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gerald-d avatar image
gerald-d asked

What can cause small Multiplus to fault under grid power?

Hi

I have often supplied and programmed Multiplus 12|500|20 units as UPS systems on lead acid and lithium batteries. All with no issues until yesterday.

The problem unit is 160 steps up the mountainside. The consumers plugged into it only measure around 200Watt. It is set to charge a lithium battery at 20 Amp. Problem is that it has sporadic tripping about 3 times a day (red LED) while connected to the grid. It behaves fine as an inverter (green LED).

I suspect that the electrician laid a thin cable up those 160 steps to the house and that the grid at the house suffers from voltage drops when big appliances switch on. (water heater for example). (PS, I have just had a knee replaced - I cannot climb to the house to measure)

On Sunday I will get the system back to my workshop and I will have a chance to re-program it. What I am thinking of doing is:
a. reduce the battery charge current to 10 Amp.

b. reduce the AC low disconnect voltage from 180 to 160 Volt (our grid is 230V)
c. reduce the AC voltage connect to 167 Volt
d. Switch Weak AC input on.

Am I proceeding in the right direction?

Multiplus-IIgrid
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5 Answers
Alexandra avatar image
Alexandra answered ·

@Gerald_D

The fault will be caused the repeated faliure to connect multiple times in a row.

The lowest the Victron will accept is 180v

Switch on weak AC. The inverter will adjust the charging based on how it sees the input voltage behaving.

See the size cable that was run find out it's rating and lower the input current limit. Or just lower the input current limit.

Is the UPS box ticked? That can also make it fussy with connection.

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gerald-d avatar image
gerald-d answered ·

Thank you Alexandra

When I received that Multiplus, the box was a little damaged. I suspect that it may have been programmed and returned by an earlier customer. How do I reset it to factory settings?

Okay, I realise I just have to update the firmware to get the factory settings.

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gerald-d avatar image
gerald-d answered ·

Got the system back this morning and quickly found the fault . . . . .

When the system left here Wednesday, the LifePo4 battery was not fully charged yet. When it got back here today, the battery was full, and the BMS was cutting in and out.

When I programmed the Multiplus originally, I just followed the voltages on the battery label: Equalized voltage 14.4V and Float Voltage 13.8V. Was in a hurry and set the Multiplus bulk charge to 14.4 and float to 13.8V. Turns out the battery's "equalized voltage" is its BMS cut out voltage. I should have known better; LifePO4's bulk charge is about 13.8V. The Multiplus saw too many BMS cutouts and went into fault state.

But it is a lesson to those buying lithium as drop in replacements for lead acid . . . . . you might see your inverter getting confused on whether it has a battery connected or not.

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frankmsc68 avatar image frankmsc68 commented ·
Hi there,that's why i choose lead carbon batteries....there are working fine already years,no problem with heat or cold or worries of explosions....personally i have never been a fan of lithium;there is a durty buisness around them! Anyway great article,thanks....Frank
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k-k avatar image
k-k answered ·

Thank you very much for that feedback. What LFP-battery brand is used?

This info might help those people || @ctsit || with smaller MP's and smaller batteries.

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gerald-d avatar image
gerald-d answered ·

The battery is a South African labelled, but imported from China, Hubble S100A

https://www.hubblelithium.co.za/s-100a

The label on the battery has different wording and numbers to what you see on the website. The label said Equalized Voltage: 14.4V

This could fail as a dropin replacement for lead acid where the charging system is set at 14.4V and above.


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Related Resources

MultiPlus-II Product page 

MultiPlus-II Manual

MultiPlus-II 230V Datasheet 

VE.Bus Error codes

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