wimsza Posted August 21, 2020 Posted August 21, 2020 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 Quote
Louisvdw Posted August 21, 2020 Posted August 21, 2020 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. Quote
Coulomb Posted August 21, 2020 Posted August 21, 2020 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. Quote
wimsza Posted August 21, 2020 Author Posted August 21, 2020 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 asrequired Over discharge current detect delay 600 mS Can set asrequired 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 mΩ 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 ℃ Quote
Coulomb Posted August 22, 2020 Posted August 22, 2020 (edited) 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 August 22, 2020 by Coulomb Quote
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