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Old 26th May 2020, 7:56 pm   #1
jrh_james
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Default Weller TCP soldering iron

Hi I have a Weller TCP soldering iron that started playing up and overheating and after having a read around I took apart the thermostat switch and cleaned the contacts and it seems to be behaving itself again.

I noticed that some TCP irons have got a capacitor across the switch, presumably to reduce arcing and stop the contacts welding shut. Would it be worth adding a capacitor to my iron to extend the life of the switch? What type of capacitor do I need?
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Old 26th May 2020, 8:08 pm   #2
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Default Re: Weller TCP soldering iron

In light of previous threads, please don't turn this into an A-Z of soldering irons
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Old 26th May 2020, 8:29 pm   #3
duncanlowe
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Default Re: Weller TCP soldering iron

As far as I know the capacitor is to reduce interference when the thermostat operates. Thermostat contact welding seems to be a well known issues which is why spares are available.
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Old 26th May 2020, 10:48 pm   #4
Craig Sawyers
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Default Re: Weller TCP soldering iron

I have two Weller TCP soldering irons.

On one the connecting lead internal insulation broke down (went like biscuit - the pictures are in another thread on here somewhere) and, long story, burnt out the transformer. Weller refused point blank to accept responsibility. So I bought a new lead, and in true Franken-iron style used an ex-BBC valve heater transformer with 4 x 6.3V windings wired in series. The entire blue body, much modified is screwed on top of the massively overrated transformer.

I then made the mistake of buying a new one around a year ago. That is incompatible with the older bits - so needs me to buy a range of bits that I typically use to suit. And that one has started to play up too! Goes cold - a good whack of the handle starts it working again. Internally it looks fine, but there must be a problem with the magnetically operated switch.

I take Bill's point about A-Z, but twice bitten with declining customer care and flaky quality from Weller, I will never buy another of theirs.

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Old 27th May 2020, 12:24 am   #5
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Default Re: Weller TCP soldering iron

Mine has one, I thought they all did!
I assumed for arcing, but interference is more or less the same thing in a different guise.
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Old 27th May 2020, 6:58 am   #6
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Default Re: Weller TCP soldering iron

Mine had a small RIFA X type, finding a replacement of the right size was tricky amongst my spares. An X type would be best I guess.

Andy.
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Old 27th May 2020, 10:30 am   #7
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Default Re: Weller TCP soldering iron

I have never thought of this before, but I wonder if a worn-out RIFA is the reason why the switch contacts eventually suffer from the effects of arcing and need cleaning up?
At only 24 volts I have never seen one go *bang* (yet...) but the capacitance might gradually fall with aging in the same way it does with mains voltage transients.
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Old 27th May 2020, 12:39 pm   #8
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Default Re: Weller TCP soldering iron

Quite possible, that is how they work. Repeated transients are more or less guaranteed!
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Old 27th May 2020, 12:52 pm   #9
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Default Re: Weller TCP soldering iron

I thought the early ones didnt have the capacitor and later ones did. I assumed that it was for EMC compliance in light of legislation.

I've never understood why a capacitor & resistor is not used.
For example if a capacitor across a switch reduces rfi or sparking when the contact opens, by way of reducing the rate of rise of voltage, (dv/dt) why is it ok to close the contact and allow a rapid discharge of the same capacitor?

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Old 9th Jun 2020, 8:36 am   #10
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Default Re: Weller TCP soldering iron

I'm also just 'refreshing' a TCP iron, with a cracked RIFA cap - anyone know where I can source a suitably sized replacement ?

The existing RIFA is marked "PME 261 KA", 400V-/220V-MP, 40/070/56, and it's a small ca. 10mm lead pitch size. I'm reading it as 47,000pF, 220VAC, but most of the equivalents I'm seeing online are 15 or 20mm lead pitch.

Alan
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Old 9th Jun 2020, 8:49 am   #11
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Default Re: Weller TCP soldering iron

Quote:
Originally Posted by McMurdo View Post
I've never understood why a capacitor & resistor is not used.
For example if a capacitor across a switch reduces rfi or sparking when the contact opens, by way of reducing the rate of rise of voltage, (dv/dt) why is it ok to close the contact and allow a rapid discharge of the same capacitor?
It isn't - in my book. However, I suspect the rapid discharge causes less RFI than the high dv/dt on opening, so capacitor alone is used.

(Personally, I'd use capacitor in series with a few ohms of resistor, as you say).

Weller irons - I have a mains-driven Magnastat which occasionally fails to open, the iron glows a very dull red. And I use a couple of 24V TCP irons. No trouble except a fatigue-broken lead near the connector.
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Old 9th Jun 2020, 1:48 pm   #12
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Default Re: Weller TCP soldering iron

The early TCPs without the capacitor showed no worse problems with sticky thermostats. I think they are entirely for EMC reduction.

David
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Old 10th Jun 2020, 6:14 am   #13
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Default Re: Weller TCP soldering iron

Found this one Alan at Farnell - https://uk.farnell.com/kemet/r463f24...ial/dp/2495809 checked datasheet - = 10mm lead spacing. Here's the page for all 47n X series caps - https://uk.farnell.com/c/passive-com...itance=47000pf

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Old 10th Jun 2020, 11:16 am   #14
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Default Re: Weller TCP soldering iron

Cheers Andy - just what I needed, thanks
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Old 14th Jun 2020, 9:47 pm   #15
Radio1950
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Default Re: Weller TCP soldering iron

Weller TCP User Operation and Spares Leaflet, from about 1990.

I have two of these units which have worked perfectly for thirty years.
.
Attached Files
File Type: pdf Weller TCP IMG_20190808_0003.pdf (1.05 MB, 126 views)
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