QW-MS3010D 30V 10A Variable PSU Blown MOSFET

[RukyCon]

Originally Posted by sam_sam_sam

How long did you have them in storage because I have had some that I have bought at least 5 years or more and have had no issues using them I have values from 0.47UF to 47000UF

One thing that I do power on the device at low load and leave it powered on for hours to at least 24 hours before turning the device off

Then use the device normally after this

It's not how long i had them in storage, it's how long the store (that i bought them from) had them in storage. But i reformed them (according to the instructions i found online) and they seem to work fine.

I'll plug a small load into it tomorrow and leave it plugged in and see if it holds up.

[pc7fan]

I have an QW-MS605D (same basic circuit as the 3010D except for a few components) the IRF840s in mine failed while running a 200W load. While it failed, it took out Q4, Q5, Q6 and Q7 - as well as the gate resistors. They are 47 ohms as well. The KA7500 was unharmed, and used some salvaged 2SK2915s from an old Delta PSU instead of more IRF840s. It now can do its full 300W without the primary FETs failing.

[RukyCon]

Isn't the MS605D the 60V 5A version? I'm also wondering if i could use this in series with another identical power supply to get a higher voltage (i have two of these things, the second one was a free replacement for the first), IIRC the owners manual said they could be used in series, but to contact the supplier, but i don't remember who i got them from (and eBay seems to have also forgotten).

I did a burn-in test and it seems to work fine.

[pc7fan]

Yes, it is. Yes, you can put them in series. However unground the outputs.

Another common problem with these power supplies is the P75NF75 linear regulator FET fails D-S. (makes the supply lose regulation and mashes the output at 100% power)

These supplies are alright after you know their quirks...

The way you can cause that FET to fail is...

1. When you short the output when you set the voltage too high, hence dumping the supply's cap into the linear regulator FET, shorting drain-source.

2. Disconnect the load (esp. if an inductive load) while the supply is on. This scenario can cause inductive spiking, can cause the FET to short.

When this happens, the supply popped the output caps once on me. Mine had 2x 63V 330u caps, those vented, installed 1x 330u 100V and 2x 150u 100V. All Rubycon ZLHs. And I've got a few spare FETs.

Try to not do the two scenarios and your supply should do you well.

[sam_sam_sam]

Originally Posted by pc7fan

Yes, it is. Yes, you can put them in series. However unground the outputs.

Another common problem with these power supplies is the P75NF75 linear regulator FET fails D-S. (makes the supply lose regulation and mashes the output at 100% power)

These supplies are alright after you know their quirks...

The way you can cause that FET to fail is...

1. When you short the output when you set the voltage too high, hence dumping the supply's cap into the linear regulator FET, shorting drain-source.

2. Disconnect the load (esp. if an inductive load) while the supply is on. This scenario can cause inductive spiking, can cause the FET to short.

When this happens, the supply popped the output caps once on me. Mine had 2x 63V 330u caps, those vented, installed 1x 330u 100V and 2x 150u 100V. All Rubycon ZLHs. And I've got a few spare FETs.

Try to not do the two scenarios and your supply should do you well.

If this is true what you have here then correct me if I am wrong but this to me is poorly designed switching power supply

[pc7fan]

The PSU design itself is OK, it's the parts that are not adequate for its rating, but after doing my modifications, it can deliver its full 300W and can short it without breaking anything. It was built down to cost but as a basic bench PSU, it's fine as long you know its limitations (there are many). In stock form, I wouldn't run the supply or any of its variants over 150W continuous.

[RukyCon]

Well, the power supply is back on the healing bench, as the voltage regulation has gone out the window, especially at lower voltages, the main transformer also makes this awful and inconsistent hissing sound, The unit also seems to shut down randomly at voltages below 6v, and only restarts after the voltage drops to 0v. I did swap a few caps on the control side of the circuit, but stopped since it wasn't making any visible change to the condition of the unit. I also checked the primary caps, and they seem fine, so i'm not quite sure what to do next.

[CapLeaker]

So the CC isn’t working properly? Maybe look at the sensing circuit.

[RukyCon]

The thing is, the PSU isn't going into constant current mode when this happens, and i've triple checked it just to make sure.