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LiFeP04 not reflecting correctly on BV712


wimsza
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I finally have all my comms and management working on my installation.

Recap:

  • Inverter - RCT Axpert 5k
  • Batteries - 2 x LiFeP04 (2nd life) 120AH 6Kwh
  • BMS - Victron 712
  • Management - ICC on Raspberry Pi4
  • Panels - 6 strings (2 x Canadian Solar 410W panels per string)

Issue:

ICC battery SOC and Voltage differ from that displayed on Battery

I did manually sync the BMS with the batteries when SOC of batteries was 100%

 

What should I try next as this is a substantial difference in SOC

 

 

BMS712 V.JPG

LifeP04 Volt_SOC.JPG

BMS712 SOC.JPG

Axpert V.JPG

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A difference in capacity set between the BMV and the RCT will make the SOC calculation be different between the 2 systems.

So your battery might actually be more that the 120Ah. Up the 120Ah on the RCT until you can see the SOC are close enough.

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59 minutes ago, wimsza said:

ICC battery SOC and Voltage differ from that displayed on Battery

The difference is only 0.36%. I would not worry about that; you can find that sort of difference in the voltage drop across the cables.

59 minutes ago, wimsza said:

What should I try next as this is a substantial difference in SOC

This model of inverter will never display a reasonable SOC, since it can't talk to the battery's BMS and guessing by voltage is pretty hopeless.

However, with the appropriate cable, ICC should be getting the correct SOC from the battery's BMS or the Victron BMV, and that's what is important.

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So I am using the following cables:

 

16mm cable from battery to Shunt, and shunt to inverter

1 x red power cables from each battery to Shunt, first one connected to top battery and 2nd one not connected. 

So in my world all should be ok. BTW, the BMS also keep on coming up with midpoint warnings, so I have disabled it.

 

The concern is not so much the Inverter, but rather the difference between the BMS and the battery monitor on each the battery box. Btw, it has a "dumb" BMS/equalizer inside the box (LBSA BMS 120A 15S 48V LifePO4 Lithium Ion Phosphate) as installed by battery supplier

Electrical Parameters: Room temperature 25℃, humidity 55%

 N0   DESCRIPTION SPECIFICATION UNIT REMARKS
1 Discharge Continue discharge current 120 A  
2 Charge Charge Voltage 54.75 V  
    Charge current 60 A  
3 Over Charge Protection Over charge detect voltage 3.75+-0.05 V  
   
Over charge protection delay
1
S
 
   
Over charge release voltage
3.55±0.05
V
 
4 Balance
Balance detect Voltage
3.50
V  
   
Balance release voltage
3.50
V  
   
Balance current
30±5
mA  
5 Over discharge protection
Over discharge detect
2.2±0.1
V  
   
Over discharge detect delay
600
mS  
   
Over discharge release voltage
2.5±0.1
V  
6 Over Charge current protection
Over discharge detect
200±12 A Can set as
required
   
Over Charge current detect delay
600
mS Can set as
required
   
Over Charge current protection
release condition
Off load Off load Off load
7 Over discharge current protection
Over discharge current detect voltage
400±50 A Can set as
required
   
Over discharge current detect delay
600 mS Can set as
required
   
Over discharge current
protection release condition
Off load Off load Off load
8 Short Circuit
protection
Short Circuit protection condition
Short circuit of external load Short circuit of external load Short circuit of external load
    Short circuit detect delay 250 uS  
    Short circuit protection release Off load Off load Off load
9 Temp
Protect
Temperature protection degrees / No
10 Weak Current
Switch
No      
11 Inner
Resistance
Main Circuit Conduct Inner
resistance
<20  
12 Self
Consumption
Working current 100 uA  
    Sleeping current( over-discharge) 50 uA  
13 Working Temp Temp range -20~70  
  Storing Temp Temp range -40~80

 

 

 

Battery 1.JPG

Shunt 1.JPG

LBSA BMS 120A 15S.jpg

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21 hours ago, wimsza said:

16mm cable from battery to Shunt, and shunt to inverter

16 mm² wire is good for about 75 A; a 5 kW inverter could draw about 107 A.

Re the SOC discrepancy between the BMS and the BMV: It could be the BMV is not resetting to 100% when the battery is full; there is a BMV setting for that. Check that the BMV actually does read 100% when full.

You also need to tell the BMV the capacity of the battery, and the Peukert coefficient. These are also BMV settings. The Peukert coefficient will likely default to a reasonable value for a lead acid battery; for LFP it should be 1.01 to 1.06 (per the first search result I found for "peukert LFP"). The BMS is probably assuming 1.00, so perhaps start with 1.02 for the BMV.

Edit: looking at the photo, it appears that you have two battery modules paralleled, without diagonal takeoff. You need diagonal takeoff to share the load roughly equally between the modules, especially with those screw terminals. It also appears that the battery current travels through the mounting screw of the terminal; I'm afraid that doesn't impress me.

Edited by Coulomb
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