240V-120V=Magic Smoke JBC Edition

[FRR]

I received a JBC CD-1BB 120v soldering station that was accidentally plugged into a 220v outlet. The unit does have a fuse and it was the first thing I checked. Blown. I took the unit apart and was greeted with burned wiring from the transformer to the PCB.








I checked the PCB and sure enough damage on there as well.




I wanted a closer look so I removed it from the housing and desoldered the flex cable. Only one component failed in great fashion.






The damaged component was a bit difficult to identify until I traced back the wiring and figured out that the this is where the 24v rail for the heater is connected. I desoldered the blown TVS diode and scrapped away all of the left over carbon that was burned into the board. A replacement has been found and will be added to my next order from Mouser.




Next I pulled the transformer from the case and carefully removed the covers. Burned primary winding just like in the Weller unit that had no fuse. The transformer is made by Roqmo in this older unit but the newer units use an equivalent transformer from Perkan. I have sent them an email with the hopes that they would sell me a replacement.




I decided I may as well grab a few transformers I had laying around and see if I can get the unit to power on. I first started with just hooking up the 12v transformer. The unit powered and I was greeted with a warning #13. Interesting error description.






In my mind this error had to be due to the fact that I am missing the 24v rail so I hooked up a 24v transformer along with the 12v and sure enough the unit loaded all the way. I was able to access the the menu no problems.






I opened another JBC station to compare the winding and based on the measurements both of the secondary winding should be fine. If I don't hear back in the next few days about a replacement transformer I think I will go ahead and tear the transformer down and rewind it since I already have a large spool of magnet wire.

I will update this post as I make further progress. The moral of the story is do not plug your 120v device into 240v. Your mains fuse will not save you.

[genghisnico13]

Seems that bad input protection design is common in soldering stations.
My 240V JBC survived 365V+/- when the power company decided to send a phase through the neutral after a brownout, it only lasted a few seconds until I realized it and cut the power, fortunately the fuses on my multimeter and PSU blew up.

[EEVblog]

Interesting, what's the value of the mains fuse?

[EEVblog]

The moral of the story is do not plug your 120v device into 240v. Your mains fuse will not save you.

The moral of the story is that 240V into 120V gear mistakes happen all the time, and that some fuse is better than no fuse because they do blow when that happens.

[schmitt trigger]

Excellent forensic work.

Keep us posted about your progress. Or lack of.
Either way, you’ll gain lots of trouble shooting experience.

[Fungus]

Interesting, what's the value of the mains fuse?

And was it the correct fuse? Was it internal, had it been replaced with an incorrect value?

[EEVblog]

Interesting, what's the value of the mains fuse?

And was it the correct fuse? Was it internal, had it been replaced with an incorrect value?

My CD-2BB is external fuse in the IEC, 1A for the 240V model. I presume the 120V model will be circa 2A?

[EEVblog]

I'm surprised at the damage, although a primary fuse capable of delivering circa 240W, and presumably no secondary fuse obviously led to trouble.
Perhaps Weller can loan JBC one of their 3 secondary protection devices 

[Brumby]

The moral of the story is do not plug your 120v device into 240v. Your mains fuse will not save you.

The moral of the story is that 240V into 120V gear mistakes happen all the time, and that some fuse is better than no fuse because they do blow when that happens.

Obviously we cannot say that a fuse will save you from damage - but it will limit the damage ... all on its own.

Dave's Weller experience might still have produced damage and smoke, but it is unlikely that he would have needed to rush in to limit smoke production - and possible more extreme failure outcomes ... like fire.


This is where I see the fuse being of great value - in the ability of the unit to limit the extent of the consequences of failure, without the reliance on external intervention.

[floobydust]

The fuse is on the big side, the station has a 130W "peak power" rating.
2A fuse will hold almost 3A 5x20mm Littelfuse curves. Previous user might have put a larger fuse put in, or maybe it's slow blow.

[FRR]

The moral of the story is do not plug your 120v device into 240v. Your mains fuse will not save you.

The moral of the story is that 240V into 120V gear mistakes happen all the time, and that some fuse is better than no fuse because they do blow when that happens.

I should have phrased that differently. It won't save your gear, but it should save your building from burning down. From what I understand the fuse stopped the damage from getting even worse without having to pull it from mains.

It was the stock 2A fuse in the IEC.

[FRR]

Also, I forgot to mention that the secondary side of the transformer does have TO-92 looking component with 1 leg cut off. I haven't looked to see what it is, but I will get to it in the rewind or when I get a new transformer. One leg shares a connection with the 12v winding.

[floobydust]

Great... it has no safety approvals or certification whatsoever. Just CE. No wonder there's some uh issues.

[CDaniel]

Unfortunatly the fuse is not there to save an 120V transformer plug at 230V ( maybe only in exceptional cases ) ... because of the inrush current at start any fuse is much larger for this purpose . So only protects your house from burning down 

[2N3055]

Like I said in another topic.
Current increase is not enough to burn the fuse quick enough. Trafo usually gives first.
Fuse (thermal or electric) is there to stop things to set on fire.

I have a lot of experience with this many years ago with audio equipment brought back home from Japan (120V). We had 220V than (now 240 like the rest of EU).

I had a really nice audio setup made out of repaired equipment. I had a buddy that worked in transformer factory..

Good thing about quick burning trafo and TVS in JBC is that it saved electronics...

Sad part is that it is trivial to make an auto switch circuit.

[rsjsouza]

I got bored with the other discussion and the nonsense there from the distortions to the original main topic of the video.

This new event shows me what we predicted before: the fuse limited the consequences of the failure by interrupting the power source. It was never intended to "save" the equipment.

Also, just like in the other case, there is no implication the manufacturer owes the user a compensation for the issue.

But Weller's secondary protection is really great when compared to JBC's..

[floobydust]

The smoke highlights a couple design issues. Many would be caught while getting approvals for the product.

Everything downstream of a fuse must be rated for the fuse's trip current and available energy.
A 2A fuse is 3.34A trip and at 120VAC there is up to 400W coming into the station before the fuse clears.
After a perfect 24VAC transformer, that's over 16A at the secondary!

The 24V wiring, flex cable, wand cable, PCB traces, vias etc. get tested to remain safe at that current, during the approval stage.
The flex cable is rated 3A max and twinned up, so 6A is not enough and it melted.
A secondary fuse would prevent that from happening, but do little for the primary cooking due to saturation.

The other important aspect is the PE grounding, I have no idea if JBC did it properly.

[CDaniel]

Maybe is good for shorts at nominal mains voltage 120V , but is very wasteful to design mass products for the few people who will  plug them in an 220V outlet ...

[Electro Detective]

I'm betting on a wrong mains fuse value,

and unfortunately for OP the transformer successfully protected the fuse   

Correct me if wrong but AFAIK a T-2A primary fuse has no hope of blowing out if the 120 volt 75 watt iron hits a 150 watt fault current and beyond, especially on a 240 volt zap 

I'm guesstimating a 750ma to 1 amp fast blow glass fuse would glow and blow on a fault before the windings do,
or obliterate itself on a fault or 240 volt accident.

Someone didn't do their homework and or didn't have a pair of UNI-T or Aneng meters to measure currents (much less Fluke or EEVblog meters  )

and instead worked it out in their head    and released the product   


I wonder just how much of this 'no fuse' or 'wrong fuse' fiasco has gone un-noticed over the years   


Seriously, it's not rocket science to work out the correct value fuse,
and rig a unit to survive 120 volt and 240 volt zaps,
or even 440 volt 3 phase wiring stuffups 

Behringer has been doing it for over 20 years on budget musician/recording gear. 
They obviously prefer their customers to stay raw, uncooked, and in a healthy spending state,
with no 'firestarter' bad reputation for the company to think about


And how hard is it to glue/press/embed a temperature cutout switch on the primary windings in case they decide to simmer n smoke,
for -whatever- the reason?   


What are some/all? soldering station manufacturers smoking? 

Perhaps they should try their own lit up product fumes    at the next Save A Silly Buck Bored Meeting... and get a clue 

[Fungus]

I'm betting on a wrong mains fuse value,

Me, too. There's no way a transformer should melt before the fuse blows.

Someone didn't do their homework and or didn't have a pair of UNI-T or Aneng meters to measure currents (much less Fluke or EEVblog meters  )

and instead worked it out in their head    and released the product   

(Aussie accent) She'll be alright!

[CDaniel]

There is no way to put a fuse rated at the nominal power consumption , even a slow fuse ... the current when the transformer is first energized is limited only by the coil resistance , thats why you can't use a big power transformer  without some form of soft start circuit ... otherwise will blow any fuse . https://www.quora.com/What-is-a-transformer-inrush-current

Beside this the secondary is shorted until the filter caps are charged .

The thermal fuse has a long delay before can reach the temperature , is for slow overload not for quick events .

[capt bullshot]

Also, I forgot to mention that the secondary side of the transformer does have TO-92 looking component with 1 leg cut off. I haven't looked to see what it is, but I will get to it in the rewind or when I get a new transformer. One leg shares a connection with the 12v winding.

The transformer appears well underrated for the peak power delivery capabilities of the station. So I believe it is a thermal sensor used to sense the windings temperature and limit or shut down the output.

Regarding the fuse blowing before or after the transformer releases the smoke, it's indeed quite difficult to rate a correct fuse for such a small transformer. Its impedance is way too high to blow a fuse fast enough if the fuse is intended to not degrade due to inrush or peak power delivery. If one rates the fuse on the nomimal power capability only, the fuse nomimal value will be too small for the inrush and/or peak power demand, and degrade over time. At some point the fuse will go open for no obvious reason and produce a confused user to the supporter.
So for that, the fuse has done it's intended job as designed here.
For higher power rated transformers, it's easier to find a fuse that will blow fast on a 240V applied to 120V rated event but will stand inrush and peak power. So I don't have any doubt that equipment exists that blows the fuse on wrong input voltage and doesn't get damaged. But for sure, one will find quite a beefier transformer inside than this tiny one.

[floobydust]

Soldering stations only go full power for say a minute at most. So "135W peak" is from say 75VA transformer for one minute.
The transformer is never run at 100% duty-cycle, so it's a place to save money due to pulse loads. I agree, this transformer looks much less than than a full-time 75VA part.

The black three-lead thing looks like a splice? A thermal fuse on the secondary is in the wrong place and monitoring transformer temperature to keep things cheap just derates the output power without you knowing what is going on.

[digsys]

As far back as I can remember, the STANDARD practice for mains inputs was - Fuse (fast / slow - depending on inrush etc) and a MOV ! as a minimum.
Then usually a filter, either simple cap (+res if needed) or full common-mode. There was always a MOV though .. it solved all this mess.

[JPortici]

I will update this post as I make further progress. The moral of the story is do not plug your 120v device into 240v. Your mains fuse will not save you.

yup.