going on with d287’s charging session mentioned earlier, but here’s what I was getting while fast charging at EA just now. Perhaps the rate display works differently with L2 charging; perhaps the software is wonky. I know which way I’m leaning.
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