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Infini 3KW plus goes out with a bang!


bluwater
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I disconnected the PV input wiring from the Inverter tonight to rearrange the cables and make them neater. The PV breaker was switched off, grid input to the inverter was on, the battery was also connected, but the Inverter was under no load. So after rearranging the wires I tried to re-connect the PV input wires (DC breaker was still off) making sure the polarity was correct, but there was a loud bang and something blew really violently from inside the inverter. The inverter started beeping and an error code 04 started flashing on the inverter which as per user manual means "Inverter soft start is time-out". I also noticed that the AC breaker had also tripped. After about 30 seconds of beeping, the Inverter switched off completely.

So after a couple of minutes I turned it on again and I was getting the same 04 error and the Inverter switched off after 30 seconds. Turned it on again and this time, I reset the AC breaker. The Inverter detected AC input and switched to grid input after a few seconds and there was an OK message on the screen instead of the error code and then suddenly something blew again, just as before. The AC breaker tripped again, this time error code was 05 "An inverter overcurrent event is detected". The inverter switched of automatically after 30 seconds. I turned it on again after a few minutes (AC input was still disconnected) and it was flashing 04 error "Inverter soft start is time-out" and shut down after 30 seconds. I thought about reconnecting AC power and turning it on again, but then thought why risk another blow-up.

So first of all I can't figure out what I did wrong in the first place. All the wiring was connected as before. I just disconnected PV Input and reconnected it after a few minutes and the PV breaker was also switched off even though it was the middle of the night and there was hardly any voltage in the PV input. The polarity was also correct, I just don't know what went wrong. May be I should have turned off the Inverter completely before reconnecting the PV wires.

Now what am I looking at here in terms of damage. Any thoughts?

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@bluwater, sorry to hear about this. Strange for your Model, first time I here about one blowing up. 

9 hours ago, bluwater said:

May be I should have turned off the Inverter completely before reconnecting the PV wires.

9 hours ago, bluwater said:

disconnected the PV input wiring from the Inverter tonight

9 hours ago, bluwater said:

PV breaker was also switched off even though it was the middle of the night

I will rule out it had anything to do with the PV wires if it was at night. 

As to what could have blown, I am not sure, normally the DC side blows, but in your case the AC breaker tripped, and the alarm message points to an AC over-current. I have seen DC circuits blow on an infini and that gives completely different alarms. Maybe someone else has experienced AC problems and might shed some light on this. 

@plonkster and @Coulomb knows and understands the inside and working of inverters pretty well. Lets see what they say.. 

 

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This morning I rechecked all the wiring. Everything seems to be in order. Connected the laptop to the Inverter to try and get some error codes. I turned it on with just the battery connected. It turns on and beeps continuously and then I get a "WR" (warning) in the LCD display, which stays for a while and then it changes to OK and stops beeping, showing just the battery powering the load and then a few seconds later it changes to "04" and starts beeping and shuts off after about 30 seconds. Below is a screen shot of the fault log data. The first blow up occurred around 23:38 yesterday when I connected the PV input. The breaker was off but still it is seeing 2.7V on PV input. The second blow up occurred at 23:53 when I reconnected the inverter with the grid. As you can see voltage was fine. I'll take the Inverter in to the dealer on Monday and get it checked out. Fingers crossed.

Untitled-1.jpg

Edited by bluwater
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4 hours ago, Jaco de Jongh said:

understands the inside and working of inverters pretty well

I don't really know what that error message means. Think it has something to do with how it charges the high voltage DC bus, and then if it doesn't manage to do that within a certain time then it raises that error. Don't know this inverter well enough. That would mean something broke in the boost converter that runs from the battery side. I've had enough cases in my life where the explanation for things is "coincidence". You can never discount coincidence. Ever since I had a car that blew a fuel pump fuse on the first start after replacing the distributor cap... for no reason I could ever figure out. Also never ever did it again after that. Just dumb coincidence.

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The big bang means it's probably not a trivial fix. It will at least have blown two IGBTs, possibly more. I don't know the Infinis at all.

A bus soft start failure usually means shoot through of IGBTs.

There is the concept of "inverter soft start" as well as that of "bus soft start". The latter is merely pre-charge of the bus capacitors; in an Axpert, there is a small power supply (chip, MOSFET, and multi-winding inductor) dedicated to this. 

I've not had the opportunity to figure out what soft start of the inverter is. I'd say it does a series of things, designed to prevent your second loud bang. Evidently, it failed. But I think that's why there was such a delay before the second bang, after the AC input was connected.

I'd have little faith that your supplier will be able to repair the unit, except to replace the main board. That might be 50-75% of the cost of a new unit, at a wild guess.

As for what you did wrong, I also don't know. Certainly, I would have disconnected the battery and AC input when working on the PV wiring, or anything else. I assume that this model has a higher voltage MPPT, with some 500 V at the input. All I can think of is that some capacitor somewhere retained a nasty charge, and that somehow found its way to the "DC bus" (the ~400 VDC rail that the inverter IGBTs run off). In an Axpert, the SCCs connect to the battery terminals, so there's another system between the SCC output and the DC bus.

Sorry to hear about the blow-ups, and sorry I can't be more help.

As a point of interest, was the AC breaker that you mentioned tripped on the grid connection, or the AC output (sensitive loads, inverter output)? I'm assuming here that Infinis have two inverters; one for grid interaction, and one for running sensitive loads, but I could be way off with that. As I say, I don't know the Infinis at all.

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14 hours ago, Coulomb said:

As a point of interest, was the AC breaker that you mentioned tripped on the grid connection, or the AC output (sensitive loads, inverter output)? I'm assuming here that Infinis have two inverters; one for grid interaction, and one for running sensitive loads, but I could be way off with that. As I say, I don't know the Infinis at all.

AC breaker did not trip instantly. In the Infini you can manually adjust the time delay between when it detects AC input and when it actually switches load over to it. It only tripped 30 seconds later, after a relay kicked in that was supposed to transfer the load to grid instead of battery. That is also when the second big bang happened.

I am not that technically aware about the inner workings of an Inverter, but it definitely seems like two IGBTs have in fact exploded. Repair is certainly not an option, probably the entire board will need to be replaced. Will post an update when I hear something from the supplier.

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