Instrumentation Options for a Portable Generator
In various online forums, people are routinely asking for help when faced with a generator that’s being overloaded. This may be in the context of a food truck, mobile pet salon or delivering whole house backup power.
It’s believed that management guru Peter Drucker once said, “You cannot manage what you cannot measure.” I have been making a lot of use of that quote when offering answers to such questions. If you are placing a significant load on the generator, you need to monitor the load to know when you are nearing overload. Allowing it to overload is disruptive, time consuming and potentially dangerous. Without hard data to inform your decisions, you’re only guessing about how to address the problem.
Option #1: Built-in Load Monitoring
If you don’t yet have a generator, you might well consider instrumentation in making that choice. For example, my Harbor Freight Predator 9500 was one of the first of a new crop of high-power inverter models that became available in 2021. It does not have any built-in instrumentation. So, it was incumbent upon me to provide such capability externally.
In contrast, a bit over a year or two later a neighbor bought a Pulsar PGD95BISCO from Home Depot. This Pulsar if effectively a cousin to my Predator. They’re both made in China by Chongqing DK power machinery Co.,LTD. The Pulsar model was introduced later in February of 2023. To be competitive it has a few more features that the Predator. One of the nicer features is a built-in load meter.
The built-in LCD shows the output voltage, frequency and aggregate load on the generator in real-time. This is very handy. I wish my Predator had this feature.
I discovered just how handy when helping this neighbor with an initial test, running his home on the Pulsar. They have more electric appliances that our home. Also, a 2-stage central air conditioner. It made some sense to see just what they could safely use while on backup power.
When we first put the house on backup power everything was fine. However, when their AC unit switched on, it immediately overloaded the generator. It did this every time. And each time, the load meter indicated 9.5 kW. The generator did not shut off, but it consistently tripped a circuit breaker to protect itself.
It was swiftly apparent that he would need to have a soft start unit installed to the air conditioner. Once that was done, the Pulsar ran the whole house, including AC, without issue.
Yes, built-in instrumentation is handy. It’s definitely something to consider when choosing a generator.
Option #2: DIY External Load Monitoring
There are loads of places online where you can find guidance on building your own power monitoring rig for use with a portable generator. Today I will highlight Eddie Wright BBQ in Mississippi who has a short video highlighting the solution he built to monitor power to his shipping-container-turned-BBQ space.
In truth, I think this design originated with Gavin at the Generator Superstore. Gavin, a fellow Houstonian, is a great resource for info on portable generators.
This approach is affordable and quite practical. It typically puts the ability to monitor in the wiring from the generator to the load. That means that it’s going to be outside, likely close to the generator.
I suppose you could connect it closer to the load than the generator, if that were more convenient.
Option #3: Wireless Load Monitoring
I took a very different approach. I installed a Shelly Pro EM50 directly into our breaker panel. This device monitors the power being drawn, making that data available via Ethernet, Wi-Fi and Bluetooth. Shelly makes a variety of current sensors, from 50A single phase to 400A 3-phase.
Diverse means of connectivity provides a lot of flexibility. In a permanent installation at our home, it connects to Home Assistant via Wi-Fi. Honestly, I’d rather use Ethernet, but it’s complicated to bring Ethernet into the breaker panel.
At the house, the Shelly sensor is right in the breaker panel. I can read the load in the Shelly app on my smart phone (pictured.)
In a food truck or grooming truck, the EM50 could be installed to the truck/trailer breaker panel. Alternatively, it could be installed to a plastic box with and plug and socket, like Gavin’s inline monitoring rig.
The EM50 foregoes a built-in display, instead providing for wireless remote monitoring from nearby. I’m ok with that.
In a food truck situation, I could monitor the load via Bluetooth using the Shelly app on my phone. That means being able to monitor the load from inside, not outside in the hot sun or rain. The app allows for trigger-based actions. That means it could issue a notification if the load crests some predefined measure.\
If it were my food truck it would likely have a local Wi-Fi network. That would provide connectivity over a reasonable distance.
Regardless of the method of connectivity used, the EM50 is a recording device. It keeps a track of the load over time. This can be read by the Shelly app or external things, like Home Assistant.
Close
There you have it; three different approaches to load monitoring when using a portable generator. However you choose to go about it, measuring the load is better guessing. It means you have real data you can use to manage the situation.