sethmad

is it safe to run the Main power supply without the RCD Snubber circuit? i got one inverter with failed UC3845... but the Q71 mosfet is not damaged. this is the first design that i see without RCD Snubber. Is this cost saving or something else?

Hi @sethmad i have experienced the same problem. But in user mode, if you have not many batteries and juste 3 or 4 batteries, you will have problems like me when the batteries are low the inverter does'nt cut the batteries and the BMS will cut instead. So when the inverter have no batteries voltage it will not restart (experienced with Axpert King inverters, newer models works without but display "BP" error and does not charge the batteries). In USER mode, the inverters calculate the SoC based on batteri voltages, that doesn't represent correctly the real battery SoC.
I recommend you to update to the latest Pylontech firmware (for US2000C, 3000C and newer) that modify the charging and floating voltage to 52,8V instead of 53,2V. Sadly, this update is not available for older US2000 batteries (asked pylontech staff but no answer from them) so you have to use a US2000C as master battery if you have one or keeping the USER mode.

Best Regards

Problem with Pylontech is that even when the data communication from BMS to the inverter is working, the BMS tells the inverter to charge till 53,5V. (=3,57V per cell). 
Add the facts that:
1) The voltage is not distributed perfectly among the cells. Some will be At 3,4V while the others will be at 3,6V already. It is a job for the balancer to level the cells.
2) Pylontech balancer is quite weak, unable to burn amps of current.
3) Inverters like to overshoot voltage when AC load fluctuates.
The result is constant stress and hidden overcharging, as discussed in the Victron threads many times. On the Victron side this was fixed by firmware tweaks, luckily. But when comes to Axperts, the problem is even more dangerous as it is not solved in the official firmwares, AFAIK.
IMHO, the first step on the road to hell is that one of the cells gets damaged by that hidden overcharge. Then a chain reaction starts as all other cells become stressed even more. From that point there's no way back. It does not make sense to replace the cells if all other parts of the system will stay configured the same, as the damage will appear again.
From my experience, for the longevity, the best is to ignore charging voltage value that BMS is announcing and set 52,6V instead. Based on the setup it might be +-0,2V but definitelly not 53,5V. Shame is, the batteries that already experienced the stress for weeks or months cannot be saved as some of the cells started to swell already.

Well, Pylontech buys these cells from some Chinese manufacturer or two or three. The manufacturer gives a guarantee for the cells, but it is probably just made up, thumb suck. Pylontech then puts a thumb suck guarantee on their batteries, hoping for the best. They also know they cannot put a short guarantee as their batteries won't sell, so they put an inflated 10 year guarantee to compete with other battery manufacturers that thumb suck as well. Now after all this thumb sucking the thumb is no longer in good condition. If things go wrong, which most likely it will, they will just insist that the customer is at fault, stuff like like overvoltage, bad battery temp, overcharging, undercharging, etc, whatever they can thumb suck to get out of a claim.

Some more schematics here. These are from Easun SMW 8kW which is, I believe, identical to Axpert Max 8kW. In this case the control board did have part references printed so most of those in the schematic should be correct. It's a multilayer board but only power planes are on the inside layers so it's not that hard to trace. The main difference, compared to Anern, is that this board uses multiplexers for 8 of the ADC's inputs, increasing total number of available analog inputs to 24.
I also made a schematic of the SCR board and some fragments of the main board.
I'm not going to make schematics of any power supplies as these are already pretty obvious. Just note that the topology in this case is different from Anern's. There's no intermediate SPS_IN (150V+) branch. The main power supply and bus softstart are located on the main board and powered directly by the battery voltage through a diode. The grid/AC power supply and solar power supply are on a separate board, both of these output around 63-66V and also provide power to the main power supply through diodes. Unlike Anern's, this topology does not need a relay in the softstart circuit.
I made a note of some critical parts (MOSFET type, shunt resistor value and how they deal with voltage spikes):
main SPS: JCS86N25WT, 0.15R, RC snubber 2x47R (parallel), 2.2nF
softstart: SIF13N50C, 0.62R, RC snubber 2x22R (parallel), 220pF
grid SPS: SVF9N90F, 0.47R, RCD clamp 15k/5W, 10nF
solar SPS: SVF9N90F, 0.47R, RCD clamp 15k/5W, 10nF
Original KiCad files and PDF schematics are available on my GitHub: https://github.com/solar-pwr/axpert/
There will be errors as usual, so every feedback is appreciated.

Here are some schematics that I reverse engineered from Anern Victor Max 10.2kW inverter. Should be very similar to Axpert VM models. Of course, part references and connector pinouts are different. Also ADC and GPIO assignments do not match genuine Voltronic's.
The SCC board schematic is complete - PV boost circuit, voltage and current measurement, AC power supply and bus soft start circuit.
Then there's a schematic of the two power supplies on the main board - this inverter uses an auxillary 150V power supply to start from the battery.
Also a I attempted to trace the analog part of the control/DSP board. This was little bit harder as there were no printed part references on the board. But all op-amps are there, nothing important (for understanding the circuit function) should be missing. [15/Aug/2025 added the remaining "digital" part]
I think there will be some errors, so every feedback is appreciated. I can provide KiCad project files if anyone is interested.

Hello, I have an older EASUN Igrid SV4 inverter and I need to upgrade firmware from U1 56.00, U2 80.25 to U1 56.13, U2 80.41. What is the correct order to do this update? U1 then U2 or the other way around? I attached FW U1 56.13 in case somebody else needs this upgrade. 4165-08G RS232 FW Upgrade_28066_DSP INFINI V IV 5.6K 56.13.7z

I'm not sure what was the reason to remove the snubber, but the power supply seems to run fine without it as long as the output current stays within normal range. But when there's a short circuit (and that can be on the COM port also), the voltage spikes can be high enough to cause arcing on the transistor drain or transformer pins.
If UC3845 failed, don't forget to check R253. The power supply may run even if this resistor is open-circuit, but UC3845 will stay at 50% duty cycle, just switching on and off according to the voltage feedback. In this mode, the spikes on the primary will be extremely high.
Currently I'm running two inverters with RC snubber added between source and drain of the MOSFET without any issues (that's not an RCD clamp as show in the schematic). I used 100pF/3kV MLCC capacitor and 33R/5W resistor as already mentioned.

This is not my area of expertise. But my guess is no, it's not safe in the long run; this seems like the worst kind of penny pinching to me.

SOLVED. there was another bad zenner in parallel with the good one. on this particular model, the MPPT IGBT's are powered by the same power supply.

SOLVED. there was another bad zenner in parallel with the good one. on this particular model, the MPPT IGBT's are powered by the same power supply.

A good way to start may be powering the inverter through the battery terminals and watching the bus voltage (red and black wire from the SCC board). When the soft-start circuit gets enabled, it should raise to somewhere around 400V within a few seconds. If this does not happen, then the corresponding output driver (ULN2003) may be faulty. Otherwise, it can be an issue with the ADC inputs, op-amps, possibly multiplexer (if this model has one).

What is Inside My Inverter?
Hello Everyone
This thread is Made To Help you know the Inverter internals, Considering It A Good Judgment of its quality, Spec, and true capability in comparison between them.
In this thread, you will find pictures that contain inverters Model, MPPT Specs (Some of it), and weight
this information is gathered from Inverters Datasheets and Main Boards Sellers (MPP Solar Distributor) and Repair Videos and will add more Model when good intel found or Provided.
- From the included Picture (Considering it the True Voltronic design not a cheap Clone) :
1- it is noted that the VM III 4kw, 6kw Similar to the Original VM III with an extra Aluminum Cooler on the MPPT and One Less Bus Cap
2- VM II 5.6kw Almost Equal to VM III 6kw (Without The Extra Aluminum Cooler on the MPPT) But use different UI (VM II's) and Less Software Features
3- King II 5kw is similar to MKS IV 5.6kw but the MKS is A higher end Model (Extra Components)
4- VM II 5k Premium Close to VM III 6kw Twin but Have a separate MPPT Board (Preferd Among Technicians) and Extra Bus Cap
5- Felicity Solar Inverters Uses Different Design Than Voltronic (And Have Way Less Models) Closer In Design to Mks Models Components Wise (Separate SPS Board + Not Negative Liner Voltage Regulator + RTC battery on the Main Cpu Board Like Mks)
The Thread contains these 24v and 48v Models:
Felicity Solar: IVEM 3024 - IVEM 5048
Voltronic: King II 5kw - MKS IV 5.6kw - VM II 3k Premium - VM II 5k Premium - VM II Twin 5.6kw - VM III 4kw Twin - VM III 6kw Twin - VM III 5kW

Note: Voltronic Mix and Match and rerelease same model name with different/extra features Example (VM II: they added Twin, Premium, Premium Lite, Elite, Premium Plus).
Note: There is alot of Cheaply made inverter with same looks and models with cut down components and cheap semi conductors this Thread dose not factor those Models in the comparison and not responsible for any Misguiding from cheap clones.

Expert Feedback is Welcomed

Adding More Models (2025-5-16):
MPS-V 3500w Plus this model is a modded Voltronic clone (Probably from Sumry Factories) with separate MPPT, and have 12 Mosfet on the input section with VMII interface (Better than the Voltronic VMIII 4kw Models Component wise (more Bus Caps and Input Mosfets and one more transformer).

See

There are many shorts between pins on the paralleling boards. Assuming that the same cards are used in Infini/iGrid models as in Axpert/iSolar models, I have traced the schematic of the paralleling boards here:
https://forums.aeva.asn.au/viewtopic.php?f=64&t=6007&p=90479#p90479

There are ways of extracting the bootloader, but it's far from straightforward. I prefer not to publish it widely as it presumably only helps the clone makers.
I assume that there isn't a huge need for this, as few people would be able to swap the processor without ruining the PCB. A colleague and I tried once on a similar PCB, and made a mess of it. It's just so easy to lift those thin tracks.
If I'm wrong and there is a really good reason for this, PM me and convince me that you're trustworthy (not a clone maker), and that it's a worthwhile project (e.g. saving poor people from going without electricity).

I can replace uC, but i don't find firmware with bootloader to write via jtag, also can't read from good control board

Fault code 53 is inverter (not bus) soft start fail. So the bus voltage is OK, and conditions are right to turn on the main inverter (DC->AC converter). Early on, this is done with the output relay off, I believe. The target voltage is set to 5 VAC, and the inverter output voltage is measured. If 10 volts or more lower than the nominal voltage (usually 230 V, but it could be set to 220 V o 240 V), the target voltage is set to 5 VAC higher. This continues until the output voltage is less than 10 volts short of the nominal voltage. Normally, this should cause the DC->AC converter output to ramp up to nominal voltage in just under one second. If it takes 5 seconds, then the inverter soft start fails. If it happens in less than 5 seconds, the inverter soft start passes, the target voltage is set to the nominal value, and the output relay turns on, powering the load.
I'm reading his from old firmware, because this is the only place I've commented it reasonably well, but I'd expect the same basic test to happen in all models.
So I'd say you still have something wrong with a DC->AC IGBT gate driver, the IGBTs themselves, or maybe the buck transistor is open circuit.
Consider using my "functional test" of the gate drivers here. You need two power supplies, and it's a bit tedious, but you can see the actual gate voltages for both IGBT on and IGBT off conditions, on the bench.

No, sadly. I've started a few times, and was frustrated by tracks running under large components like connectors, and not seeming to come out the other side.
We do have names for the pins on the 3 16-pin headers for one inverter model here.

Hallo!
BOOM!!! this processor (STM32F107VCT6) is not read protected!!! I can read good processor and write in new processor data to repair any communication board and display detachable for voltronic inverters! I see any board have jtag connection for this.
Now can use empty processor without bootloader.
I have some readed data from STM32F107 and will post soon




 


 
 

That's the printed circuit assembly part number, not the inverter serial number.
Use the VM II service manual I uploaded to this forum this morning. Perhaps also the attached check guide.
The most likely culprits are the 16 MOSFETs. At least one pair will be shorting battery + to battery -.
I've only ever seen 200 A fuses in 5 kVA models. And they very rarely if ever blow. Clear the short before trying again.
 
3-5KVA GE check manual 20170203-2 13 13-17.pdf

Hi @sethmad  welcome to our discussion.
We actually never got to the bottom of this . We introduced an MKS4 machine for a second opinion , the result were slightly better , but still did not resolve our issues. We subsequently added another panel that increased the open voltage pv input from 190V to 230V , and that solved a lot of issues. It appears that below 230V the mppt does not seam to be in a happy space. There is still pv power jitter when the battery is full and load is at 100W , but we decided to live with that .
My own MAX7.2 at home has exactly the same pv voltage , but much more stable at low (100W) loads. So whether there is an issue with my son-in-law string I don't know , because the panels delivers very well when the power demand increases.

First of all, there will be large electrolytic capacitors across the PV input. These do not like reverse polarity, and could fail spectacularly. But they may not get time for much in the way of fireworks.
High PV voltage solar chargers are essentially boost converters. So: inductor in series, active switch in parallel, diode in series, capacitor in parallel. With reverse polarity, the free-wheeling diodes (back diodes, antiparallel diodes) in the switches (IGBTs usually; 500 V is too high for MOSFETs) will short the input via the inductor. So far, nothing too bad happens; the free-wheel diode is rated for the same current as the IGBT, and is fast as well. But then the inductor will saturate in a fraction of a second, making it very low impedance, and this will (I think) cause the PV diodes to fuse. But wait, the inductor has considerable stored energy (E = ½LI²), where does that energy go? It doesn't go towards the load, because the diode (the boost diode, not the IGBT free-wheel diode) is reverse biased now. The inductor is bursting with energy, and does not want to allow a rapid change of current as the fuse is demanding. So it generates an enormous (multi-kilovolt) back-emf to try and find a path for the current to continue to flow (in the "wrong" direction, opposite to normal operation). This high voltage will break down something, probably the boost diode, and that transfers the bad polarity to the DC bus. That does no favours to the bus capacitors. It now could be transferring energy to the buck stage's inductor, which is also hefty. From the carnage usually seen, I suspect that a pulse finds its way across the transformer to the MOSFETs and causes problems there.
Sorry, I don't have great detail, but let's just say that it's highly desirable to avoid this situation if at all possible. Interrupting big inductors' current flow with a "mechanical" switch or fuse never leads to good things. There are movistors in there to absorb transients, but these things are the size of a few coins stacked atop each other, and can't compete with a ferrite toroid a hundred times its size and weight.

I recently linked a messy partial schematic of a high PV voltage MPPT that I didn't realise someone had posted:
https://forums.aeva.asn.au/viewtopic.php?p=101874#p101874