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chrisu avatar image
chrisu asked

Multiplus-II and Pylontech: Battery Low Alarm

Hi there,

I just installed a Multiplus-II 5000 with two US3000C Batteries as AC-ESS.

The batteries were well balanced. The new US3000C Version is designed for a deep-cycle of 5%, when I set this to the ESS Setting as SOC-Minimum, I get "Low Battery: Alarm" at 46.5V from the VE-Bus Device Multiplus when discharging.

I've read the ESS FAQ how to disable low batt warnings, and of course the system is configured correctly according to Victron & Pylontech UP2500, US2000, US3000, US2000C, US3000C, UP5000, Phantom-S, Force-L1 & L2 [Victron Energy]

Any help would be great



Multiplus-II
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3 Answers
Paul B avatar image
Paul B answered ·

46.5 volts is quite flate and I would think thats close to when the batteries BMS will turn off anyway, so check what the batteries cut odd is.

46.5 is 2.91 per cell but that does not mean that all the cells are the same.


if you want to drive them lower then check the settings in your ve configure program

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chrisu avatar image
chrisu answered ·

hmm, then it seems Victron's recommendation is not right for this

Recommendation is

VEConfigure Inverter Parameter Setting
DC input low shut-down 44V
DC input low restart 48V
DC input low pre-alarm* 48V


The "dynamic cut-off" for ESS is at 46V

what does low restart and low pre-alarm mean?

Pylontech say this about their US3000, the operating Voltage is 45...53.5V.

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nickdb avatar image nickdb ♦♦ commented ·
Victron don't make up the values, these are determined by Pylon. If their guidance changes, so does the doc. Probably a question best asked of Pylon support.
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nickdb avatar image nickdb ♦♦ commented ·
Restart is the level that the voltage must return to before the multi will reactivate again.

Pre-alarm is when it will start sending you complaints (alerts).

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Alexandra avatar image Alexandra ♦ commented ·

@chrisu

Dynamic cut off is the rated voltage drop under load settings. Not the same a dc low cut offs.

It allows the battery voltage to be temporarily drawn under the cut off voltage without shutting down the system.

All set to the same value to suppress low battery warnings in ess

If you draw your batteries down to the 46V your system will no longer be able to power assist (as voltage drops when current is frawn oit of the batyeries). And will switch off when loads turn on. Not a good place for any of the components.

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nickdb avatar image
nickdb answered ·

At 5% I doubt they would drive much of a load, as Paul says, that is low and not great for the battery.

I guess it's one of those just because you can, doesn't mean you should moments.


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chrisu avatar image chrisu commented ·

The new US3000C from Pylontech has a DOD of 95% for 6000 cycles. So 5% should be normal working condition for this battery.

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Alexandra avatar image Alexandra ♦ chrisu commented ·
Voltage drop under current will cause the voltage to fall under the 46v can damage cells. You dont want this. Basically you will draw cells under their low cut off under load. So will be out of parameters and out of warranty.
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chrisu avatar image chrisu Alexandra ♦ commented ·
so how can I get the correct numbers for the 95% dod? I think the first pylontech batteries were sold with dod of 80%, so there should be a difference to the new ones.
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nickdb avatar image nickdb ♦♦ chrisu commented ·

Chris, SOC is a relative measurement of capacity, it is not related to voltage, which is absolute.

The physics of lithium and lithium cells hasn't changed much, nor has the design of that battery.

Pylon have no doubt done the maths from the install base, as the product has matured, and realised they can keep allowing deeper discharge under warranty, which is a brilliant sales tool.

While that battery may deliver some power within specs that low down, it will unlikely deliver what you are expecting without dropping beneath limits and affecting your warranty.

Has the spec sheet changed? Do they make commitments of what loads it will run at 95% DOD? Doubt it.

Nonetheless, it is not up to victron to set these limits nor to suggest you deviate from the doc.

The warranty and support is with Pylon, only they can put it in writing that you may adjust them lower, I would be surprised if they do though, but I am an eternal optimist.


EDIT: The only difference between the previous and current ops guide for the 3000C wrt to discharge voltage limits is that it changed from a 45V to 53.5V range to 44.5V to 53.5V, so 0.5V lower. Still, you need to get them to confirm you can deviate without voiding the warranty and support.

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nickdb avatar image nickdb ♦♦ chrisu commented ·
The batteries haven’t fundamentally changed, just the terms and conditions. Best log a ticket with pylon support.


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