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Noobie
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So my Axpert has popped again!

No idea why?

I am hoping to have it repaired and keep it running until I am able to afford some Victron equipment.

I wanted to get feedback from victron users to see the pros and cons of the equipment setup.

Is anyone running a hub-2 victron system?

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25 minutes ago, Noobie said:

I wanted to get feedback from victron users to see the pros and cons of the equipment setup.

Well, the pros is that it can pretty much do anything you want. The cons is that it costs three times as much as an axpert and at least 50% more than its natural competitor (the Infini), and sometimes there are specialised things that might not be fully supported and might be stuck behind other more pressing matters, so it might take a while to get it fixed.

I made a little comparison some time ago -- I have to say again that the Multiplus is NOT in the same class as the Axpert -- but since people insist on doing the comparison, here it is. I kept it back because this is often a sensitive matter.

Not in the same class:
  - Multiplus is a hybrid inverter, Axpert is off-grid plus changeover switch.

Quality of construction
  - Multi is IP21, Axpert is IP20. A draw.
  - Multi has thick alumium case.
  - All screws have pre-cut thread on the Multi. All screws are stainless.
  - Multi fan blows the right way (up), Axpert fans blow the wrong way (down).

Electronics and electrical
  - Axpert has 63V capacitors on DC bus, too little margin for a 48V bank.
  - Input voltage range, Axpert has trouble on the top side, capped at 60V.
  - High idle current (about 25% more than the Multi). Multi has AES mode that
    further reduces consumption without having to use Search mode.
  - Earth: Multi comes with a built-in bonding relay that makes a SANS
    compliant install easy. Axpert needs an external relay unit and is only
    supported in some firmware versions (See Firmware observations below).
  - No proper SoC (state of charge) measurement on the Axpert. Most users add
    A Victron BMV to their system to get this. Multi has good SoC measurement
    included but it only works if you use the AC-charger or a BlueSolar MPPT
    with the CCGX/Venus-GX to handle communication.
  - Axpert SCC (solar charge controller) has a tendency to overshoot and is
    slow to find the power point after a load change.
  - Actual failure reports (on the internet) seems to indicate that the Multi
    is more reliable.

Software and firmware
  - The software that ships with the Axpert is limited. There is no official
    monitoring support and most users use PVoutput.org or emoncms. This is to
    be expected as Voltronic is an OEM manufacturer. The Multiplus has
    extensive software support from the manufacturer and free access to the VRM
    site for monitoring.
  - All Victron equipment integrates seamlessly with the CCGX to provide
    control and monitoring. Similar Axpert functionality provided by community
    projects.
  - All the firmware for the Multi is in one place. Axpert firmware is often
    hosted and maintained by third parties and it isn't always clear if the
    firmware will work on your equipment. Again, this could be due to the
    manufacturer being OEM.
  - The multiplus has an extremely powerful assistant-stack that allows
    additional functionality to be enabled when needed. When used in a
    grid-fallback fashion -- configured to behave like an Axpert set to SBU
    -- you have more control over when switching happens. You can tune for
    short-duration loads.

Support and Warranty
  - Multiplus 5-year warranty, Axpert has maybe two years, it is unclear.
  - Victron support is responsive and very good, Voltronic, as pointed out
    before, is an OE manufacturer, support is provided by someone else and
    often very poor.
  - To be fair, Voltronic does appear to be listening: They uprated the
    capacitors and MOSFETs in the 2017 model.

Value for money
  - The Axpert comes with a built-in MPPT, with the Multi this is external and
    costs extra.
  - The Axpert provides parallel capability for very little money.
  - The Multi costs 2.5 times more than the Axpert (and that excludes the
    MPPT).
  - When all is said and done, a price comparison really ought to be made
    against the Infinisolar which is also a hybrid. Then the difference
    is less stark.

33 minutes ago, Noobie said:

Is anyone running a hub-2 victron system?

The hub systems are deprecated, they are replaced by ESS in most cases (there are a few documented exceptions). I think the hub-2 setup (grid-tied inverters on the output of the inverter) is more common than what was formerly called hub-1 (PV is injected on the DB bus using MPPT charge controllers), but I run a hub-1 setup (or ESS with MPPTs doing the power injection).

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For completeness, I do know of one Multi failure. A contact on the transfer switch got stuck and it blew half the FETs on the output side. So it does happen. If you google for it, you'll find a few posts from more than 5 years ago of yacht-owning Americans swearing at it and saying MasterVolt is better. That's literally all I could find in my research.

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Thanks Plonkster, I appreciate the feedback.

I need to do some homework (and saving!) 

How do you prevent your Multiplus exporting to the grid and does your PV plant still generate during a grid failure?

Would you mind sharing the finer details of your setup?

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3 hours ago, Noobie said:

How do you prevent your Multiplus exporting to the grid

I have a grid meter, in my specific case it's the Carlo Gavazzi EM24, but they switched to the cheaper ET112 which is a much cheaper option, less than 100 Euro. This is connected to the CCGX/Venus-GX/BBB/Rpi using a RS485-USB cable, and the hub4control software continually adjusts the inverter to avoid feedback. I have a Conlog BEC23 prepaid meter which supposedly trips if you reverse-feed, and so far it has never tripped, but then I must also point out that I'm not capable of pushing back more than 1000W with my setup so I cannot say if it will pull back quickly enough with larger setups, just that it seems to work well enough.

3 hours ago, Noobie said:

does your PV plant still generate during a grid failure

Yes, it operates like a standard off-grid system when there is no grid power. I made a typo above, I said "DB" instead of "DC". I have "standard" low-voltage PV arrays making far less than the 150V allowed by my MPPTs, charging directly to the 24V battery. The inverter takes as much as it needs from the battery to feed into the grid, pushing the grid meter towards zero, within the configured SoC and maximum power limits. If the grid goes out, it operates like a standard off-grid system powering only the loads on the inverter output (it stops feeding back on the input connection) powering everything from the combined PV/Battery DC bus.

4 hours ago, Noobie said:

Would you mind sharing the finer details of your setup?

It looks almost exactly like this, just with a BMV between the batteries and everything else, and Pb instead of Li batteries. Also, I have the anti-islanding device with a contactor on the input side of the inverter, which is not shown here and is included in the inverter if you use the MultiGrid instead.

dc-coupled-ess.thumb.png.d9941442b73fd4230211b1af6c21fb2d.png

When the power goes out, the critical loads stay up and it functions like an off-grid setup. The other loads can benefit from surplus generation, but they go down with the grid.

Also, re anti-islanding, it should be noted that the Multiplus does isolate the grid and is approved for grid-tied use as is in many markets (eg the UK), it fails only because it doesn't have a second mechanical disconnection device as required by NRS097. It is safe even without the anti-islanding BUT (major disclaimer here), I cannot in good conscience tell you to do that because it is against the regulations.

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3 minutes ago, Chris Hobson said:

Just a quick question do you know how SMA inverters work around the islanding problem? 

They have built-in anti-islanding hardware, like almost all GTI/Hybrid inverters :-) The difference is that SMA is German and has to comply with VDE AR N 4105, which is much closer to NRS 097, hence a better chance of getting one of those on a local list.

I got some feedback on the Multigrid: It is not yet certified for NRS 097 (though it does have VDE AR N 4105). Though one would expect that compliance with the German standard ought to be enough, that is not the case, it still needs to be tested locally. That means, for the foreseeable future, you'll need the Ziehl if you want it to be fully compliant :-(

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4 minutes ago, plonkster said:

They have built-in anti-islanding hardware, like almost all GTI/Hybrid inverters :-) The difference is that SMA is German and has to comply with VDE AR N 4105, which is much closer to NRS 097, hence a better chance of getting one of those on a local list.

I got some feedback on the Multigrid: It is not yet certified for NRS 097 (though it does have VDE AR N 4105). Though one would expect that compliance with the German standard ought to be enough, that is not the case, it still needs to be tested locally. That means, for the foreseeable future, you'll need the Ziehl if you want it to be fully compliant :-(

The budget is generous so 2 Ziehls (one for each point is not going to break the bank). The Ziehl "talks" to the inverter via Hub 4?

Addition: Where can I get hold of the COC compliance list? The municipality I am installing under I doubt has woken up to GTIs. I think they have other more serious problems.

 

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2 minutes ago, Chris Hobson said:

The Ziehl "talks" to the inverter via Hub 4?

No, completely standalone. It's job is only to detect a vector shift or a drift in voltage/frequency that is out of bounds, and if it sees that, to open the contactor and physically disconnect the inverter. NRS097 requires two switches in series, one of which must be mechanical. The Multi already has the other half sorted, so the Ziehl just fills the gap.

It's a belt-and-suspender thing. The Multi will open it's internal transfer switch when it detects that the grid is out, thereby removing power from the Ziehl and the contactor and it will simply drop out because there is no power from the grid BUT, if something odd happens and the multi does not notice the grid outage (unlikely) and feeds back enough power to keep the Ziehl powered and the contactor pulled in, the impedance change caused by the grid falling out will cause a vector shift and the Ziehl will then open the contactor. But there is no comms... the Ziehl is overkill for the application but does the job.

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3 minutes ago, plonkster said:

. the Ziehl is overkill for the application but does the job.

So the Ziehl does not prevent gridfeed back? In a 300k+ install I want to be absolutely sure that those blerrie Conlog prepaid meters behave themselves.

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30 minutes ago, Chris Hobson said:

So the Ziehl does not prevent gridfeed back?

Nope. It ensures that you don't feedback into a dead grid connection (and kill a line worker), but it won't stop you from doing it with a live grid connection. Preventing grid feedback is done by telling the inverter to back off, and that is done via the RS485 power meter (or the internal meter inside the inverter if you decide to use that) and a bit of software that adjusts power feedback in an attempt to zero the power meter.

This is a rather technical topic, I hope I do it justice, but the thing with AC is that you cannot really talk of current flowing in a certain direction, because the direction of current reverses 100 times a second. You can however talk of power flowing in a certain direction, which as we all know is the product of the voltage and current waveforms multiplied by the cosine of the phase angle. What that means is that you don't know which way the power is going unless you spend some TIME measuring both waveforms and their vector product, and with reactive and other non-linear loads power is actually ALLOWED to go in the wrong direction for really short time spans. That means that most meters will be interested in some kind of average power over  a small time window, and it turns out that in this case the prepaid meter has the same problem as the grid limiter: It works on an estimate and it has to leave some room for error.

In practice, this means your grid limiter has to be faster than your prepaid meter. In the case of the conlog meter, according to their manual, the window is 15 seconds big within which the average reverse power must be less than 40 watts. So what happens is that the Multi will be happily pushing back 2kw of power when suddenly the kettle turns off and it has to back off to avoid feedback. It's going to take a few cycles for the power meter to detect that, and a few more milliseconds before the new power level is communicated to the software, and a few more milliseconds for the software to do a calculation and communicate with the inverter, the whole thing appears to take about a second in total from my experience, but for that whole second I might be pushing back over 1kw of power and the prepaid meter allows it because it cares about the average over 15 seconds.

But getting back to the Ziehl: It is a safety device. It's there so that you don't accidentally push power into a dead grid connection and kill someone who is working on it and thought it was dead. The Multiplus already has this included, it will work fine without the Ziehl, it will avoid feedback if you run ESS with a grid meter, it just won't be legal because you need that extra physical contactor. In fact, I know some people (not directly, someone who knows someone) who sneakily run without the extra anti-islanding.

Also, getting back to SMA, I now realise you're asking me how they avoid grid-feedback. As I said earlier, the SMA already has anti-islanding built in, it will not energize a dead grid connection, but it will gaily spin meters backward if the connection is live! There is a protocol for communicating with these inverters and instruct them to back off. I believe it is part of SunSpec, and I believe SMA supports SunSpec. So with the addition of a grid meter and some kind of software solution to adjust the GTIs, you can avoid grid feedback.

Victron already has support for Fronius inverters in the CCGX. The Fronius is also SunSpec, far as I know. So in theory all of this can be done with existing software solutions, but don't ask me if it works because I just don't know, I think a whole heap of tweakery will be required :-)

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Thanks gents, appreciate all the feedback.

I and having the Axpert repaired as it was less than R4k to do so.

This will allow me some time to do more extensive research and decide on which system is best suited and most cost effective.

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49 minutes ago, Noobie said:

I and having the Axpert repaired as it was less than R4k to do so.

It would be good to know what caused it to fail. Finding real data for failures is rather difficult, most reports are anecdotal at best. In the car space one guy got so irritated by that that he started TrueDelta to build a crowd-sourced statistics tool. This is actually kinda awesome, if you own a car (any car), you register and every three months you report the current mileage, if it has been to the shop, what was wrong (which subsystem), and how much it cost. You can then log in and check for any car (with enough data points) what kind of "trips to the shop per annum" you're looking at, as well as your lemon-odds, what are the chances of ending up with a lemon if you buy such a car.

Car ownership is a bit more ubiquitous than inverter ownership though :-)

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I can only imagine that the failure was caused due to the PV input?

I have decided to install the repaired unit and not connect the PV panels to it.

This does however mean that I will have PV panels sitting on the roof doing absolutely nothing, not ideal but I will have to wait till I can get a grid tie inverter unit that will not back feed into the eskom grid. I dont want to trip my meter

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39 minutes ago, Noobie said:

I can only imagine that the failure was caused due to the PV input?

What makes you think your PV array was responsible for the failure?

 

40 minutes ago, Noobie said:

I have decided to install the repaired unit and not connect the PV panels to it.

This does however mean that I will have PV panels sitting on the roof doing absolutely nothing.....

You could for not excessive money install an independent SCC.

 

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1 hour ago, Noobie said:

I can only imagine that the failure was caused due to the PV input?

I believe when the PV side goes (the SCC, solar charge controller), the inverter side keeps working as in it still powers the loads from the batteries but it stops charging. Is this what happened? I believe the usual point of failure on these inverters is either the capacitors on the DC bus, the FETs for the boost stage, or a combination of the two. I've seen some suggestions on another forum that maybe the gradual degradation of said capacitors causes the DC ripple to rise which in turn starts to hurt the FETs until something lets go.

Of course the charge controller also bears some responsibility for the DC ripple, so it could well be an unholy alliance of three things.

30 minutes ago, Chris Hobson said:

You could for not excessive money install an independent SCC.

Depends what you mean by not excessive. I don't know anything decent for less than 4k, which is more than half of what that inverter costs now, so on a relative scale it kinda is excessive... for some value of excessive. You might as well get a BlueSolar MPPT and never ever look back, I think the 150/35 is around 4.5k, and that is the smallest one in the range that can handle 48V.

Speaking of blue stuff again (how I infuriate people!), I came across this blog post from last year. These people are serious about their stuff... :-)

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5 minutes ago, plonkster said:

Depends what you mean by not excessive.

I would spend R4-6k to get R12-15k worth of panels working - especially if I was eyeing blue equipment anyway. (Is that how one gets a blue eye?)

Addition: I have a 2 year old Axpert installation that has not given me any drama. It paid for itself Nov last year. I might be more willing than most to spend money as an anticipated battery replacement looms.

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10 minutes ago, Chris Hobson said:

Is that how one gets a blue eye?

Oh wouldn't that just complete the picture! Some of you manne were in the army, julle sal my goed diktik! :-)

You know how in politics, lately, everyone is wrong except Mr. Nr. 1? That's kinda what I see in this space too. Everyone is overpriced except Mr. A :-)

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1 minute ago, plonkster said:

 Everyone is overpriced except Mr. A :-)

When I first was looking at inverters I reasoned that the Axpert was very well priced even adding a BMV to cover for its poor SOC calculations. Now that I know a little more there are very few inverters that have good SOC and even the Multiplus is going to need some CCGX tweaking to achieve this.

My thinking is now with the addition of an independent SCC one ends up with a very good system for still R20k less than it competitors. Whilst writing this I have had a brain fart and perhaps disabling the Solar Power Balance would rein in the Axpert SCC. I am going to try this and we'll see in the coming weeks.

 

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1 minute ago, Chris Hobson said:

even the Multiplus is going to need some CCGX tweaking to achieve this.

Yup, that has always been somewhat of a problem. The Multi has excellent SoC functionality, but only if it actually does the charging. Kinda obvious init? :-) So in a setup with grid-tied inverters, nothing extra required. But the moment you're using DC solar chargers (aka MPPTs) or wind turbines or any other sources, well then someone needs to do the accounting and in comes the BMV.

There is another option. If you already have a blue MPPT, then instead of the BMV, you can use a CCGX or one of the lower cost alternatives to bridge the communications gap. Then the Multi is informed about what the MPPTs are doing, and it can do proper SoC without a BMV. It also syncs the controllers re voltage and charging phase. But then all your charge controllers must be blue and must be monitored, which means you also need ve-direct cables and an mk3-usb, so no real cost advantage over the BMV.

There is one last overlooked option: If you get a Lithium battery with a supported BMS... then you don't need a BMV either. No cost advantage here either.

So... yeah. Mr. A is still right... sorta. :-)

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So I collected my inverter from repairs and they gave me the board which had originally failed.

The back of the PC board looks ok but there are a couple of components which have blown on the front, anyone know what they are and what could have caused them to fail?

Attached pics

 

IMG_1783resize.jpg

IMG_1785resize.jpg

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4 hours ago, Noobie said:

So I collected my inverter from repairs and they gave me the board which had originally failed.

The back of the PC board looks ok but there are a couple of components which have blown on the front, anyone know what they are and what could have caused them to fail?

Attached pics

 

IMG_1783resize.jpg

IMG_1785resize.jpg

Those are 80V N Channel Power MOSFETs. Their ratings are higher rated than the earlier model Axpert's 75V MOSFETs.  The Australian gurus recommend 100V MOSFETs and feel that these battery side MOSFET failures are due to ageing of the capacitors near the end of their 2000hr lifespan. The cap ageing is due to them being run near maximum temperature and voltage for extended periods. The MOSFET failure is due to impending capacitor failure. In some units examined MOSFETS were placed with inadequate paste.

I am due to receive a lightning damaged Axpert  and so I hope to take it apart and understand the beast more fully. 

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I'm not sure if those are FETs or IGBTs. The ones on the left (with numbers starting with IRF), those are definitely FETs. Those are usually used on the boost stage.

(Hint, if the number starts with IR, it's made by international rectifier, usually :-) ).

The others appears to be made by Texas Instruments. Can't find a datasheet for them. The reason for distinguishing, your IGBTs are usually on the output stage, the high voltage "chop it up into AC" part of things.

Will try to find that number when I'm at a full keyboard.

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