Switch EV Load using Contactor

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winnie said:
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
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Thanks Jon. It's a creative suggestion, but I don't think it would work too well in practice. Each time you want to use the steamer, you'd need to launch the app and turn off vehicle charging for both vehicles (and reverse the process after completion). And if you forgot to do this and turned on the steamer, it would trip the main breaker.

Your suggestion did motivate me to explore using the Tesla charger's communication interface which as you say is used for load balancing. I did find an approach that uses a raspberry pi single-board computer to control the available power to the Tesla chargers. Here's the video:

Using this method, I sketched out a possible approach for my specific use-case (see attached diagram). I'm not sure what the implications would be here for passing electrical inspection from the local authority.
 

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My personal opinion is you are better off getting the service size you really need but if economics are such that you can't do that I would be inclined to get myself three big contractors. One for the steam generator and one for each of the battery chargers. You could have a switch near the steam generator to select either the steam generator or the battery chargers.

As someone mentioned if the potential hum were to bother the homeowner getting a contactor with a latching mechanism on it could solve that problem.

To be candid none of this is going to be real cheap anyway.

Is there any possibility that there is an enable input available on the chargers? That would be a whole lot cheaper to implement.
 
Tarmac said:
Thanks Jon. It's a creative suggestion, but I don't think it would work too well in practice. Each time you want to use the steamer, you'd need to launch the app and turn off vehicle charging for both vehicles (and reverse the process after completion). And if you forgot to do this and turned on the steamer, it would trip the main breaker.

Your suggestion did motivate me to explore using the Tesla charger's communication interface which as you say is used for load balancing. I did find an approach that uses a raspberry pi single-board computer to control the available power to the Tesla chargers. Here's the video:

Using this method, I sketched out a possible approach for my specific use-case (see attached diagram). I'm not sure what the implications would be here for passing electrical inspection from the local authority.
Click to expand...
Fixed an error on the diagram...
 

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petersonra said:
My personal opinion is you are better off getting the service size you really need but if economics are such that you can't do that I would be inclined to get myself three big contractors. One for the steam generator and one for each of the battery chargers. You could have a switch near the steam generator to select either the steam generator or the battery chargers.

As someone mentioned if the potential hum were to bother the homeowner getting a contactor with a latching mechanism on it could solve that problem.

To be candid none of this is going to be real cheap anyway.

Is there any possibility that there is an enable input available on the chargers? That would be a whole lot cheaper to implement.
Click to expand...
You would think the manufacturers would start putting a hardwire enable input on the controllers. It would make it so much easier to do load shedding/prioritization.
 
I think you should incorporate a couple of Tesla Powerwalls into this contraption. The guy likes Tesla, and you could probably mark them up a bit.

How long do people stay in a steam bath anyway? Personally I can't understand why anyone would want to be in a hot and humid place on purpose.
 
Joethemechanic said:
I think you should incorporate a couple of Tesla Powerwalls into this contraption. The guy likes Tesla, and you could probably mark them up a bit.

How long do people stay in a steam bath anyway? Personally I can't understand why anyone would want to be in a hot and humid place on purpose.
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Powerwall is good idea, but it's outside the scope of this project. When you turn on the steamer, you can set the timer from 10 - 20 minutes. So, similar to turning on the hot tub jets.
 
LarryFine said:
Are there any chargers with a disable input?
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No, there is no simple disable input.

Apart from the L1/L2/G power terminals, the only other terminals are used for communication between multiple power chargers for load sharing purposes. The communication block uses RS-485 signalling (see the youtube video) which is discussed in that youtube video that posted earlier in this thread...
 

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Tarmac said:
Powerwall is good idea, but it's outside the scope of this project. When you turn on the steamer, you can set the timer from 10 - 20 minutes. So, similar to turning on the hot tub jets.
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So the original plan was to just sense voltage at the heating elements and use it to open a NC contactor controlling the chargers? Didn't @hillbilly1 or somebody mention using a NO contactor with a reversing relay in the control circuit?
 
Tarmac said:
Using this method, I sketched out a possible approach for my specific use-case (see attached diagram). I'm not sure what the implications would be here for passing electrical inspection from the local authority.
Click to expand...

I would not do anything to modify these chargers. Apparently 72A chargers are no longer available from Tesla, so if you break anything you will be particularly stuck.

Anything you do has to be sold to the customer as an improvement, not a workaround.

I personally believe that load balancing is a better approach for this application than a feeder upgrade, but the feeder upgrade is a well understood solution; everything else is inventing.

Clearly the desired functionality is available 'in principle'. The ChargeHQ account can be set to adjust charging rate based on available PV excess. This could easily be used to limit charge rate based on available feeder capacity.

Again, I'm not sure that I trust the ChargeHQ cloud model, but it is very clear that a programmer with the correct information from Tesla could write a simple app that reads the status of the steam generator and limits the charge rate.

Jon
 
winnie said:
I would not do anything to modify these chargers. Apparently 72A chargers are no longer available from Tesla, so if you break anything you will be particularly stuck.

Anything you do has to be sold to the customer as an improvement, not a workaround.

I personally believe that load balancing is a better approach for this application than a feeder upgrade, but the feeder upgrade is a well understood solution; everything else is inventing.

Clearly the desired functionality is available 'in principle'. The ChargeHQ account can be set to adjust charging rate based on available PV excess. This could easily be used to limit charge rate based on available feeder capacity.

Again, I'm not sure that I trust the ChargeHQ cloud model, but it is very clear that a programmer with the correct information from Tesla could write a simple app that reads the status of the steam generator and limits the charge rate.

Jon
Click to expand...

Digging a little deeper into ChargeHQ... Tesla Wall Chargers are not supported since they don't support the Open Charge Point Protocol. That's unfortunate because this would indeed be a way to control the wall charger so they don't supply current to EVs (and draw current from the main) when the steamer is switched on. ChargeHQ does have a Tesla-specific workaround by controlling Tesla EVs themselves and how much current demand they place on the wall charger.

Charge HQ's cloud APIs are quite limited and allow your home's solar power generation to publish a continuous stream of power generation measurements over time. The idea is that ChargeHQ can use this API to monitor your home's solar power generation in order to ensure you are only charging your EVs when there is excess solar power (ie. free charging). So, you could use this same cloud API to trick your EVs into not drawing any current by pretending that you are not generating any solar power whenever the steam generator is turned on.

However, this introduces a lot of fragility into the power management process as it now relies on the concurrent availability of several services (i.e. steamer on/off switch connection to the internet => Charge HQ cloud service => Tesla vehicle connection the Internet). So, if any one of these services go down while the steamer is in use, it will trip the main breaker.

Also, if you have any overnight guests who need to charge their EVs then ChargeHQ won't be configured to control their power demand. So if they are plugged in when you turn on the steam generator, it will once again trip the main breaker.
 
Perhaps it would be possible to use one of the Leviton 2nd generation smart breakers to turn the power to the chargers off and on.
 
I see what you mean. Since I was just looking at ChargeHQ for 'proof of concept' I didn't look too deeply at it.

The software doesn't control the chargers, rather it is controlling the cars to reduce current drawn. On top of this using ChargeHQ would require everything to move across the cloud. While the existence of ChargeHQ demonstrates that this could work in concept, I agree that it isn't a practicable solution.

IMHO as this discussion has progressed, I concur with others that the 'upgrade the service' is the best approach.

Not the most elegant approach; when you have short transient loads IMHO automatic load balancing is a much better solution. But given the constraints of the 'wall connectors' requiring hacking to make it do what you want, the available tools to control the car being cloud based, and the customer being very 'particular', I don't think trying the build anything to do the elegant job would be worth the hassle.

Some customers want elegant; they want to be cutting edge and want efficiency. For that sort of customer I'd say replace the chargers with 'Open EVSE' units that already have load balancing control capabilities built in, and hire a programmer to integrate them with a home energy monitor system. Have the system default to slow charging the batteries, and give the customer a 'quick charge' button, and explain that the batteries will be happier charging more slowly when they don't need a quick charge. The customer will need to think more, but they will be smug putting that extra effort in for the improved efficiency.

It sounds like your customer wants to have their systems just work without thinking about it. They want their car to always charge as quickly as possible (so that they can go on a road trip at a moment's notice) and want to be able to take their shower when they want to take their shower.

Yes, I think you could build the system you opened the thread with; having some sort of control or sensor so that when the steam generator is turned on the power to the chargers gets interrupted. IMHO the hum issue is real but you can deal with that by using proper carpentry; simply make sure that the sound gets isolated from the customer. But now you are building the hardware and will be stuck maintaining it for a 'particular' customer. (See above about customers who want 'elegant'.) To be most price efficient about this, I'd look to see if there are automatic transfer switches which can be used 'in reverse' to select between loads rather than between sources.

-Jon
 
Barbqranch said:
Perhaps it would be possible to use one of the Leviton 2nd generation smart breakers to turn the power to the chargers off and on.
Click to expand...

I looked at that. I think they are only available up to 60A, and would require a panel change.

But it looks like the Leviton system is building the smarts for the load shedding/balancing right into the panel. Gotta wonder how much their system also depends upon a cloud connection.

-Jon
 
Given the further information supplied by the OP in later posts I suggest the following.

The timer that controls the steam generator may have a NC contact on it that could be used to control contactors that power the chargers. That way anytime the timer is allowing the steam generator to operator the chargers would be off. This is about as simple as it gets.

If the timer does not have an NC contact on it, a relay could be added to get one.
 
petersonra said:
Given the further information supplied by the OP in later posts I suggest the following.

The timer that controls the steam generator may have a NC contact on it that could be used to control contactors that power the chargers. That way anytime the timer is allowing the steam generator to operator the chargers would be off. This is about as simple as it gets.

If the timer does not have an NC contact on it, a relay could be added to get one.
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The control pad gets installed in the same room as the steam generator and is essentially a thermostat with built-in temperature sensor and a timer. It has a ribbon cable that terminates to a male RJ12 connector that in turn plugs into the steam generator. So your suggestion of using whatever control signal is being used over this ribbon cable to control the contactor on the steam generator can also act as the control for the contactor to control power to the EV chargers makes total sense. Thanks for the suggestion!
 
synchro said:
To avoid a buzzing noise from a contactor, you might use one with a DC coil like those listed here:

https://www.mouser.com/datasheet/2/16/contactor7-2307566.pdf

Of course you'd have to contact Mouser or another supplier for availability.
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This is a good suggestion to reduce the buzzing sound. However, this contactor like most others is normally open, and as others have suggested, it's much more difficult to find NC contactors without placing a custom order with a long lead-time.

As an alternative, it looks like solid-state, high-current, NC relays are much more readily available. They operate silently, have rapid turn-off time (I'm guessing faster than the steamer's contactor) and a very long operating life. Crydom appears to be the major vendor in this category and it looks like their parts are both UL and CSA certified. There is also decent inventory at Mouser. Not sure if anyone has worked with solid-state relays and sees any downsides with this approach.


 
It would probably cost ~$1000 but have you looked at a motorized changeover switch? ABB and Socomec make them.
 
Wouldn't a contactor with NC contacts, changeover or reversing contactor even a transfer switch, any those with probably a 100 amp rating needed cost enough that you maybe just consider upgrading service to 200 amps?
 
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