28 Jul 2021

Communicating with our inverter

by John O'Brien

232+ reasons to join the 21st century

We live off grid. Most of the time, it’s just like being on grid. Switch on, electrons flow, device works. When we hear on the grapevine that the local power network is down yet again, we know that our freezer contents won’t spoil. Yeh, yay us for self-sufficient solar. But it’s not all feet up and smug schadenfreude. When our system fails, so does our self-satisfaction.

Last week, we awoke to the incessant beeping of an inverter alarm. Battery low voltage warning. Bugger, hadn’t even ground the morning coffee yet! Not good. I used the front panel to give the inverter some cancel culture but it went into shock jock mode and kept shrilly yelling. Cursing back helped none but me. Cancel. Get the kettle on the gas. Cancel again. Enough caffeine left for one brew. OK, there is hope now. Cancel, you *&^$^*.


Let’s have a yack to the inverter and check out its woes

Next, fire up the laptop, take it out into the cold (did I mention that it was about 2 degrees at this point?) and plug in to the inverter, successful hundreds of times previously. No comms. What? Try another virtual COM port – nadda. Crap. Cancel again, grr.

Just as we were flapping around trying to work out the next step, the sun poked out and spared us a few rays to eke into the system. Within 10 minutes, this was enough to tickle the batteries back up past their low voltage threshold. Alarms silent. Phew. Take that, grumpy electronics.

Now with some system stability, we had time to calmly formulate a plan. As the first morning brews finally took their desired effect, my dearest wisely suggested that the system installer should be up and about by now. Yeh, good call. Dana knows this inside info because she also happens to work there 2 days a week. Handy, huh?

Talking to humans is mostly easier than talking to machines

I got on the phone to tech guru Martin to talk over what we were seeing and what could be done. With a sunny day ahead to charge everything full again, the urgency was reduced, so he suggested that the best approach was keep trying to establish connectivity and measure the individual cells first thing next morning (before the sun hits but after the brew is done) to see if we have a dodgy cell. They are sturdy beasts: 12 x 2V SLA @ 1420AH and all checked out healthy.

His Diagnostics 101 approach said: “You had comms recently but not now. What has changed since then?” Me: “Oh nothing, same computer, same drivers, mmmmmm, new Windows install, but nothing otherwise.” We laughed as old friends do while I sheepishly added driver updates to the day’s list. Over 3 hours, nothing worked and I resigned defeated. Martin came by a few days later and connected immediately. Obviously a problem for me to resolve with my laptop.

When talking to humans is harder than machines

The crux of the problem is deeper. Short of the minimal front panel interface, high level communications with our power system have been limited from the start. This design flaw came about through one crucially bad assumption – both system designer Richard and I assumed that the inclusion of a serial port on the inverter model selected would allow appropriate comms to my interface of choice. They had used this port for just that on previous jobs and the inverter exceeded all my briefs on every other spec – robust, reliable, high output and locally made. So, we went with it. Ethernet on inverters was not common then.

When it came time to commission the system, I contacted the manufacturer for a copy of the serial protocols, so that I could start interfacing with an old control processor that I had lying around. “No go, our policies have changed” said the company rep. “We’ve had too many systems borked with end users fiddling around with stuff they didn’t understand.”

I could empathise to an extent – I’d just come from 8 years professionally supporting and trouble-shooting much bigger kinds of mess for many other electronics manufacturers, agents, and installers. I’d talked to hundreds of devices via USB, Bluetooth, Ethernet, RS-232, RS-485, RS-422, 0-9V, low voltage relays and IOs. Surely this would qualify me as a power user.

Further, I offered to own any mistakes that I made and repair at my cost – hang the warranty. Happy to go under NDA and I even offered to share any findings with their techs to help them improve their product. But no, the corporate heads had declared “no 3rd party electronic access on domestic installations” across their range. Extended correspondence went nowhere and we were stuck with what we had. Case closed.

The only monitoring option they could offer was running their software on a Windows based computer, over a serial DB9 link. No other OS supported. Reports only available in MS Excel with macros enabled. Remote web access and easy data exports – forget it! In 2012, the rest of the world was already rapidly going Ethernet or Wi-Fi and dedicated serial ports on laptops had all but disappeared. Without the finance for a one-use-only PC in the cabinet, nor time to sniff comms and try to decipher protocols, a USB to serial adaptor was our only choice.

Getting Serial

Serial communications are very robust. If you get cable length, pinouts, transmission rate (bits per second, or ‘baud’), data and stop start bits, parity and flow control correct, it is stable and reliable. I’ve used it heaps in all sorts of situations. Getting this to be as reliable when converting over another layer like USB can be problematic. 

I’d had no end of fun with USB-serial dongles in my recent employ (some would talk to many devices, some only one, none all) but had a few favourite units to test with. My no-name cheapy won out yet again and I installed the Belkin drivers that it so loved. Plug in, fire up inverter software and “Hello World”, I’m in. Cool.

With the magic dongle permanently attached, hauling the laptop outside to interrogate the inverter had worked stably for over 8 years since. It had done so with 4 different machines and 6 Windows installations. But doing so takes my primary work tool offline and into a dusty, harsh environment and those are both a pain in the bum. Last week’s problem was the first major hiccup.

Communication breakdown nearly drove me insane

It might have been avoided if I had completed the house-wide comms network. When the inverter company recently released an Ethernet converter for our model, I bought it straight away, sceptical but hopeful. But I’ve not yet finished all the RJ45 terminations and rack work so, when last week’s drama unfolded, it was gathering dust. When the network is done, we should be able to see our battery system status directly from the comfort of our study desks.

Meanwhile, I scoured the internet for wisdom as I faffed with drivers and virtual COM port settings. Today, I finally won. I had an electronic conversation with the inverter. Downloaded all logs, checked statuses and did a little jig. Comms restored. Woohoo.

What was the fix? When I reinstalled Windows recently it did ‘the right thing’ and updated all my drivers to their latest release. For most software and drivers, this is a surprisingly good feature and generally works well. In this case though, the fresh OS had reassigned my virtual COM ports to be “Standard Serial over Bluetooth link”. Not what I needed. It had also hidden the legacy “USB-to-Serial Comm Port” ports that I did need.

I selected ‘view hidden devices’ to see: “PL2303HXA PHASED OUT SINCE 2012. PLEASE CONTACT YOUR SUPPLIER”. Okee dokee…been working for me until 2021, but yeh. More research revealed that some PL2303 chips are wrong’uns and manufacturer drivers have recently been updated to not talk to apparent fakes. Windows compounds this by auto-updating drivers to the latest versions. I found a legacy driver, tried installing it to the hidden COM port, only to have it fail and revert to the ‘phased out’ warning every time I physically plugged in to the inverter. Before phasing out myself, I then installed the legacy driver whilst plugged in and it stuck. Let’s hope it stays that way for a while.

The good feels…for the good life

When the sun is out, we care not for the convenience of the grid. If we are careful with consumption, our monthly power bill is less than $10 to fuel the backup generator. Though it did cost a bit to set everything up to be cheap to run, that investment is paying off. It’s a nice feeling.

It’s not so happy vibes when this illusion of independent nirvana shatters. Tethered by communications to the outside world, we also rely heavily on solid comms with our basic life support infrastructure. My current hack will work for a little while but methinks it’s time to move forward with finishing the whole house network. Then we can kick back content, knowing that communicating with our power system is but a click away.

P.S. (written 2 weeks later)

It turns out we did have a dodgy cell. Low voltage alarm tripped again a week or so later and one read 32mV. Three-hour round trip to grab a replacement 80kg lump and a two-hour swap in. Charged from gennie, sat down to dinner and sudden darkness! Arrgggh, dug out some candles and had an early night. Checked next morning, the new cell was so bad it had reversed polarity. Arranged another emergency visit to grab two more second-hand cells. Installed and charged the one that read 2.14V but, as the sun dropped, so did the battery and we plunged back to candlelight for another evening. Next morning, we tentatively swapped in the third cell, then charged and set to equalise.

Nature smiled and gave us a long sunny day to fill the bank up and fortune left us enough electrons to rejoin modern life. Good crisis management also kept our perishables from spoiling. That night, and in the nights since, we have thoroughly enjoyed the simple conveniences of lights, telly and phone charging. We also appreciate how very fickle that can sometimes be. We are content but concerned…and have a managed PoE switcher on the way.


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