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100 Amp and 50 Amp Service in my garage. Overkill?

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Tip 1.: we have one of our 14-50 outlets on the opposite wall of the garage to the HPWC; that we we can charge both cars without juggling parking spaces plus it helps out visitors.

Tip 2.: we let the Roadster charge when it's plugged in and charge the Model S on the timer when I know the Roadster is (always) finished. We have enough service to manage both simultaneously but charging the S at 3.00am (that it's regular time) means we also have no conflict with dishwasher, washing machines etc and the least amount of conflict with the air conditioning.

Tip 3.: we store waste paper/recycling stuff etc in the garage until collection day. It's best to make sure it's well away from any charging source so that, in the unlikely event cables overheat, there's no flammable materials around.
 
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I have an 80 Amp HPWC, as well as two 14-50's in my garage. It's not overkill.

For day to day driving, I like to set the current to 57 Amps (80/sqrt[2]). That puts 1/2 the resistive heating on many components, including the charging modules in the cars. In addition, it has the side benefit of using both charging modules in the car on a regular basis, so you can detect a failure. Even though both modules are in use, because electronic component failure rate is exponential with temperature, running both modules at lower temperature should reduce total failure rate.
 
I have an 80 Amp HPWC, as well as two 14-50's in my garage. It's not overkill.

For day to day driving, I like to set the current to 57 Amps (80/sqrt[2]). That puts 1/2 the resistive heating on many components, including the charging modules in the cars. In addition, it has the side benefit of using both charging modules in the car on a regular basis, so you can detect a failure. Even though both modules are in use, because electronic component failure rate is exponential with temperature, running both modules at lower temperature should reduce total failure rate.

Funny, I chose 55-60A for the exact same reasons, but w/o a specific equation to guide me. Now I know it was a good choice! I definitely wanted to exercise the 2nd onboard charger on a regular basis and I hoped that they would evenly split the load. I do occasionally use the full 80A (or in my case, it usually delivers 79A).
 
Funny, I chose 55-60A for the exact same reasons, but w/o a specific equation to guide me. Now I know it was a good choice! I definitely wanted to exercise the 2nd onboard charger on a regular basis and I hoped that they would evenly split the load. I do occasionally use the full 80A (or in my case, it usually delivers 79A).

Great minds run in the same gutter... :wink:

A lot of the numerical displays in the MS are truncated instead of rounded. I have seen the 79 Amp number a lot also. My guess is that it is often 79.9 Amps, displayed as 79 Amps.
 
Ah, so the EVSE draws 80A, but only 79A makes it to the car? Actually that doesn't seem possible. You might see a voltage drop, but not a current drop. That would imply current is leaking out somewhere, which shouldn't be a design feature :)
 
Anything worth doing... is worth overdoing. :cool:

I think the flexibility is a great idea.... especially when you consider that the cost is minimal while you have all the panels open and are already running wire through conduit, etc... might as well plan for unanticipated future needs while you are at it.

Nice installation... and congrats on the car. You'll love it.
 
Ah, so the EVSE draws 80A, but only 79A makes it to the car? Actually that doesn't seem possible. You might see a voltage drop, but not a current drop. That would imply current is leaking out somewhere, which shouldn't be a design feature :)

No, that's not what they were saying. I asked whether it was a rounding vs. truncation error and was told that the car's chargers are specifically drawing only 79A while charging, and it was necessary to assure they kept the total load under 80A when they considered the EVSE overhead for the contactor and its power electronics.

My clamp meter shows 82-83A anyway when I'm at 79A charging, but that's within the tolerances of my clamp meter.
 
Ah, so the EVSE draws 80A, but only 79A makes it to the car? Actually that doesn't seem possible. You might see a voltage drop, but not a current drop. That would imply current is leaking out somewhere, which shouldn't be a design feature :)

Actually it is possible, and it was designed that way. The car and much of the EVSE control circuit are wired effectively in parallel. Suppose the EVSE power supply, contactor, and control circuit board with multiple sensors uses 1A, that leaves only 79 for your car. A couple of things in the EVSE like the large fuses and contactor will reduce voltage slightly and don't require a reduction of amps consumed by the car.

What surprises me is the significant vampire load that the HPWC consumes. I remember testing one of their early units once and it was about 100W when the car was charging! Even when it wasn't charging and the contactor was open it still consumed an embarrassing amount of power.
 
If you look inside a Clipper Creek EVSE, the circuit card is powered by a brick with a power draw on the order of a few watts. This isn't even a rounding error on the 19.2 kW you could draw at 80A, 240V.

There's no way any conceivable EVSE could draw 1A at 240V - that would be 240W. The thing would heat up like an oven inside. In the extremely unlikely event that the EVSE drew that much power, it would most certainly be designed with a pilot signal of 79A.

I think Tesla should simply draw the power that the EVSE reports.
 
If you look inside a Clipper Creek EVSE, the circuit card is powered by a brick with a power draw on the order of a few watts. This isn't even a rounding error on the 19.2 kW you could draw at 80A, 240V.

There's no way any conceivable EVSE could draw 1A at 240V - that would be 240W. The thing would heat up like an oven inside. In the extremely unlikely event that the EVSE drew that much power, it would most certainly be designed with a pilot signal of 79A.

I think Tesla should simply draw the power that the EVSE reports.

We really don't know how close / granular it comes. It may be 79.9A with truncated value, it may be 79A with only 1A granularity. The answer I received spoke of overhead and tolerance in a very simple answer.

I can understand if they wanted to be conservative - even 80.1A > 80A, technically, as miniscule as that overhead is, and the J1772 spec doesn't allow them to vary duty-cycle to 1A increment. So they have to build in a tolerance and reduce slightly. Hopefully it's more granular than just 1A and we're not seeing a whole amp wasted, but we just don't know - my meter doesn't have the tolerances required to confirm.
 
When I ordered the Schedule EV service from Virginia Dominion Power which provides a separate metered connection for EVSE's, I asked them to increase the standard 100A service to 200A. They did some calculations and was fine with it. So now I have 600A to the house and 200A to the garage. I did this so that I could have 2 x HWPC at full power or downgrade the 2 x HWPC and add a 30A J1772 also for 3 x EVs.

I'm on Dominion's whole house EV plan but am considering running a new feed to the garage to support a second 80A HPWC. How much did it cost you to run the 200A service? Underground or overhead?
 
I'm on Dominion's whole house EV plan but am considering running a new feed to the garage to support a second 80A HPWC. How much did it cost you to run the 200A service? Underground or overhead?

My entire install was going to be pricey, one way or another. About 100' of run to the garage, no matter what I installed. My county inspector required that the disconnect of the separate meter be located in the same location as my other panels, so I had to pay for that extra run too. So this was in conduit attached to the outside of the house in the back, then into a 200A panel in the garage. Then about another 50' to go from the panel to the HPWC. The incremental cost from going from 100A to 200A was probably $300. The total w/o HPWC was somewhere around $2750.