Author Topic: Easy repair to blown 12V 50A power switching supply.  (Read 808 times)

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Offline DinkyMods

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Easy repair to blown 12V 50A power switching supply.
« on: July 28, 2018, 02:59:02 am »
I was actually kinda impressed with the build quality on this One Hung Low power supply. Everything is well held in place, two screws to easily remove the cover, and a clean looking layout with sensible cooling.  I had a totally crap power supply next to it fail giving off a LOT of heat which is my most likely suspect in this failure. Looks like it popped the two MOVs but that’s all I see so far.   I’m seldom this lucky on repairs so I’m sure I’ll find something when the replacement movs get here.


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Offline CJay

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Re: Easy repair to blown 12V 50A power switching supply.
« Reply #1 on: July 28, 2018, 06:44:58 am »
MOVs usually have a smooth epoxy encapsulation, NTC resistors more often have the rough, matt encapsulation on that part, the part even has NTC written on it (though that may just be an unfortunate coincidence)


If it is actually an NTC then it's highly likely that there's some significant fault 'further in' which has caused it to destroy itself like that.
 

Offline DinkyMods

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Re: Easy repair to blown 12V 50A power switching supply.
« Reply #2 on: July 28, 2018, 10:18:08 am »
MOVs usually have a smooth epoxy encapsulation, NTC resistors more often have the rough, matt encapsulation on that part, the part even has NTC written on it (though that may just be an unfortunate coincidence)


If it is actually an NTC then it's highly likely that there's some significant fault 'further in' which has caused it to destroy itself like that.


Stinking replacement part title as MOV right there in it after the NTC 5D-15 so it threw me off. (https://www.amazon.com/dp/B015AUEXBQ/ref=cm_sw_r_cp_api_a4dxBb9C60454)

I’m trying to think happy thoughts and that the failure was either do to the heat exposure or it just doing its job as input protection. Either way it’s a clean enough design tracing down anything else that turns up shouldn’t be hard.

It will be interesting getting it pulled apart and probing around a bit, visually at least everything else on it looks new so that’s as least a good start compared to what I expected when cracking it open considering the heat buildup it faced. There was a 2nd power supply that was next to it that had a fan failure and went critical. The enclosure they were in was too hot to touch on the other side of the CAC plate they were on so I excepted a bunch of popped caps too. They are getting replaced while I’m there anyway after that heat exposure.  I’ll post a follow-up reply when replacement parts get here and I start testing it for real.


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Offline Gyro

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Re: Easy repair to blown 12V 50A power switching supply.
« Reply #3 on: July 28, 2018, 11:16:38 am »
MOVs usually have a smooth epoxy encapsulation, NTC resistors more often have the rough, matt encapsulation on that part, the part even has NTC written on it (though that may just be an unfortunate coincidence)


If it is actually an NTC then it's highly likely that there's some significant fault 'further in' which has caused it to destroy itself like that.

It's certainly worth checking for other faults before replacement but I've seen NTC thermistors fail as a result of frequent rapid power cycling. If they haven't had chance to cool down, the high peak current can blow them.
Chris

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Offline CJay

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Re: Easy repair to blown 12V 50A power switching supply.
« Reply #4 on: July 28, 2018, 11:38:28 am »
MOVs usually have a smooth epoxy encapsulation, NTC resistors more often have the rough, matt encapsulation on that part, the part even has NTC written on it (though that may just be an unfortunate coincidence)


If it is actually an NTC then it's highly likely that there's some significant fault 'further in' which has caused it to destroy itself like that.

It's certainly worth checking for other faults before replacement but I've seen NTC thermistors fail as a result of frequent rapid power cycling. If they haven't had chance to cool down, the high peak current can blow them.

They can, but it's not common. Definitely worth checking further first.
 

Offline DinkyMods

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Re: Easy repair to blown 12V 50A power switching supply.
« Reply #5 on: August 03, 2018, 01:14:45 am »
MOVs usually have a smooth epoxy encapsulation, NTC resistors more often have the rough, matt encapsulation on that part, the part even has NTC written on it (though that may just be an unfortunate coincidence)


If it is actually an NTC then it's highly likely that there's some significant fault 'further in' which has caused it to destroy itself like that.

It's certainly worth checking for other faults before replacement but I've seen NTC thermistors fail as a result of frequent rapid power cycling. If they haven't had chance to cool down, the high peak current can blow them.

They can, but it's not common. Definitely worth checking further first.


I got lucky. Everything else checked out good. Popped two new thermistors in there and it seems to be good as new.



After the original post I found the root cause of the failure too. The neutral on my mains power drop was broken by a tree limb on it causing surging and eventually totally failed sending 233V thru all of my 120V outlets on one floor and an energetic short to ground on the other. Had a good “chat” with the property owner about the fact none of that tripped a breaker. Looks like I’ll be getting some new stuff for free so it’s not all bad.


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