Rewinding burnt choke coil

[Dannyx]

Good day folks. Someone recently gave me a dead power supply they pulled from a CCTV system and told me I could have it since they already replaced it with a new one, so I took this one apart and the inside was really in a shocking state: there's burnt traces, blown capacitors, a jammed fan and worst of all this: fried coil.....awesome. I think what happened to this guy is the fan failed and the heat quickly became too great for some of the components to bare, so they failed, especially since the numbnuts may have put a significant load on it. It's a PNI and it claims 10A continuous which although may not sound too shabby, I doubt can be achieved - not with the state of that output...

The biggest issue here is rewinding that coil, since I suspect the enamel has come off the windings due to the heat, which is not good since the windings will short out. Can I take some 0.3mm enamel copper wire and just rewind the thing ? (yes, I measured it with calipers). It's not too tightly packed and if I carefully remove the existing wire and measure its length it seems like an easy job. Worst case scenario is that one of the rings is just going to crumble somewhere in the middle of me trying to remove it and if that happens, I'm not sure how easy it is to obtain a ring of the same diameter and thickness....what do you guys think ? It's not so much about the PSU since I'm sure it's a piece of junk at the end of the day, but about honing my skills and enjoying a good project

[stj]

Re: Rewinding burnt choke coil

looks familiar.
those are 10-20$ from places like banggood.

i like switching psu's with "cage" cases rather than sealed with a fan - that's why!!!

[goodpsusearch]

Re: Rewinding burnt choke coil

The core material has probably lost its properties.

[Dannyx]

Re: Rewinding burnt choke coil

That's another thing I need to mention: the coil was covered in some sort of paint or coating which has fallen off due to the heat so I stripped it down entirely just so it's nice and clean and I'm now down to the bare ferrite...would this still work ? It's in series with the positive rail. Is this called a common mode choke, or are common mode chokes only used in the mains filtering portion of a SMPS ? I never understood this "common mode" business :|

[CapLeaker]

Re: Rewinding burnt choke coil

I'd replace the whole choke. As it has already been said before, the heat probably damaged the core. So even if you would rewind it, it wouldn't be the same as it was.

[Dannyx]

Re: Rewinding burnt choke coil

I'd replace the whole choke. As it has already been said before, the heat probably damaged the core. So even if you would rewind it, it wouldn't be the same as it was.

Where would somebody have a chance to find such thing ? I don't know its value or anything....I'm only able to measure the physical characteristics like the total length of wire and diameter of the two rings. Each wire is 75cm in length (there's two pieces parallel to each other) for instance.

[stj]

Re: Rewinding burnt choke coil

common mode choke has + and - both going through it.
that's just a regular choke.
have you got a scope?

[Dannyx]

Re: Rewinding burnt choke coil

common mode choke has + and - both going through it.
that's just a regular choke.
have you got a scope?

I thought so too - it's what's used in the AC input filtering of a SMPS.
Sadly no I don't have a scope....yet I was thinking of getting one of those Ebay kits as a starter, since a pro scope would not only be beyond my budget at the moment but most of its features would also be kinda useless, thus making it a waste of money...

[budm]

Re: Rewinding burnt choke coil

The common mode choke is the one right next to the incoming AC fuse. That Toroid is for some other function, more like a choke for Pi filter in the DC output.

[Dannyx]

Re: Rewinding burnt choke coil

The common mode choke is the one right next to the incoming AC fuse. That Toroid is for some other function, more like a choke for Pi filter in the DC output.

Yes, I figured as much. I could probably bypass it entirely but I'd get more noise on the output...I have no idea why it ended up in such a state other than the fan jamming and the load being slightly over the PRACTICAL limit, not the one on the label...

[stj]

Re: Rewinding burnt choke coil

look at the caps.
maybe one went low-resistance and caused a load increase through the choke.

[Dannyx]

Re: Rewinding burnt choke coil

look at the caps.
maybe one went low-resistance and caused a load increase through the choke.

The thing is the caps had already been replaced once approximately a month ago....yeah, they're Samwha so I'm not claiming they were super high quality

[budm]

Re: Rewinding burnt choke coil

BTW, what is this power supply rating anyway, the coil is so big, looks like it is made for very heavy load.

[Dannyx]

Re: Rewinding burnt choke coil

BTW, what is this power supply rating anyway, the coil is so big, looks like it is made for very heavy load.

Says 10A on the label, so at 12v that would be 120w. I can provide actual models for key components like the transistor and the diode if you wish You can bump the output up to around 14.5V via that pot near the output block which makes me think it could be used as a crude battery charger....probably not

[Dannyx]

Re: Rewinding burnt choke coil

I was reading through this....yeeeeeeaah right...apparently what I'm trying to do would send the entire "coil community" in an uproar The biggest issue is the coating on the cores since I have no idea what it is or what it's made from so I can try to replicate it...

[CapLeaker]

Re: Rewinding burnt choke coil

Yes, I figured as much. I could probably bypass it entirely but I'd get more noise on the output...I have no idea why it ended up in such a state other than the fan jamming and the load being slightly over the PRACTICAL limit, not the one on the label...

The DC output caps failed and that caused too much stress on the choke. For me, I'd put that thing in my parts bin and buy a bigger PSU. It looks almost identical to these PSU's ali sells for like 25 bucks.

[stj]

Re: Rewinding burnt choke coil

The thing is the caps had already been replaced once approximately a month ago....yeah, they're Samwha so I'm not claiming they were super high quality

in that case, maybe the output diode(s) are leaky and the caps & coil got hit with ac!

actually if you think about it, that makes sense - because it could have killed the fan!

[Dannyx]

Re: Rewinding burnt choke coil

The DC output caps failed and that caused too much stress on the choke. For me, I'd put that thing in my parts bin and buy a bigger PSU. It looks almost identical to these PSU's ali sells for like 25 bucks.

Not like I need one right away, so I thought I'd go down the cheaper and more DIY route and try to fix what I already have

[Dannyx]

Re: Rewinding burnt choke coil

in that case, maybe the output diode(s) are leaky and the caps & coil got hit with ac!

actually if you think about it, that makes sense - because it could have killed the fan!

There's only one output diode, visible near the coil, just FYI...could indeed have some leakage :|

[Stefan Payne]

Re: Rewinding burnt choke coil

The thing is the caps had already been replaced once approximately a month ago....yeah, they're Samwha so I'm not claiming they were super high quality

Samwha shouldn't be that shitty.

But that doesn't help, if you choose a totally wrong series like RD wich is a general purpose one. I'd imagine that the original were something like CapXon KF or other low ESR capacitors.

So no wonder that General Purpose one died within a Month or so and possibly caused even more damage due to improper usage of the cap.

Anyway:
That PCB looks really messed up...

Has it possibly become conductive due to heat??


@stj
Do you think general purpose caps are OK for this application/PSU??