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

?????? said:
Okay I overhauled the wiring schematic a bit. In retrospect, I am not confident that designs #133 and #159 would clear ground faults while in on-grid mode. This should resolve that issue, as well as incorporate additional functionalty.

Changelog:
  • Adds temp monitoring to AT
    • Through K-type thermocouple (continuous measurement) - pictured
    • Through OEM switching PTC thermistor (?) - not pictured, optional via NodeMCU ADC
  • Ties 120/240V Load Panel neutral permanently to Main Service Panel neutral, eliminating need for G/N bonding contactor (StorEdge wiring method)
  • Removes physical cold start push button
  • Adds AT neutral current, L1/N, and power factor sensor
  • Adds conductor/conduit labels for wiring schematic/BOM
  • Changes dry contact signal from 240VAC sensing to 3vDC sensing (logic level)

View attachment 76400

The most important thing this changes is it gives the ability to log sensor data, detect trends, and throw alarms at more conservative values. Since we are now in control of all contactors within the system via software, we can do things like:
  • Attended, remotely attended (via wifi/internet), or unattended cold start
  • Controlling the switchover time of the cold start (how long we want to wait after we stabilize the AT before we allow 120V to our loads panel via the lost N safety contactor)
  • Disconnecting power to the AT, the loads panel, or both - contingent on any combination of software-configurable measured conditions, such as:
    • Over neutral current
    • Power factor
    • Over/under voltage
    • Over/under temp (either via built-in AT thermistor (?), K-type thermocouple, or both)
Things about this design I'd like to improve:
  • Low voltage (3/5/12VDC Arduino/NodeMCU) components are in the same enclosure as high voltage (120/240VAC) components and may be at risk of EMI
  • Thermocouple sensor lines 3.5 and 3.6 are run in the same conduit as L1/L2/N for the AT. Although the sensor cable is shielded, I am not sure if this will affect readings.
  • PZEM-004T current sensor has a 1s response time. It's suitable for slower moving trends, but not fast enough to catch over/under voltage conditions (the SVP-912 is 0.1s, in comparison). If we had a sensor with a faster response time, we could get rid of the 2qty SVP-912 devices entirely and control everything with the NodeMCU
Click to expand...
I'm unclear what this complex arrangement is seeking to achieve. Is all this just to alleviate a lost neutral in case of a thermal shut off, or otherwise disconnected autotransformer? Seems like a LOT of parts to potentially fail. If you install an autotransformer and monitor it for a week, it seems to me you'll know the average imbalance and associated heating incurred in normal use. If it goes higher than desired at any point, maybe rebalance the L1/L2 affected loads a little better for that time period to move the higher loads to the other side. And I doubt loads "up the line" are going to affect your installation's neutral current. Not sure you really want to be placing your inverter's neutral in common with the grid's neutral anyway? It would only be the adjacent neighbors using the same small transformer anyway (mine for example has none). I don't plan to have the utility's neutral connected to my house except when the system is bypassed.

Is this about fault current, or tripping a breaker upstream on ground fault? I haven't spent as much time studying all the concerns you guys have here that brought you to this point, but this all seems like major overkill. Maybe I'm missing something. The biggest fault to be concerned about in my opinion, is when the inverter fails, and shorts its input terminals to ground. Why would the incoming breaker not trip?

If you're that worried about an overheated transformer, like I said, I'd rebalance the loads. What 120v load do you have in a house that will place 30A or more on the panel's neutral in imbalance at any given time? On average it shouldn't happen much if balanced in the first place. If it's that large it probably should be 240V anyway.
Secondly, what I'd do is install another adjacent transformer (they're pretty cheap on Ebay, check the black enclosure ones, under $100 I believe) and have it switched into the circuit substituting the first, in case of overtemp. Involves nothing but a 30A or so relay switched by temp. That's 2 transformers sharing the responsibility in case one gets too hot. I still think that's overkill.

Just my thoughts.
 
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Yes, as we add complexity, we also add failure points. I have a friend who is a mechanical engineer and designs door latches and other new products. When he designs a new product or design, there is always FMEA done. https://asq.org/quality-resources/fmea

This is why the KISS method has stood the test of time.
 
Cornwallav8r said:
I haven't spent as much time studying all the concerns you guys have here that brought you to this point, but this all seems like major overkill.
Click to expand...
Thanks @Cornwallav8r - I'd encourage you to go through the use cases hit on in the pages of this post - I'd suspect you'd arrive at a similar design. There are a lot of details, and there's a reason for every component in the design.

To give examples:
  • The neutrals between the autotransformer and the grid are tied together to handle ground faults and avoid multiple G/N bonds. This is how SolarEdge does it with their StorEdge solution.
  • Let's say we remove the lost neutral circuit and just wire the autotransformer into the GW output. Now we've got the autotransformer trying to balance the grid transformer.
    • Let's say we remove the grid/AT neutral connection - now we've got a ground loop (low impedance ground connection) between our service and GW load panels
  • Let's say we remove the lost neutral circuit and have the autotransformer conditionally switch on L1/L2 during off-grid operation. What happens if the internal GW ATS switches but the GW dry contact is delayed (or never switches)? Now we've got 240v on our 120v loads with no protection.
Simplifying the design is tempting, but everything in the design has a purpose and a reason. I agree with KISS - but not to the point where you're missing necessary safety features. As for complexity - I'd agree that the design is more complex, but it's also designed to 'fail safe' (shut down) instead of... 'fail on fire' ?
 
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I am always interested to see people saying that this should be more simple than it is, however I see no diagrams, videos or parts lists. Not to say this can't be made simpler - I am sure it can. The most basic understanding has to be we are just a bunch of amateurs and the work is being done for free by people in their spare time at their own expense. If you have an idea on how to make an improvement, I think we are all ears. The work is in running down part numbers and building out the spec to a point where others can implement it.

What we have so far is a technical discussion on how we can keep people from burning down their house - complexity can be learned and managed - but you can't get your dog or wife back if they are killed in a house fire.

I will get off my soap box now.
 
Sorry, I’m being the devils advocate on your protection. Victron’s Autotransformer has one feature that could be added here. There have a high temp trip that trips the output on high temp. You could add a temp relay and use the temp sensor already in the Autotransformer and trip the shut breaker on high temp. It’s a pre-emptive trip. Trip before there is a problem. If you want to go a step further you could add a pi to do some monitoring so that if you do have a trip you know what caused it. (Easier to fix if you know the SOE) A SOE recorder is overkill.
 
automatikdonn said:
Here is the build video. I shot this a couple different times and I have found I suck at making good quality videos.


@rfbuehler

Yea, that is on the docket next. I was focused on getting a reliable system that will shut down in the event the neutral is lost. Next up is over temperature protection.
Click to expand...
I'm just a noob here, so I'm really not in a position to provide critical feedback, but I've been following all the comments in this and other other threads and I'm surprised it's crickets now on this one... Could it be you've put this one to rest? Like I said, all this is way above my pay grade, but what you've put together does look very impressive. The only thing I would say, is that the parts list looks like it comes to approx $500, which likely makes a ton of sense with your 3/2 combination.. maybe a little bit less so, with a 1/1 combo.. but then again, you'd be all set to scale up at that point. Congrats again.

John
 
jbmia said:
I'm just a noob here, so I'm really not in a position to provide critical feedback, but I've been following all the comments in this and other other threads and I'm surprised it's crickets now on this one... Could it be you've put this one to rest? Like I said, all this is way above my pay grade, but what you've put together does look very impressive. The only thing I would say, is that the parts list looks like it comes to approx $500, which likely makes a ton of sense with your 3/2 combination.. maybe a little bit less so, with a 1/1 combo.. but then again, you'd be all set to scale up at that point. Congrats again.

John
Click to expand...
I figured I would post up part's I know for sure will work. That said, you could surely scale back some of the components and save some $$$ for a 1/1 setup. I figure you could probably get this down to 250 dollars if you really wanted to shop.

We still need to add in temp monitoring and it would also be awesome to add on a genset switch to this setup - so everyone gets their end state and could see what a "fully loaded" setup looks like.
 
automatikdonn said:
I figured I would post up part's I know for sure will work. That said, you could surely scale back some of the components and save some $$$ for a 1/1 setup. I figure you could probably get this down to 250 dollars if you really wanted to shop.

We still need to add in temp monitoring and it would also be awesome to add on a genset switch to this setup - so everyone gets their end state and could see what a "fully loaded" setup looks like.
Click to expand...
I am a complete novice here, but let me ask a question. If you have 2 Transformers instead of one, and your 120 V loads aren't that high, wouldn't that provide a safety backup if one of them failed?
 
I finally got the time to actually look at your circuit and watch your video. One thing I'd add other than the temp protection on the transformers is I would add (3) breakers between your inverters and where you join their outputs. In this circuit there is no overload protection on the inverters and wiring coming from the inverters.

Other than that everything looks good.
 
danbussep3 said:
I am a complete novice here, but let me ask a question. If you have 2 Transformers instead of one, and your 120 V loads aren't that high, wouldn't that provide a safety backup if one of them failed?
Click to expand...
Redundancy is the most important step someone can take in this setup IMO. I however don't want to leave things to chance, I have too much to lose to be cheap on that part of the setup.
 
rfbuehler said:
I finally got the time to actually look at your circuit and watch your video. One thing I'd add other than the temp protection on the transformers is I would add (3) breakers between your inverters and where you join their outputs. In this circuit there is no overload protection on the inverters and wiring coming from the inverters.

Other than that everything looks good.
Click to expand...
Do the inverters themselves not have a breaker on the bottom of them? Is that not what that breaker already does?
That is a serious question because I haven't actually looked it up.
 
rfbuehler said:
Sorry, I’m being the devils advocate on your protection. Victron’s Autotransformer has one feature that could be added here. There have a high temp trip that trips the output on high temp. You could add a temp relay and use the temp sensor already in the Autotransformer and trip the shut breaker on high temp. It’s a pre-emptive trip. Trip before there is a problem. If you want to go a step further you could add a pi to do some monitoring so that if you do have a trip you know what caused it. (Easier to fix if you know the SOE) A SOE recorder is overkill.
Click to expand...
I was looking at the Victron AT and thinking it may have actually been a better choice to begin with for my setup. A little late now LOL.
 
automatikdonn said:
I was looking at the Victron AT and thinking it may have actually been a better choice to begin with for my setup. A little late now LOL.
Click to expand...
Are you thinking just using the Victron in lieu of your entire set up will solve the issues with grid connection and AT failure?
 
How does the ground relay play into the SPF 5000 ES neutral protection discussion, if at all? The relay appears to be designed to work with their units only. I’m curious to hear how you'd integrate the Victron AT into your system…

From the manual:
“2.4. Ground Relay
In most energy systems for residential or mobile use a TT configuration is used, which means the Neutral of the AC system is grounded. This is to ensure the GFCI breaker will trip in case there is an earth failure (The connection N/PE will ensure a current will flow in the secondary circuitry which is detected by the GFCI).


As an autotransformer is also able in some systems to “create” a neutral different from the incoming neutral, a ground relay is included in the unit. This relay can be controlled by a Multi/Quattro (by disabling the internal ground relay in the inverter/charger through VE Config or Victron Connect and interconnecting the “ground relay” terminal block in Multi/Quattro and Earth terminal block in Autotransformer by Positive and Negative conductors. In some of the diagram examples in Section 2.4.1 through 2.4.3 it is mentioned when it is possible to use the ground relay.”

Of course the built in temp protection is an advantage as well…
 
automatikdonn said:
Redundancy is the most important step someone can take in this setup IMO. I however don't want to leave things to chance, I have too much to lose to be cheap on that part of the setup.
Click to expand...
I like your protective circuit a lot. How would you modify it for 4 inverters? That doesn't look like it would be easy to do.
 
danbussep3 said:
I like your protective circuit a lot. How would you modify it for 4 inverters? That doesn't look like it would be easy to do.
Click to expand...
Sure it would. You have a couple methods to do it, easiest method being to get a 4 pole contactor. Just make sure the breakers and wiring is sized appropriately for your workload.

This one is a bit speny but is UL. The next version down would probably be just fine too. If your workload runs these inverters at 100% load 24/7, I would be looking at an entirely different setup. ( of which i have a very large power system in the works)

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