Cheap inverter repair

[ecogeorge]

My cheap chinese grid tie inverter has just stopped working. I did have a poor joint on a Mc4 connector that may be related .
Has not been subject to over voltage , fuse is good, on/off switch works.
Anyone got any pointers ?? every component looks good, no burnt triacs ,no burst capacitors , no smell of magic smoke .....
George

[RIT]

Any fault finding would most likely involve powering the unit up unless it was a very simple where a single part had failed, Which would mean high voltages all over the place and so not somewhere you want to go fault finding without a good understanding of what you are doing. Even a simple part fault needs more than a standard multi-meter unless its a resistor or diode.

What can you tell us about the device - a number of posters here have shown that they are good at tracking down hints and tips from the outer reaches of the web.

[ecogeorge]

All i can tell you is its a model no.GP_350w  DC 28-52v   220ac output. Maybe better pics here .......





George

[RIT]

I just had a look around and the only fault repair I could find was a video in Italian, so no real help apart from the fact that they replaced one of the MOSFETs which are the devices that line the sides of the board and use the case as a large heat sink.

I also found that there is a UK seller on eBay at £40. If that is the going rate for these devices now it would not make much sense to pay someone to fault find your current unit.

    https://www.ebay.ie/itm/323488002673

[Nickel2]

I paid £30 for a similar job that worked for 18 months, then the pcb broke down and it arced itself to death. New MOSFETs cost more than the original thing, so now it's in the spare-parts box for use in another project.

[ecogeorge]

Working from home has resulted in a few  online videos .....
I can confirm the mains fuse is good.
All mosfets test at 3.3k ohms which indicates good.
Next step is to power up on bench (cafefully) and have a probe .......
George

[rogeriko]

The black item in the middle marked BLX is a fuse holder. Is that the fuse you have checked?

[TT]

Rogeriko to the rescue again- ( he helped when I was trying to repair mine) good shout

What’s the white component to the right of this blx fuseholder?
Could it be a varistor?

[ecogeorge]

Yes ,blx fuse is good and so is holder -tested on back of pcb.
If i remember the inverter is completely dead ,-no lights at all - DC voltage is reduced when pv connected.
Have a 35v transformer  -need to find a rectifier to make text supply.
George

[rogeriko]

Put a rectifier and then an electrolytic capacitor. This will give you about 45 volts DC. Then you must put a current limiting light bulb in series with the dc line to the inverter. This will limit the current to 1 amp or so otherwise you will immeadiately burn out your transformer. Start off with a 100w light bulb. If it glows slightly then you have a shorted transistor. Likely.          I test big inverters like this only using a 240/240 transformer.       Dangerous.

[Nickel2]

...'What’s the white component to the right of this blx fuseholder?'...
It looks like a GDT (Miniature Gas Discharge Tube) used as a protection device to catch high-voltage spikes.
They are used in telephone exchanges on the line-side to protect against static voltages. (lightning).
Used with a fuse, they go short when they strike, blowing the fuse and isolating the equipment.
They also serve to protect anyone working on the equipment.

[TT]

Hi Rogeriko,

Can you provide more info on the testing with a series lamp as a current limiting device, haven’t heard that and interested in it myself.

Thanks!

[Tinbum]

The bulb is in effect just a resistor. If the item being tested has a short then the the current will be limited by the bulb- ie it tries to light. You don't have a dead short with a large current.

[jonesy]

I've had the transformer come adrift, breaking the fine copper primary.
Does the other side of the pcb have the control electronics? No stray nut shorting it out.
If it's completely dead, try to identify the dc-dc converter from 50v to 5v(or 3.3v) that will probably start with just the battery connected - my sma gti lights up and starts communicating with just the panels.

[rogeriko]

Tinbum is right. The lamp is just a resistor that you can see. Large inverters have big capacitor banks that are like a dead short when you first apply dc power. The lamp will come on bright as the capacitors charge, then as the charging current drops the lamp goes out. In this case with a probable shorted transistor the lamp will remain lit because there is a short. A grid tie inverter will start feeding into the mains and as the power ramps up the lamp will get brighter, then you must disconnect the dc power quick before the magic smoke gets released from your transformer, but at least you know the GTI works.