Hello,

So, back to my faulty VM IV Twin inverter. I just started the process of repairing it under my direct supervision, by a good friend of mine who studied and works in the Electronics field. First discovery right now, is that the bad repair that was done at the early days of my inverter, included replacing the MOSFETs of the MPPT and Battery side of the Board with used, low quality ones, and probably with a different model name.

Good news is that I'm starting this repair project to later sell my current inverter, and buy a new one of the exact same model for the peace of my own mind, as we all know, unfortunately, nothing is well documented ever for these Chinese stuff, so it's better to buy it from the manufacturer and never play or mess with it.

I need to make sure what is the original model name of these MOSFETs, knowing that the nearest matching Service Manual I and @Coulomb have, is for VM-III-3000 / VM-III-5000, which is not accurate but I'll attach here for reference. In this service manual, it says that these MOSFETs for VM-III-3000 are all model (CSD19505KCS 201A 80V TO 220).

Would anyone please help in confirming the correct original MOSFETs model number for Axpert VM IV Twin 4000?
My inverter's sticker: https://powerforum.co.za/uploads/monthly_2023_09/Sticker.thumb.jpg.a5117d7211dd3c82389518530ec78f85.jpg

Unfortunately, I didn't have the chance to camera shoot my own inverter while it's opened. The side of the board in question is marked with a red square on the attached photo in the very next post, is from a VM III Twin 6000 taken from YouTube, so please keep in mind that it's not a photo of my own inverter.

Kindly,

Axpert VM III Service Manual 20190122.pdf

Edited August 30, 20241 yr by Tarek Yag

This photo is for my previous post, due to forum's attachments size limit.

 

This YouTube video is exactly where I took the above photo of the inverter from. So, are you suggesting that the correct original MOSFETs model name for VM IV Twin 4000 is what is mentioned in the video? (NCEP85T16)

Nope.

I think for 24V voltage is lower than 85V like in NCEP85T16.

3 hours ago, Tarek Yag said:

I need to make sure what is the original model name of these MOSFETs,

I have seen various brands of MOSFETs in various Voltronic models. The numbers in the service manual probably represent the parts that they were targeting when the manual was written. Especially with COVID and the attendant parts shortages, all manner of other parts probably were used. It's possible that the low quality parts you found were original (replacing every MOSFET in the DC-DC and also in the solar charge controller seems excessive), though I do believe that wherever possible, Voltronic do try to avoid the cheapest and nastiest parts, aiming for more moderate price and quality.

Most of these parts are quite interchangeable, although some parts do seem to operate better with particular gate resistors. That's why often you see a gate resistor that's different to the value in the service manual, and different again to the model you saw last week.

So attempting to identify the "gold standard" that works best in these inverters is possibly a forlorn task, unfortunately.

On 2024/08/30 at 11:14 AM, Coulomb said:

It's possible that the low quality parts you found were original (replacing every MOSFET in the DC-DC and also in the solar charge controller seems excessive)

It could be the same part model, I agree. But anyhow, the MOSFETs we found installed in my inverter is obvious to be used parts, as they have different fading in the white paint between each other. Moreover, I was charged a very high cost for that hit (repair).

On 2024/08/30 at 11:14 AM, Coulomb said:

I do believe that wherever possible, Voltronic do try to avoid the cheapest and nastiest parts, aiming for more moderate price and quality.

I do agree very much, especially when it is imported by a distributor of a good reputation here locally.

Anyway, I'm going to re-open my inverter now, and I'll be back with a photo of what's inside exactly in an hour or so. Then, any advice on what MOSFET model to install is very much appreciated.

Okay, so here are the findings so far:

Battery and PV MOSFETs are of 2 mixed models, some are obviously old and used, and some seem to be new. It's a mess there! Which seem to be the original model is (NCEP85T16 1CMJ2) mixed with NCEP85T16 1CN02)

Main Board IGBTs now are of 2 mixed models, the original model which was never replaced on the right-side half (40T65HD 21442851), and another model on the left-side half (JT075N065WED).

These IGBTs were replaced by a professional a few months ago, when I took the inverter in for a first quick check and repair a couple of months ago when I bought my new battery. The older IGBTs were mixed of another two IGBT models on the first repair (hit) that messed the whole inverter since it was brand new.

I took all needed photos today after I disassembled it by myself, and checked the market for the availability of NCEP85T16 and found good quality ones.

@Coulomb, I'd love to hear from you all of your comments on the current situation. Any comments from anyone are welcome too.

VM IV Twin 4000 Mess.zip

Edited August 31, 20241 yr by Tarek Yag

On 2024/09/01 at 3:16 AM, Tarek Yag said:

Battery and PV MOSFETs are of 2 mixed models, some are obviously old and used, and some seem to be new. It's a mess there! Which seem to be the original model is (NCEP85T16 1CMJ2) mixed with NCEP85T16 1CN02)

The second (bottom) numbers will be batch code and/or date of manufacturing. It may be that some were replaced, or it might mean that they had parts from two different orders in their parts bin. Your parts with part number NCEP85T16 seem to be OK per my crude checks, which are:

* Do they have a reasonable looking datasheet online?

* Is the datasheet reasonably complete (all the usual sections, graphs, etc)

* Are the specs reasonable? Usually I only look at the headline figures, like max voltage and max continuous current, and a very few other figures, like input capacitance (should be under 10 000 pF (10 nF) for Axpert designs, since that's the limit for the gate drivers. For MOSFETs, I'll glance at their on resistance (RDSₒₙ). I'll also often glance at the delays (turn on, rise and fall times), to make sure they don't look ridiculously large.

* Is there a real company name, usually with an address.

* Do the parts have a logo that matches the datasheet? I've seen some Ali Express parts claiming loudly that they are genuine parts, yet there is no logo, and the font for the part number is very plain and uniform.

On 2024/09/01 at 3:16 AM, Tarek Yag said:

Main Board IGBTs now are of 2 mixed models, the original model which was never replaced on the right-side half (40T65HD 21442851), and another model on the left-side half (JT075N065WED).

Again, all these pass my crude checks.

Re the Aishi capacitors, they seem to have a reasonable reputation ("second tier", not quite United Chemicon or Nichicon quality). I could not quickly find the datasheet for this exact capacitor; the RF series only went to 1500μF at 35 V working. But it's not unheard of for Voltronic to use a custom made capacitor! That makes it difficult to find a suitable replacement. These seem to be rated at 6000h @ 105°C, which is quite good (if the rating is to be believed, of course). 

Edited September 7, 20241 yr by Coulomb

45 minutes ago, Coulomb said:

The second (bottom) numbers will be batch code and/or date of manufacturing.

Thank you, I really was in doubt of this fact.

46 minutes ago, Coulomb said:

It may be that some were replaced

I'm certain that they were randomly replaced, at the very first messy "repair", with used MOSFETs from several different used units. I made sure that the person who made the very first repair has no honesty.

Thank you for all the nice advices to check the integrity of a new replacement part, I'm going to consider them all when buying the new set. I'm going to proceed with this repair as soon as possible with my friend based on the recommended part model you confirmed is okay.

55 minutes ago, Coulomb said:

Again, all these pass my crude checks.

Thank you very much! I'm glad the last professional who did the replacement of the -previously replaced- used IGBTs, did a good job based on my request to use good quality parts. I guess there's no need for any repairs in these right now.

1 hour ago, Coulomb said:

the Aishi capacitors

My friend recently affirmed me that these capacitors are the original parts that are installed in genuine Axperts of good reputation brands.

Here's an update that I wanted to post last Friday, right when I've had my PV & Battery (DC/DC) MOSFETS replacement job done.

Replaced MOSFETs had different values each, with two of them having significantly different values than the rest. I, and my professional friend, tested the new MOSFETs before installation, and to our expectation, they all had almost the exact same values as manufacturer specifications. Good indicator, huh?

Bad news is that we've found two open resistors (drivers) behind a single DC/DC MOSFET, which I guess explains all the differences I have in my inverter's PV readings when grid is not present. Am I correct?

We made sure again that all four INV IGBTs were replaced properly on the previous repair which was conducted by another professional, as I stated before. The only -perhaps- negative thing we noticed is that one IGBT seems to be from a different batch, however it has the exact same model number. Additionally, all these IGBTs have almost the exact same values. Is that okay?

One last component I don't feel okay about, and I think it was tampered with on the first repair / mess, is component D82 which is located at the bus soft start circuit. When I checked my inverter the very first time I noticed a very bad soldering job and a mess on the board around it. So, I'm planning to replace this at the same time with the MOSFET drivers (resistors) I need to replace next. This time we re-soldered it quickly till we replace it the next and hopefully last repair. Any thoughts?

@Coulomb Would you please confirm that I'll be good with replacing all DC/DC drivers (resistors) with their original same values (SMD 47R0 and 4702)? And please answer my questions at the end of each of my previous paragraphs.

PV & BAT MOSFETs Repair.zip

Edited November 5, 20241 yr by Tarek Yag
Corrected one photo description

Tarek Yag hello, here are two photos with the original parts. I hope it helps.

10 hours ago, melac said:

I hope it helps

Yeah, it helped, thank you!

Actually, after a few photo reviews, I noticed that my 4 INV Bridge IGBTs were replaced with pieces from 3 different batches!!!!!! I don't know how a sane man could do this! So, even the professional who did that repair, didn't do an acceptable job from my perspective.

I'm planning now to replace them all again with brand new four pieces of model YGW60N65 and will check today if I can find a higher Amperage specification of this component. I'm tired of this mess! But at least, this way there will remain no components not re-replaced by me and my close friend at our own standards.

@Coulomb

Edited November 6, 20241 yr by Tarek Yag

22 hours ago, Tarek Yag said:

Bad news is that we've found two open resistors (drivers) behind a single DC/DC MOSFET, which I guess explains all the differences I have in my inverter's PV readings when grid is not present. Am I correct?

It looks like both the gate series resistor (47Ω) and the gate pull-down resistor (47 kΩ) were blown. To blow the pull-down resistor, there must have been very high gate to source voltage, which I would expect to cause more problems earlier in the gate driver circuit. But I would not expect it to affect PV measurements.

22 hours ago, Tarek Yag said:

We made sure again that all four INV IGBTs were replaced properly on the previous repair which was conducted by another professional, as I stated before. The only -perhaps- negative thing we noticed is that one IGBT seems to be from a different batch, however it has the exact same model number. Additionally, all these IGBTs have almost the exact same values. Is that okay?

Yes, as long as the part numbers are the same, it's fine to pair them up even if from different batches.

22 hours ago, Tarek Yag said:

One last component I don't feel okay about, and I think it was tampered with on the first repair / mess, is component D82 which is located at the bus soft start circuit. When I checked my inverter the very first time I noticed a very bad soldering job and a mess on the board around it. So, I'm planning to replace this at the same time with the MOSFET drivers (resistors) I need to replace next. This time we re-soldered it quickly till we replace it the next and hopefully last repair. Any thoughts?

That's probably the buck diode, if it came from the long heat-sink, not a small separate one. [ Edit: Duh! The photo clearly has a separate heatsink on it. Sigh. ] It's probably fine to just clean up the soldering, but replacing it won't hurt.

22 hours ago, Tarek Yag said:

Would you please confirm that I'll be good with replacing all DC/DC drivers (resistors) with their original same values (SMD 47R0 and 4702)? And please answer my questions at the end of each of my previous paragraphs.

I've actually never designed circuitry with MOSFETs or IGBTs; when repairing I've always been happy to leave the series gate resistor the same value as originally used. If you can find a recommended value for that resistor in the datasheet specs, then you could use that value. My feeling is that the Voltronic inverters are designed with fairly wide dead-time, so that they can just use whatever parts they can get for production, without having to match them to the MOSFETs.

Edited November 6, 20241 yr by Coulomb

8 minutes ago, Coulomb said:

That's probably the buck diode, if it came from the long heat-sink, not a small separate one. It's probably fine to just clean up the soldering, but replacing it won't hurt.

Not the buck diode, it is the small separate one indeed (all photos attached already). Yeah, it won't hurt, and I will replace it after your statement 😄

8 minutes ago, Coulomb said:

Yes, as long as the part numbers are the same, it's fine to pair them up even if from different batches.

New discovery in my newest reply here, which seems I wrote at the same time you were writing yours. Four pieces only from three different batches is way too much for me!

10 minutes ago, Coulomb said:

If you can find a recommended value for that resistor in the datasheet specs, then you could use that value.

I will check this out now, thank you for the hint!

11 minutes ago, Coulomb said:

which I would expect to cause more problems earlier in the gate driver circuit. But I would not expect it to affect PV measurements.

Bad news to me, and I won't figure this out until the very end of the repair! Fingers crossed with all the planned replacements this time it could fix the issue somehow someway.

7 hours ago, Tarek Yag said:

Bad news to me, and I won't figure this out until the very end of the repair!

Have you checked all the transistors, diodes, resistors, and zeners in that area? Especially for that MOSFET where the two resistors failed open circuit. Unless it was a soldering problem perhaps.

9 minutes ago, Coulomb said:

Have you checked all the transistors, diodes, resistors, and zeners in that area?

I will try to check more components around the DC/DC MOSFETs as you suggested. We're planning to do the repair job just like last week, on Friday. I just purchased all planned replacement parts, and we're good to go now! I'm hoping to get better repair outcome this time, and it won't hurt if we need one more repair session! I like the journey so far since it's not my main study field!

15 minutes ago, Coulomb said:

Unless it was a soldering problem perhaps.

Most probably not! We already checked the soldering condition of every component on the inverter last session.