Generator support

[miimura]

So you have your Gateway CTs in your main panel. Does the house load still go thorough the Gateway transfer switch? How much of what you showed do you have? And why did you install it that way?

When my system was first installed, the Grid CTs were factory placed on the Gateway's switch. The system was oblivious to the large loads that were still located in the main panel. At first, I was not concerned because I never wanted the cars to charge from Powerwall stored energy anyway and that was before TBC was deployed. However, I am still planning to install one of the A/C compressors that was pre-plumbed and wired when the house was built 6 years ago. That usage definitely needs to be powered from the Powerwalls. So, I talked to the installer and they extended the wires from the Gateway's Neurio back into the main panel and placed the CTs on the conductors between the main breaker and the main panel bus. So, now it measures everything going to/from the meter.

The following loads are in my main panel and are not backed up.
- 50A EVSE - Leviton J1772
- 50A 14-50 Outlet - Tesla Gen2 Mobile Connector
- 50A range outlet (not used)
- 40A A/C #1 (not used)
- 40A A/C #2 (not used)
- 30A Clothes Dryer (not used)
120V circuits
- 20A Tile floor heater - Laundry room
- 20A Tile floor heater - Bath #2
- 20A Generator battery charge & grid sense (not used)

These loads were originally in the main panel but were moved to the Generation Panel so that they would be backed up.
- 20A Bathroom GFI
- 20A Laundry Room outlets
- 20A Bedroom #3 outlets (AFCI)

The two 20A 240V solar circuits were also relocated to the Generation Panel.

Everything else in my house was on a subpanel in the laundry room. That 125A breaker now goes to the Gateway, through the Gateway switch, and back to the main panel where it's connected to the wires that used to go in the 125A breaker to feed the subpanel.

 

[power.saver]

Okay, thanks for explaining that.

 

[fresnoboy]

Okay, here's my simple drawing of how to implement the slave switch. The power flow is the same as the one at the top of this thread posted by @shs1 except I show a main panel instead of "utility meter" and I'm showing the two poles L1/L2 instead of single line drawing. Obviously, neutrals and grounds are required but not shown.

View attachment 396690

The assumption is that the input on the slave switch is a Normally Open type. That switch will only close and pass power from the grid when there is power in the main panel and the Tesla Backup Gateway switch is closed. The relay in the slave switch is assumed to have a 120V coil. That is why a single hot line is shown connecting from the bottom of the Gateway switch to the slave switch input. The Powerwalls and solar inverters are connected to the Generation Panel. The breaker size in the main panel is an arbitrary size, but this setup only makes sense if you need more than the 200A the Tesla Backup Gateway switch can handle. I show both poles of the Tesla Backup Gateway connected because I assume that the voltage sense in the Gateway needs to see the grid voltage from both L1 and L2. I also assume that power from the generation panel to the Gateway is needed so that it can power the Gateway computer when the grid is down and synchronize the power waveform before reconnecting the grid. However, you cannot land that line on the bottom terminals of the Gateway switch like you normally would because you would have a circular circuit when the switches are closed. You would have to cut or disconnect the existing tiny wires that the Gateway uses to sense the voltage at the bottom of the switch and connect the wires coming from the generation panel.

Do not try to implement this without Tesla's blessing. I don't work for Tesla and there may be technical considerations that I am unaware of.

I think I am understanding what your are suggesting. You take the 15 amp circuit from the service panel, and have the gateway switch that. That generates a 240VAC output to the 2nd 400A ATS. That transfer switch feeds the generator ATS on the normal utility input connection, and then upon the signal from the gateway, opens the circuit from the utility feed, so the the generator input sees the powerwalls and solar. If that drops below the normal threshold voltage, the genset ATS switches to emergency and starts the genset.

The thing I am missing is how that feeds the transfer switch? The transfer switch switches inputs based on the utility feed. What you are describing looks more like a contactor (a big fat relay), rather than an automatic transfer switch.

Have folks here found an ATS that will switch on voltage being applied to a set of contacts?

thanks,
mike

 

[miimura]

I think I am understanding what your are suggesting. You take the 15 amp circuit from the service panel, and have the gateway switch that. That generates a 240VAC output to the 2nd 400A ATS. That transfer switch feeds the generator ATS on the normal utility input connection, and then upon the signal from the gateway, opens the circuit from the utility feed, so the the generator input sees the powerwalls and solar. If that drops below the normal threshold voltage, the genset ATS switches to emergency and starts the genset.

The thing I am missing is how that feeds the transfer switch? The transfer switch switches inputs based on the utility feed. What you are describing looks more like a contactor (a big fat relay), rather than an automatic transfer switch.

Have folks here found an ATS that will switch on voltage being applied to a set of contacts?

The switch in the Tesla Backup Gateway is basically an ON/OFF contactor. That is all the function you need to isolate the batteries from the grid when there is an outage.

An automatic transfer switch is basically an A/B switch. Of course, if you don't connect one of the inputs it still works like an ON/OFF switch. Also, if you want to use an ATS as your gateway slave switch, you can choose which input to use so that the logic is correct. When the power from the Tesla switch drops, you want the ATS switch to open, so you would still use the input marked Grid on the ATS to connect to the main panel. If you need both L1 & L2 for the ATS to sense when to switch properly, you can run both of them from the Tesla Gateway switch. One potential problem with using an ATS is that you need to minimize the delay for the switch to flip back to the grid when the Tesla Gateway switch closes again. The reason is that the Gateway is synchronizing the power waveform between the Powerwalls and the grid and if the switch doesn't act within a reasonable expected time, it may lead to some weird condition that Tesla didn't account for. A generator ATS has it own consideration for when and how to switch back to the grid.

 

[JohnRatsey]

They used to say "works in conjunction with a generator" also. I can't find that statement anymore.

Tesla's list of PW software updates includes:
October 2017

Version 1.9

Generator support with Automatic Transfer Switches (ATS)

 

[fresnoboy]

The switch in the Tesla Backup Gateway is basically an ON/OFF contactor. That is all the function you need to isolate the batteries from the grid when there is an outage.

An automatic transfer switch is basically an A/B switch. Of course, if you don't connect one of the inputs it still works like an ON/OFF switch. Also, if you want to use an ATS as your gateway slave switch, you can choose which input to use so that the logic is correct. When the power from the Tesla switch drops, you want the ATS switch to open, so you would still use the input marked Grid on the ATS to connect to the main panel. If you need both L1 & L2 for the ATS to sense when to switch properly, you can run both of them from the Tesla Gateway switch. One potential problem with using an ATS is that you need to minimize the delay for the switch to flip back to the grid when the Tesla Gateway switch closes again. The reason is that the Gateway is synchronizing the power waveform between the Powerwalls and the grid and if the switch doesn't act within a reasonable expected time, it may lead to some weird condition that Tesla didn't account for. A generator ATS has it own consideration for when and how to switch back to the grid.

Actually, it's not clear to me that this has to be that complicated. We could use a 2nd ATS switch inline with the main service panel, and when the Grid power goes away, it switches to emergency power, which is not connected to anything. The ATS can do this all by itself, it's just transferring the load to the emergency source, and you don't wire the generator start signal to anything, it doesn't need any signal from the gateway to tell it to do that.

When the grid comes back, it will then connect back to the primary grid connection, which will then immediately be sensed by the PW's and they will sync back up. If the PW's etc... were offline and the genset is running, that ATS switch will fail back to the primary, though usually it waits a few secs to make sure the grid power is stable, but that shouldn't matter if the loads are all switched. There is no need for the gateway switch to be in the loop at all, though feeding it it's own grid source would probably help with compatibility.

Would the current sensors need to be put on different circuits? Maybe you just put the current load sensors on the first ATS primary feeds, and the output sensors on the ATS switch and not even wire the gateways contactors at all?

Am I missing something?

JohnRatsey, that's an interesting software release note. Is there any documentation anywhere that describes what that means?

thx
mike

 

[miimura]

Am I missing something?

Yes. You don't want the switch closest to the grid to randomly reconnect the grid when the Powerwalls are powering the house. If they are out of phase, you will immediately overload the inverters, trip breakers, or damage something. With the Tesla Backup Gateway "in the loop" you will allow the Powerwalls to align the waveform before the grid is reconnected. An ATS connected to a generator should either shut down the generator first, or have a short period of no power before connecting the grid to avoid this issue.

 

[fresnoboy]

Yes. You don't want the switch closest to the grid to randomly reconnect the grid when the Powerwalls are powering the house. If they are out of phase, you will immediately overload the inverters, trip breakers, or damage something. With the Tesla Backup Gateway "in the loop" you will allow the Powerwalls to align the waveform before the grid is reconnected. An ATS connected to a generator should either shut down the generator first, or have a short period of no power before connecting the grid to avoid this issue.

I don't think the genset ATS is the issue. If it switches back it's because the grid is there for a few secs, at which point the PW's have either shut down or synced with the grid feed. Are you saying for the 2nd ATS, the one that is in front of the genset ATS. that has to have a delay of some secs before transitioning back to grid power? How long a delay? If it's a few ms, that's easily with a mechanical switch, esp a big one. How long does gateway take to shut down the inverters etc... before it adjusts to the grid showing up? It may be possible to program that ATS to have a multi-second programmed delay on switching back to utility power.

thanks,
mike

 

[PBBear]

Tesla's list of PW software updates includes:
October 2017

Version 1.9

Generator support with Automatic Transfer Switches (ATS)

Also, the telemetry from https://(PW IPv4 Address)/api/meters/aggregates includes a 'generator' section along with sections for site(grid), battery, load, solar, busway, and frequency reference - so there is clearly some planning and capability in place to support generators in future. Might be worth attaching another Neurio sensor unit and playing with.

 

[miimura]

I don't think the genset ATS is the issue. If it switches back it's because the grid is there for a few secs, at which point the PW's have either shut down or synced with the grid feed. Are you saying for the 2nd ATS, the one that is in front of the genset ATS. that has to have a delay of some secs before transitioning back to grid power? How long a delay? If it's a few ms, that's easily with a mechanical switch, esp a big one. How long does gateway take to shut down the inverters etc... before it adjusts to the grid showing up? It may be possible to program that ATS to have a multi-second programmed delay on switching back to utility power.

thanks,
mike

What I'm saying is that if you want to use a second ATS instead of the Tesla Backup Gateway's switch, it should be slaved to the switch as I showed up-thread. If you just let it do its own thing, it's liable to mess things up because when it does close, you are directly connecting the Powerwalls to the grid. If the Powerwall output is not in phase with the grid when that happens it will be bad. I don't know exactly how bad, but I would NEVER try it with my own equipment. In my observations, it takes 20-30 seconds for the Tesla Gateway to close the switch to return to grid interactive operation after the power is restored.

You can probably let the Genset ATS do whatever it wants because it is designed to work between a grid and a generator. It will cut off the loads and switch them between sources and likely doesn't make any effort to make it un-interruptible.

 

[fresnoboy]

What I'm saying is that if you want to use a second ATS instead of the Tesla Backup Gateway's switch, it should be slaved to the switch as I showed up-thread. If you just let it do its own thing, it's liable to mess things up because when it does close, you are directly connecting the Powerwalls to the grid. If the Powerwall output is not in phase with the grid when that happens it will be bad. I don't know exactly how bad, but I would NEVER try it with my own equipment. In my observations, it takes 20-30 seconds for the Tesla Gateway to close the switch to return to grid interactive operation after the power is restored.

You can probably let the Genset ATS do whatever it wants because it is designed to work between a grid and a generator. It will cut off the loads and switch them between sources and likely doesn't make any effort to make it un-interruptible.

Sorry if I am being stupid here. If we want to make the extra ATS slaved from the Tesla gateway instead of operating around it, there has to be an input to the ATS that commands it to do the transfer instead of it';s own controller deciding based on voltage or current sensing. I can't find the ability in any of the transfer switches I have seen to command the switch to transfer like a relay. So we have the input from the gateway, but no facility in the ATS to manually control switching (not uprising since there is a reason why the switch is an AUTOMATIC transfer switch).

Now on the other hand, You can set delays up to 60 minutes in the MPAC1500 controller in terms of returning from emergency power (in the prosthetic case - with nothing connected) to utility power.

I think what is supposed to happen in the normal case, when the grid comes back, the gateway senses the grid is back, but keeps the contactor open while it turns off the inverters etc.. . Then after they are off, it closes the contactor to connect the grid to the load, and then commands the inveters to go online and sync to the utility feed which has already been restored. Do I have that right?

In the case of the ATS switch waiting 5 minutes or so, the Tesla gateway will have turned everything off and synced to the 15 AMP service panel feed, so when the ATS connects the grid again, it should already be synced and ready to go.

But I guess there is another problem, because if the gateway has that 15 amp breaker, and the gateway connects that to generation panel that is connected directly to the load panel (via the normal generator ATS) , it will try and carry the full load through that 15 amp circuit, and trigger the breaker. Even if the ATS is somehow controlled by the gateway, there will be a sec or so of the switches being out of sync. which might cause the breaker to trigger.

Sigh, why doesn't Tesla just come out with a 400A gateway instead of making us try and find kludges.

thanks,
mike

 

[miimura]

Sorry if I am being stupid here. If we want to make the extra ATS slaved from the Tesla gateway instead of operating around it, there has to be an input to the ATS that commands it to do the transfer instead of it';s own controller deciding based on voltage or current sensing. I can't find the ability in any of the transfer switches I have seen to command the switch to transfer like a relay. So we have the input from the gateway, but no facility in the ATS to manually control switching (not uprising since there is a reason why the switch is an AUTOMATIC transfer switch).

I quickly looked through some of the Kohler documentation and it may be possible to use an "Aux Input" to command their switch directly. Honestly, they have a bewildering number of permutations of switches and controls. It may even be possible to buy one of their switches without controls and use it like a giant relay. I don't have time right now to look into it and find a product that will do that.

Now on the other hand, You can set delays up to 60 minutes in the MPAC1500 controller in terms of returning from emergency power (in the prosthetic case - with nothing connected) to utility power.

Another possibility is that the MPAC1500 has the ability to reconnect the grid seamlessly when it detects that it is in phase. I would have to read a bunch more of their documentation to see if it would work in this scheme without anything connected to the "Emergency" input.

I think what is supposed to happen in the normal case, when the grid comes back, the gateway senses the grid is back, but keeps the contactor open while it turns off the inverters etc.. . Then after they are off, it closes the contactor to connect the grid to the load, and then commands the inveters to go online and sync to the utility feed which has already been restored. Do I have that right?

If you're talking about the normal case with the Tesla Backup Gateway switch, it will keep the contactor open until it can bring the Powerwalls in phase with the grid, then it seamlessly connects the grid by closing the switch. At the time of the transition there is no load on the grid and the Powerwalls are supporting the load, so there is no current passing through the switch at the instant it closes. At no point does the Gateway turn anything off. After the switch closes, the Powerwalls should go into grid interactive mode from island mode.

Sigh, why doesn't Tesla just come out with a 400A gateway instead of making us try and find kludges.

Of course, it would be better if Tesla would provide the option of a 400A switch. They support up to 9 Powerwalls in one system which adds up to 270A of Powerwall breakers, so it would seem that 200A is really not enough to support that unless they only intend the larger systems to provide more runtime instead of more power handling.

 

[Vines]

Interesting thread. While I understand the concept, I think its better for an advanced DIY rather than something we would install. I'll wait for Tesla to enable generator functionality, though that may be a year or more.

No reason why with a huge, 10 Powerwall system plus PV you couldn't serve 400A of breakers (2x200 service panel) while the Powerwall has charge.

 

[miimura]

Interesting thread. While I understand the concept, I think its better for an advanced DIY rather than something we would install. I'll wait for Tesla to enable generator functionality, though that may be a year or more.

No reason why with a huge, 10 Powerwall system plus PV you couldn't serve 400A of breakers (2x200 service panel) while the Powerwall has charge.

Since you bring up 2x200 service (which I technically have even though one breaker is not installed), Tesla should support parallel installations as well. What I mean by this is having two Gateway switches, one on each 200A main breaker, with Powerwalls installed on each branch, but acting like one system. This is another way to avoid the 400A switch problem if you don't have a generator.

 

[fresnoboy]

Vines, the normal house power consumption should be relatively modest (all LED lighting, multisplit HVAC, etc..) But the way code requires you to size feeds, combined with the desire to support electric car charging (which normally happens after hours), it's easy to get above 200 Amps, which means you put in a 400A feed to PG&E and a service panel that size. Once you have that, you have to have a 400A transfer switch etc...

It's a lot easier to hit a 400A requirement than you might think, and for us 4 PW2s is probably the sweetspot to do everything we need if the car changing is designed to work while everyone is alseep, or not at all when on emergency power.

thanks,
mike

 

[Vines]

Vines, the normal house power consumption should be relatively modest (all LED lighting, multisplit HVAC, etc..) But the way code requires you to size feeds, combined with the desire to support electric car charging (which normally happens after hours), it's easy to get above 200 Amps, which means you put in a 400A feed to PG&E and a service panel that size. Once you have that, you have to have a 400A transfer switch etc...

It's a lot easier to hit a 400A requirement than you might think, and for us 4 PW2s is probably the sweetspot to do everything we need if the car changing is designed to work while everyone is alseep, or not at all when on emergency power.

thanks,
mike

Depends on your local AHJ, there's ways around most problems with enough effort and perhaps money. I do load calculations every day, so take my advice based on that.

 

[fresnoboy]

The switch in the Tesla Backup Gateway is basically an ON/OFF contactor. That is all the function you need to isolate the batteries from the grid when there is an outage.

An automatic transfer switch is basically an A/B switch. Of course, if you don't connect one of the inputs it still works like an ON/OFF switch. Also, if you want to use an ATS as your gateway slave switch, you can choose which input to use so that the logic is correct. When the power from the Tesla switch drops, you want the ATS switch to open, so you would still use the input marked Grid on the ATS to connect to the main panel. If you need both L1 & L2 for the ATS to sense when to switch properly, you can run both of them from the Tesla Gateway switch. One potential problem with using an ATS is that you need to minimize the delay for the switch to flip back to the grid when the Tesla Gateway switch closes again. The reason is that the Gateway is synchronizing the power waveform between the Powerwalls and the grid and if the switch doesn't act within a reasonable expected time, it may lead to some weird condition that Tesla didn't account for. A generator ATS has it own consideration for when and how to switch back to the grid.

So I am wondering now is this layout is possible with 2 MPAC 1500 controlled transfer switches in an easier way than I was thinking. The Kohler 1500 controller supports 3 source systems, for use with 2 generator systems. The first switch would be configured as the slave switch. When line power fails, the the first switch flips to emergency power, which is not connected to anything. That opens the ATS and isolates the grid. At that point the Tesla power wall and solar are connected and kick in. Even though the generator has no power being generated, I think I can keep it in the "Emergency" power setting even if no power is being generated, as that's a requirement for 3 source mode.


The 2nd transfer switch is then set to detect a power failure from the solar/PW system, and then transfer to generator power.

When the AC comes back online, the primary fails back, starting up the PW's and the solar, and then the generator will transfer back.

The Tesla gateway is connected to the service panel as you describe, but the isolation is all done by the first ATS which flips off the AC very quickly.

Does anyone see an issue with this?

Of course, I have no idea how Tesla and the utility engineers would ever sign off on something like this. If this works, how would I attempt to get the needed signoffs?

thanks,
mike

 

[darrelld]

I am having Tesla 7.5kw solar panels and 2 Powerwalls installed and would like to integrate this with my 20kw Generac and whole house ATS. Right now in the permitting phase. Only drawings from Tesla so far are solar panel placement. Tesla was informed of the generator and pictures sent of the Generac ATS next to the meter.

Any one have a similar setup installed and in operation? Any suggestion you like to share?

 

[shs1]

I have an 18 kW Kohler generator installed with my now 2 Powerwall 2s. I had the generator for years before I got the PW2s, and wanted to keep it as a backup to the PW2s. I am really glad I did. Tesla resisted at first but allowed the installation as long as the PW2 and generator would never "see" each other. There is a thread on this that I started several years ago, but see diagram here. You should also review the previous posts in this thread.

 

[darrelld]

View attachment 513095 I have an 18 kW Kohler generator installed with my now 2 Powerwall 2s. I had the generator for years before I got the PW2s, and wanted to keep it as a backup to the PW2s. I am really glad I did. Tesla resisted at first but allowed the installation as long as the PW2 and generator would never "see" each other. There is a thread on this that I started several years ago, but see diagram here. You should also review the previous posts in this thread.

Thanks, I found this link most useful.
Combining Systems | Powerwall Support
Do the powerwalls handle a central ac ok. I hope to power a 4 ton 16seer off the powerwalls.