Hi Guys

(not so Wisey here today)

As the title clearly states...disaster!!

Yesterday was the day I chose to add a 20Kva diesel generator to my existing Solar set up. 4 x Axpert MKS 5Kva's in parallel, 42 x 250W PV's, 24 x 250Ah batteries. Eskom utility.

The generator is seperated from the utility by a 63A contactor.

This system has been functioning beautifully for 6 months. Providing daytime power to two households. Topping up from the utility at night - 10A

Back to yesterday. Before terminating the generator supply, I turned off all of the inverters at the switches, isolated the utility, battery bank and PV supply.

Then terminated the generator and utility and switched back on again.

Firstly supplying power from the batteries, then the PV's. I turned on the switch of the master inverter first, then the slaves. No utility.

I heard components in two inverters blow, immediately isolated the battery supply and then the PV supply

Pulled the inverters apart and discovered 9 x MOSFET transistors blown on one inverter and 3 on the other (MOSFET CSD19505kcs)

My question please:

1) Is there any chance of salvaging the main boards or should I replace?

2) If replacement of main boards - from who and where. (I am Durban based but obviously am prepped to ship in)

3) Has anyone else experienced this and repaired successfully?

Not feeling so good about myself this morning so hoping someone can change that with a bit of sunlight through the gloom?

All the best

Wisey

 

 

Edited May 14, 20197 yr by Wisey

41 minutes ago, Wisey said:

Yesterday was the day I chose to add a 20Kva diesel generator to my existing Solar set up. 4 x Axpert MKS 5Kva's in parallel, 42 x 250W PV's, 24 x 250Ah batteries. Eskom utility.

You say you have Eskom connected, but now also a generator?

Did you connect the generator to one or two of the inverters, and Eskom to the others? That could do it, though I thought the firmware would detect the lack of synchronisation and stop with a fault code.

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The generator is seperated from the utility by a 63A contactor.

Surely you don't connect the generator output directly to Eskom? Even if it's the type that would synchronise before connecting, it makes no sense to me.

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This system has been functioning beautifully for 6 months. 

Presumably, before you connected the generator.

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Firstly supplying power from the batteries, then the PV's. I turned on the switch of the master inverter first, then the slaves. No utility.

What about generator? With no utility connected, and the inverters having been working on parallel happily for 6 months, I don't see why it should blow up.

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1) Is there any chance of salvaging the main boards or should I replace?

It's certainly possible to repair the main board, but it helps a lot if you have the right equipment, including a desoldering station. Where any MOSFET is blown, replace the entire set of 4 it is paralleled with. So all 16 of the one with 9 blown visibly, and at least 4 on the one with 3 visibly blown MOSFETs. It's likely that you'll need to replace 8, since that sort of damage happens when both upper and lower sets conduct together (shoot-through).

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2) If replacement of main boards - from who and where. (I am Durban based but obviously am prepped to ship in)

Start with your inverter supplier; supply photos of the barcodes on the sticker on the side of your affected inverters.

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3) Has anyone else experienced this and repaired successfully?

Weber and I have repaired some 5 kW / 4 kVA models. However, some that we repaired blew up immediately upon re-applying battery power. You often need to replace some of the driver components. See the hardware section of the index (first post) of the AEVA PIP-4048 and PIP-5048 inverters topic.

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Not feeling so good about myself this morning so hoping someone can change that with a bit of sunlight through the gloom?

It would certainly be good to figure out what you did wrong. Let's start with how you connected the generator (if it was even connected when the event happened).

Edited May 14, 20197 yr by Coulomb

Hi Coulomb.

Thank you

1) The generator was not connected

2) The generator and utility are seperated by isolators and a 63A contactor ie. only one supply possible to the inverters. The coil on the contactor is activated when the generator starts and the supply then changes over.

3) Neither the utility nor the generator were connected. They are latent.

4) As mentioned, I turned the isolators to the battery bank on, connected the PV supply from the combiner box and then switched the Inverter on to supply AC to the DB

That is when it blew. No shorts on the AC side - protected by RCD - been functioning well

I suspect it might be an issue with the parallel connection system or the PV supply? PV supply at 103,2V. Battery level was at 53V

Will take a look at your link. 

Trying to source the transistors and have made contact with Heinz. We agree there may be additional component damage

Might be best to change the main boards - follow the instructions on start up meticulously and try again

Send the boards up to JHB for repairs?

7 minutes ago, Wisey said:

I suspect it might be an issue with the parallel connection system

It's certainly worth checking the paralleling cables. Odd though, as you say they were working happily for 6 months.

System worked perfectly...cabling never altered

At this stage trying to source MOSFET CSD19505kcs - no one in Durban has stock - Mantech etc. 

 

Given what was connected at the time and the switching sequence, it sounds like suspiciously like a PV overvoltage condition.

What is the Voc of your panels and how many are in series in a string? (42 panels over 4 inverters would mean an asymmetrical combination, is that telling as to which inverters blew?).

What was the time of day when you did this? 

The specs of that Mosfet you quote rate it for 80V max, ( although I don't know where it sits in the circuit, it may very well be in series with something that mitigates this).

17 minutes ago, phil.g00 said:

The specs of that Mosfet you quote rate it for 80V max

The ones in the photo look like the ones from the battery-side full bridge; nothing (directly at least) to do with PV voltage.

Do the inverters perhaps cop full sun for part of the day? That would cause the capacitors that protect the MOSFETs to dry out and go high impedance. They are only about 2000 hour rated capacitors. Weber and I recommend better spec capacitors and MOSFETs, if you're going to the trouble of replacing them. Suggested replacement parts are given in the AEVA topic. I run upgraded capacitors and MOSFETs myself.

54 minutes ago, phil.g00 said:

Given what was connected at the time and the switching sequence, it sounds like suspiciously like a PV overvoltage condition.

What is the Voc of your panels and how many are in series in a string? (42 panels over 4 inverters would mean an asymmetrical combination, is that telling as to which inverters blew?).

What was the time of day when you did this? 

The specs of that Mosfet you quote rate it for 80V max, ( although I don't know where it sits in the circuit, it may very well be in series with something that mitigates this).

Thanks for your contributions

Hoping mine will prevent this happening to someone else.

To answer your questions phil.g00

1) PV voltage I tested prior to disconnection as a matter of ensuring all strings were optimised. There was a variation of about a half a volt between strings. Output from both combiner boxes was approx. 103V, as you know the inverter is rated for 145 VAc please see model pic attached

2) I use 2 combiner boxes with 7 strings of 3 panels fused in each

From 2 x combiner boxes I have two feeds connected (in parallel) to all four Inverter PV inputs

3) The sun was high. I would say optimum exposure - peak 

 

The discovery now is these units (pls see attachment) are the old spec 145VDC and later models are 450VDC -  they are not compatible! 

The MOSFET's are available

My thinking towards a solution is the following:

1) the two early models (145VDC) - parallel connected (Inverter Pair 1) as one AC supply to one DB, with one array of 21 PV's - seperated from second AC supply (Inverter Pair 2) to second DB with later models in parallel and second 21PV array. 

Send the main boards off to be repaired and hold them as back up. (Any suggestions would be welcomed on who to send them to). As mentioned I am in Durban.

I would also appreciate any thoughts on the following:

1) Using the battery bank (6 x 4 x 12V 250Ah) ie. 6x48V as a common bank to both Inverter pairs with common utility and generator feed to both or should I split the battery bank too?

Again, much appreciate the contribution

All the best

1 hour ago, Coulomb said:

The ones in the photo look like the ones from the battery-side full bridge; nothing (directly at least) to do with PV voltage.

Do the inverters perhaps cop full sun for part of the day? That would cause the capacitors that protect the MOSFETs to dry out and go high impedance. They are only about 2000 hour rated capacitors. Weber and I recommend better spec capacitors and MOSFETs, if you're going to the trouble of replacing them. Suggested replacement parts are given in the AEVA topic. I run upgraded capacitors and MOSFETs myself.

Please see pic attached. I would say yes they from the battery side

No sun on the inverters. They are well ventilated 

Please PM me your contact details Coulomb

These are the replacements

Apologies - I see Maximum open circuit voltage is 145VDC

Any opinions on this course of action would be appreciated

4 minutes ago, Wisey said:

2) I use 2 combiner boxes with 7 strings of 3 panels fused in each

From 2 x combiner boxes I have two feeds connected (in parallel) to all four Inverter PV inputs

I would say that is an atypical way of connecting panels.

Don't these inverters have a maximum PV array input power ? -- It looks like 4 kWp if I'm not mistaken.

Source: http://voltronicpower.com/en-US/Product/Detail/Axpert-MKS-1KVA-5KVA

Now I know people happily over-panel to a degree without issues and inverters are supposed to clip but,

by making one massive block of PV and then turning the inverters on sequentially aren't you pushing your luck and exceeding this rating by 100's of % as you turn them on.

 

The max solar charge current will also be exceeded as you turn on them on until they are all on.

Yes. There could be something in that. However, the 4kWp is never exceeded. I have monitored the display on a bright day at noon and have never seen anything over 3kWp. That said  (if it is a PV voltage issue)  I have in the past connected one string at a time . I was aware yesterday of connecting and disconnecting a string 'under load'. A bit tricky. Probably best to disconnect and reconnect at night.

What is your view on these RCT's?

30 minutes ago, Wisey said:

From 2 x combiner boxes I have two feeds connected (in parallel) to all four Inverter PV inputs

Oh. Are you connecting all your PV inputs in parallel?

And this worked for 6 months?

As phil.g00 says, this is highly atypical, and I didn't think would work at all. The Solar Charge Controllers will be independently bucking the PV power, and I would think that the panel voltages with respect to battery negative would be all over the place. I don't see how it would have blown up the battery-side MOSFETs though.

Please give each inverter separate panels. 3 strings on one and 4 on another is fine. Though no one inverter should connect to more than 4500 Wp of panels.

If you need to replace inverters or their main boards, there will be difficulties paralleling them. My understanding is that the only way is to have 72.70 on the 4 kW models, and 74.10 (not 74.30, don't know about 74.20), and most likely a new machine will come with 74.30 or later. Maybe if you just replace the main boards (not the control boards), then the old firmware can operate the 5 kW hardware as if it is 4 kW.

If you do decide to split the loads, then I would also split the battery. It just seems the right thing to do, I can't think of a technical reason.

Are you saying that with 42 panels, you never exceed 4 kW total? That seems wrong. That's only 95 W per panel. I must be misunderstanding how they are connected.

48 minutes ago, Wisey said:

What is your view on these RCT's?

They will be perfectly good replacements, same as you have but with incompatible firmware (most likely).

So the reliability will be the same: most people have little trouble, occasionally one or two will blow up in spectacular fashion.

I'd try first for replacement main boards. Then you can leave the wiring as it is (apart from the PV inputs, if they are all in parallel).

1 hour ago, Coulomb said:

Oh. Are you connecting all your PV inputs in parallel?

And this worked for 6 months?

As phil.g00 says, this is highly atypical, and I didn't think would work at all. The Solar Charge Controllers will be independently bucking the PV power, and I would think that the panel voltages with respect to battery negative would be all over the place. I don't see how it would have blown up the battery-side MOSFETs though.

Please give each inverter separate panels. 3 strings on one and 4 on another is fine. Though no one inverter should connect to more than 4500 Wp of panels.

If you need to replace inverters or their main boards, there will be difficulties paralleling them. My understanding is that the only way is to have 72.70 on the 4 kW models, and 74.10 (not 74.30, don't know about 74.20), and most likely a new machine will come with 74.30 or later. Maybe if you just replace the main boards (not the control boards), then the old firmware can operate the 5 kW hardware as if it is 4 kW.

If you do decide to split the loads, then I would also split the battery. It just seems the right thing to do, I can't think of a technical reason.

All PV inputs on one array are connected in the combiner box and a single output (via the surge protector) is then split to the four inverters.

I think the 3 and 4 panels to each inverter is a better arrangement. The combiner box is not setup that way so I will adapt it accordingly. That way the Wp can never exceed 4000Wp.

Will do on all other suggestions. Thank you

Anyone out there willing to carry out repairs on the main boards?

 

 

5 hours ago, Wisey said:

As the title clearly states...disaster!!

Sorry to hear this, I know the feeling to well. 

Why dont you consider going blue?

9 minutes ago, Jaco de Jongh said:

Would love to but Victron prohibitively costly. I am improvising until Eskom supply installed. Which appears to be on the horizon...out there somewhere... 

9 minutes ago, Jaco de Jongh said:

Sorry to hear this, I know the feeling to well. 

Why dont you consider going blue?

2 hours ago, Coulomb said:

Oh. Are you connecting all your PV inputs in parallel?

And this worked for 6 months?

As phil.g00 says, this is highly atypical, and I didn't think would work at all. The Solar Charge Controllers will be independently bucking the PV power, and I would think that the panel voltages with respect to battery negative would be all over the place. I don't see how it would have blown up the battery-side MOSFETs though.

Please give each inverter separate panels. 3 strings on one and 4 on another is fine. Though no one inverter should connect to more than 4500 Wp of panels.

If you need to replace inverters or their main boards, there will be difficulties paralleling them. My understanding is that the only way is to have 72.70 on the 4 kW models, and 74.10 (not 74.30, don't know about 74.20), and most likely a new machine will come with 74.30 or later. Maybe if you just replace the main boards (not the control boards), then the old firmware can operate the 5 kW hardware as if it is 4 kW.

If you do decide to split the loads, then I would also split the battery. It just seems the right thing to do, I can't think of a technical reason.

All PV inputs on one array are connected in the combiner box and a single output (via the surge protector) is then split to the four inverters.

I think the 3 and 4 panels to each inverter is a better arrangement. The combiner box is not setup that way so I will adapt it accordingly. That way the Wp can never exceed 4000Wp.

Will do on all other suggestions. Thank you

Anyone out there willing to carry out repairs on the main boards?

 

 

Just now, Wisey said:

All PV inputs on one array are connected in the combiner box and a single output (via the surge protector) is then split to the four inverters.

I think the 3 and 4 panels to each inverter is a better arrangement. The combiner box is not setup that way so I will adapt it accordingly. That way the Wp can never exceed 4000Wp.

Will do on all other suggestions. Thank you

Anyone out there willing to carry out repairs on the main boards?

 

 

Would love to but Victron prohibitively costly. I am improvising until Eskom supply installed. Which appears to be on the horizon...out there somewhere... 

Can anyone make any suggestions on who to send two Axpert 5Kva main boards to - for repairs please?