Electronics > Power/Renewable Energy/EV's

Who knows what kind of SMPS is this one ?

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ym58:
I have purchased a second hand 12V/50A (600W) SMPS :D.

I tweaked the output voltage to 14.6V and limited the output current by cutting off three shunts out of 5 in the output negative rail.
No OVP triggered, I was quite lucky and happy ... until I pulled 40A output current to a 50% SOC 173A LFP4 battery (40A was the max current I could get after 3 shunts were cut-off)

I rapidly toasted (less than 10 sec) the 2 x  MOSFETs, 2 x gate power resistors and 2 x PNP gate transistors :palm:!
The fuse (on the AC input) blew up not fast enough to save the previous components life.

I decided to order parts from AliBaba (it came rather fast) and replaced all above-mentioned parts.
I decided this time to reduce the output current to 20A or so (using power resistors as load instead of the LFP4 battery)
Bang ... the same components blew up again  :o!

I changed them all again (for the last time) and managed to raise slowly the output current (by ways of using different power resistor values) from a few amps up to 10A max ... the SMPS now works fine but I am quite sure it won't be able able to output more than 150W without blowing up again  :bullshit:.

What can be wrong with this PSU  |O?
Who can suggest me a possible block diagram of this PSU (the 2 x small transformers in the pic below don't make me recognise a classic fly-back half-bridge design ... ) ?

Thanks for your helping me sorting this out  :clap:!

madires:
It's not a flyback, but likely a half-bridge with the small transformers driving the MOSFETs and the two brown caps between the large electrolytics connected to one wire of the large transformer's primary winding. Search for "half-bridge SMPS" and you'll find plenty of schematics.

Faringdon:
The capacitors may have dried out, and so you are getting overvoltages, which blow things up.
When you blow up a power mosfet in the primary of an offline smps, that smps is often kapput.
This is because the deadened mosfet can go short from drain to gate, and the gate connects to the signal circuitry...so all of that may have gotten high voltage on it....or higher than normal, and have been weakaned.
I have worked in repair shops, and when a primary fet blows...that SMPS is removed from the repair bench...and stated "beyond economical repair"

ym58:

--- Quote from: madires on December 04, 2022, 04:20:46 pm ---It's not a flyback, but likely a half-bridge with the small transformers driving the MOSFETs and the two brown caps between the large electrolytics connected to one wire of the large transformer's primary winding. Search for "half-bridge SMPS" and you'll find plenty of schematics.

--- End quote ---
Do you mean these two ones ?

2N2222A:
Is this power supply normally current limited? Or does it just have an over current protection trip that you lowered by removing some of the current sense resistors?

But yes, a bad capacitor on the input side of the choke that is on the output side of the main transformer can cause the power supply to increase its power too much to try to maintain output.

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