By now most of you have seen the DIY solar generator project on the channel and social media. Well after posting the successful benchtop test on Instagram and the blog, I thought I’d take a moment to write a small post about the PowerMon Bluetooth battery monitor from Thornwave. (Amazon link). This is the wireless battery monitor integrated into the DIY solar generator.
One of the most important aspects of having a solar generator is understanding this state of charge from its battery, as well as incoming energy from our solar panel or power supply. Having this information allows us to understand how long the solar generators going to be able to provide energy for our gear during a grid down or off grid Excursion. For this reason, one of the primary functions of the DIY solar generator project, is letting the user know the state of the system in real time. To achieve this we use an embedded wireless battery monitor. Essentially it’s like an embedded fluke meter, but a very small, very low power, Bluetooth enabled version.
About the PowerMon
Here are some of the PowerMon features.
- Remotely monitor two DC voltages, current, power, energy (Wh), battery state of charge (in percentage and Ah), and temperature.
- Measures voltage up to 60V and current up to 60A using the internal current shunt
- Sense up to 160mV of voltage drop across an external current shunt, allowing 300-600A currents to be measured.
- Control a power relay or SSR (Solid State Relay), low / high voltage disconnect, over-current disconnect, remote ON / OFF
More details and well-documenred user manual at: https://www.thornwave.com/products-btdcpm
We’ll be using the integrated current shunt for the DIY solar generator. For this configuration the ES+ and ES- pins require a jumper. These pins are connected together using a wire bent in a U shape and attached to pins 4 and 5 on the terminal block. We’ll monitor the current by routing through the 0.5mOhm shunt between the IS+ and IS- terminals.
The aluminum, hex screw terminal blocks (IS+ and IS-) can accept wire up to 6AWG in size. I chose 10AWG for these connections. It’s overkill for the 30 amps of the radio, but will also reduce any voltage losses. If you’re following the DIY solar generator build, I would suggest minimizing the voltage drop on wires and connections, by using the thickest, best quality wires supporting your projects current requirements. Doing so will reduce voltage drop, and excess Heat.
One thing which was confusing during the setup was where to tap the circuit to integrate shunt. In the end it doesn’t actually matter. The common mode voltage at IS+ and IS- can be in between -2V and +75V relative to ground. This allows the shunt to be placed on either the positive side of the circuit, or on the ground wire. Current flowing from IS+ to IS- is displayed as a positive value and current from IS- to IS+ will display as a negative value. The current sign can be flipped in the app from the device configuration menu.
As you can see, integrating the battery monitor into the solar generator is extremely straightforward. In addition to the jumper I mentioned above, there’s four connections for my particular configuration,
- Voltage +
- Shunt in IS+
- Shunt out IS-
Like the user documentation says, the shunt can be connected on either side of the circuit. I tested on both the positive and negative sides of the circuit with success. For the video the shunt is connected to the ground side of the circuit.
The PowerMon app
The PowerMon device requires a mobile device running Thornwave Labs’ PowerMon app which is
available free for both Android and iOS. It can be found on Google Play Store and Apple App Store.
Here’s what we can do with the PowerMon device and app.
- Scan for PowerMon devices and display a summary of measurements (voltage, temperature, battery state of charge and power status)
- Connect to devices and obtain real-time measurements
- Device Configuration (external shunt parameters, low voltage disconnect, high voltage disconnect, overcurrent disconnect, battery fuel gauge,…)
- Zero the current reading offset
- Calibrate the current reading
- Rename the device
- Reset the power and charge meters
- Manually turn the power relay ON/OFF
- Update the internal device clock from the mobile device current time and date
- Create, edit and delete timers
- Restore factory defaults
- Configure the password protection
- Update the device firmware
To use the PowerMon device, we need a phone or tablet with a Bluetooth Smart (LE) adapter. The app will not
install on older devices not supporting Bluetooth Smart (4.0).
I have successfully tested it on my Samsung Galaxy Tab active t365, and my Samsung Galaxy S8.
DIY Solar Generator 45ah 576wh OH8STN:
The DIY solar generator is definitely one of the most rewarding projects I’ve worked on for the channel and blog. It’s also giving me some much-needed rest from making videos, while I do my research, collect the pieces, and go through my testing. I hope you all will enjoy this project, just as much as I am having, doing it.
Managing internal temperature
One of the issues we have when we use lithium-based batteries is charging in extreme temperatures. here at 65°N, that extreme is usually the cold. One of the interesting features the shunt has, which I haven’t seen in the any commercial solar generator, is the temperature sensor. The sensor allows us to remotely check the internal temperature of the enclosure. Since our lithium iron phosphate batteries have a spec regarding low temperature charging, we can always be certain the internal temperature of the system, is within that spec when charging.
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