Author Topic: EEVblog #596 - World's Cheapest Soldering Station - Yihua 936  (Read 59779 times)

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Online Fungus

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Re: EEVblog #596 - World's Cheapest Soldering Station - Yihua 936
« Reply #125 on: July 13, 2015, 08:28:29 PM »
(large areas of the world have plugs that can be inserted either way around...)

The Australian 230V type power plug, is unique to a small number of countries, Australia, New Zealand, Argentina, ...China is similar in some areas.  This plug cannot be "inserted the other way round".
So... all those other countries are living in constant mortal danger. Got it!  :-+
 

Offline HighVoltage

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Re: EEVblog #596 - World's Cheapest Soldering Station - Yihua 936
« Reply #126 on: July 13, 2015, 08:44:23 PM »
Germany has pretty safe plugs but they can be inserted either way around and we do not have a problem because of this.
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Offline Monkeh

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Re: EEVblog #596 - World's Cheapest Soldering Station - Yihua 936
« Reply #127 on: July 13, 2015, 09:11:03 PM »
Would you care to elaborate on where, exactly, the hazard of incorrect polarity in functional switching for a double-insulated device arises?

Yep, an over-voltage or lightening strike on power line (happens a lot in some tropical areas), primary of transformer is still live (because it hasn't been switched off), shorts to earth (arc over)...the rest is obvious.  Yes, this should activate house RCDs (if fitted, RCDs are fitted by Australian standards in homes since ~ yr 1998'ish), yes its double insulated but the hazard is with the primary not being switched off.

Sorry, but again, this is functional switching, not isolation, and in many cases polarity is not ensured. It is nowhere near as big a deal as you make it out to be.
 

Online wasyoungonce

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Re: EEVblog #596 - World's Cheapest Soldering Station - Yihua 936
« Reply #128 on: July 14, 2015, 09:39:32 AM »
It's only a problem in that as stated if someone opens the unit and is working on it expecting the Active to be off...!  But in respect to switching active, 230V is a lot more electrical shock dangerous than 110V.  Body resistance decreases with increasing voltage and increasing voltage increases current flow thru the body...maybe because, this is why the active must be switch in Australia. 

I really cannot comment on other world systems and their regs.   But for Australia, this product would be banned if known...this is why I raised this.
« Last Edit: July 14, 2015, 09:41:47 AM by wasyoungonce »
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Offline Monkeh

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Re: EEVblog #596 - World's Cheapest Soldering Station - Yihua 936
« Reply #129 on: July 14, 2015, 10:16:45 AM »
It's only a problem in that as stated if someone opens the unit and is working on it expecting the Active to be off...!

Do I need to elaborate on functional switching vs isolation?

Quote
But in respect to switching active, 230V is a lot more electrical shock dangerous than 110V.  Body resistance decreases with increasing voltage and increasing voltage increases current flow thru the body...maybe because, this is why the active must be switch in Australia. 

I really cannot comment on other world systems and their regs.   But for Australia, this product would be banned if known...this is why I raised this.

The active must be switched in Australia (and the UK) only because we have the luxury of the reasonable assumption of specific polarity.
 

Online wasyoungonce

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Re: EEVblog #596 - World's Cheapest Soldering Station - Yihua 936
« Reply #130 on: July 14, 2015, 05:34:00 PM »
It's only a problem in that as stated if someone opens the unit and is working on it expecting the Active to be off...!

Do I need to elaborate on functional switching vs isolation?

Quote
But in respect to switching active, 230V is a lot more electrical shock dangerous than 110V.  Body resistance decreases with increasing voltage and increasing voltage increases current flow thru the body...maybe because, this is why the active must be switch in Australia. 

I really cannot comment on other world systems and their regs.   But for Australia, this product would be banned if known...this is why I raised this.

The active must be switched in Australia (and the UK) only because we have the luxury of the reasonable assumption of specific polarity.

Well is the item intrinsically safe?  No because potential is present in the primary of the transformer at all times unless off at the power point. 

When the assumption of specific polarity switching is found to be wrong, then pretty much IMHO it's worth mentioning.  Well I thought so.  So we have to disagree on these but understand each other perspective.
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Online Fungus

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Re: EEVblog #596 - World's Cheapest Soldering Station - Yihua 936
« Reply #131 on: July 14, 2015, 08:45:30 PM »
Well is the item intrinsically safe?  No because potential is present in the primary of the transformer at all times unless off at the power point. 
That's true but it seems like a very minor safety problem to me.

You could also point out that the wire inside the power cable is still live

(Unless you're British, in which case there's a fuse inside the plug to disconnect it! Why don't you move over there, just in case?)


 

Online wasyoungonce

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Re: EEVblog #596 - World's Cheapest Soldering Station - Yihua 936
« Reply #132 on: July 14, 2015, 09:39:39 PM »

You could also point out that the wire inside the power cable is still live

(Unless you're British, in which case there's a fuse inside the plug to disconnect it! Why don't you move over there, just in case?)

Ha move to England....my Ancestors were sent out here from England...I don't think they want us back! ;)

Yes the Blue wire is wired to the active, not switched, and yes this is fused (as mentioned) prior to the transformer...is this where your heading?  Aka any short the fuse blows?  I do concur.
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Online Fungus

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Re: EEVblog #596 - World's Cheapest Soldering Station - Yihua 936
« Reply #133 on: July 14, 2015, 10:20:19 PM »
Yes the Blue wire is wired to the active, not switched, and yes this is fused (as mentioned) prior to the transformer...is this where your heading?  Aka any short the fuse blows?  I do concur.

I'm not sure where I'm headed exactly.

I'm trying to think of a situation where "live transformer primary" is dangerous but where many lives would be saved if it was done 'correctly'.

If you've taken the cover off without unplugging it first and are poking random wires with a screwdriver then ... you could also be doing it with an intact fuse when some other component has failed and the iron isn't getting hot. Maybe you need to learn that lesson the hard way.

 

Offline McBryce

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Re: EEVblog #596 - World's Cheapest Soldering Station - Yihua 936
« Reply #134 on: July 14, 2015, 11:45:23 PM »
In many countries even if it was done "correctly" the plug can still be pushed into the wall socket in both directions (making it "incorrect" again), which is why you learn that you shouldn't "poke around with a screwdriver" if the device is still plugged in.

McBryce.
 

Online wasyoungonce

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Re: EEVblog #596 - World's Cheapest Soldering Station - Yihua 936
« Reply #135 on: July 15, 2015, 09:12:37 AM »
Sorry folks...I had an old timer moment...power active is live at the transformer before the fuse and switch, I wrote it wrong above. |O

My first thought was this item is intrinsically safe because it uses a plastic box and you really cannot touch any live part, but it's not because of the wiring.  Yes it's rare to see transformers short, but I have seen it and bejesus they stink when they go up!  But as you said it's very rare because of the way they are made etc.  But there again, if they mfgr cannot wire the switch and plug right is the transformer any better.  Well their grounding wasn't. 

Which bring me to my finalisation, yes this is not right, yes it presents little danger but it does present some hazards.  Yes it would fail Australian safety standards but is effectively safe enough for users.  But I guess I am not one of the "most" users...I pull things apart (and sometimes cannot get them back together! ;D) to check, correct and improve.

In my case, with this soldering station, I tossed all of the insides because it was under performing and make my own, changing the switch and lead of course ;)   
 
Certainly I wasn't particularly aware that OS plugs could be plugged in either way (well not quite I did have some idiot twist the pins of a 110V plug to fit an Australian socket for a light table, plugged it in and bang!), hadn't really thought about it much lately (which I admit is naive) even though I've worked with a lot of French/US Avionic gear, mostly powered by 115V 3phase.  But yes US 110V plugs would be a nightmare also aware they have 220V in some households (for higher powered domestic appliances)....going to look those plugs up now!



« Last Edit: July 15, 2015, 09:14:32 AM by wasyoungonce »
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Offline Mati256

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Re: EEVblog #596 - World's Cheapest Soldering Station - Yihua 936
« Reply #136 on: January 05, 2017, 03:27:07 AM »
Hello. I see there are 110V and 220V versions of this cheap station. Looks like 220V ships from Hong Kong adding time and money to the item. Would I be ok purchasing a 110V and changing the transformer for a 220V 50Hz or the electronics require it to be 60Hz? Would it be better to use a Power Converter (although the ones I can get here don't have a ground connection!)?

What's the secondary for this transformer? 24V?

Thanks!
 

Offline mariush

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Re: EEVblog #596 - World's Cheapest Soldering Station - Yihua 936
« Reply #137 on: January 05, 2017, 04:58:06 AM »
I don't think the frequency's a problem.

There's a 24v or 26v AC winding (i've seen 28v AC in pictures for some stations ) for the heater element  but there's also at least one other secondary winding for 10v AC or something like that, which is meant to power the electronics inside (3.3v or 5v for microcontroller using a linear regulator) and up to 15v for opamp or comparator or whatever it uses to measure temperature and compare with configured temperature limit.
I suppose you could buy a transformer with just one secondary winding and hide inside the case a separate power supply, let's say a small wall adapter to give 12v DC or something like that.
You'd have to open your soldering station and check the circuit to see what it does with the windings coming from the transformer.
 

Offline Mati256

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Re: EEVblog #596 - World's Cheapest Soldering Station - Yihua 936
« Reply #138 on: January 05, 2017, 08:00:03 AM »
Thanks for the answer. More than one secondary? That's new. They have only one secondary in the pictures I have seen.
I could always buy the 110V version, meassure all the secondary coils and buy a custome transformer, but that might end up costing more than shipping it from Hong Kong.  :-DD
 

Offline mariush

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Re: EEVblog #596 - World's Cheapest Soldering Station - Yihua 936
« Reply #139 on: January 05, 2017, 08:19:49 AM »
Thanks for the answer. More than one secondary? That's new. They have only one secondary in the pictures I have seen.
I could always buy the 110V version, meassure all the secondary coils and buy a custome transformer, but that might end up costing more than shipping it from Hong Kong.  :-DD

You can see for yourself on page 4 of this thread, where dude shows the insides of Yihua 937 he bought : http://www.eevblog.com/forum/blog/eevblog-596-world's-cheapest-soldering-station-yihua-936/msg416686/#msg416686
You can see the picture of the transformer, a 24v winding and a 10v winding.
The 10v winding is probably less than 100mA, there's a diode for half wave rectification and a capacitors to smooth out the dc voltage and then a 7805 regulator or something like that takes 7...15v down to 5v ... just for the microcontroller and the lm358 opamp  and the 3 led digits (multiplexed)
 

Offline Mati256

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Re: EEVblog #596 - World's Cheapest Soldering Station - Yihua 936
« Reply #140 on: January 05, 2017, 08:42:10 AM »
Ah, I see. But I'm talking about the 936 here, its analogue. The 937 is digital so it's a different circuit.
 

Offline mariush

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Re: EEVblog #596 - World's Cheapest Soldering Station - Yihua 936
« Reply #141 on: January 05, 2017, 11:40:28 AM »
Ah, I see. But I'm talking about the 936 here, its analogue. The 937 is digital so it's a different circuit.

The analogue 936 would still need to power the opamp or comparator with some voltage ... which won't be 24v AC.

Here's the original Hakko 936 schematic... http://dalincom.ru/datasheet/HAKKO_936_schematic.pdf

As you can see, it uses a quad opamp LM324  and it's powered with ~ -5v  and +5v , you can see there it uses two 5.1v zener diodes to create the positive and negative rails for the opamp.

Some third party designs / clones simply use a separate winding keeping the high voltage winding separate, just for the heater.  Or they use better opamps or don't care about opams not being able to get output close to 0v, so they use only ground and positive voltage instead of feeding opamps with negative and positive voltages.
 


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