How would you begin to troubleshoot this?

[rthorntn]

Hello you very helpful bunch!

I'm pretty much at my wits end, around 6 months ago I moved my house to batteries, 15.5kWh out of eight LTO batteries (Zenaji Aeon) and two "paralleled" 5kW inverters (MPP 5048MG), its not really a question about these specific parts but how you would go about troubleshooting an intermittent issue.

So for a few months I had no issues, then as the weather here started to improve the power to the house started to cut out for a few seconds every week or so, we suspected heat and so we improved the air circulation in the cabinet (it was getting hot in there), that didn't fix it but the frequency of the outages dropped to around once a fortnight which may suggest that there are multiple issues.

The inverters have no real logging and no alarm seems to be triggered during the outage, I've never been near the inverters when it happened.

How would you go about troubleshooting this, the outages happen rain or shine, morning or afternoon (never after 9pm or before 7am), so thankfully it doesn't happen when we're sleeping and it's never happened when nobody is home...

I know the inverters "freak out" if the batteries aren't connected (I've witnessed the house power becoming unstable when the batteries all tripped one time), they need a battery for "stable" operation.

I have a monitoring solution that shows me all the voltages and stuff, it really provides no clues, it just shows all the readings dropping to zero for a couple of seconds and picking up again.

Maybe the heat damaged the inverters early on, maybe I have an issue in the house wiring, I guess I'm looking for tools or techniques I could use to narrow down the issue.

The installer has no idea on what is causing this particular issue (and he's on sick leave), the inverter manufacturer is silent.

I'm logging the time / date of the outages and the battery voltage / house load / temperature at the time but it's all over the place, no real clues apart from the ones I mentioned.

I've thought about installing a camera into the inverter enclosure.  I have wondered if there is a device that can log weirdness to do with the house voltages.  One of the problems I have is the house runs off the inverters so I can't do a lot with them as they are online all the time.  The paralleling mode of the inverters probably doesn't help because it may be masking a slight issue with one inverter, the problem is I can't just disconnect one, potentially for weeks, I need both to power the power hungry devices.  Maybe I could try using a third inverter for testing (I actually have one on order)...

The power went out yesterday, the only thing that was a bit different was it lasted considerably longer, more like 10 seconds, I guess that could be a sign it's getting worse.

How would you troubleshoot?

Happy Holidays!

Thanks.
Richard

[Hugo Balls]

At least a visual inspection inside of those inverters for bad solder joints and/or burn marks
Check the temp inside see what parts get suspiciously warm

[rthorntn]

Thanks, that's a great idea, what I mean is it makes more sense than normal because I can AB with both inverters running on what should be a nearly identical load, I loaned out my FLIR TG165, time to get it back.

The MCU will probably be warmer on the master inverter.

[james_s]

I think I would start by setting up a logger to monitor the battery voltage as close to the inverter as possible, probably good to monitor the output voltage too, that doesn't need to be precise, a simple power transformer salvaged from some small device would do. Then if the output voltage sags you can correlate that to what the input voltage is doing. I find it pretty surprising that the inverters don't have any sort of fault detection or error logging, I'd expect that sort of thing on something so large.

[CaptDon]

We need to know a bit more about your setup. Are the inverters
actually running (producing power from the D.C. batteries) all
the time and the line is supplying more power into the batteries
than the inverters are consuming?? This is a 'full run' scenario
used with very sensitive and high reliability systems where no
transition glitch is allowed. The output from the inverters never
varies regardless of line input. Or is your system one where the
line is powering heavy transformers inside the inverters and when
the line dies then a bunch of mosfets start using battery voltage
and PWM to continue to drive the transformers until the line returns??
Or is your system on a relay style transfer switch where the house
is completely on line power and if the line drops the inverters switch
to producing power and a transfer switch moves your house from
line to inverter?? Are your inverters linked together with a small
signal cable so they each know what the other is doing?? Are
your inverters even designed or allowed to operate in parallel??
Parallel inverters need to be phase syncronis often done with a small
communication cable between the pair. If they are not sync'd or
fall out of sync they will fault out and either overload or take
a bit of time to re-sync then come back up. Each system I described
is very different and each will have a slightly different troubleshooting
approach.

[Doctorandus_P]

I find the use of "paralleled" inverters quite strange.

Here in Europe it's quite common to have 3-phase power, but I have no appliances that use all three phases together. Just different phases go to different parts of the house.

How many power hungry devices do you have?
And what is the most power hungry device. Does it need 5.5kW?
I very likely would not have put those inverters in parallel in the first place, but routed them with separate cables to different appliances.

It's also possible it's just a bad connection in the wiring. A common way to check for this is with an Infra red camera. You can also put on some rubber gloves, boots and a face shield and start pulling on the wiring to see if it moves in the wrong places.

[james_s]

I don't find the idea of paralleled inverters to be all that unusual, I would need more than 5.5kW for my house, my clothes dryer alone is 5.5kW and with that running I would not be able to run anything else. It wouldn't be practical to provide the dryer with its own separate inverter that sits idle most of the time. If the air conditioning was running I wouldn't be able to use the microwave and the toaster at the same time, or my air compressor, or various other combinations of loads, especially motor loads with high inrush currents. As has been discussed at length in other threads, 3 phase power in homes is very rare in most of the world.

While not exactly the same, in a similar concept almost all inverter type portable generators are parallel capable. The Honda EUxxxxi series for example is very popular among RV campers, and they will often have a pair of them connected in parallel, most of the time just running one but when there is a need to operate higher power loads like an air conditioner or microwave oven they can fire up the second generator and it will operate as a slave syncing to the frequency of the master and sharing the load. A pair of smaller generators is more economical than one larger generator if you can get away with just running one of them much of the time. There's no reason battery to AC inverters can't work the same way. It's much simpler to have everything fed from a single panel than to have multiple smaller panels each fed from their own separate inverter and trying to get loads balanced properly between them.

[rthorntn]

Thanks everyone, I'm no expert in this but I know enough and can find out more, the inverter has two main modes battery and utility.

I try to keep it on battery mode but the weather often messes with my plans, I have been on battery constantly for the last 3 days.

So there are solar, utility and battery inputs, if I have enough solar the house runs off it, if I have extra solar it charges the battery.  At night (in battery mode) I run completely on battery.

Utility is only used if I go below 44V on the battery.  It will stay on utility until the solar gets it back to 48V.

There is a transitional glitch, the lights flicker a little but that glitch is short enough that computers stay on.

It is "proper" paralleled, there is a special parallel PCB with a comms cable thats installed (I believe) it uses CANBUS, they share the load equally.

For anyone interested in learning more there is a great thread https://forums.aeva.asn.au/viewtopic.php?f=64&t=5830 on the guts of these inverters.  The inverters are cheap as chips, with hindsight, probably not the best inverter to run a house from (bad support, terrible for troubleshooting, so-so components).

I do need 5kW+, my AC inverter uses pretty much all of that on its own, the oven, AC and the pool pump would be around 8kW.  I also factored in that they might last longer if I spread the load, that's one of the reasons why I'm adding a 3rd inverter (the other reason is I want to add more solar panels).

Someone asked about three phase, I don't have it and because of the age of the "lead in" enclosure upgrading would have cost a small fortune.

Thanks again.
Richard

[geggi1]

Start up simpel.
Check all connections between battery and inverters. Look for loose wires and signs of heat to the cables and terminals.
Try to split the inverters  and run some circuits on each inverter. Inverters and VFDs dont like to run in parallel especial during low load, they will start to fight and usually one will one of them will tripp.
You can also run only one during low load and see if it is possible to duplicate the falult.

[rthorntn]

Thanks everyone, happy holidays, interesting, I just noticed that the UPS I setup to keep the NBN up during these outages is clicking a lot, multiple times an hour (it's going to wear the relay out), the house is on battery right now, the UPS switching like that suggests issues with the input power, or is it a symptom of running from inverted power?

[james_s]

A UPS will kick in when it detects the voltage is above or below the acceptable range, most will detect a very brief transient. The inverter power shouldn't matter, assuming it's a pure sine inverter which I'd expect something in this application to be. Have you monitored the voltage with a multimeter?

[wizard69]

At least a visual inspection inside of those inverters for bad solder joints and/or burn marks
Check the temp inside see what parts get suspiciously warm

This is the very first thing that came to mind.    In fact I'd go further  and look at all the wiring feeding the inverters, and the inverter wiring feedign the house distribution system.    Bad connections in power systems can most certainly lead to the described problems.

Also finding somebody with a thermal camera might help Zero in on hot spots needing addressing.

[wizard69]

The first thing to ask here is do you have any sort of multimeter?    When working with AC powered devices you should verify the AC voltages if problem crop up.    Now it could be glitches or brown outs, a cheap meter might not be able to tell you which but can get you started on debug.   In all honestly though I'd do what is called PM work, which is to make sure all the electrical connections are made up tight and that there is no corrosion.    You wold be surprised how many times I've worked on huge pieces of automation hardware and have the line come to a screeching halt because of a loose connection.   This type of work doesn't require much in the way of equipment just some hand tools and knowing where the shutoffs are in your system.

Now this doesn't mean your inverters are all good, just that I would address something that should be done periodically anyways.   That is all electrical systems should be inspected on a regular basis.   Often these days it is done with thermal cameras but they will not catch every issue.

Thanks everyone, happy holidays, interesting, I just noticed that the UPS I setup to keep the NBN up during these outages is clicking a lot, multiple times an hour (it's going to wear the relay out), the house is on battery right now, the UPS switching like that suggests issues with the input power, or is it a symptom of running from inverted power?

[Gregg]

I would suspect the battery connections because of the very high current required.  A poor connection anywhere in the DC system could cause enough of a voltage drop for either inverter to drop out.  Do you have separate batteries for each inverter, or do they both use the same or paralleled batteries?  Certainly your Flir would be a valuable tool for checking the connections.  The problem could also be in the solar regulator.
Edit: To start out, use a multimeter and check for voltage drop across all connections while the system is under load. 
Also, the two parallel inverters may have circulating currents between them; a clamp meter may be able to spot this if the output currents of each inverter do not add up to the total load current.

[rthorntn]

Thanks all!

I have a DMM, or three.

The system is around 6 months old, the installer put it all in, checked it with his FLiR on install day and a month later he came back and checked with the FLiR again.

Over on the AEVA forum someone has posted to say he has similar issues and it seems completely random 

The house wiring is fairly crappy, the house was built in the 1920's, the meter box has an archaic looking star earth arrangement with more and more earth wires all clumped in together, the installer mentioned that I should get that upgraded.

My installer actually installed a Lantronic SATS (Solar Transfer Switch, discontinued now) so (when I have excess solar) I could switch my panels over to my old grid-tie inverter to feed in, except when I hit the switch it kills the power to the house, it wasn't immediately obvious why and so the installer was going to come back to fix it, then he fell and broke his ankle and so he hasn't had a chance to take a look since.  Not sure if that's connected.