grid tied inverter repair

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liquidhandwash
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grid tied inverter repair

Post by liquidhandwash »

Hi everyone, Just want some help repairing a Latronics PVedge grid-tied inverter. I'm not trained in electronics but I have repaired lots of electronics and built lots of kits. I've repaired 2 of these inverters before, by just replacing all the electrolytic caps but I've had a few issues with the latest one which keeps cycling through the grid check and grid fault. sometimes it tries to start but gives a 50hz buzz which is not normal and goes back to grid fault.
I've replaced all the electrolytic caps and the 2 relays and to 1uf mains caps. most of the caps were out of spec when I checked them with an ESR meter. The MOSFETs all check out ok there are no shorts, and there is no burning smells or damage.
It has quite a number of Zener diodes which all check out with a multimeter in the circuit, but I'm not sure how to test the breakdown voltage. Are zeners something that gives problems? they all look ok.
the regular diodes all look good and test ok with a meter, as do all the resistors.
Latronics refuse to give out a circuit diagram and are not helpful at all.
The user manual is below mine is the pve1200, which runs at a voltage of 70-90 volts dc and steps it up to 240v ac.
Any ideas would be great, Im always up for learning something new
thanks
https://www.latronics.com.au/sites/defa ... 3_year.pdf
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Downunder35m
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Re: grid tied inverter repair

Post by Downunder35m »

Zener diodes can fail but IMHO they are rarely the cause of problems.
So far I only had 2 failed ones and for them it was obvious that they failed because they got so hot that all markings on them disappeared.

I still have two 48V off grid inverters here that kept failing in bridge mode.
Had to repair them a couple of times for the same reasons as you.
Seems a solar shed in AU isn't the best place for caps rated for a max of 50°C LOL

Anyway...
From what little I remember from those grid inveters it seems to me that you have a syncronisation issue.
If I recall correctly the grid check makes sure the Voltage and frequency are within specs.
I assume you tried both, the inverter with no DC input and with a usable input.
Is there a chance you can trace the mains path?
It could be as simple as a bad contact on a relay or a faulty filter capacitor.
If these yellow caps are on the mains side then see if your meter still gives them correct values.
The brown wire goes through a thingy that provides a Voltage corresponding to the load.
It might also be the essential part to check the mains frequency.
Check those small blue caps around it and if you can the P2950 transitor as well.

I am sure our admin has a few more nice ideas ;)
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liquidhandwash
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Re: grid tied inverter repair

Post by liquidhandwash »

Thanks, Downunder, I've replaced the 2 1uf mains filter caps and replaced the relays. I've got 2 other inverters running off the mains with no problem So I don't think that would be an issue, Replacing all blue caps might me the next step.
Downunder35m
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Re: grid tied inverter repair

Post by Downunder35m »

Not really easy if they refuse to hand out the shematics and layouts :(
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Orngrimm
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Re: grid tied inverter repair

Post by Orngrimm »

but I'm not sure how to test the breakdown voltage.
Normally, you can measure them with your Multimeter in diode-mode. Instead of measuring the "correct" way, you measurte just in reverse to see the voltage needed for 1mA (Normally) current flow in reverse direction which means: You reached the zener-Voltage for reverse breakdown
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Orngrimm
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Re: grid tied inverter repair

Post by Orngrimm »

https://www.thebackshed.com/forum/ViewT ... p?TID=2498 has a problem which was solved. Shot in the dark, but hey...

- Check if the internal voltages are generated properly (For ICs and such) like at the LM7812 with it 12V-out
- Check if all the enable-Pins of the ICs are properly tied up/down. May need a DSO as it may be only a short enable-Pulse
- Check if there are voltage-dividers to read back outside or generated voltages. The R's may be a bit borderline and generate juuuust a bit off-limit Readbacks
- Check if the FETs are even driven: If there isnt even any action on the gates of the FETs, it has to be something BEFORE even trying to generate the output
- i guess you already did the AC test and DC-Test as written on the DIP-switches on the PCB?
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liquidhandwash
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Re: grid tied inverter repair

Post by liquidhandwash »

Thanks for your reply, I did see the AC and DC test but I have no information on what that test does. The inverter only has 4 LEDs on the front, so I'm not sure even what a pass /fail would look like.
It has a couple of regulators which seem to check out one output 5 volts, and the other is 24volts which looks correct as there is a 24-volt fan on the bottom. There is also 18volts on one of the test points which I thought was a weird voltage, but no service manual and no idea what I'm doing makes it hard. :-)
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Orngrimm
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Re: grid tied inverter repair

Post by Orngrimm »

LM7812 makes 12V. The Part is labeled on the silkscreen.
Measure the voltage either on Testpoints if available or from centerpin (GND) to right pin (when reading the labeling). Is there 12V?

The LP2950 is a LDO as well for 5V, 3.3V or 3.0V depending on what part it is: https://www.ti.com/product/LP2950
LP2950-50 = 5.0V
LP2950-33 = 3.3V
LP2950-30 = 3.0V
Measure this as well...

The IR2181 is the driver for the MOSFETS: https://www.infineon.com/dgdl/Infineon- ... c93cdd16ce
Check if it is powered at all (will be the 12V from the LM7812)...
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liquidhandwash
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Re: grid tied inverter repair

Post by liquidhandwash »

Thanks Again, I was able to buy a new inverter from a guy who bought about 1000 of them from a company that went broke. $250 is a great price for a 3000watt system to nearly three times the size of the PVedge inverter. I had to reconfigure the panels to output a higher voltage and was able to add another KW of panels, as the new inverter runs at 200- 600 volts.
Anyway, I don't have any panels left to test the old inverter so Ill think I'll shelve it for now, If I can find a couple more cheap panels Ill have another look at it
thanks for your help
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Orngrimm
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Re: grid tied inverter repair

Post by Orngrimm »

YW
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