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Old 10-19-2021, 08:08 PM   #1
Crystaleyes
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Default Tenma (Farnell-rebranded) 21-10115 solder station question

Olá.

Looking for some help clarifying something.

I have a Tenma (Farnell-rebranded) 21-10115 solder station which recently burnt out the ceramic element.
The station is 60W / 28 volts, 110v.

Right now I'm in Brazil and finding an equivalent element has proved to be not possible, so today I bought a 'Yaxun' 50W 24v iron in the hope that it would work.

Both irons have a five pin plug.

The Tenma had pins 1 & 2 and pins 4 & 5 shorted with pin 3 being the ground. No means of measuring the temperature.

The Yaxun had the two element wires plus two sensor wires along with the ground.

After doing the relevant iron rewiring however, the Yaxun just keeps heating up until it glows red and only displays 65 or so degrees Celcius.

Even though it had no sensor wires the Tenma used to accurately display the temperature of the iron.

What can I do to stop this going into meltdown?

The new element measures 11.9Ω

Even though the other is burnt I think it was around 14Ω

Any ideas as to how this iron can be used with this station?

How could the station measure the temperature and how can that be imitated?

Last edited by Crystaleyes; 10-19-2021 at 08:31 PM..
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Old 10-19-2021, 11:45 PM   #2
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Default Re: Solder station question

Short answer: I think the two stations use incompatible tips, no matter how you try to rewire them.

Although I'm not familiar with that Tenma nor the Yaxun, it sounds like the Yaxun is using the more "classic" approach with a separate heating element and temperature sensor... whereas the Tenma uses the more "modern" approach, with the heating element used both as a sensor and a heating element at the same time (it alternates between sending power to the heating element, then stops and reads the resistance of the heating element to determine the temperature, then based on that, regulates how much power to give again to the heating element, and ad infinitum.) So in other words, the design of the two stations is different, making the tips incompatible.

But again, I'm not familiar with either of these stations, so perhaps someone else can chime in and confirm or disprove my theory above. All I can tell you is that I've tried a similar thing with two stations many years ago, and ran into the same exact problem... and of course in my case, that's exactly what the issue was, as I described above.

Last edited by momaka; 10-19-2021 at 11:49 PM..
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Old 10-20-2021, 08:04 AM   #3
Crystaleyes
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Default Re: Tenma (Farnell-rebranded) 21-10115 solder station question

Thanks for there reply.

You are correct that the Yaxun does have a separate sensor element.

Does the 'modern' approach use a different 'type' of element, or is it that the station knows the exact resistance of the element when cold, and therefore calculates from that reference point?

The reason I ask, is because I was wondering if it wouldn't be possible to 'fool' the station by adding more impedance to the circuit, inside the box, matching the original?

I don't know the original Ω value of the Tenma iron, however knowing the maximum wattage and voltage, we can calculate the current, and therefore the maximum impedance.

Just a thought...
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Old 10-20-2021, 12:11 PM   #4
stj
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Default Re: Tenma (Farnell-rebranded) 21-10115 solder station question

the tenma sounds like it uses the same system as hakko T12 tips,
the thermocouple is in series with the element and is read between the power pulses.

it wont be resistive btw - the element will screw that up - it will be generating a voltage

Last edited by stj; 10-20-2021 at 12:15 PM..
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Old 10-20-2021, 02:58 PM   #5
Crystaleyes
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Default Re: Tenma (Farnell-rebranded) 21-10115 solder station question

Mmm?

Well, seeing as I don't have the money here for a new station, I can see a bodge job on the horizon using an old ATX PSU, connecting the Yaxun iron between the minus and plus 12 volt rails, via a potentiometer...
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