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Marv

Axpert Repairs.

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I've dabbled on and off with inverter repairs over the last 6 or 7 years (mostly Victron and Solaredge) so this isn't my first rodeo.

I currently have a 6 year old 2kva Axpert on my bench and alas it appears one of the Mosfet's on the DC-DC converter took something of a dump. The mosfet is blown wide open and there's splatter on the board and plenty of smoke staining in the surrounding area and generally all over inside the enclosure. Unfortunately I don't have schematics for the board so before I tidy it up fit a replacement component I wondered if anyone has past experiences of Axpert repairs.

Has anyone any experience in suitable n-channel alternatives to the IRF1407 mosfet's?

What is the usual failure mode when this particular inverter blows a mosfet?  Is there likely to be collateral damage

The input voltage is 24DC, what kind of output bus voltage would you expect to see? Looking at the push-pull Tx I was guessing around 350...maybe 400v?

Any info and any past experiences would be greatly appreciated. Thanks in advance.

 

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Posted (edited)
13 hours ago, Marv said:

I've dabbled on and off with inverter repairs over the last 6 or 7 years (mostly Victron and Solaredge) so this isn't my first rodeo.

Good on ya, Tex! 🤠

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The mosfet is blown wide open and there's splatter on the board and plenty of smoke staining in the surrounding area and generally all over inside the enclosure.

They can do that. You need to carefully get rid of all the carbon black stuff as it is conductive. If any PCB traces are blown, that makes it very difficult.

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Unfortunately I don't have schematics for the board ...

This could be handy: https://powerforum.co.za/files/file/30-axpert-mks-1-3kva-service-manual-20130611pdf/  No real schematics, but block diagrams and "simplified" schematics; it's actually better than what the larger models get.

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Has anyone any experience in suitable n-channel alternatives to the IRF1407 mosfet's?

Just find any TO-220 MOSFET with similar specifications. They all work much the same, and at 24 V (perhaps 60 V with spikes), nearly any voltage rating will do. Here is a post where Weber selected suitable replacements for 5 kVA models, and how he made the selection.

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What is the usual failure mode when this particular inverter blows a mosfet? 

With the 5 kVA models, at least one upper and at least one lower MOSFET turns on at once. But this is push-pull, so that may not apply.

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Is there likely to be collateral damage

Yes. Very often, the whole transistor will fail shorted (hence all the splatting), so battery voltage ends up on the gate drivers, frying them. However, with a 24 V model, the gate drive is often 15 V anyway, so 24 V from the battery may not be such a drama as on 48 V models. So check all gate resistors (the series resistors as well as the pull-downs), and any discrete transistors that are used as gate drivers.

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The input voltage is 24DC, what kind of output bus voltage would you expect to see?

The older 48 V models have a 1:8 transformer ratio, so the bus voltage is usually almost exactly 8 times the battery voltage. I'd expect 1:16 ratio for a nominally 24 V battery, so around 385-450 VDC.

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Any info and any past experiences would be greatly appreciated.

There seems to be much more experience with the 5 kVA models; for example see the whole PIP inverter repairs and hardware modifications thread.

 

 

 

Edited by Coulomb
16:1 → 1:16 ratio

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@Marv check under the error 09 post, you will see i posted some repair manuals of this units. All the info is there. I see you in CapeTown side. Let me know if you got it fixed, i got a 48v 5000w unit thats giving problem to. Luckily nothing burned but still cant get it running after replacing some stuff. 

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Posted (edited)

Thanks for the helpful replies, much appreciated.

Thanks also for the service manual, I must admit to already rudely grabbing a copy the day I joined. I think more detailed info would be helpful so I had a rummage around some FTP servers to try find some component level boardview pdf's but nothing so far. I posted a few requests on the Chinese servers the reside in the shadier corners of the interwebs where you mention the word 'bitcoin' and anything can happen; being an optimist i'm confident something will turn up.

Even without full schematics I think there's some entertainment value in this repair so I'm going make it a project when time allows. Unfortunately there's several other priority items being resuscitated on my healing bench at the moment so it will only be in a week or two.

Thanks again for the replies, I'll keep you posted.

Edited by Marv
spelling/grammar

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