Charging speed at home vs work

[RMoore]

At home I have a ChargePoint HomeFlex hardwired on a 60A circuit (so 48A setting). Work has 2 banks of Tesla destination chargers (6 at each location, some with J1772 connectors). I've only charged at home once and charged 3 times at work:

• At home: the Charge Log in FordPass says I charged 19% (from 71% to 90%) in 1 hr and 55 min. My ChargePoint app says it delivered 20kWh.
  • 20kWh in 115 min equates to 10.4kW. Per the CP website, at 48A it should deliver 11.5kW, so I'm guessing 10.4kW is reasonable given power loss.
    • Is the charging rate fairly linear across the 10-90% range of battery capacity?
  • I assume the CP 20kWh is more accurate than the FP saying 19%. Using both numbers yields a battery capacity of 105kWh, which is higher than the 91kWh advertised.
• Charging at work is much slower. I don't know the actual output of the Tesla charger, but FP says that I charge anywhere between 5-7kW. If any of you has a similar setup at work with multiple charger, do you see rates like that? I can try to find out more, but would it suggest that those are on lower amp circuits (30 or 40A) or use some sort of load sharing?

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[RickMachE]

At home I have a ChargePoint HomeFlex hardwired on a 60A circuit (so 48A setting). Work has 2 banks of Tesla destination chargers (6 at each location, some with J1772 connectors). I've only charged at home once and charged 3 times at work:

• At home: the Charge Log in FordPass says I charged 19% (from 71% to 90%) in 1 hr and 55 min. My ChargePoint app says it delivered 20kWh.
  • 20kWh in 115 min equates to 10.4kW. Per the CP website, at 48A it should deliver 11.5kW, so I'm guessing 10.4kW is reasonable given power loss.
    • Is the charging rate fairly linear across the 10-90% range of battery capacity?
  • I assume the CP 20kWh is more accurate than the FP saying 19%. Using both numbers yields a battery capacity of 105kWh, which is higher than the 91kWh advertised.
• Charging at work is much slower. I don't know the actual output of the Tesla charger, but FP says that I charge anywhere between 5-7kW. If any of you has a similar setup at work with multiple charger, do you see rates like that? I can try to find out more, but would it suggest that those are on lower amp circuits (30 or 40A) or use some sort of load sharing?

It depends the voltage you are supplying. My house, per my JuiceBox software, gives me around 247v. 247 x 48 amps = 11.85 kW. Yet, when it's running, I get more like 11.25.

The peak charging you can get at home is 48amps, yielding 11.25kW OUT OF THE CHARGER. To the vehicle you will get some loss. Assuming 8% loss, that's 10.35 to the car. Your 10.4 is right on. You are correct in that assumption.

You can't do the math you did on the percentages and determine battery capacity. First, you didn't account for the loss. Second, it wasn't exactly 20kWh, it had decimal places. Third, the percentages aren't accurate. 71% could be 70.46, or 71.44. 90% could be 89.46 or 90.44. 90.44 - 70.46 = 19.98% not 19%. 20/20 = 100. 89.46 - 71.44 = 18.02 which gets you to 111kW battery. But that 20kW might have been 20.44. And what's displayed could be a whole number off.

You can look at the charging curve in your software. At least I can. It's a straight line.

At work, you should expect both lower amperage and possible shared lines.

 

[macchiaz-o]

First part of charging seems to be 12V battery maintenance and hv electronics cooling for my vehicle. Then when it switches to hv battery charging, the rate remains fairly linear on L2.

Tesla EVSEs can be configured to various rate limits like your CPHF can. And they can load share multiple on the same line.

 

[Ming]

You can ask someone with Tesla what numbers they get, because both current and voltage would be shown on the Tesla app during charging.

6kW is typical though. I've used quite multiple hotel chargers with 208V 32A, and often the voltage is below 208.
Load sharing is also possible, but we won't know.

 

[RMoore]

You can't do the math you did on the percentages and determine battery capacity. First, you didn't account for the loss. Second, it wasn't exactly 20kWh, it had decimal places. Third, the percentages aren't accurate. 71% could be 70.46, or 71.44. 90% could be 89.46 or 90.44. 90.44 - 70.46 = 19.98% not 19%. 20/20 = 100. 89.46 - 71.44 = 18.02 which gets you to 111kW battery. But that 20kW might have been 20.44. And what's displayed could be a whole number off.

Good point, and agree, my calculation ignored rounding errors, loss, and other sources of error. I would have thought the apps rounded up or down appropriately rather than truncated (in which case 70.46 would be 70, not 71). For a worst case scenario, assume 19% on FP was actually just shy of 19.5% (so rounded down), and 20kWh on the CP was actually just over 19.5kWh (so rounded up). That would yield about 100kWh, but if there is close to 10% loss, that would yield around 90kWh which is about right.

Glad to hear that my rates for charging at work are reasonable. And I can't complain--it's free. Only issue is that we could use more charging stations there. I'll rarely have to charge much at home though, but with the NJ rebate of up to $1500 if one installs a smart charger, I'm glad I had it installed.

 

[Ming]

Glad to hear that my rates for charging at work are reasonable. And I can't complain--it's free.

Both my wife and I get 6kW shared chargers at work, if 2 cars are plugged in each only get 3 kW. Mine is not even free.

 

[SnBGC]

At home I have a ChargePoint HomeFlex hardwired on a 60A circuit (so 48A setting). Work has 2 banks of Tesla destination chargers (6 at each location, some with J1772 connectors). I've only charged at home once and charged 3 times at work:

• At home: the Charge Log in FordPass says I charged 19% (from 71% to 90%) in 1 hr and 55 min. My ChargePoint app says it delivered 20kWh.
  • 20kWh in 115 min equates to 10.4kW. Per the CP website, at 48A it should deliver 11.5kW, so I'm guessing 10.4kW is reasonable given power loss.
    • Is the charging rate fairly linear across the 10-90% range of battery capacity?
  • I assume the CP 20kWh is more accurate than the FP saying 19%. Using both numbers yields a battery capacity of 105kWh, which is higher than the 91kWh advertised.
• Charging at work is much slower. I don't know the actual output of the Tesla charger, but FP says that I charge anywhere between 5-7kW. If any of you has a similar setup at work with multiple charger, do you see rates like that? I can try to find out more, but would it suggest that those are on lower amp circuits (30 or 40A) or use some sort of load sharing?

The vast majority of workplace L2 units will be 32A or less. It makes zero sense to install anything greater. The average commute for office staff is less than 20 miles each way so your MME only needs about 1 hour on the plug to replenish the energy used to drive into work. Your employer is not intending you to use their energy for all your EV driving. They are merely offering the plugs as an amenity for the staff.....sort of like coffee service for the office. Abuse the amenity, then expect to have to start paying to charge.

Most commercial panels are 208v so 32A is around 6.6kW compared to 32A at home which is around 7.6kW.

Then factor in that most workplace units are in pairs, which usually means 2 plugs are sharing a single 40A circuit. Even THAT is too much power. They could even put 4 plugs on a single circuit and you would still get 1.6kW per plug (if all 4 are in use at the same time...). At that rate, you car will be charged back up in 6 hours which is still less than the average 8 hour work day.

Workplace charging is a great thing but we should not look a gift horse in the mouth. Better to have more plugs at a slower speed vs 1 or 2 plugs at faster speeds. Share the love.

 

[voxel]

20 kWh is from the charger and not what was put into the battery.

There’s 7-12% loss so let’s assume 12% loss.
20 kWh x .88 = 17.6 kWh into Mach-E (FP says this is 19%)
17.6 / 0.19 = 92.6 kWh at 100% (close enough)

My work (nearly 30) chargers are capped a 6.6 kW shared. Even then we trigger breakers once a day if multiple EVs are charging on the same floor.

 

[SnBGC]

20 kWh is from the charger and not what was put into the battery.

There’s 7-12% loss so let’s assume 12% loss.
20 kWh x .88 = 17.6 kWh into Mach-E (FP says this is 19%)
17.6 / 0.19 = 92.6 kWh at 100% (close enough)

My work (nearly 30) chargers are capped a 6.6 kW shared. Even then we trigger breakers once a day if multiple EVs are charging on the same floor.

That means the EVSEs are not installed correctly. The breakers should never trip under normal operation. That is a dangerous situation and needs to be fixed.

Tesla and ChargePoint are the two most difficult brands to install and configure correctly. In ChargePoint's case, the instructions are missing some key information that the installer must know in order for the units to power share safely.

We see it all the time. There is a Residence Inn at the south end of town with 3 Tesla units wired to a 100A circuit and all 3 plugs were set to 19.2kW. One car charges fine. A second car pops the breaker. The facility guy reset the units himself so 1 plug runs at 9.6kW while the other two run at 4.8kW (which defeats a primary feature of circuit sharing). At least it works safely now.

We are ripping it all out soon and will replace with some ChargePoint CT-4000 units with cord management.
There are lots of shoddy installations out there. Especially with the Tesla destination units. That is why the Tesla Tap doesn't work everywhere...

 

[voxel]

That means the EVSEs are not installed correctly. The breakers should never trip under normal operation. That is a dangerous situation and needs to be fixed.

Tesla and ChargePoint are the two most difficult brands to install and configure correctly. In ChargePoint's case, the instructions are missing some key information that the installer must know in order for the units to power share safely.

Yup. They are fixing it. There are too many chargers wired to the same line. It primarily happens when 4-6 EVs are charging (power sharing) at 3 ChargePoint chargers next to each other. Thankfully the office is less than 20% occupied so this situation is not that common... yet.

 

[SnBGC]

Yup. They are fixing it. There are too many chargers wired to the same line. It primarily happens when 4-6 EVs are charging (power sharing) at 3 ChargePoint chargers next to each other. Thankfully the office is less than 20% occupied so this situation is not that common... yet.

Are those CT-4000 dual head units? Can put 4 plugs on one 40A circuit but the jumper staples must be installed AND the installer has to call ChargePoint to let them know how it is wired so they can configure it in the cloud.

Honestly, I think it is irresponsible of them to do it that way. The Wallbox method is far superior because they default to a safe setting if everything isn't perfect.

 

[RMoore]

The vast majority of workplace L2 units will be 32A or less. It makes zero sense to install anything greater. The average commute for office staff is less than 20 miles each way so your MME only needs about 1 hour on the plug to replenish the energy used to drive into work. Your employer is not intending you to use their energy for all your EV driving. They are merely offering the plugs as an amenity for the staff.....sort of like coffee service for the office. Abuse the amenity, then expect to have to start paying to charge.

Most commercial panels are 208v so 32A is around 6.6kW compared to 32A at home which is around 7.6kW.

Then factor in that most workplace units are in pairs, which usually means 2 plugs are sharing a single 40A circuit. Even THAT is too much power. They could even put 4 plugs on a single circuit and you would still get 1.6kW per plug (if all 4 are in use at the same time...). At that rate, you car will be charged back up in 6 hours which is still less than the average 8 hour work day.

Workplace charging is a great thing but we should not look a gift horse in the mouth. Better to have more plugs at a slower speed vs 1 or 2 plugs at faster speeds. Share the love.

You bring up some excellent points that lead to me ask another question, one that reflects my lack of knowledge about plug in hybrids. My garage at work also has a block of charging stations that are at 110V (or close to that at least). They have been there for a few years and predate the higher voltage (208 or 240V) Tesla destination chargers that are located in a different area (I have to check if the 110V stations are just receptacles or if they are Tesla units). Would 110V charging be sufficient for the typical plug in hybrid? I ask because I notice that there are several plug in hybrids that routinely charge at the high voltage Tesla destination chargers and I was trying to figure out if I should be annoyed at that when there are no slots left, or if it is perfectly reasonable for them to charge there.

 

[SnBGC]

You bring up some excellent points that lead to me ask another question, one that reflects my lack of knowledge about plug in hybrids. My garage at work also has a block of charging stations that are at 110V (or close to that at least). They have been there for a few years and predate the higher voltage (208 or 240V) Tesla destination chargers that are located in a different area (I have to check if the 110V stations are just receptacles or if they are Tesla units). Would 110V charging be sufficient for the typical plug in hybrid? I ask because I notice that there are several plug in hybrids that routinely charge at the high voltage Tesla destination chargers and I was trying to figure out if I should be annoyed at that when there are no slots left, or if it is perfectly reasonable for them to charge there.

120v isn't really that useful except for visiting friends or family and staying the weekend or longer. It charges at 2-4 miles per hour (depending on the EV).

Public L2 benefits PHEV a ton and quite frankly....BEV owners should step aside and allow PHEV to get plug time first. They have tiny HV batteries by comparison so they need the power more than we do.

The early PHEV models only accept around 3.3kW but modern versions are now capable of 7.2kW or even 7.6kW.

 

[RMoore]

120v isn't really that useful except for visiting friends or family and staying the weekend or longer. It charges at 2-4 miles per hour (depending on the EV).

Public L2 benefits PHEV a ton and quite frankly....BEV owners should step aside and allow PHEV to get plug time first. They have tiny HV batteries by comparison so they need the power more than we do.

The early PHEV models only accept around 3.3kW but modern versions are now capable of 7.2kW or even 7.6kW.

Good to know. But the "step aside" thing doesn't really apply to the work situation unless folks moved their cars during the day. They currently don't but I would be fine with signs that asked people to do that (e.g. at lunch time) so that others can get some charging time. This is something of a pilot program--my hope is that they will see that the chargers are being used and will install more of them. It is certainly nice of them to do that given the expense (though this is a big Fortune 500 company so can afford it more than a smaller company).

 

[generaltso]

Good to know. But the "step aside" thing doesn't really apply to the work situation unless folks moved their cars during the day. They currently don't

Why not? That's the first thing that needs to change. When your car is fully charged, you go out and move it so that others can use the charger. This is regardless of whether it's a BEV or PHEV.

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