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Axpert 5kVa PC board burned


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I installed 2 Axpert 5kVa inverters (in parallel) , 2 banks (15 per bank) 275w panels and 6 * 2.4 pylontech (14.4 KWh) batteries. After setting up the inverters they ran fine for about 30 min. Then smoke came out of the slave inverter, the front PC board with the USB port. Has anybody experience similar? What can the issue be?

 

inverter.jpg

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@Coulomb or @weber will be able to tell you what that bit does. From what little I know of electronics, I see to the left two opto-isolators (marked U1 and U2), so this thing has galvanic isolation. Often in such cases an isolated power supply is required "on the other side", so this might be the transformer used for that (part of a switch mode power supply arrangement no doubt). So the question would be what happened to let the smoke out of that, and in my mind plugging the wrong kind of cable into the wrong socket could maybe do that (though in my experience with other equipment, it usually has a current limiter on it for safety).

So lets see if the masters agree with me, or if they have a better explanation, since mine is based purely on seeing two chips and some knowledge of how this is normally done.

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@plonkster, you're spot on. I haven't traced that part of the comms board, but I'm 99% sure that burned part is a transformer that connects to Gnd and HFPW (High Frequency PoWer) from one of the power supplies on the main board. It provides the + and - 12 V for the RS232 signals, and 3.3 V or so for the logic.

I've never come across that fault before. All I can think of is a shorted turn in the transformer, so it just barely worked but with very poor efficiency, and burned itself out from the heating caused by the short. Or perhaps the short developed over time, due to nicked insulation on some part of the coil wire. 

Failing after 30 minutes of service is a pretty clear manufacturing problem, so you should have no issue getting a replacement comms board under warranty. Even if you had to buy a replacement, it should be fairly inexpensive. My guess is that nothing else will have been damaged, but that's far from certain. 

Edited by Coulomb
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1 hour ago, Coulomb said:

provides the + and - 12 V for the RS232 signals

I actually thought about that, though I figured it is more common to use a capacitor charge-pump type setup (aka MAX232). But if you're going to have a 3.3V supply and you must have isolation, that means you use a transformer, and then you essentially get the other voltages for free by just adding windings. So I suppose it does make sense.

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  • 1 year later...
2 hours ago, Richard Mackay said:

So can I assume that the HFPW+ supply is exclusively to power RS232 comms and is not essential if not using serial comms?

(Iv'e got a short on the primary of TX7: sound like others have experience this too??)

No, HFPW+ is used in several places, for example the parallel boards use it too, and I suspect something on the main board as well.

I think if you leave that 2-pin plug off the comms board, then you should be OK as long as the rest of the inverter gets power. It's generated straight off the main power supply. The below is from the Axpert 4-5kVA service manual (available from this board, I believe it's this one).

You may care to measure +12V_RELAY across C78 (hopefully the parts designations haven't changed) to convince yourself that all is well.

Main power supply HFPW plus.png

Edited by Coulomb
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2 hours ago, Richard Mackay said:

Further down from the HPPW+ on the the schematic is a SM diode D40 (~1A) which feeds the primary of TX7.

Oh, does HFPW+ feed D40? I guess that makes sense. Though I'm not seeing it on any schematic in a service manual. Please post if you have this.

Quote

Looks like the xfr is short because the diode has been fried (with the PCB under it).

Are you talking about the transformer on the comms board, or TX7 on the main board?

And which diode has fried? D40 on the main board, or D2 on the comms board?

Quote

Can one get spares? If so where from??

Can one get spare diodes, yes. [ Edit: look up part numbers from the marking codes; usual sources are Mouser, Digi-Key, Farnell / element14 / Newark, and RS Components. I don't know which if any of those are convenient in South Africa. ] Can one get spare transformers, no.

BTW, a possible though perhaps expensive source of comms boards might be the remote displays that can be gotten from various suppliers, I think including Ebay. They seem to come with a spare comms board just in case you need it. Then you get a remote display for "free".

Edited by Coulomb
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2 hours ago, Richard Mackay said:

Oh dear! :(

Further down from the HPPW+ on the the schematic is a SM diode D40 (~1A) which feeds the primary of TX7.

Looks like the xfr is short because the diode has been fried (with the PCB under it).

Can one get spares? If so where from??

Hi Richard can you post a photo of what you want . I have some stuff available . Comboard and 4 kW  main board that can be stripped for parts .

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16 hours ago, Coulomb said:

Oh, does HFPW+ feed D40? I guess that makes sense. Though I'm not seeing it on any schematic in a service manual. Please post if you have this.

Are you talking about the transformer on the comms board, or TX7 on the main board?

And which diode has fried? D40 on the main board, or D2 on the comms board?

D40 was smoking.. (still works but needs to be replaced) It appears that a SM zener is short cct. (Now to try and buy a replacement with lockdown weighing heavily on us!)

Looks like this PSU is supplying +5V, -5V, +15V & -15V  ..

 

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17 hours ago, Richard Mackay said:

Looking a bit closer it looks like a zener is short.. (But not having a schematic of this circuit makes it all the more difficult!) 

Man, that brings back memories. I had the same thing happen to a Microcare MPPT, years ago. Still not sure how it happened, but the Zener was shorted and the Transformer all burnt up.

In that controller this part was an isolated supply for driving the MOSFET on the high side, so it had to be some volts above the highest DC voltage in the system. It worked simply by taking 12V input, switching it into a 40Khz square wave, feeding into the transformer, rectifying, smoothing, then clamping with a 27V Zener, feed that into a 7815 (15V linear regulator), store that in a nice large cap... and use this 15V offset to switch the MOSFET.

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1 hour ago, plonkster said:

In that controller this part was an isolated supply for driving the MOSFET on the high side, so it had to be some volts above the highest DC voltage in the system. It worked simply by taking 12V input, switching it into a 40Khz square wave, feeding into the transformer, rectifying, smoothing, then clamping with a 27V Zener, feed that into a 7815 (15V linear regulator), store that in a nice large cap... and use this 15V offset to switch the MOSFET.

Got a schematic of this circuit perhaps??

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4 hours ago, Richard Mackay said:

Got a schematic of this circuit perhaps??

I doubt it's going to help much for the topic at hand... and no, don't have a schematic. Unfortunately 🙂

The designers used a spare pin on the PIC microcontroller (probably multiplexed it onto an existing timer), and that gave them a 40kHz square wave. This they used to switch an N-channel FET on the negative side of a small transformer (other end directly wired to the positive 12V).

The transformer then stepped up the voltage to something on the other side of 27V. On the other side they had a full bridge rectifier to turn it back into DC. For that they used 4  garden variety 1N4007 diodes. But what comes out there is going to be poorly regulated and have some serious ripple, and it goes off into a linear regulator (78µ15) from there. A 7815 can't take an input more than 35V, so the transformer output is clamped to 27V by a Zener, and the ripple is smoothed with a cap.

The 15V that comes out the other side, well that is going to drive a MOSFET, and switching a FET hard requires high current for a really brief time. Easiest way to do that is to put a nice large cap on that 15V too.

So that is the entire design in words. In my case the 27V Zener went dead-short. I do not have the foggiest reason why, Zener's are generally reliable little devices. With the dead short, the transformer burned. And I suspect the 12V SMPS for the whole unit also got hurt.

Edit: Oh alright, I decided I'll draw what I remember. Don't remember all the values...

boost-converter.jpg.bd62076a4c51d17d626cead6d2596956.jpg

Edited by plonkster
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And my answer to all those discrete components was one of these. Although it still didn't work right after that, I assume because of other damage elsewhere. I chucked it in the parts bin at that point.

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  • 1 year later...

Hi, I just had the same issue... a lot of smoke coming out, inverter display was flickering and turned off with some error.

Result? Burned transformer on the communication board - Axpert MK II 450V

The probable source of my error was short in the transformer likery caused by Raspberry Pi, which had poor isolation on the power supply (Cheap chinese 5V mobile adapter). So the USB cable could cause some power spike which developed in a shorted transformer...

.... anyway removing the whole communication board resulted in fully working invertor... I just could not use monitoring.

IMG_20210730_153551.jpg

Edited by Vladimir
...added picture
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