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

[??????]

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.

I think option 3 of #152 is probably the move here if a fully autonomous system is the goal. This could be executed a couple different ways:

• Blind one-shot (less effort): tie an off-the-shelf timer in parallel to the coil of the N bonding contactor. Program this timer to perform a one-shot ~4-10s hold of the cold start momentary button in #152. This will execute a one-shot, blind cold-start of the system at the same time the neutral bonding contactor is energized (when the ATS goes on->off grid). This is relatively simple to implement and uses off the shelf parts, but has no monitoring, no remote control, and no retry capability.
• Monitored (more effort): use a microcontroller (arduino, esp32, whatever) to handle the cold start process. Big benefit of this is that we'd be able to read voltages, current, and most importantly AT internal temp during bootstrap and running states, and having a connected device with GPIO also opens the door to shipping logs/data, etc.

My opinion is that there's a reason there's a temp sensor in the AT, and right now we don't have any way to monitor it. I'd also put my money on a temp sensor + microcontroller being a safer cold start solution than a human because a) the temp sensor has access to data (internal winding temp) the human doesn't have, and b) the microcontroller can act on sensor inputs many times faster than a human can as well.

 

[automatikdonn]

I think option 3 of #152 is probably the move here if a fully autonomous system is the goal. This could be executed a couple different ways:

• Blind one-shot (less effort): tie an off-the-shelf timer in parallel to the coil of the N bonding contactor. Program this timer to perform a one-shot ~4-10s hold of the cold start momentary button in #152. This will execute a one-shot, blind cold-start of the system at the same time the neutral bonding contactor is energized (when the ATS goes on->off grid). This is relatively simple to implement and uses off the shelf parts, but has no monitoring, no remote control, and no retry capability.
• Monitored (more effort): use a microcontroller (arduino, esp32, whatever) to handle the cold start process. Big benefit of this is that we'd be able to read voltages, current, and most importantly AT internal temp during bootstrap and running states, and having a connected device with GPIO also opens the door to shipping logs/data, etc.

My opinion is that there's a reason there's a temp sensor in the AT, and right now we don't have any way to monitor it. I'd also put my money on a temp sensor + microcontroller being a safer cold start solution than a human because a) the temp sensor has access to data (internal winding temp) the human doesn't have, and b) the microcontroller can act on sensor inputs many times faster than a human can as well.

I have been testing all day on both genset and POCO power and it does not changeover fast enough at all to maintain the contactor connection.

We could also use the NC side of the contactor to charge the circuit, with a timer in the middle so it can't flip on and off too quickly.

 

[??????]

We could also use the NC side of the contactor to charge the circuit, with a timer in the middle so it can't flip on and off too quickly.

This is a good idea, but I think we're just straight up without power for ~30ms during the ATS transition. It's also worth noting that the ATS (according to the docs) takes longer as you add more inverters in parallel. It's possible this isn't an issue with a single inverter ?‍

 

[automatikdonn]

This is a good idea, but I think we're just straight up without power for ~30ms during the ATS transition. It's also worth noting that the ATS (according to the docs) takes longer as you add more inverters in parallel. It's possible this isn't an issue with a single inverter ?‍

Well it would at least get us back to an automated circuit that does cut off AT input because it's upstream of the AT.

I have a few safety concerns with this model however because we would also have to concern ourselves with the loads that would be switched.

I think a PLC or something of that sort (Arduino, Pi) provides the most safety with maintaining degrees for automation. However we are slinging that code because I am not so sure we could use something off the shelf. I only know python, so I would be using a PI.

I don't really want to make this take any longer than necessary, but also don't want to compromise on safety. I don't know how often a system would be switching between inputs, I know mine would likely only switch if there was a problem and I would be present for that anyway. I don't know how big of a deal it is for people to have to be around.

I think we should cut a v1 BOM with the associated caveats to explain the issues with the circuit. We could have two versions, one automated but with safety risks(low, but still a risk) and one that is super safe but needs an adult to operate.

I am just one voice, so what does everyone else think?

 

[LeRoyK]

What if we had an AT temp monitoring circuit that could disconnect AT input Power?
"Lost Neutral fault" would not disconnect AT Input, this would allow it to auto-reset after an ATS transition.
AT would be protected by OCP and Over-Temp protection.

What components do we need to build the AT Over-Temp Protection circuit? We could use a shunt trip circuit breaker as our disconnect instead of a contactor. this would simplify things, allowing the breaker to do both OCP and Over-Temp disconnect.

How do we trip the shunt with AT build-in temp sensor? Does anybody know if the build-in temp sensor is a thermocouple or an RTD? I think we need something like a signal conditioner.

Here is a list of components that I think might work. (Hopefully you guys have more experience with temp monitoring than I do.)

• GMCBU-2B-30 2pole 30A Breaker Tech Specs (Changed breaker to 30A 11/22/21 9:57AM)
• GMCBU-SH110-380VAC Shunt trip for Breaker Tech Specs
• SCU-3100 Signal Conditioner Tech Specs

 

[LeRoyK]

Scaling up with multiple inverters in parallel. I think the GW internal ATS will have the same imbalanced load problem during transfer as the Schneider inverters had #129. So I would recommend if you want to use the grid with multiple GW in parallel as backup, then build a complete external transfer switch with Grid voltage monitoring relay. Do not even connect AC IN to the inverters.

 

[automatikdonn]

What if we had an AT temp monitoring circuit that could disconnect AT input Power?
"Lost Neutral fault" would not disconnect AT Input, this would allow it to auto-reset after an ATS transition.
AT would be protected by OCP and Over-Temp protection.

What components do we need to build the AT Over-Temp Protection circuit? We could use a shunt trip circuit breaker as our disconnect instead of a contactor. this would simplify things, allowing the breaker to do both OCP and Over-Temp disconnect.

How do we trip the shunt with AT build-in temp sensor? Does anybody know if the build-in temp sensor is a thermocouple or an RTD? I think we need something like a signal conditioner.

Here is a list of components that I think might work. (Hopefully you guys have more experience with temp monitoring than I do.)

• GMCBU-2B-50 2pole 50A Breaker Tech Specs
• GMCBU-SH110-380VAC Shunt trip for Breaker Tech Specs
• SCU-3100 Signal Conditioner Tech Specs

Can you explain what a shunt trip breaker is? How does it work?
I have never heard of this before.

 

[automatikdonn]

Scaling up with multiple inverters in parallel. I think the GW internal ATS will have the same imbalanced load problem during transfer as the Schneider inverters had #129. So I would recommend if you want to use the grid with multiple GW in parallel as backup, then build a complete external transfer switch with Grid voltage monitoring relay. Do not even connect AC IN to the inverters.

I thought putting the legs on separate contactors resolves this issue.

 

[??????]

What if we had an AT temp monitoring circuit that could disconnect AT input Power?

I agree - the more I read about transformer failure, the more I see that the industry seems to use ferrite core temps as the single most important health metric for dry transformers like the AT we have here. The AT ships with temp sensing, and I pulled one apart to see that the leads are between the windings and the ferrite core - right where we want them.

Measured resistance of this probe is very low, effectively zero on my ohmmeter. Therefore, I do not believe it is an RTD. It is likely a K or T type thermocouple, and I'm led to believe it's a T type since neither conductor appears to be magnetic.

Re: system design, we're at a decision point:

• Standalone temp sensor (#165) - AT is held by twoconditions (below). This trades the cold-start challenge with the fact that the AT's power source is no longer conditionally monitored by its 120v legs:
  • Temp is below threshold
  • 30A DP OCPD feeding the AT is not tripped
• Integrated temp sensor (#159 with arduino) - AT is held by threeconditions (below). We need to implement either a timer (naieve) or arduino-esque (informed) automated method of cold-starting:
  • Temp is below threshold
  • 30A DP OCPD feeding the AT is not tripped
  • 120v +/- tolerance is held on both legs of the AT

In practice, we're likely to see high temps on our AT windings way before we ever 'lose a leg', so #165 is probably just as good as #159 + automated cold start, and it's zero dev work.

#159 + arduino/esp32/etc has some nice potential 'future-features' though:

• Remote access
• Logging (current, voltage, kWh, etc)
• Multiple transformer/inverter temp sensing through SPI bus
• Orchestration/peak shaving of priority loads on branch circuits during on/off grid states

 

[LeRoyK]

Can you explain what a shunt trip breaker is? How does it work?
I have never heard of this before.

A shunt trip device is an optional accessory in a circuit breaker that mechanically trips the breaker when power is applied to the shunt trip terminals. The power for the shunt trip does not come from within the breaker, so it must be supplied from an external source.

 

[automatikdonn]

A shunt trip device is an optional accessory in a circuit breaker that mechanically trips the breaker when power is applied to the shunt trip terminals. The power for the shunt trip does not come from within the breaker, so it must be supplied from an external source.

Any ideas how we could wire that up, as we are monitoring a loss of power. I am not doubting it will work, I just have zero experience with them.

 

[LeRoyK]

Any ideas how we could wire that up, as we are monitoring a loss of power. I am not doubting it will work, I just have zero experience with them.

monitoring a loss of power.
We are only monitoring the loss of Neutral and Disconnecting the Output (loads) from the AT.
AT Input will only be disconnected by Over-temp condition or OCP.
Loss of power during transfer will not cause Shunt trip Breaker to Trip.

how we could wire that up?

• Wire AT build-in temp sensor to SCU-3100 Signal Conditioner input
• Run 240V thru SCU-3100 Signal Conditioner Relay output to Shunt
  • How does it work? AT Temp is monitored by Signal Conditioner
  • If AT Temp goes above a preset alarm temp, then Signal Conditioner closes relay contact and puts power to Shunt to trip the breaker that feeds the AT.

 

[automatikdonn]

monitoring a loss of power.
We are only monitoring the loss of Neutral and Disconnecting the Output (loads) from the AT.
AT Input will only be disconnected by Over-temp condition or OCP.
Loss of power during transfer will not cause Shunt trip Breaker to Trip.

how we could wire that up?

• Wire AT build-in temp sensor to SCU-3100 Signal Conditioner input
• Run 240V thru SCU-3100 Signal Conditioner Relay output to Shunt
  • How does it work? AT Temp is monitored by Signal Conditioner
  • If AT Temp goes above a preset alarm temp, then Signal Conditioner closes relay contact and puts power to Shunt to trip the breaker that feeds the AT.

I see, so this would be for temp protection. I wasn't picking that up. It would be awesome if we could use a shunt trip breaker to also turn off GW output in the event of a neutral leg loss too.

 

[LeRoyK]

I see, so this would be for temp protection. I wasn't picking that up. It would be awesome if we could use a shunt trip breaker to also turn off GW output in the event of a neutral leg loss too.

Shunt trip breaker results in having to do a cold start.

We want to be able to auto-restart on "loss of neutral" because every time inverter transfers we will have a "loss of neutral".

 

[Jim Lee]

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."

I don't understand the utility first priority??? Don't most people that want an off grid converter that is grid tied because they want PV first then battery then grid then generator. Doesn't that cover all the bases. Power no matter what. I'm in the planning process and ready to purchase 30 - 295 watt panels. 2 x 6s2p and 1 x 3s2p. Each of the 3 string is wire to 1 of the 3 Growatt SPF 5000 ES inverter. 6 Li Fe EG4 Batteries connected to the inverters. The 3 inverters connected to a separate circuit box with a 50A breaker each. That breaker box set up with 1 or 2 (if safer) split phase Mid point transformers connected with 50A breakers. That breaker box is connected to my home main breaker box with a 60A or 100A breaker (not sure yet) connecting both circuit boxes. The Grid and my 19.5Kw Generac Generator pass through the 200A Transfer switch keeping the grid safe during grid outages is already installed. According to Signature Solar this is the system they want to sell me. You guys have me so worried I'm having trouble starting the whole project. Please explain to me why this won't work and what I need to do to make it work. I really don't want to burn my house down trying to improve it. Another question is when the grid goes down I think my generator will auto start even if I have PV or battery power. How could I control that. Any other suggestions would be appreciated, but please keep it simple if possible.

 

[automatikdonn]

I don't understand the utility first priority??? Don't most people that want an off grid converter that is grid tied because they want PV first then battery then grid then generator. Doesn't that cover all the bases. Power no matter what. I'm in the planning process and ready to purchase 30 - 295 watt panels. 2 x 6s2p and 1 x 3s2p. Each of the 3 string is wire to 1 of the 3 Growatt SPF 5000 ES inverter. 6 Li Fe EG4 Batteries connected to the inverters. The 3 inverters connected to a separate circuit box with a 50A breaker each. That breaker box set up with 1 or 2 (if safer) split phase Mid point transformers connected with 50A breakers. That breaker box is connected to my home main breaker box with a 60A or 100A breaker (not sure yet) connecting both circuit boxes. The Grid and my 19.5Kw Generac Generator pass through the 200A Transfer switch keeping the grid safe during grid outages is already installed. According to Signature Solar this is the system they want to sell me. You guys have me so worried I'm having trouble starting the whole project. Please explain to me why this won't work and what I need to do to make it work. I really don't want to burn my house down trying to improve it. Another question is when the grid goes down I think my generator will auto start even if I have PV or battery power. How could I control that. Any other suggestions would be appreciated, but please keep it simple if possible.

There is no reason to worry. Transformers are reliable technology. Get no less than 2 transformers for redundancy purposes.

The OP asked a question and we are trying our best to give a technical explanation, diagram and BOM for others to use that have this use case.

Your use case is likely to be more standard operating procedure.

Again, there is no reason to be scared or worry about midpoint transformer technology. There is a risk if you have only 1 that it could fail and leave you with a dangerous situation... So get two and sleep tight. If you want some extra protection, you could implement what is outlined in the thread. If not, there is a 99% chance you will turn this system on and never look back and be totally fine. I have not seen a single complaint of one of these failing and I have searched.

I hope this helps you and others feel safe about using these devices.

As for your other questions I would suggest starting a thread for a design review with your use case and stated goals. I think you will get a similar reaction from the community and IMO should be standard operating procedure. When my system is complete I plan to do a writeup on my goals and then post some photos so people can poke holes in my design. If we all help each other out, we can all end up with a very safe, very reliable system.

 

[automatikdonn]

Hey I did a mockup with one way to do the automated circuit and figured I would share

 

[Jim Lee]

There is no reason to worry. Transformers are reliable technology. Get no less than 2 transformers for redundancy purposes.

The OP asked a question and we are trying our best to give a technical explanation, diagram and BOM for others to use that have this use case.

Your use case is likely to be more standard operating procedure.

Again, there is no reason to be scared or worry about midpoint transformer technology. There is a risk if you have only 1 that it could fail and leave you with a dangerous situation... So get two and sleep tight. If you want some extra protection, you could implement what is outlined in the thread. If not, there is a 99% chance you will turn this system on and never look back and be totally fine. I have not seen a single complaint of one of these failing and I have searched.

I hope this helps you and others feel safe about using these devices.

As for your other questions I would suggest starting a thread for a design review with your use case and stated goals. I think you will get a similar reaction from the community and IMO should be standard operating procedure. When my system is complete I plan to do a writeup on my goals and then post some photos so people can poke holes in my design. If we all help each other out, we can all end up with a very safe, very reliable system.

Thanks, I already started a new thread called

SPF Growatt 5000 ES System. Design review and suggestions​

Please visit that thread. your input would be greatly valued.

 

[Jim Lee]

There is no reason to worry. Transformers are reliable technology. Get no less than 2 transformers for redundancy purposes.

The OP asked a question and we are trying our best to give a technical explanation, diagram and BOM for others to use that have this use case.

Your use case is likely to be more standard operating procedure.

Again, there is no reason to be scared or worry about midpoint transformer technology. There is a risk if you have only 1 that it could fail and leave you with a dangerous situation... So get two and sleep tight. If you want some extra protection, you could implement what is outlined in the thread. If not, there is a 99% chance you will turn this system on and never look back and be totally fine. I have not seen a single complaint of one of these failing and I have searched.

I hope this helps you and others feel safe about using these devices.

As for your other questions I would suggest starting a thread for a design review with your use case and stated goals. I think you will get a similar reaction from the community and IMO should be standard operating procedure. When my system is complete I plan to do a writeup on my goals and then post some photos so people can poke holes in my design. If we all help each other out, we can all end up with a very safe, very reliable system.

I did start one called

SPF Growatt 5000 ES System. Design review and suggestions​

please visit it and comment.

 

[??????]

Nice @automatikdonn - looks like #177 video is an implementation of the blind bootstrap method of #161 with clever use of the 2s delayed-on timer within the 240v (and 120v) over/under voltage protection device (for those who may not be familiar with that feature). Even though the delay-on feature of this circuit does cold-start the system, I'm really concerned that there is no stop/failure criteria. That 240v protection relay will continue to send voltage to your 240v loads panel even if the system fails to bootstrap. I think this could be improved by replacing the 240v protection relay with a simple timer board. I dunno about that specific timer board, but I've got a few of these and some of them have like 20+ different built-in functions with user configurable params, and I'm almost certain the blind bootstrap would be satisfied by one of them. Doing so would bound your error and permanently de-energize the AT if bootstrapping failed.

Here's an example of how it'd look, the way I'd do it:

• GW on-grid. 240v on AC OUT, AT powering 120v loads, all systems go.
• Grid failure. GW ATS transitions to off-grid. Temporary loss of 240v on GW AC OUT.
• GW AC OUT comes back online after a couple seconds. Timer circuit is energized by N/C poles of main 240v loads panel contactor (same circuit that powers your 240v over/under protection relay). Timer executes one-shot cold start logic (goes high for ~6s, then goes and stays low), ending the sequence on a logic low, and remaining there as long as it continues to receive 240v from GW AC OUT

This is the system I'd recommend to people who feel the unlikely risk of AT failure is offset by the benefit of a system that automatically starts. Anybody else, I'd recommend human-in-the-loop cold start only.

I personally know I won't be happy until I have the temp sensor of the AT instrumented, so I'm fixin to implement #159. I think this design scales to automated control most elegantly, and right now we have no way I can think of to read the AT thermocouple outside of a 3rd party temp controller or similar. I picked up a chip that converts K-type thermocouples to SPI bus readings. Gonna take some time to integrate to a NodeMCU/etc but if it works I'm happy to open source the code and process. I think this system beats the safety of even human-in-the-loop cold starting, and it's automated.