Multiplus-II GX, DCL and Power Limit not working as expected under Inverter load

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mgb07 asked May 24, '22

Multiplus-II GX, DCL and Power Limit not working as expected under Inverter load

My MultiPlus-II 48/5000/70-50 GX is combined with 1 Pylontech US2000C (test setup) and a CT is configured as a grid tied ESS system (AC IN connected only). The Multiplus II GX detected the batteries correctly. The Discharge Current Limit (Pylontech battery -> Parameters) is 25Amps. ESS assistant is installed of course and firmware is up to date.

When a largish load engages, such as the water heater, the Pylontech battery starts discharging at well over 25Amps (50Amps or greater sometimes) which then causes the red led on the battery to start flashing! Why does the system not keep the discharge to 25Amps?

I have tried to Limit Inverter Power and set the Maximum inverter power to 1000W using the ESS functionality for example (see below), but this does not seem to be effective either.

I know that in theory the MultiPlus-II 48/5000/70-50 GX requires more battery capacity to provide the power requirements from heavier loads which is the aim eventually (when more batteries are obtainable), but I assumed that the functionality of the Discharge Current Limit or Limit Inverter Power would allow this set up to work without overloading the single battery currently in use?

Current set up:

Overcurrent in action:

DCL:

Limit Inverter Power:

Multiplus-II

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Alexandra answered · May 24, 2022 at 07:15 PM

@MGB07

You have also told the system it is allowed to discharge the battery to 10%. Without battery life is set. So it will discharge the battery.

Your experience is the reason why there is a minimum requirement set in the online manual.

What is your grid set point and input current limit? Possibly there is some mixed signals there.

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Alexandra answered · May 25, 2022 at 05:51 AM

@MGB07

The draw from the battery is pretty close to the DCL. Are there any (red) warning lights on the battry when it is doing that? If not I would not stress too much.

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lifeingalicia answered · May 25, 2022 at 10:07 AM

Hi it is a bit weired once scheduled charging reaches SOC it stops charging BUT during the scheduled time it wont discharge.

So I set my SOC to 30 as I never go lower (except grid failure).

So this schedule stops the bat from discharging during the period

Set your SOC to 10 or so and it never charges or discharges...

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lifeingalicia answered · May 25, 2022 at 10:12 AM

just checked a slight discharge may occour as multi reacts with battery first to demands... but it works

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Answer 1 · 2022-05-24T21:35:22Z

mgb07 answered · May 24, 2022 at 09:35 PM

The grid point is where the power comes into the house, just after the main supply fuse and electric company meter. The Input Current Limit is currently set at 10 Amps in the Multi Remote Console.

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Alexandra ♦ commented · May 25, 2022 at 05:40 AM

Grid set point is set on the GX. It works with the input current limit.

ESS uses a form of power assist.

Try increasing your input current limit to about 20Amps since there is no solar seen by the system.

The system will be trying to power assist the loads switching on with the settings you have. You can leave the max invert power at the 1000w.

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Alexandra ♦ commented · May 25, 2022 at 05:44 AM

@MGB07

The reasoning in my previous post is this.

Your inverter can do 5000VA with correct batteries. But with what you currently have it can do 1000W.

So you need to allow the system to be able to draw the rest of the 4000w from grid, but with an input current limit of 10A (2300W) you have ruled that out, making the battery the only other source as there is no solar (seen by the system). So the system is following your rules.

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Answer 2 · 2022-05-25T08:25:43Z

mgb07 answered · May 25, 2022 at 08:25 AM

@Alexandra Great answer, makes sense, many thanks. More batteries on order and I will increase the input current limit as suggested, I didn't realise that the Multi in ESS mode works in that way.

The Multi also behaves like this even when charging from what I can see. For example if I schedule a charge of the battery at night to take advantage of cheap rate electricity and also schedule the water heater to come on at the same time, the Multi stops charging and starts discharging. Is there any way to inhibit the inverter during a scheduled charge time that you know of?

And yes, the Pylontech does complain when such large currents are drawn (flashing red warning light) but it doesn't stop the discharge which is surprising.

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Alexandra ♦ commented · May 25, 2022 at 08:55 AM

Victron have a feature called power control there as well, so basically if you set the input limit down to the load size, there is not enough current left to charge. It will not charge (or only send the few amps left to the battery). So that is what I would expect. Incresing the inout current limit will take care of that for you.

The Pylontec does allow for a time the huge current draw. I think there is a limit, although I have never run batteries like that long enough on a test to see how much it tolerated.

I have also seen cells balloon (and explode the battery case) on other systems. So it seems they don't seem protect themselves like that.

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Answer 3 · 2022-05-25T08:43:27Z

lifeingalicia answered · May 25, 2022 at 08:43 AM

It's reverse I have a scheduled charge set to the time of my water boiler charging 2 hours instructing multi to charge battery to SOC 10% as I always have at least 30% it does not charge or discharge during this time allowing only the boiler to draw from grid, During schedule multi does not draw from grid,

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lifeingalicia commented · May 25, 2022 at 08:47 AM

Sorry meant draw from bat,

Ps. CT and ESS don't forget to check external current sensor

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Answer 4 · 2022-05-25T09:32:07Z

mgb07 answered · May 25, 2022 at 09:32 AM

@Lifeingalicia Interesting, I have my schedule set up like this but I can see that the Multi stops charging during this period, when the water heater engages, and starts to discharge to aid the supply.
Does this look similar to your schedule?

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