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Understanding charging info on screen
- Thread starter Mwhusa
- Start date
That screen says that you are charging at 9kW (of power), you have added 13kWh worth of power to your car, and you are charging at 38amps, out of a possible charging speed of 38 amps (which is a strange max charging rate to be charging at), at 242 volts.
The 38 Amp / 38 amp charging amperage looks strange to me. Where are you charging, and what is the max charging rate its supposed to be able to charge at?
Silicon Desert
Well-Known Member
As an electronics engineer, I won't bore you with the details. I'd just say that the key piece of information you care about is at the very top telling you how long it will take to charge your car to the level you set 
A 40amp connection is only supposed to charge at 32 amps due to the fact that its a continuous load. You need to set that charger to 32 amps if you had a 40 amp connection put in.
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RayK
Active Member
I'd want to know five things:
- What is the breaker in the electrical panel rated for? (e.g., 40A, 50A, 60A)
- What is the wire gauge used to connect the breaker to your outlet / EVSE ("fixed wire charger")?
- What is the brand / model of EVSE?
- Who installed it?
- Is the circuit used by the EVSE shared with anything else in your house?
To answer your original question, you will need to understand a bit of the concepts.
Instead of gallons as a quantity of energy you can transfer or burn, we use kWh. Your car's battery might contain around 75kWh of energy total, as an example. There are a few battery models in model 3s but let's use that as a rough example. A kWh is just 1000 Wh, kilo means 1000 in the metric system.
So far in your example you've added 13kWh to your battery.
The "speed" at which electricity enters your car for charging is measured in kW. You are getting 9kW in your example. If you get 9 kW of power during a whole hour, you get 9 kWh of energy. There are losses but I'm keeping them out for simplicity.
242V is the voltage of the electricity you're getting in. Homes in America run on 240V and 120V circuits. You are also pulling 38Amps (38A) in that connection.
Watts are simply Volts multiplied by Amps. In your situation, 242 * 38 = 9196W, or 9.196kW, rounded to 9kW on the display.
Instead of gallons as a quantity of energy you can transfer or burn, we use kWh. Your car's battery might contain around 75kWh of energy total, as an example. There are a few battery models in model 3s but let's use that as a rough example. A kWh is just 1000 Wh, kilo means 1000 in the metric system.
So far in your example you've added 13kWh to your battery.
The "speed" at which electricity enters your car for charging is measured in kW. You are getting 9kW in your example. If you get 9 kW of power during a whole hour, you get 9 kWh of energy. There are losses but I'm keeping them out for simplicity.
242V is the voltage of the electricity you're getting in. Homes in America run on 240V and 120V circuits. You are also pulling 38Amps (38A) in that connection.
Watts are simply Volts multiplied by Amps. In your situation, 242 * 38 = 9196W, or 9.196kW, rounded to 9kW on the display.
Thanks for the layman terms. It makes sense to me. I know understand what the screen is telling me.
RayK
Active Member
Thanks for that info. I believe that 8AWG is too small for a constant 40A of current. 6AWG would be preferred if I'm not mistaken. That could explain the strange 38A max you see. For now, I would manually lower the charging current to 32A (or less) by using the "-" button on the charging screen.
Yes and no..
Cerrowire Resources - Ampacity Charts says 8AWG is okay IF its conductors-in-conduit. If its NMB(romex), the limit is 32A continuous, and it should have a 40 amp breaker.
RayK
Active Member
@Mwhusa I guess that leads me to ask another question... What type (brand) of outlet is being used? I'm assuming it's a NEMA 14-50 since you said you have a Tesla Corded Mobile Connector. The plug (left) and socket (right) should look like this:
A quality (i.e., commercial) 240V 50A outlet should be used. I think most people here would say Bryant, Hubbell are better than the $10 Leviton (residential) outlets you find at Home Depot. Even if you're not going to be unplugging/inserting the Corded MC that much.
A quality (i.e., commercial) 240V 50A outlet should be used. I think most people here would say Bryant, Hubbell are better than the $10 Leviton (residential) outlets you find at Home Depot. Even if you're not going to be unplugging/inserting the Corded MC that much.
RayK
Active Member
Oops... I hope I'm not causing confusion... the mobile charger is 32 amps max. I read "fixed wire" to mean hard-wired.
RayK
Active Member
I did too at first
. Then I re-read OP's posts which is why I asked specifically what was being used.What does "fixed wire" even mean?I did too at first
AlanSubie4Life
Efficiency Obsessed Member
Now that you have mastered that information, step 2:Thanks for the layman terms. It makes sense to me. I know understand what the screen is telling me.
1) The screen doesn’t tell you the amount of energy you have pulled from the wall. As mentioned already, it does not include the charging losses.
2) More surprisingly, it also doesn’t tell you the amount of energy you have added to the battery. (Though it is well correlated.)
3) This kWh number shows up when range display is set to %. The kWh value displayed is (to my knowledge, I really need to go back and verify various corner cases sometime, and to make sure there has been no change to this behavior) just the number of rated miles added (visible when you switch to distance) multiplied by the charging constant for your vehicle. Each rated mile represents a certain amount of energy. And that calculation is what is displayed on the screen.
4) For reasons that aren’t worth delving into, the displayed kWh are actually about 4.5% higher than what is actually added to your battery. (Short explanation is that each displayed mile added contains 4.5% less energy than the charging constant).
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