It was the first 5kVA -4kW Axpert inverters. Always switched the slave off. There was no down time for AC - out.

On 2024/01/30 at 6:51 PM, onobeka said:

For me it would be important to know if I can switch off the DC-AC part of one unit, while the other inverter would continue to work undisturbed without any impact on running loads.

The DC-AC converter is only about 15 W (fixed, more losses with higher I²R, i.e. higher loads) on a 5 kVA model. Perhaps 12% more on a 5.6 kW model. I have the ability, due to my fully patched firmware, to turn off one of mine, but I find that it makes so little difference that I have lost the appetite to use this feature. The feature, however, is highly asked-for, by users that don't have it.

Without this patch, however, doing this is fraught with danger, as others have reported. There is and never will be fully patched firmware for the high PV voltage models, so my suggestion is to put it out of your mind.

On 2024/01/30 at 6:51 PM, onobeka said:

the indication that the Master/Slave selection is ad-hoc and the fact that you can set the 28 setting by turning off the rocker (which in theory will not be simultaneous) and then restarting the units, gives me hope.

When you have paralleled units, you must never ever dynamically change setting 28. That's just a recipe for disaster. Changing setting 28 to SNG means that there is no need to synchronise the output with anything else, although it will always synchronise, though importantly not instantaneously, with the AC-in if/when present. I don't see what dynamically changing setting 28 would achieve; probably I am misunderstanding your comment.

When inverters are paralleled, you should always have separate breakers on each output. In Australia, we only break the active; I don't know how it would work in a country where it is expected (mandated?) to break neutral as well as active. I would never parallel inverters before checking with a multimeter that the voltage difference between AC-out active terminals is low. To do that, the AC-out neutrals have to be connected.

3 hours ago, onobeka said:

As per manual, there should be just one AC-in and one AC-out breaker for the two inverters (in my case).

My Parallel Installation Guide does not show AC-out breakers at all in their diagram, I assumed that this was to reduce the clutter. It does show just one AC-in breaker, and indeed my system has only the one, but I sometimes wish I had separate ones.

I disagree with Voltronic on this one. A breaker is cheap compared to the peace of mind it brings, at least to me.

Edited January 31, 20242 yr by Coulomb
"never change" -> "never dynamically change"

Thank you @Coulomb. I do not intend to change setting 28 (PAL) with my intended setup, rather leave them both on PAL (parallel mode) and turn off the rocker at the bottom of the inverter -> no AC out on one of them -> less battery consumption over night (I hope). Would this work? My plan was to use as said a relay to turn on off via a relay by means of an AC load measurement (tinyControl + clamp). Even if both inverters are set on PAL mode (single phase output), only one will be producing AC out 24h/7, the other would join the loads when necessary (>4kW load) and otherwise will work in MPPT mode (as today). Actually I am not sure that's entirely correct, except if there is no AC-in connected. Does it need to be connected on both paralleled inverters or just the 24-7 one? I guess if it's connected also on the secondary unit, it will never switch off during the night. There is also no need for it to run (loads less than 4kW so in theory it should never be turned ON during the night). OTOH if something fails with this control and I have AC-in on one unit only, it may trigger a fault (best case).

 

I follow what you say with individual AC out breakers, to be able to check the voltage difference between the two and only then to feed the loads. But that's the only advantage of the two separated breakers, which can also be done if the Ns are connected together and the measurement is made on the output L connectors (without cables connected). Is it common that a difference of voltage is observed between two paralleled inverters? 

 

Edited January 31, 20242 yr by onobeka

6 minutes ago, onobeka said:

Thank you @Coulomb. I do not intend to change setting 28 (PAL) with my intended setup, rather leave them both on PAL (parallel mode) and turn off the rocker at the bottom of the inverter -> no AC out on one of them -> less battery consumption over night (I hope). Would this work? My plan was to use as said a relay to turn on off via a relay by means of an AC load measurement (tinyControl + clamp). Even if both inverters are set on PAL mode (single phase output), only one will be producing AC out 24h/7, the other would join the loads when necessary (>4kW load) and otherwise will work in MPPT mode (as today). Actually I am not sure that's entirely correct, except if there is no AC-in connected. Does it need to be connected on both paralleled inverters or just the 24-7 one? I guess if it's connected also on the secondary unit, it will never switch off during the night. There is also no need for it to run (loads less than 4kW so in theory it should never be turned ON during the night). OTOH if something fails with this control and I have AC-in on one unit only, it may trigger a fault (best case).

 

I follow what you say with individual AC out breakers, to be able to check the voltage difference between the two and only then to feed the loads. But that's the only advantage of the two separated breakers, which can also be done if the Ns are connected together and the measurement is made on the output L connectors (without cables connected). Is it common that a difference of voltage is observed between two paralleled inverters? 

 

Just a point on switching one off. It will either draw about 40W from the grid if AC in is on or from battery. 

If you need max 4kW it's always better that each one provides 2kW than 4kW from one and zero from the other. 

22 minutes ago, onobeka said:

I do not intend to change setting 28 (PAL) with my intended setup, rather leave them both on PAL (parallel mode) and turn off the rocker at the bottom of the inverter...

That's good. I got a different impression, and didn't want others to get a similar different impression, and end up in trouble.

23 minutes ago, onobeka said:

Would this work? My plan was to use as said a relay to turn on off via a relay by means of an AC load measurement (tinyControl + clamp).

This is unknown territory for me. I vaguely recall turning off the switch of one of my paralleled inverters and getting an instant fault code. It was some time ago, so I can't recall the details, but if accurate, that would be a problem (assuming it held true for your much later models).

As for @Scorp007's point about consuming 40 W from AC, that would also be a problem. My 2015 models have no AC power supply, so that can't happen in my case, unless the inverter is in bypass mode, and then you'd expect AC-in to power the static load for the electronics, display etc. It sounds like you'd also need to interrupt AC-in when you turn off the switch.

However, you are at the mercy of Voltronic's firmware to ensure that it always does the right thing when the power switch comes back on. Also, when a load suddenly comes on, you likely want the sleeping inverter to power up as soon as possible, but it will be waking up, yawning, performing soft starts of the bus and the DC-AC converter, scratching its bum, and finally contributing to the load many seconds later. I guess by then it will have had plenty of time to synchronise with either or both of AC-in and the signals on the CAN bus / paralleling boards. I get the impression that synchronisation happens via opto-couplers from the master to all slaves via a dedicated wire, rather than CAN bus messages. The CAN bus messages seem to be for sending parameters, fault code information, that sort of thing. I haven't discovered if it checks for inconsistency between AC-in and this synchronisation signal; I would hope that it would.

So I would take this into consideration, along with possibly low gains, before implementing this.

BTW, our fully patched firmware for Dynamic Load Control (turning units to low power) operates more or less by making (the) target machine(s) behave as if their power switch is off. However, the big difference is that with our patched firmware method, which operates on an RS-233 command with unusual values, we can't let the inverter completely turn off, otherwise you can't dynamically turn it back on. On low PV voltage models, the solar charger has its own computer that wakes up when there is some 5 V more PV than battery voltage, and it has a "private line" to the main power supply that wakes up the main computer at sunrise even if the switch is off. That's fine for many circumstances, but not for "wake on significant load".

Thank you both for the clean and exhaustive answers. If this on the fly turn on/off does not work or not with my expected benefit, then the best option would be to have them running 247 time and take the hit of night consumption. 

Ok, now I need to decide if I want to run them in parallel or to split the loads into different phases, different AC-outs.

There is the advantage of dynamically sharing the loads when one the the phases would be loaded more if the software is able to nicely achieve that. I am not looking for a perfect 50-50 split between the two units, rather a 40-60 would be acceptable as long as this does not go to 80-20. 

Distinct phases is similar to a triphasic inverter feeding loads hooked to each phase, which will never be equally balanced.

Edited January 31, 20242 yr by onobeka

6 hours ago, onobeka said:

As per manual, there should be just one AC-in and one AC-out breaker for the two inverters (in my case).

Sadly, as so often with Voltronics, it rather depends on which manual you look at.  The Manual I linked to above agrees with what you said.  There is another manual (4KVA/5KVA Parallel Installation Guide) that clearly shows breakers for each inverter on both input and output side.  Take your pick...

7 hours ago, onobeka said:

but is there an issue of using just one set o breakers?

I have mine installed as per the King manual - just one AC-in and one AC-out breaker.  No problems so far (4 years)

Having separate breakers on the output can cause an issue: if one trips (or is switched off) the system will detect a current sharing fault and shut down all A/C output.

I quite like having only a single breaker: it removes the (very strong) temptation to "service one inverter while the other can be in service".  (I am trying to give up blowing things up 😅)

Thanks Calvin, I did search for that manual and I've found this one, as 4KVA/5KVA Parallel Installation Guide: https://www.mppsolar.com/v3/catalogs/PIP-HS_MS Parallel Guide.pdf. Anyway, I am sure you know what you are talking about. I will probably try first the single breakers route (as it's simpler for me, I just need some 6mmp cables), but I will do the measurement Coulomb recommended before connecting the L wires in the breakers.

More confusion - the parallel manual you found is very different from mine! (see attached).

The one you found says shared breakers, the attached one says separate.

Apparently either is OK. 😕

Parallel installation.pdf

Yes, I see it. Indeed, it looks that in the version you've shared they've put more thought into it. 

I have the Axpert 5.6kw inverter. I needed to purchase another one and parallel it as I needed more panels in a different direction. After getting advice about having to purchase parallel cards and make sure firmware is the same etc... I just went and bought a brand new Deye inverter. 

It was an expensive lesson as I should have spent the extra R5k and bought the Deye inverter when I installed the system. We live and learn. 

But the Axpert Inverter is a GREAT inverter, I won't lie. The single MPPT is my only issue. 

3 hours ago, Zweli said:

The single MPPT is my only issue.

You could also have bought an inexpensive external MPPT that directly charges the battery. However, I don't know if any of those work with high voltage strings. If not, you would have had to have different PV configurations, which is not ideal.

I have four chargers: 

- the Easun iGrid IV which works currently as inverter as well; 2 strings of 6 panels in parallel, 240V.

- another Easun iGrid IV, which works currently only as an MPPT <- this one is the subject of the above conversation, to set it up also as inverter, to be able to stop the inverter side based on load; 2 strings or 5 panels in parallel, 180V.

- one small Easun 80A mppt charger, 150V; 3 strings of 2 panels in parallel, 80V.

- one Victron Smart Solar 250/60. 2 strings of 4 panels in parallel, 150V.

 

They are all connected to DC custom busbars with fuses on the positive only side. 

 

They all are feeding 3xus5000 batteries, based on voltage settings. 52V float, 52V bulk and it works pretty well as the Pylontech BMS will limit the charging to 20A, above 90% SoC.

I used to have BMS communication between the inverted and the Pylontech bank. I could still run it as such, but it used to take the batteries to 53.3V, to high in my opinion.

I've limited the maximum charging current to the batteries either from the chargers or panels (you cannot limit the small Easun mppt). Current maximum, theoretical is 140A, which is below 0.5C of the 300A battery, but it rarely goes that high. Probably during summer months I will lower the maximum current as the days are longer.

Also I am running two sets of Pylontech cables between the batteries and the busbar, so 50mmp.

Edited February 2, 20242 yr by onobeka

2 hours ago, onobeka said:

I have four chargers: 

- the Easun iGrid IV which works currently as inverter as well; 2 strings of 6 panels in parallel, 240V.

- another Easun iGrid IV, which works currently only as an MPPT <- this one is the subject of the above conversation, to set it up also as inverter, to be able to stop the inverter side based on load; 2 strings or 5 panels in parallel, 180V.

- one small Easun 80A mppt charger, 150V; 3 strings of 2 panels in parallel, 80V.

- one Victron Smart Solar 250/60. 2 strings of 4 panels in parallel, 150V.

 

They are all connected to DC custom busbars with fuses on the positive only side. 

 

They all are feeding 3xus5000 batteries, based on voltage settings. 52V float, 52V bulk and it works pretty well as the Pylontech BMS will limit the charging to 20A, above 90% SoC.

I used to have BMS communication between the inverted and the Pylontech bank. I could still run it as such, but it used to take the batteries to 53.3V, to high in my opinion.

I've limited the maximum charging current to the batteries either from the chargers or panels (you cannot limit the small Easun mppt). Current maximum, theoretical is 140A, which is below 0.5C of the 300A battery, but it rarely goes that high. Probably during summer months I will lower the maximum current as the days are longer.

Also I am running two sets of Pylontech cables between the batteries and the busbar, so 50amp.

Very interesting that you mention with comms the battery went to 53.3V. We have seen quite a few members having to dump Pylontech as the were not replaced under warranty when they over charged and no warning from the BMS. 

Yes, that happened from day 1. I’ve added one new module to the bank every 3-4 months later, and always the new module became the master. But that’s the information us5000 communicates as well, that it should be charged to 53.3V. 
During a normal day it would reach 100% at lower voltage, even 51.5V from what I remember, stop charging but later in the day it would charge a bit more and eventually reach 53.3V. That is 3.55V per cell, not too dramatic. However I prefer lower. That’s why I went with voltage and 52V.5V bulk and 52V float.

Sort of unrelated to the 53.3V thing, but even with the 52.5V setting, I do have a sort of an issue I believe with the newest module, after 92-95% one of the cells would imbalance to a difference of 0.120V: highest ca reach 3.6V, lowest would be 3.48V. The bms temperature will rise, meaning that the balancer is busy. The cell temperatures remain around 20C, while the BMS can reach 40C. The module will stay there for a while, at 98%, the other two modules will be already at 100%. After that while(can be one hour) the module will finally be at 100%, cells would be balanced and the voltage of each cell would be around 3.48V.

No alarms, no records in the logging. Pylontech says it’s normal. I do not consider it to be very normal.

 

 

 

 

Edited February 3, 20242 yr by onobeka

3 hours ago, onobeka said:

Sort of unrelated to the 53.3V thing, but even with the 52.5V setting, I do have a sort of an issue I believe with the newest module, after 92-95% one of the cells would imbalance to a difference of 0.120V: highest ca reach 3.6V, lowest would be 3.48V. The bms temperature will rise, meaning that the balancer is busy. The cell temperatures remain around 20C, while the BMS can reach 40C. The module will stay there for a while, at 98%, the other two modules will be already at 100%. After that while(can be one hour) the module will finally be at 100%, cells would be balanced and the voltage of each cell would be around 3.48V.

I agree with you on 53.3V being too high.

For me however 52.5 V is too low - it would take a too long a time to reach 100%.  I originally used 52.6V on my US3000Bs but after some firmware upgrade I had to increase that to 53.0V to get it to get to 100% SOC reasonably quickly (< 5 minute gap from first to last for my 8 batteries). In order to prevent overshoot I reduce max charging current to 60A (for 8 batteries) once the voltage gets over 51.5V.

Lithium batteries hate being fully charged, especially at high temperature.  On a daily basis I leave them at 100% for 1 minute and then reduce the setpoint voltage to 50.5V, Once every 10 days I leave it at 100% for 10 minutes.  Reducing the setpoint to 50.5V means it quickly discharges to about 99.5%, which is a small price to pay for the increase in battery life one expects.

Calvin, that is a lot of management that you do. I do not follow why you think they will overshoot in case not all batteries reach 100% nearly at the same time. In case one takes longer to get to that stage, it means it's in balancing mode, and needs to "burn" some current from one cell in order to make room for the another to raise the voltage. Hmm, but yes, maybe it will overshoot.

On the matter, I've set the two inverters in parallel, using just set of breakers. They work well and I can stop/start an inverter on the fly even if that is the the master, the other would become master instantly. There is no downtime at the loads. Also, I've measured the AC out voltage before connecting the L wires together while the N wires were connected. The voltage difference observed between the two L wires was 2-3V. Thx @Coulomb.

23 minutes ago, onobeka said:

I do not follow why you think they will overshoot in case not all batteries reach 100% nearly at the same time

I was obviously not clear: The overshoot is a concern due to the tendency of the Voltronics inverters to overshoot the target.  When your target is as high as mine (53.0V) the inverters (I have 3 in parallel) will easily overshoot to 54V (the battery cutout) if charge current is set at say 120A.