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wytco0 avatar image
wytco0 asked

ESS Charging - limited Grid Current, CT placement and settings.

Yesterday I asked a question 'DVCC Maximum Charge Current setting - Is this expected behaviour' and found that I had stupidly mistaken DC Amps for AC Amps !! that has now been corrected and works. However another part of the problem has not been resolved.

My MPII is only connected to AC In 1 and is only being used to charge and discharge its attached batteries. Charging is enabled via ESS to take place when we have cheap rate electricity between 2330-0530 each day, discharging is being enabled manually when the Growatt batteries reach minimum allowed SoC.

The MPII not handling or switching any loads and the Victron Grid current limit is set to 20 amps (temp MCB is only 20 amps).

Following further testing I now believe that the MPII is limiting ESS charging based on the total load on the house which it sees on its CT clamp, I had assumed that the 20 Amps grid current limit would apply only to the load through the MPII rather than the house load?

Last night I changed the inverter to charge only mode and when ESS charge was active and I could see some charging but only when the total load that the MPII was seeing was below the 20 Amp Grid Limit, for most of the cheap rate period our use is well above that and averages about 6-8kw.

Thinking about this the MPII actions do make sense but It give ma a problem which I am not sure I can resolve, I could disconnect the CT from the MPII and let it use its internal sense (set jumper) but if I do that then it won't see any demand when it should be discharging its batteries. I could move the CT clamp somewhere else but I am not sure where? Are there any other options? e.g. a manually offset of the CT reading to reduce it? some other Victron settings?

I have attached a very poor simplified diagram of my system which may help.

screenshot-2023-12-31-130947.jpg


For background only:

  1. This is a temporary setup, the aim is to move to full Multiplus control but that required extensive rework of my CU to remove some high current circuits (ASHP and car charger)
  2. My original installer has disappeared and I am struggling to find someone with Victron knowledge to take over.
  3. I have G99.
  4. I have PV attached to the Growatt but non on the Multiplus.
Multiplus-IIESS
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1 Answer
electronicsuk avatar image
electronicsuk answered ·

As I recently discovered, the external CT implementation with the Multi is a bit of a mess. It would be far better if there were some way to have both the internal and external CT connected and measured simultaneously, but that's just not how the hardware is set up.

In your situation, it makes sense that the Multi would stop charging or inverting when it senses >20A on the external CT. It simply doesn't know what the internal CT is doing to be able to measure the current on AC in 1, so it has to use the only measurement it has, which is the external CT.

In your case, until you can get a bigger supply to the multi, why not simply limit maximum charge current in the DVCC settings and turn off any limiting on the AC supply? Assuming that your battery is 48V and ignoring losses, limit to 96 Amps and you'll be in the ballpark.

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wytco0 avatar image wytco0 commented ·

Interesting as it confirms what I thought I had found regarding the CT, It seems that the Victron Multiplus is designed with the assumption that all loads will go through it, which is fine but I think with small changes it could be better ;-)

Thanks for the suggestion of limiting the maximum charge current in DVCC, i will give that a try this evening, I have also today managed to get my MCB swapped to a 40 Amp version so I have more headroom to play with.

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