Battery Monitoring

Wattmon has built-in features for battery monitoring, and with a few configuration settings you can keep track of a battery bank with voltages ranging from 12V DC to over 300V DC. For low voltages below 60V DC (a 48V battery bank) Wattmon can be directly connected to the batteries via the cable provided, and voltages will be measured from the same cable. For higher voltages an additional power adapter is required.

How does it work?

There are various ways of determining the remaining capacity in a battery. One of these ways is called Coulomb Counting. Another uses voltage to determine the remaining energy. A third method will actually check the specific gravity of the battery liquid to determine the state of charge.

Wattmon monitors inbound and outbound current from the battery bank and uses the Coulomb Counting method. Current flowing through the sensors is read once a second and accumulated in registers.  By configuring the total capacity of the battery, an accurate view of remaining energy is then calculated by subtracting and adding from this value. 

For example: 

A 100 Ah (Ampere hour) battery will be (theoretically) able to supply 10 Amperes for 10 hours (10 A/h * 10h = 100 Ah).  If you take out 10 A for 1 hour, Wattmon will show your battery State of Charge (SoC) as 90%.  If you then charge the battery at 10 Amps for 30 minutes, the battery will show 95% full (90 Ah + 5 Ah).

The Algorithm

Wattmon lets you set the various parameters in the Control Panel. Wattmon will reset the battery status to full when the battery voltage is higher than the 'full voltage' threshold (adjustable) and the current drops below a specific value (adjustable) for a set period of minutes (adjustable). This flexible set of options ensures that most requirements can be easily met.

Different battery chemistries have different efficiencies. You can enter the charge efficiency if you desire to get even more accurate results. If you are using a lead acid chemistry, you can also enter the Peukert constant of your battery bank to get an accurate discharge profile for higher currents.
This method has in our experimental setups proven to be quite accurate. It is definitely more than sufficient to get a good overview of remaining energy.
The device will, based on the remaining energy and the average load over the last few minutes calculate the run time through a web interface from your PC or mobile.

Accuracy

There are many devices which claim to have an accuracy of below 1%. We claim no such thing! It is accurate when it comes to estimating the remaining capacity, however there are cases when it can be off by up to 5 or 10%. Lead acid chemistry is in general difficult to measure accurately. There are temperature differences and many other factors that will affect the state of charge of a battery.

The Hardware

In order to monitor a battery bank, you will require a WattmonPRO and a current sensor module.  Depending on the current you need, this could be the C252 (25A), C502 (50A) or C752 (75A) or the C100s (100A) modules. The two sections below explain how to connect up the system to monitor different types of setup.  Please note that if only one channel is required (for example when only using an inverter and no solar) the left channel of the current sensor module can be ignored.

Monitoring Battery Banks of Upto 48V DC

The following diagram shows the components required to monitor battery banks of up to 48V DC.

Diagram: Monitoring battery bank setups of up to 48V DC

Monitoring Battery Banks of Upto 330V DC

The following diagram shows the components required to monitor battery banks of up to 300V DC.  This requires an additional AC to DC or DC/DC power adapter to power the WattmonPRO device.

Diagram: Monitoring high voltage battery banks (up to 330V)

The battery ground needs to be tied to the power adapter ground. 

Tip: Using a switch mode power supply, you can connect the power adapter directly to the high voltage battery terminals.

View WattmonPRO Details

View C752 Dual Current Sensor Details

Wattmon Add On Devices

DS18B20

DS18B20 Waterproof Temperature Sensor on Dallas Onewire bus with RJ45 connector

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IF1

Frequency and Counter Module with 0.1Hz to kHz resolution and Modbus RTU communication

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IP1

PWM Output Module with high voltage DC sense input and Modbus RTU communication

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I3O2

3 Digital Inputs and 2 Relay Output Module with Modbus RTU communication

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C252

25A Dual Channel Current Sensor module with Modbus RTU communication

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C502

50A Dual Channel Current Sensor module with Modbus RTU communication

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C752

75A Dual-Channel Current sensor module with Modbus RTU communication

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A5S1

5-Channel Analog Input and 1-Channel Shunt Module with Modbus RTU communication

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