question

peternielsen avatar image
peternielsen asked

Low Battery but the battery is fine, multiplus II with LiFePo4 and 2 wire bms.

Hi,

Here are my settings :

1612179175558.png

the voltage is atm 53V and the Multi states low battery BUT it's in Inverting mode which i don't understand. First the battery is not low and from what i can tell i have set the switch correct from the BMS so right now the Aux 1 is Open but never the less the Multi states low battery and more bizarre it is in Inverting mode whereas if it was really low battery then it should be in Charge only mode. I don't understand. Could somebody explain what am i missing ?


/peter

Multiplus-IIESSLithium Battery
1612179175558.png (32.9 KiB)
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4 Answers
seb71 avatar image
seb71 answered ·

What voltage is the "DC input low pre-alarm" set to (in Inverter tab in VE Configure 3)?


Your 0.005C cutt off voltage is too high at 52V. For a 16 cell LiFePO4 battery, that would mean 3.25V per cell (on average).


First the battery is not low and from what i can tell i have set the 
switch correct from the BMS so right now the Aux 1 is Open but never the
 less the Multi states low battery and more bizarre it is in Inverting 
mode whereas if it was really low battery then it should be in Charge 
only mode. I don't understand. Could somebody explain what am i missing ?

It goes in charger only mode when Aux 1 is closed. Right now you say it is not closed.

Low battery does not mean empty battery.

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peternielsen avatar image peternielsen commented ·

@Seb71 thank you for replying. I only used the default values. Can you suggest what the value should be for LiFePo4 ?

Here are my settings :

1612180995985.png

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seb71 avatar image seb71 peternielsen commented ·

Those values are way too low for LiFePO4. But when using ESS the shutdown voltages should be the ones set in the ESS assistant (the dynamic cut-off voltages).

Just in case you remove the ESS, set the "DC input low shut-down" to 48V.


I have my "DC input low pre-alarm" set at 50.4V (that's 3.15V per cell).

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peternielsen avatar image peternielsen seb71 commented ·

I am using ESS and i left everything default, have i selected something wrong ? It states during the ESS wizard that the Dynamic cut off voltage should rarely be changes since they are set correctly for the chosen battery type which i did select to LiFePo4, so what exactly should i change ?

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peternielsen avatar image peternielsen seb71 commented ·

This is the default in the assistant :

1612181871415.png

So i don't understand, does the DC-input low pre alarm get used when setting the Dynamic cut-off ?

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1612181871415.png (18.4 KiB)
seb71 avatar image seb71 peternielsen commented ·

One is just an alarm (that your battery is getting low), the other shuts down the inverter.

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peternielsen avatar image peternielsen seb71 commented ·

So i still don't know what do change to get rid of the low battery warning. Any suggestions ?

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seb71 avatar image seb71 peternielsen commented ·

The values you have there, while wrong, do not explain why did you get a low battery warning at 53V.


Check the graphs in VRM for clues.

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marekp avatar image marekp peternielsen commented ·

At what point did you measure this 53V?

On battery terminals or Multiplus terminals?

What is the voltage drop between two points?

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peternielsen avatar image peternielsen marekp commented ·

I have this info from my diyBMS and also from the Victron Shunt which both agree on the voltage.

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marekp avatar image marekp peternielsen commented ·

Ok, so you are measuring at battery terminals., because shunt is probably next to the battery.

Now measure voltage drop between battery and MP.

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seb71 avatar image seb71 peternielsen commented ·

Check the History tab on SmarShunt. What is the lowest battery voltage recorded?

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peternielsen avatar image peternielsen seb71 commented ·

Is this what you mean ?
1612187070171.png

1612187173778.png

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peternielsen avatar image peternielsen peternielsen commented ·

The system is just setup few days ago.

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marekp avatar image marekp peternielsen commented ·

This battery voltage and current VRM gets from the shunt?

What is the voltage on MP battery terminals?

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seb71 avatar image seb71 peternielsen commented ·

VictronConnect - SmartShunt - History - Minimum battery voltage

or in VRM:
Battery History - Smart Shunt - Minimum voltage

-------

In the VRM grahps you have to zoom in, because the graphs are "smoothed out" in that view (and do not display the true min/max values).

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peternielsen avatar image peternielsen seb71 commented ·

I see 12v , is that the problem ? IDK where it came from. 1612189435101.jpeg

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1612189435101.jpeg (454.4 KiB)
seb71 avatar image seb71 peternielsen commented ·

That 11.95V minimum voltage it's probably from when you connected the SmartShunt to the battery.

Since this is a new install, I would clear the battery history (using VictronConnect), because you won't see there the true minimum.

But do not reset it again after that.


Edit:

Preferably reset the battery history when the battery is fully charged. Or take a note of the SOC value right before the reset and re-enter it manually right after that.

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wkirby avatar image wkirby ♦♦ peternielsen commented ·

What grid code do you have selected and what are settings?

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peternielsen avatar image peternielsen wkirby ♦♦ commented ·

I run Denmark Grid code. Here is my config.


d41243b4eb7b_inst_ttyS4_Interfaces_Mk2_Tunnel.zip

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wkirby avatar image
wkirby answered ·

This is your problem - I think.
This is conflicting with your BMS onAux1.

aux1.jpg

Uncheck this box, should solve your problem.


aux1.jpg (72.4 KiB)
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peternielsen avatar image peternielsen commented ·

Not sure why that would create a low battery warning ? I can't uncheck it since I need a password.

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wkirby avatar image
wkirby answered ·

I have also spotted another problem.
You have chosen "Two signal BMS", but you have chosen both signals (Full and Empty) on the same input.

1612199099461.png


Why not put the battery full signal on Aux2 and the battery empty signal on Temp Sense Input (if you have no temp sensor there). Then that leaves Aux 1 available to the Grid Feed disable signal.

1612199219155.png



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peternielsen avatar image peternielsen commented ·

You are right that i chose to do that. I can easily change it without any issues but i still not sure it will solve the problem. Until now i had Grid turned off so i could learn how things are working. Now i have turned on the Grid and the low battery dissapeared but i am unsure how to configure the charger for LiFePo4 and the 2 wire bms.

My problem is that in my BMS i have following :

1612208525560.png

1612208532935.png

1612208540243.png

The last two checkboxes on the right are my relays that are connected to the multi but i only use the last one at the moment. Relays on the BMS are connected with Multiplus with Normal Closed eg. On means open circuit and Off means the circuit is closed. The relay is set default to be On. I am in doubt what this means in Victron because the Ve.Config states :

1612208840963.png

How does this correspond to ESS messages :

1612208895674.png

In my case right now it shows this :

1612208950576.pngand the relay on Aux 1 is On in the BMS meaning it's Open circuit eg. means the battery is full but the charging specs in VE Config says this :

1612209182157.png

so it should not float yet but i guess it's because the BMS told it it's full it goas into float as specified in ESS. Maybe all problems are here because i configure the BMS wrongly and the BMS should only interfear with the charging if the voltage goes really high or very low whatever that must be for LiFePo4 which i don't know yet. As you can hear i am confused but i am certain all problems can be solved if i configure BMS correct and the way 2 wire BMS works in Victron.

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wkirby avatar image wkirby ♦♦ peternielsen commented ·

So BMS on means that it is open circuit.
In ESS Assistant Aux 1 open circuit means battery is full - charging must be disabled, ES code #3.

You also have ESS Assistant Aux 1 closed means battery is empty - charing must be disabled. So as soon as you BMS allows charging and the relay closes, then discharge will be disabled straight away.

Battery is full and battery is empty need to be on separate inputs of the MultiPlus.
You have chosen Aux 1 for both, try to choose a different input for the battery is empty signal. If you are not using the battery is empty for now, then set i to closed, but they can't both use Aux1.
Two signal BMS means two signals into two inputs of the MultiPlus.

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peternielsen avatar image peternielsen wkirby ♦♦ commented ·

great so i have now changed it to following :

1612211051463.png

1612211075882.png

1612211253700.png

Relay 3 is Temp Sensor and Relay 4 is Aux 2. Default relay state is Off (eg. means Closed circuit).

In Ve.Config i have it as following :

1612211173875.png

So this means BMS does not do anything at the moment since no rules are fullfiled and that means the current state is :

1612211325114.png

I don't know why there is a usage of 51W atm, have no idea what consumes that, no loads are there at the moment. The setpoint is set to 50W, no Energy Mounted yet. Maybe it means something else, i must read the ESS manual again. So all in all i guess this is correct, now i need to put the correct data for LiFePo4 in BMS, do you know those ?

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wkirby avatar image wkirby ♦♦ peternielsen commented ·

Good, that looks good to me. It is good to have relays go open when rules are met. If there is a fault with the wiring then it also goes open circuit and stops charge /discharge to be safe.

Kind of strange where it thinks it is putting 50W.

Sorry, no advice to give on BMS settings. I don't know your BMS or what cells you have.

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peternielsen avatar image peternielsen wkirby ♦♦ commented ·

ok so you suggest to invert the logic so if the bms loses power the ,ulti stops charging ?

I am using LiFePo4 16s of 160Ah.

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marekp avatar image marekp peternielsen commented ·
I don't know why there is a usage of 51W atm, have no idea what consumes that, no loads are there at the moment. The setpoint is set to 50W, no Energy Mounted yet. Maybe it means something else, i must read the ESS manual again. So all in all i guess this is correct, now i need to put the correct data for LiFePo4 in BMS, do you know those ?

Atm battery consums 16W and Multiplus the rest from 51W

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peternielsen avatar image peternielsen marekp commented ·

Weird, Multi has 18W zero load consumption but this is 35W.

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marekp avatar image marekp peternielsen commented ·

But this 16W is on the battery side. How much MP uses to produce this 16W on the charger output? Efficiency is low at those power levels.

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Leslieanne avatar image
Leslieanne answered ·

Hi, I can answer the simple part of your question. (Luckily others have sorted out your more serious problems!) If you read the manual carefully, in ESS low battery warning is given when voltage drops below the dynamic cut-off value PLUS the offset ( ie the restart offset) which is 1.2V for a 48V nominal lithium system. So....anything below 53.2 V with your current settings will give that low battery warning at no or low load. Personally I think the 52V cut off is too high. I use 50.8 on my similar system, so the low battery warning does not start till low load voltage drops below 52V.

Cheers, Leslie



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seb71 avatar image seb71 commented ·

Right. I missed that the low battery pre-alarm (the one set in the Inverter tab in VE Configure 3) is also overridden when using ESS.

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