Switch EV Load using Contactor

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Tarmac

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Electrical Engineer
Residential client has a dedicated 90 Amp service that is currently being used exclusively to power two Tesla chargers. Tesla chargers draw maximum of 240V, 72A using 3-wire (L1, L2, ground).

I need to install a 240V, 68A steam generator that requires a 240V / 90 Amp dedicated circuit (L1, L2, ground). The steam generator has a separate control pad that is powered directly from the steam generator.

The steam generator is used 20 minutes a day and when it's in use, I need to cut power to the Tesla chargers.

Can I use a NC contactor in front of charger junction box to cut power to the Tesla chargers whenever the steam generator is in use? I'd be relying on the current to the steam generator cutting out the EV current before tripping the main breaker.

Here's a circuit drawing.

Thoughts on this approach?
 
First thought is, good luck finding a 70A contactor with NC contacts. They exist, but with all the supply chain issues going on, you may have to wait months to get one.

Can’t it be done manually? I would just put in a double throw safety switch. Up, to the chargers, down to the steam generator.
 
Thanks for your suggestion.

Client is pretty particular, so going to the garage before and after running steam generator isn't going to work. Also, if they forget to switch back after using steam room, their EV's won't be charging...
 
augie47 said:
You might check into this:

DCC-9 | Charge controller for electric vehicles | RVE

The DCC-9 is an Electric Vehicle Energy Management System that allows a charger to be connected directly to an electrical panel in multi-unit residential buildings.
rve-usa.com rve-usa.com
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Thanks augie47, this is a good tip.

It looks like their DCC-10 and DCC-12 products are targeted at the residential market. The only difference is the DCC-12 has a built-in breaker. Both products offer multiple models to handle increasing levels of current (30A, 40A, 50A or 60A).

However, using these charge controllers requires you to reduce the max current that each Tesla charger can draw. Whereas each Tesla charger can currently draw a peak of 72A from the 90A main supply, by adding one of these charge controllers in front of each charger, it reduces the maximum current that they can draw from 72A to 40A (see the 90A column in the chart below).

I'm going to reach out to the manufacturer to better understand why this is the case, as my client is very particular and I'm not confident that they'd accept a 44% reduction in peak charging time. The scenario is they are preparing for a road trip and need to quick-charge one of their vehicles which would now take 80% longer to do.

EV Charger Ratings.png
 
Joethemechanic said:
Money for two teslas and a steam generator, but doesn't want to spend "All that money" to install a 200 amp 120/240 single phase service
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It could very well end up there, but this will add an extra $20K for something that will only get used 20 minutes a day...
 
Joethemechanic said:
Money for two teslas and a steam generator, but doesn't want to spend "All that money" to install a 200 amp 120/240 single phase service
Click to expand...

While upgrading the service is the best, right answer, I think it’s funny that people assume Tesla owners are rolling in money. A new base model 3 can had for less than $30K after tax credit. The average new car is $48K.
 
retirede said:
While upgrading the service is the best, right answer, I think it’s funny that people assume Tesla owners are rolling in money. A new base model 3 can had for less than $30K after tax credit. The average new car is $48K.
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I don't know, maybe it's just me. Believe me I'm not anti-EV, but I can't stand Elon Musk, so maybe that colors my opinion on anything Tesla.

Out of curiosity, did they used to be more expensive? I remember looking at them about 8 years ago and they seemed expensive. I spent the money on real-estate instead
 
retirede said:
While upgrading the service is the best, right answer, I think it’s funny that people assume Tesla owners are rolling in money. A new base model 3 can had for less than $30K after tax credit. The average new car is $48K.
Click to expand...
While I appreciate the Tesla price, I still have no sympathy for people that buy one, or any other, and then want low end pricing to maintain it for optimal performance.
 
Joethemechanic said:
I don't know, maybe it's just me. Believe me I'm not anti-EV, but I can't stand Elon Musk, so maybe that colors my opinion on anything Tesla.

Out of curiosity, did they used to be more expensive? I remember looking at them about 8 years ago and they seemed expensive. I spent the money on real-estate instead
Click to expand...

I have no use for Elon, either.

Yes, 8 years ago, there was no model 3 or Y. The S and X were much more expensive. Tesla also dropped their prices by about $10K per car earlier this year.

Also - my number above is misleading….the sub-$30K price Tesla shows on their website includes $3000 in gas savings, so in reality, it’s about $33K. I can’t believe I fell for that!
 
Tarmac said:
Can I use a NC contactor in front of charger junction box to cut power to the Tesla chargers whenever the steam generator is in use? I'd be relying on the current to the steam generator cutting out the EV current before tripping the main breaker.
Click to expand...

Regarding the DCC-x charge controllers, they are targeted for residential main panels having diversity from many loads, each of which is each relatively small compared to the the main breaker rating. And so I suspect that the DCC controllers may be designed to handle loading that "creeps up" over a period of time. Therefore they may use some filtering and time averaging to keep from falsing on currents of relatively short duration. If so, it's possible that they might not repond quickly enough to shed a large load that suddenly exceeds the main breaker rating by a significant factor. This is only speculation, but if you're going to be communicating with the DCC vendor you may want to get clarification on how quickly their controller would respond in your application.

One possible approach would be to have an occupancy sensor near the steam room which could trigger the disconnection of the EV chargers before the user accesses the controller for the steam generator. That would prevent the main breaker from tripping. A timer could be used to keep the EV chargers disconnected for a time duration that would exceed the expected usage of the steam room with some margin. A current sensor could also be used to lengthen the duration of the charger disconnection if sometimes there was extended use of the steam room.

Even with the approach in your diagram, I think a timer would be helpful to ensure that the chargers remain disconnected when the temperature controller is turning on and off the heating elements in the steam generator during its operation.
 
synchro said:
Regarding the DCC-x charge controllers, they are targeted for residential main panels having diversity from many loads, each of which is each relatively small compared to the the main breaker rating. And so I suspect that the DCC controllers may be designed to handle loading that "creeps up" over a period of time. Therefore they may use some filtering and time averaging to keep from falsing on currents of relatively short duration. If so, it's possible that they might not repond quickly enough to shed a large load that suddenly exceeds the main breaker rating by a significant factor. This is only speculation, but if you're going to be communicating with the DCC vendor you may want to get clarification on how quickly their controller would respond in your application.

One possible approach would be to have an occupancy sensor near the steam room which could trigger the disconnection of the EV chargers before the user accesses the controller for the steam generator. That would prevent the main breaker from tripping. A timer could be used to keep the EV chargers disconnected for a time duration that would exceed the expected usage of the steam room with some margin. A current sensor could also be used to lengthen the duration of the charger disconnection if sometimes there was extended use of the steam room.

Even with the approach in your diagram, I think a timer would be helpful to ensure that the chargers remain disconnected when the temperature controller is turning on and off the heating elements in the steam generator during its operation.
Click to expand...

Thanks synchro, these are all excellent suggestions. Yes, I will ask the manufacturer to clarify whether they are a good fit for this scenario.
 
Switching off power to the charger is probably not the best way to accomplish the desired goal.

There are ways to tell the chargers or the car to draw less power for load balancing reasons.

You have 2 72A chargers on a 90A feeder. They already need to be communicating with each other to prevent overload.

Look up OCPP and the Charge HQ app.

Note: I have no direct experience with this and am leery of the security implications of the Charge HQ app. Just want to suggest an alternative approach before you re-invent the wheel.

Jon
 
You can always use a relay to reverse the logic, and use a normally open contactor. N/C contact on the relay would drop the contactor out when the relay is energized.
 
hillbilly1 said:
You can always use a relay to reverse the logic, and use a normally open contactor. N/C contact on the relay would drop the contactor out when the relay is energized.
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Yes, but…

Contactors, especially larger ones, will have a noticeable humming sound that many people dislike. If the contacts are held closed for the chargers, which will be most of the time, that hum might become an annoyance. So by using the NC contacts in the charger, then the NO contacts only for the steam generator, the contactor coil is only closed 20 minutes per day.
 
Jraef said:
Yes, but…

Contactors, especially larger ones, will have a noticeable humming sound that many people dislike. If the contacts are held closed for the chargers, which will be most of the time, that hum might become an annoyance. So by using the NC contacts in the charger, then the NO contacts only for the steam generator, the contactor coil is only closed 20 minutes per day.
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Yes, but just saying a N/O contactor would be easier to get. I agree, N/C would be ideal.
 
Jraef said:
Yes, but…

Contactors, especially larger ones, will have a noticeable humming sound that many people dislike. If the contacts are held closed for the chargers, which will be most of the time, that hum might become an annoyance. So by using the NC contacts in the charger, then the NO contacts only for the steam generator, the contactor coil is only closed 20 minutes per day.
Click to expand...
Just use a pair of mechanically latching contactors. No hum.
 
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