Adding a Tesla charger onto an existing 150A service?

[tx2step]

I'm out of town without a code book, and one of my co workers sent the following load calc to me to check tonight!

He is wanting to add a Tesla car charger to an existing service without upsizing the existing 150A 120/240 service. I've never installed a Tesla charger - it'll be put on a 100/2 circuit breaker added to the existing panel. I think he left off the 120 V air handler for the a/c (I think he is only showing the condenser), plus I think the Tesla charger may run for over 3 hours and should be figured as a continuous load? Is that correct?

I can't reach him tonight to ask him any questions, and I'm going to be busy tomorrow!

Can any of you guys see anything missing or done incorrectly? I don't do many residential load calcs, and can't do a manual one in my head without a code book & appendixes to refer to (and my computer).

What do you guys think?

Thanks for the help!

Existing residence with a 150 amp 120/240 service

GENERAL LIGHTING LOADS:
1,922 sq. ft. x 3 va/sq. ft = ​5,766 va
2 sm. appl. circuits = ​3,000 va
1 laundry circuit = ​1,500 va
Total = ​10,266 va

First 3,000 @ 100% = ​3,000 va
7,266 va @ 35% = ​2,543 va
​=======
Total general lighting load = ​[5,545 va]

1 DRYER = ​[5,000 va]

(Range & water heater gas)

APPLIANCE LOADS:
1 microwave 120 v/15 amp​1,800 va
1 dishwasher 120 v/10 amp​1,200 va
1 disposal 120 v/6.5 amp​ 780 va​
1 Tesla car charger circuit
240 v/80 amp load​19,200 va
Total appliance load = ​22,980 va

22,980 va x 75% = ​[17,235 va]

HEATING & A/C LOADS:
1 central A/C unit
240 v/25 amp​[6,000 va]
(gas heat – omit)

25% largest motor (A/C)​[1,500 va]

TOTAL SERVICE LOAD = ​35,280 va / 240 volts = 147.0 amps

150 amp, 120/240 volt, single-phase service existing

 

[tx2step]

Does anyone know how long the charge time for a Tesla is? If it's 3 hours or more, that would shoot down his idea.

He wants to submit his calc to a plans examiner tomorrow, but I don't think it'll be approved!

 

[ActionDave]

Does anyone know how long the charge time for a Tesla is? If it's 3 hours or more, that would shoot down his idea.

He wants to submit his calc to a plans examiner tomorrow, but I don't think it'll be approved!

Continuous load is one that pulls Maximum current for three hours. I would think the load on a battery charger would taper off.

 

[tx2step]

Continuous load is one that pulls Maximum current for three hours. I would think the load on a battery charger would taper off.

A Tesla is all electric. If it is close to fully discharged, I'm thinking it will be charging at 100% for quite a while so they can advertise as short an overnight or travel recharge time as possible. But I don't have any experience with them, so I don't really know. I was hoping someone here would know, since I'm sure that some on the forum have put several in by now.

Thanks!!!

 

[GoldDigger]

Continuous load is one that pulls Maximum current for three hours. I would think the load on a battery charger would taper off.

The load on a battery charger for a lead acid battery will taper off once the State Of Charge (SOC) gets above about 80%.
But the Tesla battery is a high performance Lithium chemistry battery pack with cell level monitoring and cooling. The rapid charger would not have to taper off much if at all as it approached the 80-90% SOC that is probably the top of the normal operating range of such a battery pack.

The length of time depends on the charger speed and the size of the battery pack. The standard Tesla 240VAC charger draws 40A and can take 8 hours or more for a full charge on an 80kWH pack.

BTW, the Tesla Supercharger station uses a direct connection to the battery to do a 50-80% charge (depending on battery pack size) in under 1/2 hour. But that is not relevant to home charging.

 

[tx2step]

The load on a battery charger for a lead acid battery will taper off once the State Of Charge (SOC) gets above about 80%.
But the Tesla battery is a high performance Lithium chemistry battery pack with cell level monitoring and cooling. The rapid charger would not have to taper off much if at all as it approached the 80-90% SOC that is probably the top of the normal operating range of such a battery pack.

The length of time depends on the charger speed and the size of the battery pack. The standard Tesla 240VAC charger draws 40A and can take 8 hours or more for a full charge on an 80kWH pack.

BTW, the Tesla Supercharger station uses a direct connection to the battery to do a 50-80% charge (depending on battery pack size) in under 1/2 hour. But that is not relevant to home charging.

That is what I was thinking. It will probably charge at 100% for at least 3 hours...maybe longer. Also I didn't see the air handler blower motor in his service calc, and it'll be operating if the condenser is running.

His service calc is so marginal at 147A that I think the blower motor alone would push it over.

Looks like to me the service needs to be upgraded to a 200A?

 

[ActionDave]

The length of time depends on the charger speed and the size of the battery pack. The standard Tesla 240VAC charger draws 40A and can take 8 hours or more for a full charge on an 80kWH pack....

So that's like $85 for a fill up after driving two hundred miles?

 

[al hildenbrand]

So that's like $85 for a fill up after driving two hundred miles?

:? $85? I think I missed something. I sounds like you are saying you pay about a buck per kWh.

 

[JFletcher]

So that's like $85 for a fill up after driving two hundred miles?

You're off by a magnitude of order: more like $8.50-$10. or 40+MPG @ $2/gal gas prices.

 

[ActionDave]

:? $85? I think I missed something. I sounds like you are saying you pay about a buck per kWh.

You're off by a magnitude of order: more like $8.50-$10. or 40+MPG @ $2/gal gas prices.

Sitting on my couch running numbers through my head, 10 and .10 look a lot alike up there this time of night.

That's still quite a jump in my electric bill compared to gassing up my '98 Honda that will go 400 miles on twelve gallons of gas.

 

[Fulthrotl]

Looks like to me the service needs to be upgraded to a 200A?

yup. iirc, the hi capacity tesla draws about 80 amps until close
to full charge. it's right at 80% of the circuit limit.

i'm thinking they limited it to a 100 amp branch circuit, as most
residential services are limited to 200 amps.

 

[drcampbell]

... That's still quite a jump in my electric bill compared to gassing up my '98 Honda that will go 400 miles on twelve gallons of gas.

$9 for a 200-mile fill-up vs. $30 for a 400-mile fill-up? Seems like a pretty good deal even if gasoline prices remain low, we never encounter another shortage and you don't install solar panels.