Design Review - Growatt SPF 5000 ES Grid Backup & Neutral Bonding

[??????]

In the current schematics, you guys are not disconnecting the input side of the AT, only disconnecting the loads from the AT.

Good idea - however I can't think of a way to auto-disconnect the AT when running off-grid that doesn't introduce the cold start problem - needing a human-in-the-loop to physically close the AT contactor to bootstrap the system. We could add this - but we'd have a system that needs an external power source (be it a human with a screwdriver, or a battery-backed-up servo or similar) to cold-start.

Also re: high current contactors, something like this 200A generac ATS may work, but it looks like it's just a glorified knife switch that's operated by two opposing solenoids. Correct me if I'm wrong since I don't have personal experience with an ATS like this, but if it's solenoid actuated in both directions of the throws, that means we'd need a power source to 'fail safe'. If this were mechanically (spring) fail-safe, then this would work. Maybe it is? Anybody know?

 

[automatikdonn]

Good idea - however I can't think of a way to auto-disconnect the AT when running off-grid that doesn't introduce the cold start problem - needing a human-in-the-loop to physically close the AT contactor to bootstrap the system. We could add this - but we'd have a system that needs an external power source (be it a human with a screwdriver, or a battery-backed-up servo or similar) to cold-start.

Also re: high current contactors, something like this 200A generac ATS may work, but it looks like it's just a glorified knife switch that's operated by two opposing solenoids. Correct me if I'm wrong since I don't have personal experience with an ATS like this, but if it's solenoid actuated in both directions of the throws, that means we'd need a power source to 'fail safe'. If this were mechanically (spring) fail-safe, then this would work. Maybe it is? Anybody know?

I think you are correct. I do not believe that switch defaults to a no load situation but I don't have any experience with that model. I know my critical circuits version of the generac switch did not have a requirement for power input to maintain a connection. Whichever side of the coils were energized is what it would flip to. Great for switching between POCO and genset, but IDK about usage for load failure disconnect.

 

[LeRoyK]

Good idea - however I can't think of a way to auto-disconnect the AT when running off-grid that doesn't introduce the cold start problem - needing a human-in-the-loop to physically close the AT contactor to bootstrap the system. We could add this - but we'd have a system that needs an external power source (be it a human with a screwdriver, or a battery-backed-up servo or similar) to cold-start.

Sometimes I feel we are overthinking all this, I don't think that the inverters with the build-in transformers have this much fault monitoring and disconnects build-in.

I am not trying to derail your safety circuits, just trying to keep things in perspective.
Where do we stop?

 

[automatikdonn]

Sometimes I feel we are overthinking all this, I don't think that the inverters with the build-in transformers have this much fault monitoring and disconnects build-in.

I am not trying to derail your safety circuits, just trying to keep things in perspective.
Where do we stop?

I think we stop at a Full BOM and a working circuit that keeps peoples houses from burning down. The requirements for that are pretty simple IMO. If the neutral leg fails, turn off the things. If the utility power is being passed through, don't bond the neutral leg to the ground in the downstream panel. There has been a lot of great content, and if all someone wants to do is switch off the system when the AT fails, then they are likely to be done. In the spirit of answering questions people ask to the fullest possible extent, I would say we are very close conceptually, but no solid BOM. For me getting in parts to even test our theories has been a whole thing and it's very frustrating because I have a complex of not wanting to wait.. I believe they call it impatience.

The thread may be useful for other things, but I think we are trying to get to the answer for the OP. "This seems to be a very popular setup, but I haven't found anybody who's cracked the DaVinci code of using a Growatt SPF 5000 ES with a SEAUTO-TX-5000 Auto-Transformer and using the AC input of the Growatt in a 'utility first' configuration."

 

[??????]

Sometimes I feel we are overthinking all this, I don't think that the inverters with the build-in transformers have this much fault monitoring and disconnects build-in.

I am not trying to derail your safety circuits, just trying to keep things in perspective.
Where do we stop?

I think we're at a pretty good solution for a single GW with #133 and can probably call it a day after conductor/conduit schedules and layout/BOM are nailed down. I think #133 can work for multiple GWs in parallel as well, provided you can limit your 120VAC loads to < 30A.

Re: going overboard on failsafes: I'm not sure exactly what failsafes SolarEdge bakes in, but I do think there's a lot of circuitry that can go overlooked because it resides on a PCB instead of in an electrical enclosure. I agree with you that this post may seem excessive at points, but as an example, I know we're missing the temp sensor portion of the AT (pg 68 of attached pdf, screenshotted below):



I've got access to a SE7.6kW with the StorEdge option, so I'll try to make some time to see how it's set up. If anybody else is in a similar situation and wants to compare notes, please do.

 

[lns]

What do y'all think about connecting the SolarEdge AT directly to a small breaker panel WITHOUT any breaker? Would the AT just lose neutral when the Growatt can't provide the 240V ? I just have a wellpump to run 240v and booster pump on 120v, water softener and some lights.

 

[automatikdonn]

What do y'all think about connecting the SolarEdge AT directly to a small breaker panel WITHOUT any breaker? Would the AT just lose neutral when the Growatt can't provide the 240V ? I just have a wellpump to run 240v and booster pump on 120v, water softener and some lights.

I wouldn't recommend connecting anything without a means of OCPD.

When the GW stops putting out 240V, it is correct that the AT would stop making a neutral leg from it. However the purpose in this discussion is to prevent the loss of the AT while the GW is still putting out 240V. The intent is to create a protection mechanism that is built into split phase unit's that this model GW does not have.

In the event your AT failed, your 120V loads would become very unhappy.

If you don't want to build these circuits, then you could massively lower your risk by just dropping in a second redundant AT. It's unlikely that even a single transformer is going to fail, and two failing at the same time is even more unlikely IMO. That doesn't mean they can't or won't, it just means that in my experience its very unlikely.

 

[automatikdonn]

Good idea - however I can't think of a way to auto-disconnect the AT when running off-grid that doesn't introduce the cold start problem - needing a human-in-the-loop to physically close the AT contactor to bootstrap the system. We could add this - but we'd have a system that needs an external power source (be it a human with a screwdriver, or a battery-backed-up servo or similar) to cold-start.

Also re: high current contactors, something like this 200A generac ATS may work, but it looks like it's just a glorified knife switch that's operated by two opposing solenoids. Correct me if I'm wrong since I don't have personal experience with an ATS like this, but if it's solenoid actuated in both directions of the throws, that means we'd need a power source to 'fail safe'. If this were mechanically (spring) fail-safe, then this would work. Maybe it is? Anybody know?

I kinda liked your cold start idea, so I ran with it this evening. I wanted to take the new contactors for a spin anyways. I guess its not such a bad thing to have a human in the path in case there is a failure. I would guess you would want to at least come check it out, but that not might be for everyone. The only time you should have to cold start is maintenance (which you are likely there for) and or a failure.

Should be done processing in the next 15 minutes or so...

For those who are interested, I made a video of a cold start circuit that uses the GW 240v output as a bootstrap. The rest is pretty much off the chart we have been working on this thread.

 

[automatikdonn]

In the current schematics, you guys are not disconnecting the input side of the AT, only disconnecting the loads from the AT.

I have a video demoing this to show it is completely possible and to be honest not such a bad idea.

 

[??????]

@automatikdonn - this looks great! Really cool that you're birddogging this effort with the real world setups to validate the schematics - thanks for taking all this time to share.

Feedback:

1. Cold-start with a 3-position switch is a great idea - but I think it can be simplified further. If you can manually actuate one (or more) of the coils of your three contactors, you could just manually close the contacts for the ~2s that the voltage protection relay would need to 'pick up' the 120V monitoring and take over the job of electrically holding the coils on those contactors. I'll noodle this idea this weekend - I think I have an idea to remotely simulate a manual push button for folks who may not have physical access (i.e. cabin in the woods)
2. I think there may be a significant design flaw here with placing the 240V AT feed on the same panel as the 120V loads. If you do have a faulty AT (let's say it puts out 195V on one leg), the bootstrap process would expose the loads on that '120V load panel' to this voltage - which is exactly what we're trying to avoid. I think we need to place the ATs upstream of the contactors at all times to avoid exposing any 120V loads to stray voltages even during bootstrapping.
3. I think the wiring you have on the three contactors exposes them to the imbalanced load breaking problem that @LeRoyK brought up in #129 and #130 - if we've got two switched phases (L1, L2) on the 3PDT contactors you're using, I think we're limited to a max of two contactors, each contactor switching 150A (50A x 3 poles). Each phase would be distributed across the three switched poles of each respective contactor. Unless we find different hardware I think that's our physical design limit.

 

[Desert_AIP]

I'm not understanding the desire for an unattended cold start (restart).
If there is a failure that causes one of these safety mechanisms to activate (deactivate), I would think you would want to require manual intervention to identify the cause of the failure before restoring power.

 

[??????]

I'm not understanding the desire for an unattended cold start (restart).
If there is a failure that causes one of these safety mechanisms to activate (deactivate), I would think you would want to require manual intervention to identify the cause of the failure before restoring power.

@Desert_AIP - the reason for potentially wanting an unattended cold start is because the system must be attended for a cold start even if the system is operating normally. It's arguable if the AT disconnect contactor is even needed (creating the cold start problem in the first place), since the AT is protected by the 30A CB on the inverter disconnect service panel. There's also the (untested) use case of the grid-to-offgrid transfer within the GW internal ATS. The manual says this is 10-30ms transfer time. That might be enough to lose the electric field in our contactor coils and force us into a cold start scenario to get our 120V load center back.

Here's my proposed solution to the cold start problem. This design (should):

• Disconnect L1/L2 input to the AT in the event the AT does not produce 120V +/- tolerance on its two legs
• Isolate the 120V load center from the cold start process (solves issue number 2 of #150)

But there's more - this proposed design can have the cold start contactor functionality extended with a few different options:

1. Attended (least risk, pictured in attached diagram): A plain-jane 2PDT HVAC contactor - the operator physically actuates the throws of the contactor (there's a button on the unit for this purpose) - no electricity required - to bootstrap the system from a cold start. Operator must be on-site.
2. Remote-attended (medium risk): A wifi switch that runs on the GW AC OUT 240VAC and actuates the coil of the cold start contactor. This would allow a remote operator to 'push the cold start button' from anywhere in the world via wifi/cellular/etc.
3. Fully autonomous (highest risk): A logic controller that effectively emulates the remote operator of #2 above. It attempts to bootstrap the system n number of times, and throws an error (optional) if bootstrapping fails. No operator required.

 

[Desert_AIP]

That makes a bit more sense.
I would think you would want a fail safe (require manual intervention) for a loss of neutral situation.

The other scenarios, switching, etc. autonomous.

I've used cascading relays before where you have to press a momentary button to "arm" the primary relay, and it's wired into a self latching configuration.
The primary relay's contacts then feed one side of the coil to a secondary relay that controls a load.
And then the switching of the load is controlled by the other input to the secondary coil.

The primary coil is dependent on some critical factor, and if that fails, the entire system shuts down and requires manual reset.
But as long as that critical factor is maintained, the load can be readily switched on and off.

You're using some of the same logic in your diagram.

If you wanted to auto restore a situation initiated by a lost neutral, you'd HAVE to verify the neutral was restored first.

 

[??????]

If you wanted to auto restore a situation initiated by a lost neutral, you'd HAVE to verify the neutral was restored first.

Yep - exactly right. If we wanted autonomous cold-start (option 3 of #152), the neutral verification is performed by the two over/under voltage protection relays - protecting the 120/240V load panel at all times. The only thing the cold-starting potentially risks is the AT, which is still protected by a 30A DP CB at all times. If anybody has transformer failure experience, that'd be valuable to have here for perspective.

We should keep in mind that the OP intent was to solve the David Poz problem of a trip of the 30A CB for the AT and losing a neutral due to that. I'd say #133 does that already, and #152 is possibly overkill. However, we don't monitor AT temp, which is something SolarEdge does do (#145), so maybe #152 isn't a bad idea, just-to-be-safe.

My personal opinion is that - if @automatikdonn can test the grid/offgrid ATS, and it holds the contactor coils (does not need a new cold-start), I'll probably implement #152 with option 1 (attended cold start). Grid going down for a period that wouldn't be supported by battery - and I wouldn't be present for - is very unlikely in my case, and the added AT safety is nice to have. People's use cases/risk tolerances may vary and they should implement accordingly.

 

[Desert_AIP]

I'm thankful for this thread and discussion. Relocating in a few months and want to install a system like this with a ground array.

 

[automatikdonn]

@automatikdonn - this looks great! Really cool that you're birddogging this effort with the real world setups to validate the schematics - thanks for taking all this time to share.

Feedback:

1. Cold-start with a 3-position switch is a great idea - but I think it can be simplified further. If you can manually actuate one (or more) of the coils of your three contactors, you could just manually close the contacts for the ~2s that the voltage protection relay would need to 'pick up' the 120V monitoring and take over the job of electrically holding the coils on those contactors. I'll noodle this idea this weekend - I think I have an idea to remotely simulate a manual push button for folks who may not have physical access (i.e. cabin in the woods)
2. I think there may be a significant design flaw here with placing the 240V AT feed on the same panel as the 120V loads. If you do have a faulty AT (let's say it puts out 195V on one leg), the bootstrap process would expose the loads on that '120V load panel' to this voltage - which is exactly what we're trying to avoid. I think we need to place the ATs upstream of the contactors at all times to avoid exposing any 120V loads to stray voltages even during bootstrapping.
3. I think the wiring you have on the three contactors exposes them to the imbalanced load breaking problem that @LeRoyK brought up in #129 and #130 - if we've got two switched phases (L1, L2) on the 3PDT contactors you're using, I think we're limited to a max of two contactors, each contactor switching 150A (50A x 3 poles). Each phase would be distributed across the three switched poles of each respective contactor. Unless we find different hardware I think that's our physical design limit.

1. Yea I was thinking a simple push button momentary switch would have worked really nicely, but I didn't have one. I would also like to wire in a green light so I know when the system is active. (mainly for the wife who may have to operated it from time to time). And sure a screwdriver works to active the contactor as well, I was just out of hands for my video.

2. You are 100% correct and there should only ever be 240V loads coming from this panel. There even needs to be a sticker if I am not mistaken that says "240V ONLY" . The single pole breakers in that box in the video were just there from the other panel I tore apart to make the new disconnect panel. I am terrible at misplacing things and if they are in the box they can't get lost. Anyone find my 10mm sockets, please send them my way.

3. The contactors I have are 50amp, so I would only be able to switch 100 Amp if I switched the hot legs over two contactors no? How does that work, I am not really picking up what you are putting down with this. Is each pole rated for 50Amp? I get the reasoning for doing it and it makes total sense to me. 99.999% of the time the system will only see a max load of 62.5 amps anyways, so we are really only talking about surge.

I think if I can wire this stuff up and show people it works and is safe, maybe they can trust the schematics and BOM a little more.

I can check on switching from grid / offgrid. I think these units are UPS fast at switching, so I think the timer on that 120v relay would never even notice. It would be nice to know for sure though.


I have also been thinking about the neutral auto bonding circuit and how it plays into portable genset usage. I have several portable gensets and not a one of them is floating neutral. I even made a video on how to hack the inverter gensets I have to make them floating... But with your auto bonding setup, you wouldn't really have to worry about it anymore and just run the generator like it was mains power (for those that have that use case).

 

[automatikdonn]

@Desert_AIP - the reason for potentially wanting an unattended cold start is because the system must be attended for a cold start even if the system is operating normally. It's arguable if the AT disconnect contactor is even needed (creating the cold start problem in the first place), since the AT is protected by the 30A CB on the inverter disconnect service panel. There's also the (untested) use case of the grid-to-offgrid transfer within the GW internal ATS. The manual says this is 10-30ms transfer time. That might be enough to lose the electric field in our contactor coils and force us into a cold start scenario to get our 120V load center back.

Here's my proposed solution to the cold start problem. This design (should):

• Disconnect L1/L2 input to the AT in the event the AT does not produce 120V +/- tolerance on its two legs
• Isolate the 120V load center from the cold start process (solves issue number 2 of #150)

But there's more - this proposed design can have the cold start contactor functionality extended with a few different options:

1. Attended (least risk, pictured in attached diagram): A plain-jane 2PDT HVAC contactor - the operator physically actuates the throws of the contactor (there's a button on the unit for this purpose) - no electricity required - to bootstrap the system from a cold start. Operator must be on-site.
2. Remote-attended (medium risk): A wifi switch that runs on the GW AC OUT 240VAC and actuates the coil of the cold start contactor. This would allow a remote operator to 'push the cold start button' from anywhere in the world via wifi/cellular/etc.
3. Fully autonomous (highest risk): A logic controller that effectively emulates the remote operator of #2 above. It attempts to bootstrap the system n number of times, and throws an error (optional) if bootstrapping fails. No operator required.View attachment 72980

For #3 I was trying to come up with a safe way to use the NC side of the contactor, but I couldn't crack it.

 

[automatikdonn]

I'm thankful for this thread and discussion. Relocating in a few months and want to install a system like this with a ground array.

Well I am running my 3k shop on this setup right now. If I could just get the 3 Phase to run off this too I would be set.

 

[??????]

Okay next iteration - this one is #152 with the following changes:

• Uses 120v coil N safety contactor instead of 240v coil contactor (50A 3-pole DIN-mount instead of 40A 2-pole non-DIN mount)
• Adds electrical momentary cold start switch

This (should) allow electrical actuation of the cold start relay with a momentary pushbutton (option 1 of #152). Note that the cold start relay must be a 240v coil since the only power source available, with the AT off, is the 240v from GW AC OUT. Also note that this momentary pushbutton could be replaced with a wifi switch to allow remote or autonomous cold starting (options 2 & 3 of #152).

One detail is that the cold start button must be at least a 2PDT switch, with one set of N/O and one set of N/C contacts. The N safety contactor coil is routed through the N/C contacts of this switch to avoid closing the N safety contactor during the cold start process (exposing the 120/240v load center to potentially out of tolerance voltage).

The cold start process should look like this:

• Cold start button pressed. N safety coil de-energized. Cold start coil energized. AT receives power and begins forming neutral.
• First over voltage protection relay sees L1/N 120v. 2s delay before N is forwarded to second over voltage protection relay.
• Second over voltage protection relay sees N/L2 120v. 2s delay before L2 is forwarded to the top side of the cold start switch. N safety contactor coil is not energized because its L2 is routed through the cold start switch, which is N/C (so at this point, it's open).
• Cold start switch button is released
  • Coils of cold start contactor change from being powered directly from L2 of the second voltage protection relay.
  • N safety contactor coils are powered from L2 of the second voltage protection relay via the N/C contact of the cold start switch.
  • System is fully functional (if both voltage protection relays pass tests)

So, in short:

• Push the cold start button
  • AT is immediately energized
• Wait 4 seconds
• Release the cold start button
  • Happy path (both 120v leg pass check):
    • N safety contactor should engage immediately afterward
  • Unhappy path (either 120v leg fails check):
    • AT will de-energize immediately after the cold start button is released
    • N safety contactor will never close, leaving 120/240 loads unpowered

 

[automatikdonn]

Yep - exactly right. If we wanted autonomous cold-start (option 3 of #152), the neutral verification is performed by the two over/under voltage protection relays - protecting the 120/240V load panel at all times. The only thing the cold-starting potentially risks is the AT, which is still protected by a 30A DP CB at all times. If anybody has transformer failure experience, that'd be valuable to have here for perspective.

We should keep in mind that the OP intent was to solve the David Poz problem of a trip of the 30A CB for the AT and losing a neutral due to that. I'd say #133 does that already, and #152 is possibly overkill. However, we don't monitor AT temp, which is something SolarEdge does do (#145), so maybe #152 isn't a bad idea, just-to-be-safe.

My personal opinion is that - if @automatikdonn can test the grid/offgrid ATS, and it holds the contactor coils (does not need a new cold-start), I'll probably implement #152 with option 1 (attended cold start). Grid going down for a period that wouldn't be supported by battery - and I wouldn't be present for - is very unlikely in my case, and the added AT safety is nice to have. People's use cases/risk tolerances may vary and they should implement accordingly.

It does NOT hold the contactor coils.. at all. Which gives me faith in the protection circuits, but bums me out because we still have a cold start issue.