Grid Tie Inverter Repair - Transformer Check

Started by electron, Mar 28, 2024, 11:32 PM

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If your Grid Tie Inverter has a bad transformer it's not going to be a simple fix.

The GTI shown here is a 300W Power Jack style one, also the "sun" GTIs have the same board type.

If you have measured all the mosfets already and found that none of them are shorted, then you can move on to the next thing and check the transformer.

Measure using the low ohms setting on your meter, mine has a 200 ohm position.

Short your leads to see what a "zero" reading really is, mine reads 1 ohm or so, yea it's cheap but it doesn't matter, you now know what "zero" (a complete short circuit) looks like.

The DC side of the transformer here as "A" and "B", when you measure across the "A" pins, you will see "zero" ohms, same across the "B" pins. The "A" pins are one side of a center tapped transformer coil, "B" is the other.

On the high voltage output side of the transformer you will measure low ohms, maybe a couple ohms across the "C" pins and then measure across the "D" pins. The "C" pins and the "D" pins are separate transformer coils.

If you measure high ohms (more than say 100) or open on any of these measurements then the transformer is open and bad.

You can remove the transformer and see if you can repair it. It is possible that a wire came off a pin or they didn't solder it right at the factory, check all that.

We are talking about simple wire wound around inside the transformer, so if you can find the break and fix it without causing any short circuits, then you may be able to save it.

Other than that you will most likely not be able to find a replacement, but you might find a motor rewinding place that would be willing to rewind it, maybe. If they have the equipment.

If only one of the output coils "C" or "D" are bad then you can still use the GTI but at lower output power and it will probably lose some efficiency.

On the newer models of this GTI, they have the output coils connected in parallel, so you will have to lift one of the jumpers on the bottom of the circuit board to measure the coils separately. A low output on a newer model would indicate that one of the output coils has gone open.

Hi Sir , I hope you can help me out.
I got an almost exact version of GIT.
I checked transformers as you describe , seems ok.

Few months ago , my GIT stopped workin.
I ordered exact replacement parts for the MOSFETS.
Following instructions found in Youtube I changed 2 of the AC side Mosfets for new ones. Although I was not absolutely shure they where bad.
The reparation did not work out.
I found out later that LM317 regulator was not working ok. I replaced it and the unit starded working again.
It did so on the bench with a Pc power unit. Lights blinking and power converted ok.

As I go to connect to my solar panels , the unit worked a short time ( minutes ) and goes off again.

Back to the bench I found out there now is a short on DC main side, the LM317 does not get the DC input voltage on corresponding pin.
I have checked almost everything , to no avail.

Please, if so kind, how I can further check this DC input side short.

Thank You very much

Please, if so kind, how I can further check this DC input side short. On the DC side the mosfets are in parallel, one set on each side of the transformer, also the transformer looks like a short so it's hard to figure it out easily.

You should be able to tell which side is really shorted.

Generally, but not every time, the G - Gate pin is shorted too, and the gates are not completely paralleled with the other one so there is a small resistance, so you can check that and maybe get lucky and tell which one is gone.

The other way is to pull both mosfets and then check each of them.

Thank you very much for prompt answer.

I will try check this, I am not shure if I did understand well.

I will start a new threat titled "Grid Tie Inverter Repair - I have 6+4 = 10 Mosfets on one side and 4 diodes on he other.

Maybe you are in the mood and make an analysys about this.

I would very much appreciate it.

I am shure there are many trobled DIY users out there stuck with broken cheap GIT's.

Thank you again. :)

Greetings from Chile

I will start a new threat titled "Grid Tie Inverter Repair -. I have 6+4 = 10 Mosfets on one side and 4 diodes on he other. Sorry, but I can't teach a class in electronics repair here, there is way too much information out there on the net for me to spend time on that.

If you don't know how to use a ohm meter, I suggest you practice and mess around with it on a old radio or something or go on youtube and learn about it.

If you can't trace down which mosfets are on the DC side you are in trouble already, the traces are right there.

Sorry, but I already said what to do.

Like I said, just remove the DC side mosfets and test them one at a time, that is the easy way if you don't know much else.

Fearless has some good videos on youtube about GTI repairs, maybe you can figure it out that way. You could have found them by searching on youtube or even google.

I have a powerjack 1200 with a short dc
I removed the 8x dc mosfet pin "s" from all, and they are ok
With diodetesting they show 600

I removed the elkos to

BUT without the mosfet there is still a short between "s" and "d"

Can the transformers be the cause of the shortcut ???You mean you cut the S pin and are going to solder it back?

Interesting idea. That might work well on a Sun GTI since the mosfets are bent over from the board and laid flat. Actually on the Sun's you can leave long leads to solder on a new mosfet and not have to take the whole thing apart.

It's not easy to fix the DC side since things are in parallel.

But if the S pin is disconnected, the transformer coil should be "disconnected" basically.

Maybe the capacitors are what you mean by "elkos" ? The caps are across the DC too so that is something to check but not likely unless they look bad.

Is it possible one of the S pins is still making connection?

I am not sure what is left to short out the DC side except maybe a bad voltage regulator?

Could your meter DVM be tricking you somehow with caps charging?

I am assuming that you mean the short is still across the PCB pads marked S and D. Solder bridge somehow?

Get a good light on it and look around.

My GTI is labelled "smart grid tie microinverter". It comes with 15 years limited warranty, but the small print says the customer has to send the unit to Taiwan at his expense and risk.
So when it stopped working last week I decided to do surgery myself and transformed a small  torxx tool bit to fit the triangular holes of the Chinese screws. After removal of the circuit board I saw in the center an SMT diode marked M7 that was cracked. This is an 1N4007 in a very small package, but there is plenty of space there, so I replaced it with an old fashioned one. Above the diode there are two wires going to the on/off switch.
I connected DC, switched the unit on and immediately saw smoke coming from a capacitor next to the diode. That part (and all other SMT caps) is unmarked, so you can only judge the capacity by the package size. This one is 0402, so probably a ceramic one, around .01-.022 uF and 25V.
I fitted a small .01/50V ordinary cap there, applied DC and saw that the red and green LEDs started to blink.

The inverted is back on the wall, shows a green light and fan just started to work, so I guess my repair was successful!