Coulomb

My understanding is that the relatively weak power of the bus soft start circuit coupled with the flyback topology means that the output is approximately constant current. Constant current into a capacitor results in a constant dV/dt, i.e. a constant rate of change of voltage with respect to time.
What he has on his piece of paper is quite different to what I and others have traced. That's why I was curious as to what model this is supposed to be from.
Compare his sketch:

with what I'm used to seeing:

Note the complete absence of anything other than the diode (and its snubber capacitor) on the output of the "transformer". My first guess is that the video author was unaware of previous schematic traces, and mistraced the circuit. But the other guess is that this is a different circuit from a model that I'm not familiar with.  The board at the bottom, which I assume is a solar charger, is not familiar to me. Edit: Though it's obviously a high PV voltage solar charger, which I know little about.
Edit 2: It's also possible that I and others have missed this feedback part of the circuit, but I doubt that.

What model is this schematic trace from? It seems unusual.
It depends on the design. In the versions I've seen, there is no voltage feedback.

That's telling, but I don't immediately know what. [ Edit: That should not be possible. The diodes and the fee-wheel diodes in the MOSFETs (inherent or explicit) should be combining to limit the negative PV voltage to some -0.8 V, perhaps a little over a volt if the current is very high (and it won't be, here). So I'm thinking that this measurement is spurious, or I'm misunderstanding you, or the power parts are blown. ]
I have to ask: are you sure that you have connected the PV power supply correctly? I guess you must because you heard the click soon after. Though it should take about 5 V above battery voltage for the power supply to come on:

D2, D20 and Q20 Vbe should add up to about 0.4 + 3.3 + 0.4 = 4.1 V before any sort of conduction should happen. So you should need more than a single volt difference between the PV power supply and the battery. So you might have to eventually get the battery voltage down to about 53 - 5 = 48 V, at least to start the SCC's power supply. Schematic is from this post.
So I would check this part of the circuit carefully. Once that is working, check that U3 is powering itself (via D10). Of course, your parts designators could be different, and even details of the circuit may differ, but I'd expect it to be pretty close. Check that there is 5 V for the micro chip, and there should be sensible voltages on the various power supply outputs.

The gates of both FETs and IGBTs are capacitors (sort of - actually non-linear compound capacitors, but it is an accurate enough simplification for this discussion).
So, with a gate capacitance of C and a turn on voltage of V, we require a charge of Q = C * V to turn the device on.
In truth, while we say the devices are voltage controlled, they are actually charge controlled. Because of the above equation, they are largely interchangeable.
But it is the charge on the gate capacitor which provides the electrons in the channel/base of the device. And it is also the number of electrons (and therefore charge) that limit the charge carrying capability of the device.
So the more current you need to carry, the bigger the charge required.
But we also have Q = I * t. So for a specific turn on/off time 't' we require I = Q / t.  So the required gate current is proportional to the gate charge, which is proportional to the current carrying capability.
This is a little over-simplified, but it should give a good, basic understanding of the device parameters.

That's a Fivestar inverter. Axpert clone.

SCCs are a bit tricky to test, because of the maximum power point tracking. I assume that this is a 145 V max PV type; I've never worked on a high PV voltage solar charger. These require serial commands and responses from the DSP to get them operating.
You didn't say if your 53 V power supply was current limited or not; it really needs to be current limited. Otherwise, the MPPT even if working properly will try to draw 60 or 80 amps from your power supply. I would initially limit the current to about 0.5 A, and try it at the power supply's maximum if all goes well.
Unfortunately, you really need a real battery (a small one should do, especially initially) for the SCC output. Otherwise, the charge current will have nowhere to go, and the output voltage will rise to silly levels, endangering other parts of the inverter. That's unless you have a special battery simulator test device, but those are unusual and expensive. That battery should have a DC rated fuse, because even a smallish battery is quite capable of blowing things up.
Using a resistor in series with a non current limited power supply is not ideal. As you have found, things get crazy hot very quickly. It might be possible with the right value resistor and a lot of heat sinking (like a bucket of water).
I've been lucky with my 145 V max SCC repairs; the only faults were fairly obvious like bad opto couplers preventing serial communication, and actually transistors on the control board at the other end of the serial comms cable. The actual switching part seems to be fairly robust; I don't seem to hear a lot about the MOSFETs failing.

That sounds like the premature float bug to me. Is this on solar charging, or utility charging, or both?
It should reach the bulk voltage, and stay there until the charge current drops to a low level; that's the absorb stage. A bit of a misnomer for lithium batteries, but it's still very important. Without that, the battery won't be reaching 100% SoC.
When you set the battery type to USE, then the battery's BMS is no longer in control, and it's all strictly voltage based.

Those panels are fine to mix, their specs are very close. If the 9 panels are wired up in 3S3P, would it not be the easiest solution to just rewire them at the combiner box and change them from parallel to series? With 9 panels in series that would be around 450Voc.

On Voltronic MPPTs, it can take tens of seconds to react, I suspect because of integral wind-up. It's frustrating to watch... ok, getting close, time to back off... ok, inverter, back off... BACK OFF! Clunk! Too late; the PV contactors have dropped out to save the battery from over-charging.

I would say so. There has to be a limit obviously, but I doubt that the power supply is that close to its limit.

Yes, on user defined settings, what you're seeing is expected
 
You may want to read through this thread
 
https://powerforum.co.za/topic/11820-kodak-and-pylontech-battery-comc-error-bms-cable/

Do you have BMS Communication to the inverter or are you using it in user defined voltage mode? If the latter, the inverter is basically "guessing" the SOC based on the voltage

Err, no. The "BT" of IGBT stands for Bipolar Transistor. That's why they have an emitter and a collector, just like a 2N2222A, but of course much bigger. The base is replaced by a gate, the IG (Insulated Gate) of IGBT. But that doesn't mean it's a Field Effect Transistor. FETs and MOSFETs conduct like a resistor; power MOSFETs measure in the milli-ohms. But a bipolar transistor (conventional or insulated gate) has a saturated junction voltage drop. So they behave somewhat differently. The 0.2-0.4 V Vcesat doesn't matter too much at higher voltages being switched. So for that and other reasons, MOSFETs tend to dominate at low voltages (e.g. the battery side), and IGBTs at higher voltages (e.g. the main DC-AC converter full bridge, if there is one).

I've often wondered this, but since I don't have an inverter that attempts to be grid tied, I can't do any experiments.
When load shedding starts, I assume that some giant switch or relay disconnects the high voltage feed to a set of transformers. So as BritishRacingGreen suggests, your DC-AC converter's output will suddenly be trying to power the entire area's load (along with some other inverters perhaps), and it's very likely that this will overload the DC-AC converter at least momentarily. How the inverter usually copes with this, I have no idea.
As an experiment, and maybe as a lasting work around, you might consider switching the inverter from SUB output source priority (where the above scenario will happen), to something like SBU, so that the inverter will be in battery mode. If you know when load shedding is due and they are accurate with the timing, you might be able to do this semi-automatically a few minutes before it's due. That way, you won't be connecting to AC-in when load shedding happens, and hopefully you've only lost a few minutes of battery run-time. Presumably, the onset of load shedding will have no effect, and you keep the lights, computers, etc on.  Depending on various factors, this might or might not be a good compromise. For example, if they are very sloppy about the timing, you might find that you end up often wasting half an hour of battery run-time that way.
Having said all that, presumably this is still not normal behaviour, and you should usually see just a very brief period where the lights go out or dim, then the relay drops and the inverter is in battery mode. So it's possible that the power supply is marginal, and you can get "normal" behaviour with some sort of repair, e.g. replacing the "usual suspects" of electrolytic capacitors. Again, this is a judgement call; will it be worth the hassle and expense, and lack of backup power while this happens?

The V+ is cheaper but too noisy.
The 3.0+ (non V version (v for value)) is quiet and customer is happy and works perfectly with 2x hubble s100. The inverter sits in the dining room.

Another customer has a V+ and this one sits in the garage with the cars where it can make all the noisy fan sounds that it desires where it is away from people.

That one too I have connected to hubble S100 (2x) and works like a dream (5 hours with a barfridge, 2x standard 200-300w fridges, 1x freezer) with some life still left in the batteries.

On both installs I have installed a battery balancer from Geewiz to keep the voltages across both batteries consistently the same.

Hi I replaced all the Capacitors with Hitano Low ESR capacitors and that solved the problem. I must still just test all the functions but all looks good so far.
Thanks for your help.

Any progress on this? I'm finding more and more text boxes that have no text.

I suspect, but can't confirm, that VM IIIs have 3-pin fans. Hence the lack of variable speed control. A VM III service manual should confirm. I'm away from keyboard at present. 

Oops, I missed that [ edit: about the guy changing something ], I assumed that your two posts were identical. My bad.
Yes, we need to know details:
* Brand and model of battery modules, or photos thereof
* Battery related settings: settings 05, 26, 27, 29, 12, 13.
* Are you charging by solar?
* Is the battery getting fully charged? Please tell us what voltage it gets to, about what time on a good solar day, and how long it stays at that voltage before dropping. Preferably with a multimeter, but it would be helpful to know what battery voltage the inverter reports as well.
* Eventually, I'm going to ask for the main firmware version number. It may be that patched firmware can help dramatically with something called the "premature float bug".
Wow, that's a lot of homework, sorry. But it really helps us to help you.

Oops, I missed that [ edit: about the guy changing something ], I assumed that your two posts were identical. My bad.
Yes, we need to know details:
* Brand and model of battery modules, or photos thereof
* Battery related settings: settings 05, 26, 27, 29, 12, 13.
* Are you charging by solar?
* Is the battery getting fully charged? Please tell us what voltage it gets to, about what time on a good solar day, and how long it stays at that voltage before dropping. Preferably with a multimeter, but it would be helpful to know what battery voltage the inverter reports as well.
* Eventually, I'm going to ask for the main firmware version number. It may be that patched firmware can help dramatically with something called the "premature float bug".
Wow, that's a lot of homework, sorry. But it really helps us to help you.

The OG7. 2 upwards has fan size of 80x80x37mm as opposed to 80x80x25mm. Also they are specified at 0.9A which much higher current. So I think you need to stick with the 5kW machine specs, ie. OG5. 48 ones. 

272.66 fixes the premature float bug. In some cases, this might be reason  enough to choose it all by itself.
The only other change is that the threshold to skip the "race to the bottom" code (which leads to being stuck at 90 V on the panels) is reduced from 0.50 A to 0.05 A. This is usually enough to provide a noticeable improvement in PV production, especially in cloudy or rainy weather when you really could use every joule of energy you can get.
In all my patched firmware update files, there is a .txt or more recently a .asm file that has comments on what it changes. As an example, dsp_272.66_patched_05.asm starts with:
Edit: As for which one is "better", it's a user preference. The patched files are all amateur experiments, but sadly, they tend to perform better than the factory firmware.

I note that in the bottom photo, the battery modules are not paralleled properly. The leftmost module will do most of the work, and get most of the charge current, while the others have a siesta.
Don't copy this practice!

The fan circuit is remarkably simple:

Since the right hand fan works, and the fans are basically connected in parallel except for the sense wire, it's unlikely to be a hardware issue, unless it's a blown or corroded PCB track. But you swapped the two plugs, and if I understand correctly the right fan continued to work and the left stayed stopped, so it has to be the fan. Probably an open circuit coil or more likely failed driver electronics inside the brushless "DC" fan. It's really an AC fan with a DC driver circuit included.
It may actually be possible to repair the driver electronics, but probably better to replace the fan.
You may want to consider reversing the fan flow direction; as it is, the idling fans basically oppose the natural convection (hot air rises). Also consider a fancier, quieter fan, but make sure it moves about the same volume of air per unit time (usually measured in cave-man units that I won't utter here 🤢).
Edit: I just noticed that I left the highlight on from my search. Under the word "CN5" is the word "FAN2". Sorry about that.

The fan circuit is remarkably simple:

Since the right hand fan works, and the fans are basically connected in parallel except for the sense wire, it's unlikely to be a hardware issue, unless it's a blown or corroded PCB track. But you swapped the two plugs, and if I understand correctly the right fan continued to work and the left stayed stopped, so it has to be the fan. Probably an open circuit coil or more likely failed driver electronics inside the brushless "DC" fan. It's really an AC fan with a DC driver circuit included.
It may actually be possible to repair the driver electronics, but probably better to replace the fan.
You may want to consider reversing the fan flow direction; as it is, the idling fans basically oppose the natural convection (hot air rises). Also consider a fancier, quieter fan, but make sure it moves about the same volume of air per unit time (usually measured in cave-man units that I won't utter here 🤢).
Edit: I just noticed that I left the highlight on from my search. Under the word "CN5" is the word "FAN2". Sorry about that.