EV charging calculations

[electricguy61]

When you're doing loads calculations for EV charging stations, do you include the charger in the general load (that would be at 40% after the 1st 8kw), or after the general load? 2500 sq ft home w/ 100amp service, underground service so not readily upgraded. Note the load calcs:

Lighting Load: 2500 sq st x 3 watts = 7500 watts

(2)small appliance circuits @ 1500 watts = 3000
(1) laundry circuit @ 1500 watts = 1500
(1) dishwasher @ 1188 watts = 1188
(1) garbage disposal @ 1140 watts = 1140
(1) clothes dryer @ 6000 watts = 6000
(1) AC condenser load = 5842
(1) blower fan load = 1127
Charger load (TESLA) (40a x 230v) = 9200
Total calculated load w/o load factoring = 36497 watts
First 8kVA @ 100%(NEC 220.83) = 8000
Remainder of load (28497) @ 40% = 11399
Total load for service calculations = 19399 watts / 230v = 84.3 amps

But.......... if they run the AC, including blower motor (6969w), clothes washer (1500w), dryer (6000w) and the charger (9200w) at the same time: 23,669 watts /230v= 103 amps. And that doesn't include any general lighting load.

What do you think? Is it safe? Does it meet code to install the charger?

 

[Ponchik]

This is what I came up with.

https://www.dropbox.com/s/pxocjs8tjn10ug6/load calc.pdf?dl=0

 

[growler]

This is the way I see it. Maybe not the right way.

If it were a new house and I was doing a load calculation I would ( for sure ) install a larger service.

If it's an existing service it may work out OK and if it doesn't it's not any more work to upgrade the service later than it is now.

From the load calculation I see they must have a gas range and water heater, is the house set up for a gas dryer?
They next dryer they may want to look at a gas one.

 

[JFletcher]

When you're doing loads calculations for EV charging stations, do you include the charger in the general load (that would be at 40% after the 1st 8kw), or after the general load? 2500 sq ft home w/ 100amp service, underground service so not readily upgraded. Note the load calcs:

Lighting Load: 2500 sq st x 3 watts = 7500 watts

(2)small appliance circuits @ 1500 watts = 3000
(1) laundry circuit @ 1500 watts = 1500
(1) dishwasher @ 1188 watts = 1188
(1) garbage disposal @ 1140 watts = 1140
(1) clothes dryer @ 6000 watts = 6000
(1) AC condenser load = 5842
(1) blower fan load = 1127
Charger load (TESLA) (40a x 230v) = 9200
Total calculated load w/o load factoring = 36497 watts
First 8kVA @ 100%(NEC 220.83) = 8000
Remainder of load (28497) @ 40% = 11399
Total load for service calculations = 19399 watts / 230v = 84.3 amps

But.......... if they run the AC, including blower motor (6969w), clothes washer (1500w), dryer (6000w) and the charger (9200w) at the same time: 23,669 watts /230v= 103 amps. And that doesn't include any general lighting load.

What do you think? Is it safe? Does it meet code to install the charger?

The dryer will not be pulling 6kw continuously. Also, the garbage disposal... how often do these run, a few seconds at a time with any amount of load on them? Do they really pull ~9A unloaded? I dont think it too likely someone would be running the washer and dryer in the middle of the night along with the charger either

 

[electricguy61]

The dryer will not be pulling 6kw continuously. Also, the garbage disposal... how often do these run, a few seconds at a time with any amount of load on them? Do they really pull ~9A unloaded? I dont think it too likely someone would be running the washer and dryer in the middle of the night along with the charger either

I agree about the dishwasher and garbage disposal.

But as I stated, it is not beyond the realm of possibility that someone would be doing laundry, running the AC, and charging the car at the same time. True, the dryer heat will cycle on and off, but that cycle isn't readily controllable.

I'm thinking of a controller that would only allow either the AC or the charger, but not both.

 

[electricguy61]

This is what I came up with.

https://www.dropbox.com/s/pxocjs8tjn10ug6/load calc.pdf?dl=0

BTW: 220.83 (2011 NEC) says 8K when not adding HVAC load

And this is in the San Francisco Bay Area, where folks don't typically run their AC at night.

It's still troubling to me that it could be a problem.

My question to the panel was, should the charger be figured under the general load (which is derated to 40% after the first 8K) or after?

Before, it's meets code. After, it doesn't

And I my proposal strongly suggests a gas dryer

Thanks

 

[growler]

My question to the panel was, should the charger be figured under the general load (which is derated to 40% after the first 8K) or after?

I'm pretty sure that you would have to use the after as I don't see a demand factor ( these thing are used for hours , maybe every night). I would think that a car charger would be calculated the same as electric heat or AC.

If the charger is protected by a 40 amp breaker I doubt if the actual load is that high. Probably less than 80% of that. I think you would need to use 100% of the actual load.


I wonder who put a 100 amp panel in a 2500 sq ft house in the first place, that's really going cheap.

 

[electricguy61]

I'm pretty sure that you would have to use the after as I don't see a demand factor ( these thing are used for hours , maybe every night). I would think that a car charger would be calculated the same as electric heat or AC.

If the charger is protected by a 40 amp breaker I doubt if the actual load is that high. Probably less than 80% of that. I think you would need to use 100% of the actual load.


I wonder who put a 100 amp panel in a 2500 sq ft house in the first place, that's really going cheap.

It's a 40amp load on a 50amp breaker.

Here, it's pretty common for a 2500 sq ft tract home built in the 1990's to have a 100 amp underground service. The builders went as cheap as they could, on the devopmement utilities and the services in the homes. They didn't include AC, and certainly didn't allow for EV charging. Gas heat, so no large electrical loads. To upgrade the underground service to 200amp costs $10-15K, including the utility costs (increasing transformer size seems to always be part of the job)

New homes now require 200amp solar ready service.

 

[Ponchik]

It's a 40amp load on a 50amp breaker.

Here, it's pretty common for a 2500 sq ft tract home built in the 1990's to have a 100 amp underground service. The builders went as cheap as they could, on the devopmement utilities and the services in the homes. They didn't include AC, and certainly didn't allow for EV charging. Gas heat, so no large electrical loads. To upgrade the underground service to 200amp costs $10-15K, (Not to mention the months of waiting :rant::thumbsdown:) including the utility costs (increasing transformer size seems to always be part of the job) I have NEVER seen a transformer upgraded when we do 200A upgrades. But yet they do charge for it, engineering cost, and some other BS charges (end of rant):rant:

New homes now require 200amp solar ready service.

I can't find whether or not the EV charger gets applied with the reduction or it is added as the AC does. I guess you can do either way and see what the end result is.

 

[Rampage_Rick]

When you're doing loads calculations for EV charging stations, do you include the charger in the general load (that would be at 40% after the 1st 8kw), or after the general load? 2500 sq ft home w/ 100amp service, underground service so not readily upgraded. Note the load calcs:

Lighting Load: 2500 sq st x 3 watts = 7500 watts

(2)small appliance circuits @ 1500 watts = 3000
(1) laundry circuit @ 1500 watts = 1500
(1) dishwasher @ 1188 watts = 1188
(1) garbage disposal @ 1140 watts = 1140
(1) clothes dryer @ 6000 watts = 6000
(1) AC condenser load = 5842
(1) blower fan load = 1127
Charger load (TESLA) (40a x 230v) = 9200
Total calculated load w/o load factoring = 36497 watts
First 8kVA @ 100%(NEC 220.83) = 8000
Remainder of load (28497) @ 40% = 11399
Total load for service calculations = 19399 watts / 230v = 84.3 amps

But.......... if they run the AC, including blower motor (6969w), clothes washer (1500w), dryer (6000w) and the charger (9200w) at the same time: 23,669 watts /230v= 103 amps. And that doesn't include any general lighting load.

What do you think? Is it safe? Does it meet code to install the charger?

Worst case you can set the EV charger to a lower amperage, just will take longer to charge their Tesla. The Tesla HPWC has dip switches to set it anywhere between 40-100 amp breaker (in 10 amp increments) so at the 40A setting you'd be looking at 32A for your load calc.

90% of the other charging stations on the market are 32A (40A circuit) since few EVs beside Tesla can charge faster than 6.6kW