zeroco2 avatar image
zeroco2 asked

External Control: how to set a SoC max ?

Hi there,

My configuration is: Multiplus II + 3 MPPT + 2 Pylontech stacks of Force L2 + Lynx + Cerbo GX.

It is off-grid (with no grid code), without any assistant (like ESS) but with the VS (virtual switch) on "Dedicated AC Ignore" to maximize self-consumption.

My MPPTs seems under the "external control" of the Pylontech BMS.

I try to limit the charge of my Pylontech stacks to 90% (or below) but they keep charging till they reach 97%, ignoring my general settings of the Multiplus (see the VE Config).

Is it because of the "external control" mode ?

Any idea how I can set a SoC max of 90% ?

Should I try to set this SoC max of 90% directly at the BMS level ?




Multiplus-IIBMSPylontechsmart solar charging behaviour
config1.jpg (97.3 KiB)
config2.jpg (69.1 KiB)
configmultiplus2.pdf (563.1 KiB)
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3 Answers
JohnC avatar image
JohnC answered ·


What you could try is using Assistants rather than Virtual Switch. They can't be used together, and Assistants are more complex to set up. But they can use SOC.

I'd also disable the Multi's battery monitor, so there's no chance it can play any role. The Assistants should pick up the Pylon's SOC.

Note well that I haven't personally tested this with Pylons, but I'm interested to see how you go with it.

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zeroco2 avatar image zeroco2 commented ·

Hi, thanks for your return. Without a grid code (not allowed to connect and to feed energy to the grid), I am not sure I can use the assistants. Anyway, I gave a try to the assistants (setting a grid code), but since I was interested into maximizing my self-consumption and using the grid as a last resort, I would have used the Hub-1 policy 3 that the ESS cannot implement, so I reverted to the simplest solution (AC ignore with the virtual switch). The system now behaves exactly as I was expecting to... put aside the fact that my Force L2 will charge till they reach a SoC of 97%.

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nickdb avatar image
nickdb answered ·

Pylons warranty is dependent on you following their setup guide exactly.

Nowhere do they want you to stop charging at 90%. Doing so will prevent the batteries balancing correctly and likely cause more harm than good.

Leave the batteries to do what they were designed to do.

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zeroco2 avatar image zeroco2 commented ·
Hi there. I read the Pylontech battery installation manual, and I still don't get how to communicate and set them up. Whatever, I am surprised to read that letting them charge up to 97% is good for them and that they were designed to do so on a regular basis. And I think that the Victron settings allow to charge these Pylons stacks to a high SoC once in a while to balance them.
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nickdb avatar image nickdb ♦ zeroco2 commented ·

SOC is a relative metric that is calculated, not measured, based on the configuration of the BMS. The BMS is keeping the cells in an optimal zone, voltage wise. In the design and configuration of a commercial battery the manufacturer has already taken everything into account to make sure the battery lasts.

If you are building your own battery from cheap cells bought online you would do the same at the battery management level, not from the inverter.

You will notice that cell min/max voltages are in a good range at 100% SOC and far away from the min/max range used in unrealistic charger regimes by cheap cells to maximise their capacity.

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kevgermany avatar image kevgermany ♦♦ zeroco2 commented ·
To add.

In your setup the Pylontechs control the charging, not the Victron kit.

You might be mixing up L-ion and LiFePO4 charging needs when you want to limit to 90% SOC.

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hominidae avatar image hominidae kevgermany ♦♦ commented ·

right, I actually missed that part...hence control via dbus, DVCC max. charge current, will not work (which is for AC / inverter side only).

is there a complementary control from the DC solar chargers side in dbus? -> here:

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hominidae avatar image
hominidae answered ·

LifePo4 batteries can reach a longer lifespan, when used between 20-80% SoC.

However, SoC is a calculated value by the BMS.

Therefore it is required to fully recharge these from time to time (but not required to recharge to 100% daily...also it is good advise to not let these sit at 100% for too long (reach 100% at dawn, preparing just before discharge during night is a good strategy).

You can use Node-Red to monitor SoC and then disable charging by setting Charge Current limit in DVCC to 0A. NodeRed is part of VenusOS Large.

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nickdb avatar image nickdb ♦ commented ·
If I compare similar sized pylon stacks which are used differently, there is absolutely no difference in SOH for packs which do or don’t spend significant time at 100% SOC.

The main driver in degradation is time and temperature and you can do nothing about that.

Considering the data pylon has on their batteries and how they are configured, there is nothing anyone can do to improve the life of their set. They can only make it worse by assuming advice that is based in one context is relevant in another.

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hominidae avatar image hominidae nickdb ♦ commented ·
Well, nobody has one of an age old enough, right.

Anyhow, my main focus was to answer the the original topic.

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nickdb avatar image nickdb ♦ hominidae commented ·

Plenty old enough. They have the longest track record of, probably, any of the current manufacturers.

There are people who can reference their stamina vs other early offerings.

Bottom line, if it breaks they must fix it, and they most likely will as a proven vendor.

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