MPP Solar PIP-5048MG Inverter Repair Attempt

Korishan

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2:32 Center bottom there is an 8-pin IC. It looks like there is a white spot on top. Make sure this is not a blow out point on the IC
5:22 The red parts are high voltage capacitors. The one on the far left looks like it "could" be damaged. Make sure there is no damage to the casing


As for the FETs, I would have replaced all of them. Don't take any chances with this kind of failure.
 

LithiumSolar

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I found some additional damage on the bottom side of the board. Unfortunately, there is no number visible on those tiny transistors, even if I scrape away some of the coating on top :/

20201213_155117.jpg 20201213_135105.jpg

As for the FETs, I would have replaced all of them

Would you have replaced all of the small ones too? I guess I just need to learn more about how these inverters work. Based on comments from others, the small side is the high frequency switching side that feeds through the transformer. I don't understand what the function of the IGBTs is then. Unless they're taking the high frequency and turning it in to 50/60hz? But I don't see how that would be a pure sine then.

5:22 The red parts are high voltage capacitors. The one on the far left looks like it "could" be damaged. Make sure there is no damage to the casing

It's just blown transistor dust. I cleaned it off with the isopropyl alcohol and it looks fine visually. If I measure the pins while they're all soldered, there is no short there. It seems the short is on the DC input side of the board, so my guess at this point is that one or more of the small transistors is blown unfortunately.
 

Korishan

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Would you have replaced all of the small ones too? I guess I just need to learn more about how these inverters work. Based on comments from others, the small side is the high frequency switching side that feeds through the transformer. I don't understand what the function of the IGBTs is then. Unless they're taking the high frequency and turning it in to 50/60hz? But I don't see how that would be a pure sine then.

It's just blown transistor dust. I cleaned it off with the isopropyl alcohol and it looks fine visually. If I measure the pins while they're all soldered, there is no short there. It seems the short is on the DC input side of the board, so my guess at this point is that one or more of the small transistors is blown unfortunately.
Not all the FETs will be activated at the exact same time, or turn off at the exact same time. They pulse on a different times to help give a sine like wave. Then smoothing capacitors and the inductors (the donut looking thing with thick heavy wire wound around it) take the somewhat jittery wave and make it a nice clean sine wave.

The small transistors are just small voltage switches to turn on the higher powered FETs. Think a small 5V relay to turn on a larger 120V relay.

You may not find a number for those small transistors. Though you may be able to find a replacement. @rev0 might be able to help out with this, not sure.
 

Korishan

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Hrmm, why would they use "that" kind of diode??? Looking at them again, I see that the two legs on the IC side are tied together. 🤔
 

kc8adu

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got one of those chinese componant testers?
since you have several identical channels grab the diode from either side.
the tester will tell you if its a plain diode or a zener.
the ic behind it is likely an optocoupler and bad too.
any part on the gate of a failed fet is suspect.
and if you dont resolve all of the problems it just goes BANG! when you power it up again.
 

iDIYot

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any label on the driver ic (8pin)?
most companys have design guides or reference designs -> find a suitable diode
 

kc8adu

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btw the time to test all the drive parts was before reinstalling that heatsink and igbt's
you have 5 identical channels so a problem one will stand out.
clean off the 8 pin ic's and post the number.
 

completelycharged

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For testing avoid using a battery and fuse/circuit breaker and drive the unit from a current limited source. For my test setup I use a 1200W or 1800W boost converter powered from a 30V power supply, which is then limited to about 300W output power (30V @ 10A). This has saves a few potential magic smoke occurances.

The dead short is more than likely the input capacitors appearing as a dead short. Capacitors when discharged can look like a short to a multimeter. This is partly why powering from a boost converter would allow powering up with a very limited damage potential.

The Dx is more than likely a gate drive (diode or transistor) which blew as the FET arced out internally and then back fed a high voltage. The power went somewhere after that component in order for it to blow, unless it was not actually damaged and broken/chipped before it was ever powered up. Due to the way the FET's blew out and one survided it may just be one gate arc failure you have to deal with.

Before desoldering (in future) mark the FET's so that you know where the blown FET's were in relation to the circuit board. The one FET which was a short seems inconsistent with the others and this one could be the reason for the Dx blow out.

The 500V capacitors are the high voltage common bus, which is fed by the MPPT output and drives the output via the FET's to create a sine wave by pulse modulating and changing the polarity (2 pairs of FET arrays taking alternate turns to power the output). The MPPT would unlikely be damaged as the 500V capacitors would have to have suffered first... The HV bus is usually charged to around 350V.

The FET's then just pulse modulate to create a sine wave and with this output not able to syncronise to an external power source when the mains is connected (out of phase) the result can be in worst case situation a 220V (supply) + >300V (HV bus capacitor charge) short or somewhere around 500V.

The FET's are rated for 190A each and with 5 in parallel th fauly current would have needed to be well over 1000A...
 

completelycharged

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kc8adu

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enough energy to blast that diode=dead driver opto.
and likely other parts.
on high cost parts jobs i replace everything.
then test via dim bulb.
idea is to have enough resistance in circuit to limit current if something gets latched up .
a bulb does that and serves as an indicator.
 
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