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cruisey1987 avatar image
cruisey1987 asked

ESS startup procedure without grid?

I'm curious if there is a process to startup an ESS system when the grid is unavailable (essentially in backup power mode)

For example, let me illustrate a system I have in mind:

An 8kVA Quattro inverter with the grid on AC2 and a small (~5kW) generator on AC1 to provide backup power in case of a serious outage

Some solar panels connected to a Victron charge controller

A CAN bus controlled battery like a Pylontech

A Cerbo GX to control the whole setup

The components are connected to a common DC busbar with isolators on each component so they can be disconnected individually


So here's my hypothetical situation; some disaster occurred whereby the grid is unavailable for an extended period. An issue occurred with the ESS system requiring it to be shut down

Now I'm trying to restart the ESS system without the grid, what order to I start the various parts of the system up?

My guess is that it's something like the following:

  1. Disconnect all loads on the AC output of the Quattro
  2. Disconnect the grid input of the Quattro
  3. Power on the battery and close battery isolator, check battery SoC
  4. Power on the Cerbo GX and allow to boot up
  5. Connect charge controller to solar panels and DC bus, switch on and allow to start up
  6. If the battery SoC is too low to allow the Quattro to safely start, then charge the battery from solar or using the generator and an external battery charger (would need to temporarily disconnect generator from the Quattro to do this)
  7. Once the battery SoC is high enough, connect the DC input of the Quattro and switch on, allow to start up
  8. Slowly reconnect the AC loads to the Quattro, allowing for any high startup current to pass before moving onto the next device
  9. When the grid is restored, reconnect the grid input to the Quattro

Anything I missed or got wrong?

I realise it's a hopefully rare scenario, but I think it's possibly the worst state one could reasonably recover from and it's good to have a procedure just in case

ESS
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1 Answer
Kevin Windrem avatar image
Kevin Windrem answered ·

The Quattro will start up from DC or from AC-in-1 if the battery is low, so you should be able to charge the battery from the generator through the Quattro. (You can NOT start the Quattro from AC-in-2 if the DC input is too low.)

I don't see a need to disconnect the grid. If it is present, great, of not, the Quattro's AC 2 input relay will just remain open.

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cruisey1987 avatar image cruisey1987 commented ·
I presume if starting up from AC in 1 then I would need to ensure the generator can supply sufficient peak power for the Quattro to start (~12kVA for an 8kVA Quattro if I remember correctly)?


My hope would be to use a smaller of around 5kVA generator since it should only be for emergency situations

Is it possible to soft start a Quattro from the AC in 1?


Regarding the grid isolation, my reasoning was if the grid was unavailable for an extended time then it's probably better to open the isolator on AC in 2 just in case there's any instability, and then close it when the grid is restored


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Kevin Windrem avatar image Kevin Windrem cruisey1987 commented ·
You can program different input current limits for the AC 1 and AC 2 inputs so you can set AC 1's limit to avoid overloading the generator. This limit includes charging current as well as AC loads not covered by assist from the inverter.

There's also "Dynamic current limiter" which ramps up the grid/generator current to prevent sudden changes from overloading the generator.

The Quattro does a decent job of validating the incoming AC before closing the input relay. About the only protection not provided is for extreme overvoltage. Disconnecting the grid connection is optional but better safe than sorry.

The startup current/power of the Quattro won't be significant if there is DC already supplied to it. There would be a brief inrush if the DC is disconnected as the DC input capacitors charge. I would recommend connecting the batteries even if they are low in voltage since this will significantly reduce the AC inrush current. Significant sustained AC input power won't occur until it starts supplying loads or the charger kicks in. At which point the input current limit comes into play.

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cruisey1987 avatar image cruisey1987 Kevin Windrem commented ·
Thanks for the help Kevin, hopefully these are my last few questions
  1. I presume it's fine to start the Quattro with the AC loads disconnected? I would probably be powering a heat pump among other things from the ESS system and it seems prudent to ensure the ESS is fine before connecting any heavy loads
  2. I would change the procedure above to start the generator manually before starting the Quattro to ensure it has power available for charging the battery. Once I've built up some buffer in the battery and I'm happy the system is working correctly then I would connect the AC loads and put the generator back to automatic start. Does this sound correct?

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