{"id":678,"date":"2023-11-09T14:40:08","date_gmt":"2023-11-09T19:40:08","guid":{"rendered":"https:\/\/wheng.ca\/?p=678"},"modified":"2023-11-23T13:15:26","modified_gmt":"2023-11-23T18:15:26","slug":"scmc-system-lifepo4-battery-capacity-sizing","status":"publish","type":"post","link":"https:\/\/wheng.ca\/index.php\/2023\/11\/09\/scmc-system-lifepo4-battery-capacity-sizing\/","title":{"rendered":"Solar Charge Maximizing Controller System Lithium Iron Phosphate (LiFePo4 or LFP) Battery Capacity Sizing Rules"},"content":{"rendered":"\n
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Rules of sizing the battery bank capacity to ensure the Solar Charge Maximizing Controller System will function Properly<\/h2>\n<\/div><\/div>\n\n\n\n

The LiFePo4 Battery Capacity Sizing Rules Differences Between Solar Charge Maximizing Controller Systems and other MPPT Solar Charge Controller Systems <\/h2>\n\n\n\n

In a Conventional MPPT Solar Charge Controller Systems, the capacity of the LiFePo4 batteries<\/strong> are sized according to capacity requirement in the pre-defined power consumption conditions. The battery must be able to power the assumed load for a certain period of the time when the system could not be charged by the PV system during the nights or during cloudy days when the PV system may only have minimum solar radiation conditions.<\/p>\n\n\n\n

The designer would not have to worry about how much is the system charging current in Amps, rather focusing on the capacity of the system in KWH (Kilowatt Hour). For example, in a 5KW solar array system with an expected power consumption of 20 KWH per day (average 2 KW load for 10 hours), the designer may determine that the minimum required solar battery storage capacity is 20 KWH, to last for one day when the Sun is not shining on the next day (cloudy day). The sizing rule is also based on the assumption that the PV array and the MPPT charge controller may charge the battery for minimum 5 hours at an average 4 KW capacity each day when the Sun is shining.<\/p>\n\n\n\n

So the LiFePo4 battery capacity sizing rule is based on the capacity requirement to satisfy the power consumption needs for certain applications. Of course, the current of the system shall also be verified to ensure the cable will not be over-currented, and the MPPT charge controller can handle the charge current expected between the MPPT controller and the load. The load refers to the DC load expected, and the charging current of the battery.<\/p>\n\n\n\n

The Minimum DC Current Charging Capacity for LiFePo4 Battery in the Solar Charge Maximizing Controller System: <\/h2>\n\n\n\n

In Solar Charge Maximizing Controller System, the LiFePo4 Battery capacity sizing rule is not exactly the same as the sizing rules for the conventional MPPT Solar Charge Controller System. The charging and discharging CURRENT<\/strong> capacity of the LiFePo4 Battery is critical. Because the ENERPAK Solar Charge Maximizing Controller can maximize the system charge current, and the SCMC will allow the maximum current to pass the controller at the maximum design condition of the solar array at the maximum solar irradiance conditions.<\/p>\n\n\n\n

As you may see from the image below, the Solar Charge Maximizing Controller does not limit the current passing through the controller, as the current is handled by the mechanical switches inside the controller, unlike the PNP or NPN junctions in the conventional MPPT solar Charge Controller which would limit the current flow to prevent overheating. <\/p>\n\n\n\n

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So it is very important that the LiFePo4 battery must be able to accept the charging current from both the SCMC controller and MPPT Solar Charge Controller, minus the minimum current that can be consumed by the DC load during the day at maximum solar irradiance conditions.<\/p>\n\n\n\n

We must also keep in mind that the LiFePo4 Battery<\/strong> storage capacity is different from the current capacity. Because the current capacity is limited by the wire gauges that the battery manufacturer installed inside the LFP battery. The “C” rating <\/strong>of LiFePo4 battery becomes critical in the SCMC system. The “C” rating of a LFP battery is the current capacity ratio of a LFP battery. The “C” rating of 0.5 of a 100 AH battery means that the battery can handle a 50 amps charging and discharging current without any concerns. <\/p>\n\n\n\n

Trying to feed too much current into a LiFePo4 battery will cause the Battery Management System<\/strong>‘s reaction to limit the current flow and the BMS will cut out (disconnect) the battery to cause system over voltage, and further shutdown the SCMC & MPPT controller, causing the waste of the solar energy.<\/p>\n\n\n\n

When written in formula, <\/p>\n\n\n\n

LiFePo4 battery CURRENT capacity of a Solar Charge Maximizing Controller (Amps) =<\/strong><\/p>\n\n\n\n

The maximum current capacity of the solar array from both SCMC & MPPT Controllers (Amps) – <\/strong><\/p>\n\n\n\n

The minimum current consumption of the DC load during the day (Amps)<\/strong>.<\/p>\n\n\n\n

Following YouTube Video “The Principle & Definition of Solar Charge Maximizing Controller System” also explains it clearly about how the current is handled in a Solar Charge Maximizing Controller System. Please make comments or ask questions if you still have any doubt about the differences between the SCMC system and the MPPT solar charge controller system.<\/p>\n\n\n\n

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