Victron Solar Power Supply for Tiny House project

Victron Solar Power Supply for Tiny House

• The aim of this project is to set up a small Solar 12V power supply (PVS) for a Tiny House experiment.
• The PVS will power an Arduino Uno to monitor the battery, the solar panel and the Load (current drawn from the battery) using a Victron MPPT Charge Controller.
• The MPPT Charge Controller provides this information to the Arduino Uno via serial communication (VE.Direct Serial port).
• In this experiment the MPPT Load outlet will be connected to the Arduino Uno using the power socket on your Arduino board.
• Use a 5.5mm diameter cylindrical plug with 2.1mm pin hole. A Positive voltage is on the inside pin hole and the Negative (or common/ground) voltage is connected to the outside cylindrical sleeve of the connector plug.
• For safety, a 5A DC fast acting fuse is connected to the positive terminal of the battery.
• The maximum charge rate of the 12V 8Ah battery is 2 Amps. The maximum draw currently will be less than 1 Amp for most applications.
• The Arduino Uno typically draws 40-50mA (12V - 0.6 Watts).

Parts

• [SPP040201200] Victron 12V 20W Poly Solar Panel (Victron) 440x350x25MM • SERIES 4A • POLYCRYSTALLINE WITH SILVER FRAME - $50 - Springers Solar. Panel is too small to maintain charge over winter.
• [SPP040451200] Victron 12V 45W Poly Solar Panel (Victron) 425x668x25MM • SERIES 4A • POLYCRYSTALLINE WITH SILVER FRAME - $81 - Springs Solar [1]

• [BAT212070084] Victron 12V 8Ah Deep Cycle AGM (Victron) 1.000 ABSORBED GLASS MAT BATTERY (AGM) • VALVE REGULATED LEAD ACID BATTERY Unit (VRLA) • 12V MAINTENANCE FREE DEEP CYCLE AGM BATTERY - $39 - Springers Solar [2]

• SCC010010050R Victron BlueSolar MPPT 75/10 Retail - $120 - Every Battery [3] - Note that this product does not include Bluetooth.

• VE.Direct Bluetooth Dongle (Victron) - $89 [4] - used to configure the Victron MPPT Charge Controller with battery charge parameters.

• JST Jumper 4 Wire Assembly (Core Electronics) - $2.75 [5] connector for the VE-Direct serial connection on the MPPT.
• DC Barrel Jack Plug - MaleDC Barrel Jack Plug - Male (PRT-11476) - $1.75 (Core Electronics or Jaycar) - used to deliver external power to the Arduino Uno.

Charging a Victron AGM 12V 8Ah Battery

To charge a lead acid AGM (Absorbent Glass Mat) battery with an 8Ah capacity using C values, you will need to consider the charging current and the recommended charging rate.

The C value represents the charging or discharging rate relative to the battery's capacity. For example, a C/10 charging rate means the charging current is one-tenth (1/10) of the battery's capacity.

Here's a step-by-step guide on how to charge your lead acid AGM battery using C values:

• Determine the charging rate: Calculate the charging rate based on the C value. For example, if you want to charge the battery at a C/10 rate, you will use a charging current of 0.8A (8Ah / 10).
• Set up the charger: Connect your swallow battery charger to a power source and make sure it is set to the appropriate voltage for your battery (usually 12 volts for lead acid AGM batteries). Also, ensure that the charger is compatible with AGM batteries.
• Connect the battery: Connect the positive (+) and negative (-) terminals of the charger to the corresponding terminals of the battery. Ensure a secure and proper connection.
• Start the charging process: Once the connections are made, turn on the charger to initiate the charging process. The charger will provide the charging current based on the C value you calculated earlier.
• Monitor the charging process: Keep an eye on the charging process and monitor the battery's voltage. AGM batteries typically have a recommended voltage range for charging. Check the manufacturer's specifications for your specific battery model to ensure you stay within the appropriate voltage range.
• Charge until fully charged: Continue charging until the battery reaches its full capacity. A fully charged AGM battery typically has a voltage of around 12.8 to 13.0 volts.
• Disconnect and store: Once the battery is fully charged, disconnect it from the charger and store it in a safe place.
• Remember to follow all safety guidelines provided by the charger and battery manufacturer during the charging process to ensure safe and effective charging. It's also advisable to refer to the specific instructions and recommendations provided by the battery manufacturer for optimal charging of your AGM battery.

C value of Batteries

The C value with batteries refers to the charging or discharging rate relative to the battery's capacity. It is commonly used to describe the rate at which a battery is charged or discharged.

The C value is determined by dividing the charging or discharging current by the battery's capacity. For example, a C/10 rate means the charging or discharging current is one-tenth (1/10) of the battery's capacity.

For a 12V 8Ah battery, the C value can be calculated as follows:

C value = Charging or discharging current / Battery capacity

Let's assume we want to calculate the C value for a charging rate. If the charging current is 2 amps, then the C value would be:

C value = 2A / 8Ah = 0.25 (or 1/4)

So, in this case, the C value for the 12V 8Ah battery at a charging rate of 2 amps would be C/4.

The C value provides a reference point to determine the appropriate charging or discharging rate for a battery based on its capacity. It helps ensure the battery is charged or discharged at a rate that optimizes its performance and longevity.

Measuring Current Draw using a Milli-Amp Meter

Battery Voltage with fixed Load

• The load in this example is 70mA.
• The battery is a Victron 12V 8Ah AGM Deep Cycle Lead Acid battery.
• The load was applied for approximately 24 hours and represents the equivalent of 1.68Ah (0.07A x 24 hours).
• Based on a battery capacity of 8Ah this load represents 20% drain on the battery.
• At the end of 24 hours the battery voltage (while still under load) is 12.25-12.3V.
• We will take this as be lower battery voltage when running experiments.
• Draining more power from the battery will shorten its life.

• Based on the GEL and AGM Battery data sheet from Victron Energy - based on a 30% Depth of Discharge the expected life of an AGM Deep Cycle Battery (Blue graph bar) is 1500 cycles.
• Note that some Gel Long Life batteries can have up to 4500 cycled if the Depth of Discharge is kept to 30%.