Huntkey HK340-72FP SMPS shut on load above 2 amps

[abhishekkumar1902]

I have this Huntkey HK340-72FP PC SMPS where I am facing a strange problem where the SMPS shuts down when the load on any of its 12v output rails goes above 2 amps while the rating of each 12v rail is above 10amps capable.

I have checked the following:
1. All output caps are OK, and all output rails read correct voltages at no load
2. All output diodes are OK
3. NTC is ok
4. Hi voltage cap on input correctly reads 150uF on LCR meter per the spec, also the bridge rectifier is OK
5. No short in main switching MOSFET
6. All other components visually look OK, no signs of burns or anything
7. Standby 5V supply is good, which is why also the SMPS is able to switch ON when green wire (PS_ON) is shorted to ground

When I connect let's say a 5 amp load on any of the output 12 v rail, it shuts, and it works fine till a 2 amp load with a stable 12v reading.

Surprisingly the SMPS doesn't turn off if I directly connect the load before the rectification of the 12v rail which is directly on the secondary winding of the HI-POT transformer.

What could be the issue? any help is appreciated.

[stj]

Re: Huntkey HK340-72FP SMPS shut on load above 2 amps

maybe the rectifier is failing under load?

[CapLeaker]

Re: Huntkey HK340-72FP SMPS shut on load above 2 amps

Nah, probably something with the current sensing or supervisor. If it has a supervisor IC, disable it and try again. Only problem with that is, that all protection is gone.

[abhishekkumar1902]

Re: Huntkey HK340-72FP SMPS shut on load above 2 amps

Nah, probably something with the current sensing or supervisor. If it has a supervisor IC, disable it and try again. Only problem with that is, that all protection is gone.

Thank you so very much for responding. Yesterday, I was testing it and found out the exact same thing that you just mentioned. I actually bought these supplies from a friend of mine and planned to fix them so that I can use them in any future project.

For a quick high-load capability test, I usually connect a 12v, 60-watt car halogen bulb on the 12 rails. And with this specific supply only, it tripped when I connected this 60-watt bulb to the 12v rail when the supply was ALREADY SWITCHED ON. Surprisingly, when I did it the other way, that is when left the load connected, and then switched it ON, magically it started and kept the load running without any issues at all. I then even abruptly connected another 60w bulb and then it didn't trip at all.

So yes, the SMPS seems to be working fine. It seems like it's just with this SPECIFIC SMPS design, they designed it NOT TO TOLERATE high INRUSH CURRENTS. I usually connect this same 60w load to other SMPS supplies I have even when they are already switched ON, and they take and run this load easily, maybe something specific to this Huntkey SMPS only in terms of inrush currents tolerance that it trips.

But can you please tell, why doesn't it TRIPS when I switch the SMPS post connecting the load? How does the SMPS handle inrush currents in such cases when the load is connected prior to turning the SMPS ON?

[CapLeaker]

Re: Huntkey HK340-72FP SMPS shut on load above 2 amps

Supervisors can be doing funny things. I’ve had a run in with that before a few times. If you want you can read the story about a PowerMan IP with a WT supervisor that I repaired a while ago. I would start poking around the supervisor. Does this PSU a have load resistors on the 12V rail? Maybe the output caps are a bit small. Add some more capacitance and try again.

[abhishekkumar1902]

Re: Huntkey HK340-72FP SMPS shut on load above 2 amps

Supervisors can be doing funny things. I've had a run in with that before a few times. If you want you can read the story about a PowerMan IP with a WT supervisor that I repaired a while ago. I would start poking around the supervisor. Does this PSU a have load resistors on the 12V rail? Maybe the output caps are a bit small. Add some more capacitance and try again.

Yes, they have a 100-ohm power resistor on the 12v rail, and the total capacitance on each rail is around 3000uF. I tried adding another 6800uF cap on the 12v rail but observed the same shutting down.

Though I am fine with this behavior, I was planning to use this SMPS in the future for powering some projects and stuff (not for computers though), but is there anything that I can do to let the supervisor not shut the switching circuit on high inrush currents? Have you seen this kinda behavior/design in other power supplies which is NORMAL per the design?

[CapLeaker]

Re: Huntkey HK340-72FP SMPS shut on load above 2 amps

Check out the supervisor IC. It probably detects something and kills the PSU.