Axpert inverter blew internet battery fuse

[JacoR]

I have got an Axpert 5kVA inverter which blew the internal 200A battery fuse.

I was only charging the batteries and there was no load on the inverter. I do have a 100A circuit breaker on the battery-bank  but for some reason that did not trip. 

 

Any ideas what could've caused this? 

[Richard Mackay]

Fuses are very fast devices and are preferred for real protection.  They are often not easily replaced which makes them a pain to deal with.

But they are orders of magnitude faster than a CB. 

Fuses also get fatigued with inrush currents that are not great enough to blow them but do age the fuse.

If you replace the fuse and it doesn't blow again I wouldn't worry. Leave it and see how long it lasts..

[JacoR]

I was thinking of replacing it. Any ideas where to get the fusible link? I am going to try a automotive spares shop tomorrow. 

[Richard Mackay]

Is it like the automotive fuses with the connector blades at right angles?

And is it soldered in the circuit? (I've seen that before!)

[JacoR]

Luckily it is not soldered. It is just a fusible link, tightened nuts.

[Chris Louw]

37 minutes ago, JacoR said:

I was thinking of replacing it. Any ideas where to get the fusible link? I am going to try a automotive spares shop tomorrow. 

The fuse left is a 5kVA Axpert fuse .    The fuse on the right from  4*4 Direct . They sell different tipes of strip fuses .

[Richard Mackay]

In the good old days for house wiring protection they had fuse wire wrapped onto terminals on a ceramic fuse holder..

Go have a look in the DB..maybe still some left there..

[JacoR]

5 hours ago, Richard Mackay said:

In the good old days for house wiring protection they had fuse wire wrapped onto terminals on a ceramic fuse holder..

Go have a look in the DB..maybe still some left there..

My house was built in the 1970's, so not that old.

[SYC]

12 hours ago, JacoR said:

Any ideas what could've caused this? 

What type and size batteries do you have?

Check your setting max ac/pv charge should be 10% of bank for Lead acid,Gel,AGM,etc (example 100ah bank 10amp)

On Lithium if its Pylontech 25amp per battery

@Coulomb @Chris Hobson might be able to shed more light

In my opinion fixing the symptom without the cause is useless

Edited December 7, 2019 by Quat Allah Alshams

[Richard Mackay]

4 hours ago, JacoR said:

My house was built in the 1970's, so not that old.

Just poking some fun..

If the fuses cost plenty one can install a temporary fuse to check if it will blow immediately..  (So no need to install the proper one if that's the case)

[JacoR]

@Quat Allah Alshams

I have got a 200Ah Lead acid battery bank. I will have to confirm my charge settings if I get it working again. If the settings are higher than 10%, will that cause the fuse to blow? 

 

I got a fuse from the one battery supplier here in Secunda, will test it when I get home. He did not charge me anything. 

[JacoR]

Ok, replaced the fuse, the inverter powers up but after a few seconds gives Fault 09, which, by searching the forum, means that there is an issue on the DC bus. Will have to some further investigation.

[Coulomb]

3 hours ago, JacoR said:

replaced the fuse, the inverter powers up but after a few seconds gives Fault 09

So what probably happened is that the battery-side MOSFETs shorted the 50 V bus, causing a large fault current. This blew the fuse while also fusing some of the MOSFET leads. So when you replaced the fuse, the fact that the MOSFET leads have blown away prevented another high fault current event.

I'd say that unfortunately you will find something like this inside:

The circled MOSFET (you may have to zoom) has two legs blown off. Other MOSFETs have their semiconductor chips blown away or are otherwise failed open circuit (having failed short circuit briefly).

I thought that the inverter-chargers that have the stamped fuse inside (as opposed to the more normal looking fuse with plastic parts and "200" stamped on it) came with one spare "fuse" in the box. We've probably all lost our fuses long ago.

[JacoR]

This is what I found so far. The one IGBT marked QA1 is blown. The resistor R137 for that IGBT also burnt. I still want to measure the MOSFETS and check if they are fine.

 

There might have been a fuse in the box, might have thrown it away with the box

.

[Coulomb]

10 hours ago, JacoR said:

The one IGBT marked QA1 is blown. The resistor R137 for that IGBT also burnt.

Wow! A fault in the inverter proper managed to blow the fuse, but not (in an obvious way at least) blow the battery-side MOSFETs? I'm surprised.

There may be more driver components blown that are not so obvious; see my partial schematic trace. Interesting that they didn't bother with the second gate resistor and ultra-fast diode for your unit. I hope that's because the particular style of IGBTs used doesn't need them, not because they are skimping on one cent parts.

10 hours ago, JacoR said:

I still want to measure the MOSFETS and check if they are fine.

Definitely. They do look fine, and usually a massive over-current through them is very obvious, but they must have had to endure current sufficient to blow the fuse. I suppose it must have been a (wild guess) 250 A draw for several seconds, as opposed to a 2000 A draw (also a wild guess) for a fraction of a second.

Edit: I would also replace the opposite IGBT (high side if this was low side, or vice versa), since usually the current spike is from a pair shorting the DC bus. Also, the fault code 09 indicates such a fault. The other transistor may not be as obviously damaged. Sometimes, you can't see the damage at all, or it's just a hairline crack that you have to look very carefully to see. Obviously, test all 4 for shorts, as well as the 4 high-voltage-side MOSFETs and the buck transistor.

Edited December 8, 2019 by Coulomb

[Richard Mackay]

On 2019/12/06 at 5:30 PM, JacoR said:

I have got an Axpert 5kVA inverter which blew the internal 200A battery fuse.

I was only charging the batteries and there was no load on the inverter. I do have a 100A circuit breaker on the battery-bank  but for some reason that did not trip. 

Any ideas what could've caused this? 

Were you perhaps charging your batteries with a genset?

[JacoR]

@Coulomb

Here is what I found so far, resistances measured in Ohm:

 

It looks like IGBT QB2 and QD2 is shorted. QA1 is the one that blew.

On the MOSFETs, I see a short on Q23. What should the resistance be of the high frequency transformer TX1? 

 D4 also burned.

 

 

 

@Richard Mackay I was using the normal mains, I am not sure if there was a spike causing the failure.

 

 

 

Edited December 8, 2019 by JacoR
Updated

[Coulomb]

26 minutes ago, JacoR said:

What should the resistance be of the high frequency transformer TX1?

Milli-ohms. It would read as a dead short on an ordinary multimeter, primary and secondary.

[Coulomb]

40 minutes ago, JacoR said:

On the MOSFETs, I see a short on Q23.

And also Q40 etc? But perhaps this is via TX1 and Q40 etc would test OK when Q23 was removed and/or replaced.

All the MOSFETs should show 11.75 kΩ gate to source; the fact that one quad doesn't show this means that some of the 22 Ω gate resistors are open circuit; see the partial schematic trace here.

[Richard Mackay]

3 hours ago, JacoR said:

 

 

@Richard Mackay I was using the normal mains, I am not sure if there was a spike causing the failure.

 

 

 

Hmmm...

I'm trying to find a reason as to why this happened..

Is there any local support for Voltronic gear?

[Richard Mackay]

Just to repeat the question:

Is there any local support for Voltronic gear?

[JacoR]

I have no idea. Will have to find out.

[Adri]

For my 5 cents worth.

I have read every post and if I was handling the soldering iron I would replace every power device in that part of the circuit. As has been said earlier other power devices took a heavy strain and could be partially damaged - perhaps just enough to keep working for a week...

Not worth the hassle. Change them all....                                                                       t

 

[KLEVA]

1. Yes, even just connected to Mains this can damage the internals of a Voltronics (normally MOSFETS first) before the fuse blows. Sometimes it is just the supply from Eskom or Municipality that goes nuts (had a few internal household items blow at same time), or even a spurious induction from a lightning strike nearby.
2. I personally still haven't found something to protect it properly, so advice for future failures would be helpful from others? My current Imeon doesn't seem as sensitive as the Axpert to those spikes and has just tripped itself and all the circuits before the Invertor.
3. My thinking is that if you have multiple faults visible on the same board as the MOSFETS, then rather just get a new board than trying to replace piece by piece.
4. For temporary fusing in case you think it may pop again, there are places (similarly named Voltex for example) that still sell the old housing fuse wire. Buy a bit of it at AC Rating for the DC current (Amps in DC is close enough to Amps on AC when going through a piece of wire - NOT A CIRCUIT BREAKER!), its' far cheaper than actual fuses for testing.

[Richard Mackay]

On 2019/12/16 at 1:41 PM, KLEVA said:

1. Yes, even just connected to Mains this can damage the internals of a Voltronics (normally MOSFETS first) before the fuse blows. Sometimes it is just the supply from Eskom or Municipality that goes nuts (had a few internal household items blow at same time), or even a spurious induction from a lightning strike nearby.
2. I personally still haven't found something to protect it properly, so advice for future failures would be helpful from others? My current Imeon doesn't seem as sensitive as the Axpert to those spikes and has just tripped itself and all the circuits before the Invertor.
3. My thinking is that if you have multiple faults visible on the same board as the MOSFETS, then rather just get a new board than trying to replace piece by piece.

Item 1&2: Lightening is hectic for any electronics. If you have ever owned an ADSL router you will probably have replaced it due to lightening entering it via the telephone line. If you are wanting to prevent lightening damage disconnect (isolate) your precious inverter from mains supply completely during thunder storms.

Item 3: This is what the agents will do when they 'repair' your device.