EEVblog #1160 - Weller Responds

[Wolfgang]

But still it's really silly stuff from Weller - You design countless products with a fuse as per safe industry practice and then very deliberately design out a protective device in a few of your low end products. Crazy. I do not understand to mindset at the company to do this.

It's about how the product is perceived by the customer. Product marketing has to create value gaps between the different product families to justify the different prices. So a simple fuse becomes a state-of-the-art safety device for professional soldering stations with a perceived value of US$50. The only problem is that it doesn't work with EEs because we see a simple fuse as best current practice and know that the IEC snap-in socket with integrated fuse holder is just 50 cents more.

... just as an idea the product marketing people should put their value gaps in nicer colours or other freaky features, not in basic safety features.

I always knew why marketing people are hardly ever good for an engineering product.

[fsr]

But still it's really silly stuff from Weller - You design countless products with a fuse as per safe industry practice and then very deliberately design out a protective device in a few of your low end products. Crazy. I do not understand to mindset at the company to do this.

It's about how the product is perceived by the customer. Product marketing has to create value gaps between the different product families to justify the different prices. So a simple fuse becomes a state-of-the-art safety device for professional soldering stations with a perceived value of US$50. The only problem is that it doesn't work with EEs because we see a simple fuse as best current practice and know that the IEC snap-in socket with integrated fuse holder is just 50 cents more.

If that's the case, it's a really stupid decision, because as you say, when your products are used by people with electronics knowledge like in this case, it's almost guaranteed that someone will notice, and the result is that the company's reputation will suffer. That should be a lot more valuable than a cheap-ass fuse.

[chris_leyson]

Somewhat off topic but safety related. Take a small 10W flyback converter for example and lets say a transient or some other fault condition takes out the primary side switch and the controller chip lets out the magic smoke. You could conceivably use a small fast blow fuse or a fuseable resistor between the bulk primary capacitor and SMPS controller but would it be fast enough and open before the controller lets out the magic smoke ? The fuse will have a safety rating but the controller, the component that usually fails, is NOT safety rated. It's a bit of a gray area.

[Fungus]

Having a large number of small 110VAC mains transformers around, decided to try one out on 230VAC. Connected it up, and turned on the power. Took nearly 4 minutes for it to fail with a small pop and a flash as the wire blew out.

German made transformer, made around 1982. Got hot, but no smoke, no flames and only the pop as it went out.

It's all going going to depend on whether the iron core saturates magnetically or not. When the core saturates there's not much inductive resistance and a lot of amps can flow.

Dave's went up in seconds so I'm guessing the Weller cores saturate.

(and your core didn't)

[Fungus]

Or it could be that they worked out that the fuse isn't making a large difference, so they left it out.

Of course it won't make a large difference, that's not the point.

The point is that these things aren't cheap, the people who buy them are engineers, engineers open them up and notice things like that.

An engineer does for a penny what a fool does for a dollar and in the bottom end of the market every penny counts. Many people here perceive a problem, but it has so far not really been demonstrated. SeanB's experiment shows it may not be as straightforward as it seems.

Any money they saved by not including a fuse has now been blown because they've been called on it and are getting a ton of negative publicity.

It reflects on their brand.

[Mr. Scram]

Of course it won't make a large difference, that's not the point.

The point is that these things aren't cheap, the people who buy them are engineers, engineers open them up and notice things like that.

Any money they saved by not including a fuse has now been blown because they've been called on it and are getting a ton of negative publicity.

It reflects on their brand.

My point was that it doesn't necessarily reflect bad on Weller, as the practical difference isn't huge or possibly even non-existent. The negative publicity seems to come mainly from people who pile on the bandwagon here, but people who buy Weller's products based on their practical requirements may not be deterred. The last thing we want is companies installing token parts to pacify the community. It'd be interesting to get some insight into the decision making process here, though I suspect the legal risks are too big to do so.

[james_s]

I don't even think the mains voltage is an issue, how many people with 240V sockets on their bench have 120V equipment? That's pretty much a non-issue in the real world.

How many people here have seen equipment burnt out due to voltage surges on the mains supply?

(raises hand)

I have never seen that before, ever, and nobody that I know has ever reported that either. If you are getting power surges massive enough to burn up a mains transformer then you need to talk to your utility.

[timelessbeing]

I've had transformers short internally before

Wow. I have also never heard of this happening.
TransformerS plural? Why would transformer just suddenly fail under normal usage?

[SeanB]

Having a large number of small 110VAC mains transformers around, decided to try one out on 230VAC. Connected it up, and turned on the power. Took nearly 4 minutes for it to fail with a small pop and a flash as the wire blew out.

German made transformer, made around 1982. Got hot, but no smoke, no flames and only the pop as it went out.

It's all going going to depend on whether the iron core saturates magnetically or not. When the core saturates there's not much inductive resistance and a lot of amps can flow.

Dave's went up in seconds so I'm guessing the Weller cores saturate.

(and your core didn't)

Trust me it saturated, after a minute turned off the power and felt the core, and it was at around 50C, and after the winding shorted internally it was at that point you could smell it. Was hoping it would get to smoke point, but it failed before that. Taken a few apart before and there is no internal thermal fuse in them.

Should dig up that cheap voltage converter that has a fun function, it can work as step down or step up, and has a switch to select if the input is 110 or 220V, and another to select output of 110 or 220V, and of course it has only a fuse protection, and is rated at 100VA. Input is via the usual fixed cheap and nasty cable and output is via the (in)famous universal socket. At least that has PE continued through, unlike another that has a 2 wire mains lead, yet has an earthed socket outlet that connects to the case. That did have a first for me, the screws were tight, as in almost use impact driver tight, strange for a M4 screw.

As to transformers going internally short, very common, especially on those that have large capacitive loads on them, where the peak charging current of the capacitors heats up the wire internally, or for those run at full load with high mains input and then run at 175C plus till they cook.

[Wolfgang]

Its a runaway problem. Suppose some winding part gets warmer than the rest (normally somewhere in the middle of a winding packet), the copper resistance there will rise, creating even more resistive losses and heat. This goes on until the interwinding insulation breaks down in smoke. The shorted windings draw a lot of current and heat up even more until the whole transformer burns out.

[james_s]

I've had transformers short internally before

Wow. I have also never heard of this happening.
TransformerS plural? Why would transformer just suddenly fail under normal usage?

Failure of the insulation causing shorted turns I'd imagine, I don't think I ever tore them apart to do an extensive analysis. Two of them were in 1970s HP chart recorders years ago, one was a small power transformer in something else. Then fluorescent ballasts, I think I've seen 4 or 5 of those burn up, mostly 8' slimline ballasts which are essentially just transformers. I just replaced one of those in my mom's garage last year, it got so hot that it burned the paint off the fixture and spewed out molten tar before tripping the breaker. Oh and HV flyback transformers in CRT displays, I must have replaced at least half a dozen of those over the years. Transformers fail occasionally.

[Electro Detective]

If a suss batch of transformer has weak spots and or thin on the insulation, once the excess heating starts, the product needs an old school FUSE in there to stop the 'Kiss Live' pyrotechnics

Weller can end this farce by fitting fuse/s, pumping up the price by $1? and add some safety drivel in their brochure = more or faster sales and save face

All that aside, any company that flogs their gear to 120 and 240 volt markets SHOULD KNOW BETTER that snafus like this can and will happen.
 

i.e. Put a freakin fuse in there ya cheap bastards... 

[Mr. Scram]

If a suss batch of transformer has weak spots and or thin on the insulation, once the excess heating starts, the product needs an old school FUSE in there to stop the 'Kiss Live' pyrotechnics

Weller can end this farce by fitting fuse/s, pumping up the price by $1? and add some safety drivel in their brochure = more or faster sales and save face

All that aside, any company that flogs their gear to 120 and 240 volt markets SHOULD KNOW BETTER that snafus like this can and will happen.
 

i.e. Put a freakin fuse in there ya cheap bastards... 

It'd be easier to simply use properly made and QC'ed transformers, rather than patching the problem with a fuse. It seems that may very well be what they did.

Did anyone test whether an oversized fuse for 120V would pop when used at 240V?

[fsr]

If a suss batch of transformer has weak spots and or thin on the insulation, once the excess heating starts, the product needs an old school FUSE in there to stop the 'Kiss Live' pyrotechnics

Weller can end this farce by fitting fuse/s, pumping up the price by $1? and add some safety drivel in their brochure = more or faster sales and save face

All that aside, any company that flogs their gear to 120 and 240 volt markets SHOULD KNOW BETTER that snafus like this can and will happen.
 

i.e. Put a freakin fuse in there ya cheap bastards... 

It'd be easier to simply use properly made and QC'ed transformers, rather than patching the problem with a fuse. It seems that may very well be what they did.

Did anyone test whether an oversized fuse for 120V would pop when used at 240V?

The only problem here seems to be the lack of fuse. No doubt that the correct fuse will blow, as the primary was smoking badly. If the primary windings overheated like that, imagine a fuse!
The current at 220v will double the current at 110v (at the very least).
The transformer itself isn't at fault here, as you cannot expect for it to work under twice the nominal voltage. Nor to fail safely.
The transformer isn't an overcurrent protection device. I don't understand the people that acts like if that was the case. A fuse is an overcurrent protection device.

[Ian.M]

A properly made transformer would have a non-resettable thermal fuse buried under the primary winding, with a temperature rating such that if the abs. max. temperature rating of the enamel on the wire was exceeded it would open-circuit the primary *before* it got hot enough to emit significant quantities of toxic fumes, or be an ignition hazard.  That makes it fail safe if it experiences a serious sustained overload, or a shorted turn, or heavy core saturation.  Even cheap non-SMPSU wallwarts typically have a thermally fused primary, so you really have to be a bunch of sharks squeezing the last cent out of the product to leave it out.

If it needed extra secondary side fusing it wouldn't be bodged on, but would ether have tags to support it or more likely, have a PCB mounted to its pins carrying the PTC trip (which I suspect is there as half-assed over-temperature protection) and fuse.   Extend the PCB across the top of the transformer and it could also carry a replaceable timelag fuse on the primary side if you want to save the transformer if it gets over-voltaged to saturation.

[Electro Detective]

FWIW: Behringer equipment had/still has? IEC power sockets with a flippable fuse holder for 120 or 240 volts.

You can buy these chassis mount things for cheap at most electronics stores here, Altronics, Jaycar etc without stuffing about ordering from the big players

If the fuse is in the 120 volt slot for use in the USA, flipping the fuse holder to 240 results in no power to the unit because no fuse is in that slot, and vice-versa

i.e. it's hard to balls that up AFAICT

Someone has to pull out the fuse holder to make any changes, like fit the proper value fuse as indicated on the label for 120 or 240, align it and push in   

I'll be extra optimistic and state that even if there is a mix up of the above, the proper factory installed fuse should blow anyway if the wrong voltage selected
or the torroid or circuit cakes itself at 120 or 240 volts

No fuse is bad news   

[timelessbeing]

The transformer itself isn't at fault here, as you cannot expect for it to ... fail safely.
The transformer isn't an overcurrent protection device .. A fuse is an overcurrent protection device.

Like somebody just mentioned, transformers are used in gas discharge lamps as magnetic ballasts which are .... current limiting devices.

What are fuses but thin pieces of wire.

Very likely in your automobile you have a "fusible link" which is just a short section of wire which is of a thinner gauge than the rest of the wiring.

[coppercone2]

does the thing inside of a fuse look like a normal section of copper wire to you?

[Mr. Scram]

The only problem here seems to be the lack of fuse. No doubt that the correct fuse will blow, as the primary was smoking badly. If the primary windings overheated like that, imagine a fuse!
The current at 220v will double the current at 110v (at the very least).
The transformer itself isn't at fault here, as you cannot expect for it to work under twice the nominal voltage. Nor to fail safely.
The transformer isn't an overcurrent protection device. I don't understand the people that acts like if that was the case. A fuse is an overcurrent protection device.

It was already discussed that fuses aren't always required by the safety standards, because transformers limit the current by their nature. They're essentially a coil, after all. We also shouldn't forget safety standards are designed to protect the user and not the device. This all means it's a little more complicated than no fuse equals bad, especially without knowing anything about the engineering and testing that went into the product.

[Fungus]

I don't even think the mains voltage is an issue, how many people with 240V sockets on their bench have 120V equipment? That's pretty much a non-issue in the real world.

How many people here have seen equipment burnt out due to voltage surges on the mains supply?

(raises hand)

I have never seen that before, ever, and nobody that I know has ever reported that either.

Jeez, it was only a few pages ago:

https://www.eevblog.com/forum/blog/eevblog-1160-weller-responds/msg2055256/#msg2055256

you need to talk to your utility.

Yep. They actually admitted liability last year after destroying the phone system in my wife's office.

[Mr. Scram]

Jeez, it was only a few pages ago:

https://www.eevblog.com/forum/blog/eevblog-1160-weller-responds/msg2055256/#msg2055256

Yep. They actually admitted liability last year after destroying the phone system in my wife's office.

In all fairness, the arguments for fusing presented so far seem to be increasingly unlikely scenarios requiring multiple failures or massive fuck ups. Apparently 380V coming from the mains did happen, but I can imagine that being a bit outside of what Weller can be expected to reasonably deal with.

[fsr]

The transformer itself isn't at fault here, as you cannot expect for it to ... fail safely.
The transformer isn't an overcurrent protection device .. A fuse is an overcurrent protection device.

Like somebody just mentioned, transformers are used in gas discharge lamps as magnetic ballasts which are .... current limiting devices.

What are fuses but thin pieces of wire.

Very likely in your automobile you have a "fusible link" which is just a short section of wire which is of a thinner gauge than the rest of the wiring.

Interesting, but they have to be designed to do that, and here it clearly isn't the case.

The only problem here seems to be the lack of fuse. No doubt that the correct fuse will blow, as the primary was smoking badly. If the primary windings overheated like that, imagine a fuse!
The current at 220v will double the current at 110v (at the very least).
The transformer itself isn't at fault here, as you cannot expect for it to work under twice the nominal voltage. Nor to fail safely.
The transformer isn't an overcurrent protection device. I don't understand the people that acts like if that was the case. A fuse is an overcurrent protection device.

It was already discussed that fuses aren't always required by the safety standards, because transformers limit the current by their nature. They're essentially a coil, after all. We also shouldn't forget safety standards are designed to protect the user and not the device. This all means it's a little more complicated than no fuse equals bad, especially without knowing anything about the engineering and testing that went into the product.

Well, it didn't looked like the smoking transformer in Dave's video was limiting the current, right?

[Mr. Scram]

Interesting, but they have to be designed to do that, and here it clearly isn't the case.

Well, it didn't looked like the smoking transformer in Dave's video was limiting the current, right?

Didn't it? Did you ever poke a shorted wire in the mains and did it fail as safely as this unit at twice its rated voltage?

[Fungus]

Didn't it? Did you ever poke a shorted wire in the mains and did it fail as safely as this unit at twice its rated voltage?

We don't know exactly how it failed, Dave pulled the plug out of fear before the 'experiment' ran to completion.

[Mr. Scram]

We don't know exactly how it failed, Dave pulled the plug out of fear before the 'experiment' ran to completion.

There you go.