question

kempza avatar image

ESS large battery draw on Scheduled Charge

System details :

  • MultiPlus-II 48/3000
  • Pylontech US2000B Plus 4.8kWh Li-Ion Battery
  • Venus GX
  • ESS

I'm running an ESS system and noticed that the startup of large AC loads are being powered from the battery / inverter when on scheduled charge. The scenario is as follows:

  • Scheduled charge period
  • Target charge has been reached
  • Grid is available
  • Zero PV

Under these conditions, my understanding is that the system should be relying on the grid to power the loads (with minor background losses). What I'm seeing is that the batteries are used to support the startup of large loads while the grid contribution is slowly ramped up over a few seconds. In the screenshot below, we were using a clothes iron that switched on and off frequently. This resulted in large loads being pulled from the battery each time the element switched on and corresponding charges pushed to the battery when the load switched off. Any way to change the behaviour and get the system to rely on the grid in this scenrio?



Here is less extreme example where a kettle is switched on and pulls 14A from the battery during a scheduled charge period:


ESSbattery
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1 Answer
nickdb avatar image
nickdb answered ·

@kempza I noticed the same behaviour, apparently this is normal behaviour to "buffer" loads which in many respects makes sense.

I am working with support to understand this a bit more, as on the current assistants/firmware I was able to overload the inverter (and more recently trigger low battery alarms) which seems too aggressive with "buffering" AC loads from battery.

On my 3kVA multiplus 2 it would be happy to draw just shy of 2600W and is too relaxed (in my opinion) in feeding in grid power.

I feel we need more control over this behaviour.

What I also noticed was this is more problematic when there is little to no PV, once this disappears the steady load on the DC bus also seems way higher with ESS optimised mode, and the batteries slowly leak charge. If you have larger loads that regularly kick in and out, this buffering seems to take a much higher toll on the batteries and they can run down a fair bit faster, the inverter doesn't seem to compensate enough for this process and fails to maintain battery charge.

I like to use the top 20% or so of my batteries for night usage but by the time the system cuts over to batteries, it has already lost 2-3%.

I'm hoping the support guys can provide some better insight and hopefully assistance in making this process work better.

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