Solving the Tesla Powerwall frequency problem

TLDR: Useful if Tesla Powerwall frequency shifting during outages is affecting appliances like clocks, furnaces, uninterruptible power sources (UPS), etc. Want to skip right to fixing the Tesla Powerwall frequency problem? Click here.

In February 2018, we installed a Tesla Powerwall 2.0 on our Vermont home. We get around thirty outages a year, and for the last 4 years this device has provided us with a reliable automatic backup electricity source capable of running our home through outages of up to two days. (Read more about my experience with our Tesla Powerwall here.)

Whenever there was a lengthy outage, I noticed that my old-fashioned digital clocks would run a little fast. I’d reset them to the correct time and didn’t think much about it.

Until one day…

Houston, we have a problem

Earlier this year, I reluctantly dismantled our 38-year-old solar hot water and space heating system, and replaced it with a gas boiler. (One of the system’s large, expensive solar storage tanks had sprung a leak, and I would have had to replace all three tanks. Our solar collectors were still working flawlessly, but I worried that they might not last much longer.)

The gas boiler, a high efficiency Alpine condensing boiler, was installed to heat a new stainless steel domestic hot water tank and the two existing radiant floor heating systems. After dealing with the inevitable teething troubles, the system was working well.

Until we had a power outage while the boiler was running.

Passing the small utility room that contains the heating system, I noticed a red glow that was definitely not normal. Going in, I saw that the boiler’s touch screen display had turned red. The boiler had shut down with a “hard lockout”. Looking up the displayed error message “Fault 23” told me that the boiler was unhappy with the Tesla Powerwall’s power.

This was not OK. First, the boiler would not operate during a power outage. Furthermore, it would not turn on automatically once utility power returned. That’s because you have to manually reset the hard lockout using the boiler’s touch screen.

So if we left our home for a few days and a power outage occurred during that time, the boiler would not operate until someone entered our home and reset it. Having our plumbing freeze and plants die while we were away was not acceptable.

Diagnosing the problem

It wasn’t hard to figure out what was happening, once I remembered the previously ignored clue that some of our clocks ran fast when using Powerwall power. These clocks are the old-fashioned kind that keep time based on the national electric utility frequency of 60 hertz (Hz). Clearly, the Powerwall must be providing backup power at a higher frequency.

To my surprise, a quick Google search told me that Powerwalls supply power at 66 Hz when they are at full or close to full charge! My furnace was shutting down because, unlike the rest of my appliances, it would not operate correctly at 66 Hz. But why would Powerwalls do this?

Well, it turns out that many Powerwalls are used as storage for photovoltaic (PV) solar panels. PV systems also use an inverter, like the one in a Powerwall, to generate household power. And when the house’s electrical needs are being met with the Powerwall charged to or near full, there’s nowhere for additional solar-generated electricity to go. So the Powerwall is designed to switch to 66 Hz under these conditions. PV inverters, like my furnace, see the frequency out of the normal spec and shut down. The Powerwall supplies the home until it has spare capacity to be recharged by the solar panels, and then drops its frequency down to 60 Hz. Until then, the solar inverter (and my furnace) will shut down.

Ok, so I understand the problem and the reason Powerwalls are designed this way. But I don’t have PV panels, and I want my furnace to work when there’s a power outage! What could I do?

Fixing the Tesla Powerwall frequency problem – option 1

Luckily, as you might expect, I wasn’t the first customer to have this problem. More Googling indicated that I could call Tesla and ask them to remotely update my Powerwall to reduce the frequency of power it provided under high charge conditions.

So I did. After a long hold time for Tesla Powerwall Support [(888) 765-2489], I spoke with a friendly technician, Manny. He confirmed that Tesla will make this change and placed an order for my system. Manny told me the change usually took 3 – 5 business days, and he would get back to me when they did it.

I waited. After nine days, I called back to get an update, and Andrea told me the queue was currently running 10 – 15 business days. So I waited some more.

Sixteen days after I’d spoken with Manny, he emailed me that Tesla had made the change. Great! Now, I wanted to test to see if the fix worked.

Testing that Tesla’s update worked

I didn’t want to wait until a power outage occurred while my furnace was running. So I decided to manually switch our home to Powerwall power.

I hadn’t done this before, so I investigated my Powerwall installation. It’s mounted on an external wall, so it’s easy to see the components. Please note that there are several ways to install Powerwalls — don’t assume that your configuration will be the same as mine. Here’s a photo, with the components labeled, of my setup.

Tesla Powerwall frequencyGrid power flows through my utility meter through the gateway to the Powerwall disconnect, which is hooked up to both the Powerwall and my main home breaker panel.

For my setup, to switch our home to Powerwall power manually you simply have to open the gateway box and turn off the grid disconnect switch.

Tesla Powerwall frequency

After flipping the grid disconnect switch, I went inside and turned up a thermostat so our boiler would fire up. Success! The Alpine now worked happily on Powerwall backup power!

I don’t own a multimeter that includes frequency measurement, but I found another way to discover the frequency that my Powerwall now generates. By logging in via your gateway’s Wi-Fi network, it’s possible to view the operating frequency of your Powerwall. These instructions provide a guide. I discovered that my Powerwall’s output is now between 62.1 – 62.3 Hz. Apparently, that’s close enough to 60 Hz to keep the boiler running.

Fixing the Tesla Powerwall frequency problem – option 2

Although I solved my boiler problem, that doesn’t mean other appliances or devices are immune from Tesla’s frequency switching technology. If that turns out to be the case for you, there is another option that should work, though you’d have to pay for it.

The trick is to use an online aka double-conversion uninterruptible power supply (UPS) to power the troublesome device. (Offline/Standby, Line-Interactive, and Automatic Voltage Regulation types of UPS don’t change the frequency of the power supplied.) An online UPS charges a battery that runs an inverter providing 120 volts, 60 Hz power independent of incoming power quality. When grid power fails, this type of UPS has no transfer time. Plug the problematic device into an online UPS that has enough volt-amp (VA) capacity and you’re all set. Note that the backup time such units provide is irrelevant since they will still be receiving power from the Powerwall.

The only drawback to this solution is the expense. An online UPS costs more than the other types. The least expensive unit I could find via a quick search, the Maruson 1000VA Online Double-Conversion UPS, costs almost $500.

Conclusions

Once again, I’m very happy with my Tesla Powerwall. It would be nice if an installer or owner could make this frequency change, rather than waiting for two weeks for Tesla to do it. But at least there was a fix that only cost some time for research and a couple of phone calls, and my boiler power problem is resolved.

I hope this article will help anyone else who runs into the same problem. Please share your experiences and suggestions in the comments below.

 

Listening to the UPS guy

After dinner last night I heard a familiar sound — the growl of the UPS box truck driving up our 600′ rural driveway. I knew it was our regular driver, the guy who’s been delivering for years, because if he sees I’m in my home office he’ll stop and do a tight three-point turn outside the entrance, rather than driving past to reverse by the garage.

I heard the van door slide back and went to the door to meet the guy I’ll call Roger. Roger is tall and lanky, has a sweet smile and disposition, and is open to talk if the time is right. Over the years he’s met me hundreds of times in that doorway. Mostly, he smiles and hand over the delivery, I thank him and wish him a good night, and he jumps into his truck, finishes reversing and drives away. Once in a while, when the roads are bad, we talk about his day: how he’s handled the challenges of delivering along my rural town’s sixty miles of dirt roads plus the surrounding area.

For some reason I hadn’t seen Roger for a few weeks; the other drivers had been making deliveries. So I said, “Hey, you’re back!” as he strolled towards me, package in hand.

“Well, I’ve been off a lot; my mother just passed away,” he replied.

“Oh, I’m sorry,” I said. I stood and looked at him.

“Well” he said…

…and he started to tell his story.

Roger talked about his mom. He stood facing sideways from me, with an occasional glance in my direction prompted by my occasional responses to what he was saying. Once in a while he’d swivel to face me, sharing something that was especially important. Then he went back to telling me about his frequent journeys down south to see her since she’d fallen and broke multiple bones in June, how his family had done their best to cope, and her eventual decline and death.

He told me about dealing with “picking up the pieces” now she was gone. About the last time he saw her in the hospital, when she was “all scrunched up” and seemed out of it, until he bent down and hugged her and told her “I love you mom” and she opened one eye and said “I love you too” “as clear as anything” and then closed her eye and “was out of it again”. He told me much more than I’ll share here.

Roger talked for over ten minutes, by far the longest conversation we’ve ever had. Now and again he edged away during our time together. But he couldn’t quite get himself to stop what he wanted or needed to say.

And that was fine with me. I was in no hurry, and he wanted to talk.

At the end I wished him well and he turned, got into his van, and motored off down my driveway.

It felt good to listen.