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thijs avatar image
thijs asked

ESS system fails to utilize battery

ESS system based in the south of France.

- MultiPlus-II 48/5000/70-48

- BlueSolar Charger MPPT 150/70 (VE.Direct)

- Color Control GX

- 4x 12v AGM batteries totalling 200Ah with Victron battery balancers between

This is how it has all been wired up:

img-20240802-153048.jpg

img-20240802-153057.jpg

For some reason the system barely utilizes the batteries. I have configured it to go down to 65% soc, but it doesn't get below 90%.

When a substantial load is put on the system, it looks like it uses the battery for a short period, with the low battery led flashing, and then it switches to the grid fully with the low battery led full red. Then after a short time it seems to try again, and repeat. Which means the battery is almost never utilized to supplement the power usage.

Does this mean the batteries are dead? They are quite new so that would be strange and quite expensive (again)... Or is there some other possible reason for this behaviour?

Multiplus-IIESSAGM Battery
img-20240802-153048.jpg (3.4 MiB)
img-20240802-153057.jpg (3.3 MiB)
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3 Answers
Duivert NL avatar image
Duivert NL answered ·

Hi i dont see a shunt, so how does the system know what state the batterys are…


also you really need to put some more fuses in your system, there is one on the positive and it doenst protect the batterys or the multiplus…

And i see on on the negative that wont do anything (200A?)


you are also at bare minimum on agm battery capacity on a 5k multiplus

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thijs avatar image thijs commented ·

No shunt, the system can determine the soc and voltage of the batteries itself. As per the manual: In '1.2 Components' it says: "In most situations, it is not necessary to install a battery monitor" and "The built-in battery monitor of the Multi Inverter/Charger can be used to provide data where installed batteries do not have a monitor built-in. The advantage here is that in an ESS system the charge currents from MPPT Solar Chargers will also be taken into account."

As to the battery capacity, yes, it's the lower limit, but should that have this effect? I would assume that even at the low limit the system should actually work...




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Duivert NL avatar image Duivert NL thijs commented ·

Yes you are right about the shunt part, but the mppt’s will also be taken in account with a shunt, they also will communicate that with the gx,

in my experience a shunt is the best option because its between batterys and the rest of the system (mppt and multi) and therefore much more accurate

Did you charge your batterys separetly to 100% SOC before connecting them together? If not, That can cause issues like this to

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nickdb avatar image
nickdb answered ·

Looking at that wiring makes me twitch. Yikes.

Stuffing two smaller gauge PV feeds into one MPPT terminal is a bad idea.

You need a shunt with those batteries. The built in monitor is limited and cannot see the MPPT loads, so has to guess, so your SOC is likely impossibly inaccurate.

Your settings are probably also off on the inverter cutoffs and ESS dynamic limits etc, or with those lugs mounted one on top of the other on a makeshift busbar, who knows what voltage loss may be present.

I would clean all that stuff up and look at the best practice wiring and ESS docs.


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thijs avatar image
thijs answered ·

One thing that I don't understand is that it seems like the settings I put into the configuration actually are not followed. For testing I have set the cut-off values extremely low, the lowest allowed, which iirc is 37V. But the system cuts off much sooner than that. Never have I seen the voltage drop below about 42. Is this a problem with the display? Am I just not seeing the lower voltages because the resolution/speed is to low/slow? If so, how can I get the real data that drives the system? Do I need to hook in the queue system?

This is what I see happening:

- load is supplied by solar

- if load exceeds solar capacity, the system tries to supplement from batteries

- the system somehow determines that the batteries are low

At this point the sytem seems to go to pass-through, using the grid to supply the full load, and starts charging the batteries with the solar power, even though the soc is still shown as >95% often.

What I would actually like for the system to do, is to just supplement the load from grid if it can't find the power in the batteries. Is this technically not possible? Is it possible to configure the system to do that?

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