Backup down under

wattmatters

Photon Sorcerer
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Another day, another experiment....

I wanted to test something about my AIO inverter's capabilities. As a reminder this is a clone PIP-4048HS.

It was my (and others I know) suspicion that the inverter caps PV output based on the battery max current charge setting, no matter the AC load applied. e.g. if the max charge limit is set to 20A (nominal 48V battery) then the PV output will max out at ~1kW no matter if there is ample sun for the array to supply more and the load on the AC output is >>1kW.

So today I did a test by applying a load greater than the PV array would be able to supply - a resistive element heater. I calculated the likely maximal output of the array under perfect conditions today would have been ~1.65kW.

Sure enough despite a 1.7kW load, the PV output was capped to about 1kW.

So I used Solar Assistant on my phone to change the battery charge current limit setting, increasing it from 20A to 40A.

The inverter's solar controller did a reset, output went to zero briefly before it began to ramp back up to supply the load. No interruption occurred to the AC output and the battery was at all times supplying the balance of power. This time the PV output increased to 1.5kW.

I then repeated the exercise by changing the battery charge limit back down to 20A, then back to 40A and back to 20A again. Each time the PV output was higher with the higher charge limit despite the battery not actually charging (it was supplying the balance of demand through the whole test).

Here's the chart showing the PV output and load power during the experiment:

Screen Shot 2021-09-06 at 1.41.13 pm.png

It's an interesting quirk of these inverters.

I'm guessing it's a limitation designed to prevent the prospect of the inverter having to dump load to the battery greater than the set charge limit in the event a large load is removed and before it has enough time to ramp PV production back down. It would be nice though if it were capable of managing this so it could ramp up PV output to meet the AC loads.

It won't be a limitation for me as I'm about to double the battery bank and when that's done I'll reset the charge limit to 50A, which is 0.13C and at the low end of the safe charging level specification for these batteries. 50A x 48V (nominal) = 2.4kW. My array is rated at 2.22kW so it will never actually supply 50A to the battery, but the higher setting will mean PV output will never be throttled because of this setting.
 

wattmatters

Photon Sorcerer
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One more update today, and a good one.

I had been experiencing an issue with a tripping RCD in the inverter's AC output circuit board which supplies power to the transfer switch in the main circuit board. RCD would trip if I tried to use the Utility first mode to pass grid power through to the backup circuits via the transfer switch. No issue if supplying backup power while in solar/battery mode, or if the AC supply was coming via the generator instead of the grid.

Since all the downstream circuits being supplied already have RCDs in place, we swapped out the offending RCD with a regular overcurrent protection breaker and all is working exactly as it should. The circuit supplying power to the off-grid power outlet (for the pool pump) still has RCD protection.

UPS cutover between grid and solar/battery now works perfectly. This is super nice. Now that's all working, I can move onto the next phase of the project to reconfigure the physical installation of the inverter, cabling, upgraded DC circuit protection and add the second battery bank.
 

wattmatters

Photon Sorcerer
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Well today was the day for upgrading the installation and to add the second battery bank.

Started by pulling everything out and lining the housing with cement sheet where the inverter and bus bars and fuses are being mounted. Then redid all the terminals into the AIO inverter with ferrules (much easier to install!) and reinstalled the inverter. Added the battery circuit breakers and fuses and bus bars. Lots of cable clamps and saddles to keep it reasonably tidy. Some extra conduit as well.

Inverter and cabling in/out:
IMG_3113.jpeg
Hall sensor around main battery negative for a remote battery monitoring display module. Voltage sensor wires routed to main positive and negative bus bars. Also a temperature sensor.

Fuse connection and bus bar:
IMG_3114.jpeg

Each bank of batteries will have an 80A NT00 HRC Fuse inside a Triple NT1 HRC 250A Fuse Isolating Switch (switch not shown, just the base into which the switch is fitted). Only using two of the three terminals.

Then joined via bus bar to a 150A ANL Fuse in a fuse holder and onto the AIO inverter.

One bank of batteries in situ but not yet connected:
IMG_3115.jpeg
HA02 battery balancer connected to battery terminals, one for each bank. They work quite well. Batteries connected in series with busbars and covers in place.

I have put the other bank on top but no pics, it was getting dark.

I've also made a couple of the remaining cables to connect the lower bank. Using 35mm² welding cable, lugs crimped with hydraulic crimper and colour coded heat shrink to insulate lugs ends.

It was a marathon today and I was not quite finished by the time it got dark and so I need to finish it off tomorrow.

Once I have the cables done then the process of re-commissioning. Need to get both banks to same voltage before connecting in parallel.
 

wattmatters

Photon Sorcerer
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I got the other bank of batteries in place, the extra cables all lugged and heat shrinked up and everything is in place. I now have the system operating from the second (top) bank to give those batteries a good charge up today.

That's half a tonne of battery sitting there. 8 x 190Ah @ 12V = 18.24kWh nominal.

IMG_3116.jpeg

I plan to put a removable board across the front of the batteries so they have physical separation from the rest of the housing where I store some other items (e.g. pool robot). Will help to reduce accidental catching of wires (mainly the battery balance leads).

A closer shot of the fuse holder/breaker, bus bar and ANL fuse holder.
IMG_3117.jpeg

Negative busbar below. Hall sensor for separate battery monitor in this pic is fitted the wrong way round the cable. Oops. No matter, I had to disconnect the battery to connect the other battery, so I undid the inverter's DC connection cable and flipped the sensor around.

The lead shown not connected (with the grey tape around the lug for temporary short protection) is the second (top) bank which is now connected while I rest the bottom bank. The black wire on the right is the temp sensor, which has been moved now to sit in the middle of the batteries.

IMG_3118.jpeg

I want to put another cover across the top of that busbar as the cover protects from the front but not the top. I think they are designed to sit vertically in the manner I have the positive bus bar oriented.

The 230V AC out board below. A 32A breaker feeding two output circuits - one 20A RCBO for a general power outlet (runs the pool pump and sundry items), and a regular 32A overcurrent circuit breaker feeding power to the main circuit board's transfer switch. All circuits in the main circuit board have RCD protection already.

IMG_3119.jpeg

Inverter and the 230V AC input switch below. Batteries stacked still left enough space to access the inverter's control and display panel. The switch is fed by a dedicated 20A circuit supply from main circuit board.

The large orange plug (20A) connects to the inverter's AC input. I went with a plug as I have the option to connect my generator as an alternative AC source.

I have an extension cord already made for the generator, and it also matches the power input socket for the transfer switch, so the generator can either feed the inverter if needed or directly feed the home should something go wrong and I need to bypass this inverter altogether.

Raspberry Pi sitting atop the AC switch, with Solar Assistant running.

IMG_3120.jpeg

Either tonight or in the morning I'll go through a process of trying to even up the voltage of both battery banks before connecting them in parallel. That's the one operation I'm a little nervous about.

I figure the internal resistance of each battery is ~3mΩ (factory guide says 3.2mΩ). Plus cables, terminals, busbars etc. But to be safe let's say 10mΩ is "worst" case resistance on low side.

I = V/R

If I have avoltage difference between the banks then
0.1V / 0.01Ω = 10A
0.2V / 0.01Ω = 20A

Batteries and associated fusing can all cope with 20A without too much bother, so I'll aim to be within 0.2V, hopefully much closer before connecting them together in parallel.

While in there I boarded up some gaps in the housing to reduce potential for critter ingress.

Nearly there...
 

wattmatters

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OK, now have the two battery banks connected. All is well, no sparks or issues. I applied some load to the top bank to drop its resting voltage down to match the unconnected bank, then connected it up and voila, 18.2kWh of goodness just waiting for our next outage.

Closer image of the fuse holder/breaker:

IMG_3122.jpeg

And the ANL fuse (with spare fuse in the holder at the bottom):

IMG_3123.jpeg

And all connections in place.

IMG_3125.jpeg

Not overly happy with the heat shrink I used. Not nearly as robust as the heat shrink on the pre-made cable sitting in between the two I did (orange cable). I have some more coming and when it arrives I'll apply another layer over all the cable ends.
 

JimJr

Solar Enthusiast
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Oct 25, 2020
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97
Great pictures and details , the best I have seen here in a long time. Congratulations on your project
 

wattmatters

Photon Sorcerer
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Apr 16, 2021
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Great pictures and details , the best I have seen here in a long time. Congratulations on your project
Thanks. This thread has turned into a blog about my project so I figure I may as well keep it going.

This morning I added the Ryobi battery charger inside the housing. Had a nice perfectly sized space for it!

IMG_3131.jpegIMG_3132.jpeg

It can charge my power tool batteries from the off-grid supply. Nice thing about these batteries is the charge state LED indicator is on the top making it easy to see how it's travelling.

I need to think about what else I can use the spare solar PV capacity for.

Planning to do an outage test run tonight. I'll flip over to battery supply at some stage this evening. It should be a doddle for it. In the 8 hours from 10pm to 6am last night the three buildings consumed 3.5kWh (excluding off-peak hot water service which is excluded from backup supply). Call it 4kWh to cover DC to AC inefficiency. That's 22% of the battery's nominal capacity.

I'll program it to flip back to utility supply in case for some reason it drains too much or battery voltage gets too low.
 

wattmatters

Photon Sorcerer
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Did a test run of backup last night. At 10pm I flipped the transfer switch over to backup and let the off-grid system look after everything. All went smoothly. Handled our overnight load without issue.

Here's a plot of the power consumption and battery state of charge. Can see the fridges cycling on/off (there are three fridges, one in each building).

Screen Shot 2021-09-21 at 9.14.16 am.png

That's about as benign a test as it will get but good to know it's up for the task.

There are non-essential loads not supplied by the backup (oven, stove, air con units, one power circuit with nothing plugged in, the grid tied inverter, and the AC input for the off-grid inverter). None of these were "on" or being used but since they still had grid power supply my grid tied consumption meter recorded their consumption.

Here you can see the overnight consumption for the non-essential circuits:

Screen Shot 2021-09-21 at 12.51.34 pm.png

Bounces around 90W with a couple of hours in between with a 24W steady draw. Damn that's a lot of idle consumption.

This morning I flipped off the breaker for the aircon and the live consumption readings dropped from 84W to 8W.

Oven clock (milliwatts I guess), the grid tied inverter has an idle draw (rated at 1W) but it's mostly the air con system, especially the ducted system. It seems my ducted AC compressor has an average idle draw of ~55W This is when it is turned off at the system controller, not doing anything. It's just internal processes in the compressor, presumably keeping internal fluids at temp ready for action. That's about 1.3kW/day of consumption for a device that's not even on. Ouch!

At this time of year we barely use aircon (it's mainly for our Winter heating and Summer cooling), so the circuit could be turned off. It just needs a few hours of power to allow internals fluids to reach operating temp before using again. I reckon there's 40% of the year we can just leave it off and save nearly 200kWh/year of needless consumption.
 

wattmatters

Photon Sorcerer
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Now experiencing the first "official" grid outage since I installed the battery backup system.

4:45pm this afternoon power goes off. Apparently a 4WD hit a power pole on the other side of town. No ETA for local grid restoration but I'm happily watching footy finals! :)

Screen Shot 2021-09-25 at 5.37.13 pm.png
 

wattmatters

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Not overly happy with the heat shrink I used. Not nearly as robust as the heat shrink on the pre-made cable sitting in between the two I did (orange cable). I have some more coming and when it arrives I'll apply another layer over all the cable ends.
Today I put the extra layer of better quality heat shrink onto the battery cables I made. No pics but good to get that job done.
 

koobs

Solar Enthusiast
Joined
Nov 19, 2020
Messages
100
Very good read and nice to see all the pictures of your progress! You've done everything very professionally and neatly.
I've had an ad-hoc system running my garage here in QLD for the past year, been eagerly awaiting a power outage that hasn't happened.
In a similar situation to yours in that my house has a grid tied inverter and 6.6KW PV array already.
I've got an extra 2Kw of PV up on the patio roof with a 4kw inverter and 8KWh 24v LiFePO4 system. It rarely sees deeper cycles as it only runs my powertools and the occasional household appliances.
I've been hankering for some method of utilizing more of the bank without running separate circuits or rewiring the switchboard.

Some of the people on here have some interesting ideas with using zero-export inverters and I believe a youtuber in QLD has already demonstrated this in use.
I think I'll get a changeover switched wired like you have as I'm only on single phase. Perhaps considering an automatic one that can change-over when the grid tied PV is not producing.
 

wattmatters

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Very good read and nice to see all the pictures of your progress! You've done everything very professionally and neatly.
Thanks!

In a similar situation to yours in that my house has a grid tied inverter and 6.6KW PV array already.
I've got an extra 2Kw of PV up on the patio roof with a 4kw inverter and 8KWh 24v LiFePO4 system. It rarely sees deeper cycles as it only runs my powertools and the occasional household appliances.
Nice.

I've been hankering for some method of utilizing more of the bank without running separate circuits or rewiring the switchboard.
Yeah, the biggest DIY bug you get when you do this is looking for ways to use that energy. In my case I had one predictable daytime load with the pool pump I was able to move off-grid. But not a lot else. I don't use the power tools all that often, other than that it's the pool cleaning robot but that doesn't use much energy, about 120Wh per cleaning cycle and it might go in once or twice a week.

Some of the people on here have some interesting ideas with using zero-export inverters and I believe a youtuber in QLD has already demonstrated this in use.
That's probably Andy's Off-grid Garage series of videos. He's part intriguing off-grid experimenter, part ham. 60% entertainment, 25% useful info, 10% error correction, 5% WTF! Many videos take too long to convey the key message, or it's repeated ad nauseam. Will Prowse has a far more concise style I prefer. But I watch both.

Andy tested an inverters which does that but they are not particularly good and would not be compliant for grid tied operation.

In my opinion, once you have something which touches the grid (IOW the inverter and the grid can supply power to same circuit at the same time) then I leave that to the professionals. I think it's just better if we restrict ourselves to circuits which are isolated from the grid.

I think I'll get a changeover switched wired like you have as I'm only on single phase. Perhaps considering an automatic one that can change-over when the grid tied PV is not producing.
Single phase makes things a bit simpler.

Depending on your circuit board you might consider splitting the circuits into two groups each with it's own rail - one group for those you do want to run from an off-grid system and one for those you don't, with a suitably sized transfer switch then only having to deal with the switching the supply for the extra board between grid supply or off-grid supply. This gives flexibility to more easily move circuits between being being on grid-only, or on the backup side. You can achieve the same thing with the transfer switch alone but it's a bit of wiring jumble.

Then in future if your off-grid system has the capacity you can run the second board from the off-grid system most of the time and have the grid as backup. Much depends of the power draw you expect to need to supply through the second board.

My main transfer switch is manual but if left in the backup position, the off-grid inverter can switch modes between solar/battery supply and Utility First mode which passing through grid power. The trick in the Utility First mode is the power draw from the grid is limited to the inverter's output capacity.

This is the difference between these off-grid inverters and the grid tied one. The off-grid operates in series with the grid supply so the inverter is the choke point, while the grid-tied system operates in parallel with the grid supply and hence the grid can supplement supply if needed. This is why choosing which circuits to put on the backup/off-grid side is key.

I haven't discussed it here yet (I will eventually), but I recently installed Home Assistant on a Raspberry Pi and I have managed to integrate both my grid tied and off-grid inverters into the system. This now means some automation based on the operating states of each is possible and I have one such automation in place for the pool pump.
 

wattmatters

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I hadn't posted it before but I did add an earth wire to the surge protection in my combiner box.

IMG_3172.jpeg

My pool pump switch automation is working reasonably well. I have it timed based on a fixed offset to sunrise and sunset times so the pump duty cycle automatically adjusts to have longer runs in Summer and shorter in Winter. Can see this gradual increase in weekly load (and corresponding PV output) in the months leading up to this week. Now Summer Solstice has passed, this weekly load will not gradually start to reduce.

Screen Shot 2021-12-23 at 4.00.18 pm.png
The week with the higher load would have been one day we had a grid outage (and I performed a test as well).
 

Ozark Tinkering

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Dec 23, 2021
Messages
571
Being the end of a rural line we can get 30V swings in our voltage and 258+V isn't unusual. The 3.6kW hot water system (overnight controlled load) will see a 10V swing as it cycles on/off. Our Fronius inverter does some high voltage production limiting, it manages it quite well.
Wow! We're at the end of a very rural line along with the light bulb burning in the neighbor's hay barn and we get nothing like that. It goes out but rarely does it see swings like that. Pretty sure my Enphase system wouldn't tolerate it? When it gets bumped off due to a frequency bobble it can take til the following day to cycle back on. Is that common in Australia?
 

Ozark Tinkering

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I have a question about grounding for surge protection.

The solar PV combiner box provides a connection for surge protection. The garage already has a copper earth rod which was fitted for the electronic radio dog fence and I could run an earth wire to that without much problem.

That earth rod however is not the main home earth, which is about 25m away, and uses an outside copper water pipe (in Australia water pipes used to be the typical earth point but nowadays the standard for new builds quite sensibly requires a separate earth rod).

Given it's just for surge protection of the array I figure using the garage earth rod is fine and there's no need to use the home's earth point. Thoughts?
I know NEC doesn't apply outside the US but there's reasoning behind it and separate multiple grounds are not permitted on a single service while supplemental grounds are. So if you carried a ground along from your main service and attached it to a supplemental ground rod, that's okay. As a reminder when you're installing a sub-panel always float your neutral from the case and ground. It only grounds at the original established ground at the service.
 

wattmatters

Photon Sorcerer
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Wow! We're at the end of a very rural line along with the light bulb burning in the neighbor's hay barn and we get nothing like that. It goes out but rarely does it see swings like that. Pretty sure my Enphase system wouldn't tolerate it? When it gets bumped off due to a frequency bobble it can take til the following day to cycle back on. Is that common in Australia?
Grid frequency is very stable here. It’s voltage that varies a lot.

I’ve been experiencing particularly high voltages on one phase. Turns out last June my electrician had accidentally swapped the phase assigned to two of my aircon circuits. Our main unit which operates much of the time should be on the problem voltage phase as the load will help bring that phase voltage down. Phase B is my problem child. Here is voltage samples for this phase for entire year 2021:

BHOoXxd.png


Looks like our distribution company tapped down a local transformer by about 5V at start of September.

When sparky comes to fit my hot water diverter I’ll get him to rebalance the air on loads. It should help.
 

wattmatters

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Here’s a more recent sample covering a 2 week period showing the daily voltage cycle for all 3 phases.

u7OxzQs.png


The few days at the right are cloudy/rainy so solar PV output (and export to the grid) is low.
 

wattmatters

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I know NEC doesn't apply outside the US but there's reasoning behind it and separate multiple grounds are not permitted on a single service while supplemental grounds are. So if you carried a ground along from your main service and attached it to a supplemental ground rod, that's okay. As a reminder when you're installing a sub-panel always float your neutral from the case and ground. It only grounds at the original established ground at the service.
Any AC output/distribution is handled by my electrician. By law any such work must be done by licensed sparky.

I do note that both our outbuildings, which each have sub boards, have their own local ground post. The sub boards would have a ground wire connected back to the main panel (part of the 3-phase supply cable). So I guess they would be classed as supplemental grounds in your terminology.
 

Ozark Tinkering

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Dec 23, 2021
Messages
571
Any AC output/distribution is handled by my electrician. By law any such work must be done by licensed sparky.

I do note that both our outbuildings, which each have sub boards, have their own local ground post. The sub boards would have a ground wire connected back to the main panel (part of the 3-phase supply cable). So I guess they would be classed as supplemental grounds in your terminology.
Correct. Then to be sure your neutral bus bar at the sub-panel (floats) is electrically isolated from ground.
Some jurisdictions here don't allow homeowners to do electrical or plumbing construction on their own property. Other jurisdictions allow that but still require a contractor licensed in that discipline to sign off. Until a couple of years ago I could sign off on my own work or the work of others. By the time I had been retired for 10 years though, I couldn't see why I needed to keep paying the annual renewal fees so also retired my license. Now that falls on one of my sons who earned his master license 5 years ago.
In a 3phase configuration you should have 5 conductors entering from the main. 4 current carrying conductors including the neutral and the grounding conductor. Is that correct?
 
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