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4KW Axpert doesn't see pv's


anunnaki
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Hi all, I have an issue with one inverter ( tree in parallel ). It doesn't show presence of pv strings (4x3). The voltage on the LCD is 0, but when measure the voltage on the DC input points in the inverter shows +- 100V (as same as on another two Axperts. I've noticed that day after I replaced cylinder fuses with blade type of DC fuses for my battery bank. The green light that indicate charging didn't flesh.

I will appreciate any advice how to fix that.

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So just to clarify, the inverter use to show presence of PV strings? You replaced cylinder fuses with blade type fuses for the battery bank and now it does not work? Did you power up the inverters after the fuse maintenance together or individually? You have removed the cover and are measuring ± 100V  on the PV terminals of the inverter?

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Yes, one of tree inverters is not showing neither the voltage nor the power and it used to work as it should. I mentioned the fuses as the reason why I disconnected AC and DC supplies. I powered them one after another (individually). Exactly I removed the bottom cover of the inverter and measured the voltage on the PV terminals. The voltage as well as the power are 0 on the display but not on the multimeter. . Just to mention that other two Axperts are working normally.

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Do they measure exactly the same, or is the non-working one higher than the others? If it's not passing any current at all the non-working unit should show a higher voltage than the working ones, because Voc is higher than when it is actually working. Probably not the most useful comment here but it does indicate whether it's a problem of not charging, or a problem of not showing that it is charging.

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9 minutes ago, plonkster said:

Do they measure exactly the same, or is the non-working one higher than the others? If it's not passing any current at all the non-working unit should show a higher voltage than the working ones, because Voc is higher than when it is actually working. Probably not the most useful comment here but it does indicate whether it's a problem of not charging, or a problem of not showing that it is charging.

non-working v=0:wub:

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23 minutes ago, ibiza said:

non-working v=0:wub:

I mean with the multimeter. If the strings are identical, they should pull down to more or less the same voltage when working. If there is not at least a 10%-15% difference in voltage, you have to question whether it isn't perhaps working (ie passing current) but just incorrectly indicating a zero. That's what I'm on about :-)

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4 hours ago, ibiza said:

 

did your LCD looked the same as mine?

I restarted the inverter for several times but with no result:wacko:

 

Yes . Did you power it down for 5 min with no ac and battery connected

 

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Unfortunately Manie's  trick didn't work:wacko:

After I disconnected them from the batteries I noticed  on two working ones green light were fleshing but not on the troubled one.

Chris could be right I must send it to the supplier.

I am grateful to all of you who showed willingness to help me!

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Just now, ibiza said:

Yes I switched off inverters but didn't disconnected the PVs

Don't know how well other systems handle that, but it is generally advisable to disconnect PV first and then the battery. The PV voltage is usually higher than the battery voltage, usually at least twice, and sudden disconnection from the load (the battery) with a high voltage input and a big old inductor inside the MPPT (buck converter), well there is this thing about not leaving switch mode power supplies (which is essentially also a buck converter) without a load because of the high voltages induced on the output. So usually the designers add a small load resistor of some kind (which is why your laptop power supply don't blow up every time you rip it out), and I would hope the axpert makers kept that in mind... but I still think in general it is good to take the PV off first, then the grid, and the battery last.

For interest, there is this one MOSFET in the Microcare controller that I could never quite figure out why it is there, which I suspect acts as a safety device. It turns off the PV side if the battery side goes down. I love little details like that :-)

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12 minutes ago, plonkster said:

Don't know how well other systems handle that, but it is generally advisable to disconnect PV first and then the battery. The PV voltage is usually higher than the battery voltage, usually at least twice, and sudden disconnection from the load (the battery) with a high voltage input and a big old inductor inside the MPPT (buck converter), well there is this thing about not leaving switch mode power supplies (which is essentially also a buck converter) without a load because of the high voltages induced on the output. So usually the designers add a small load resistor of some kind (which is why your laptop power supply don't blow up every time you rip it out), and I would hope the axpert makers kept that in mind... but I still think in general it is good to take the PV off first, then the grid, and the battery last.

For interest, there is this one MOSFET in the Microcare controller that I could never quite figure out why it is there, which I suspect acts as a safety device. It turns off the PV side if the battery side goes down. I love little details like that :-)

The Axpert inverter blown something inside in this case. I haven't taken a blown one apart yet, just resent them back to the suppliers, but I know this is one of their weak spots. Perhaps a polyfuse would have been handy in this instance? Not sure if it would trip though. 

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6 minutes ago, SilverNodashi said:

Perhaps a polyfuse

Those are current limiting devices though? I think what it would need is a crowbar circuit, something like a MOV perhaps. I seem to recall building such a thing many years ago (school days), it was essentially a thyristor triggered by a Zener with a fuse in line. Voltage goes too high and the Zener starts conducting, turning on the Thyristor. Thyristor only stops conducting when the current goes to zero, so it clamps the voltage to zero. If it is a low-current transient, that's the end of that. If it is a high-current fault, the fuse goes.

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1 minute ago, plonkster said:

Those are current limiting devices though? I think what it would need is a crowbar circuit, something like a MOV perhaps. I seem to recall building such a thing many years ago (school days), it was essentially a thyristor triggered by a Zener with a fuse in line. Voltage goes too high and the Zener starts conducting, turning on the Thyristor. Thyristor only stops conducting when the current goes to zero, so it clamps the voltage to zero. If it is a low-current transient, that's the end of that. If it is a high-current fault, the fuse goes.

polyfuses are current limiting but work on low voltages. Sadly. An MOV would probably work as well. OR even a simple double action relay could have cut out when the batteries aren't present, for safety. 

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6 minutes ago, ibiza said:

This is not the first time I switch off and on inverters without switching off the PVs!!

I hope we're wrong, I hope some protection was built in. With these things, luck also play a role. Sometimes you're just lucky and the Microwave doesn't blow up when you put a metal spoon in it :-)

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