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

automatikdonn

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Nice @automatikdonn (y) - 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.
Yea I agree, I even made sure I said that in the video. This circuit could support a momentary switch easily. You might not need all of the extra when you use a push button though.

We need to find an automated one time switch or programmable method to track the number of bootstrap attempts.

The circuit is really no different than a hard wired direct connect of 240v to the contactor and no safer.

I wanted to mostly show people how easy and flexible contactors are. Maybe even spark an idea on how we solve that one shot issue. I don't know of any way that doesn't involve an externally or battery powered logic controller
 
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Yea I agree, I even made sure I said that in the video.

I don't know of any way that doesn't involve an externally or battery powered logic controller
Whoops - I must have missed you saying that. Sorry bout that.

I'm pretty certain we don't need an externally or battery powered logic controller for this. If we view our 'external power' as the 240v AC OUT of the GW, then even if we store bootstraping history/state within any volatile memory of any device, that history is retained as long as our GW AC OUT is supplied. I don't see a condition for that to continuously fail, since GW menu options 6&7 (overload and temp fault, respectively) default to *not* auto-restarting.

I am pretty sure this device, menu option P-35 will work.
1637768944372.png
You'll need a simple wall wart that does 240vac --> 12vdc (or 5v, or 24v), then use that 12vdc to both a) power the board, and b) trigger the board input (at the same time on boot). I'll grab one and test it - the docs are notoriously bad, even translation aside. Always gotta verify experimentally.

While I wait for shipping I'll see if I can get started on the NodeMCU version of the solution.
 

automatikdonn

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So todays experiment has been interesting so far. I replaced the 220v coil contactors with 120v coil contactors and the switch between shore power and battery power has been seamless. I have switched back and forth 10 times now without a single failure.

Have to go do that turkey day thing, but I thought it would be interesting information to share.
 

automatikdonn

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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
View attachment 73357
I think this will work!
 
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