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Deception In Soldering Iron Ratings

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Hello there,

QUESTION #1:
You are shown two temperature controlled soldering irons, one is 60 watt and one is 40 watt. The 60 watt iron is slightly more expensive than the 40 watt iron, but not much more. Which one do you purchase?

QUESTION #2:
You are shown two temperature controlled soldering irons, one is 60 watt and one is 50 watt. The 60 watt iron is slightly more expensive than the 50 watt iron, but not much more. Which one do you purchase?

QUESTION #3:
You are shown two temperature controlled soldering irons, one is 60 watt and the other one is either 40 or 50 watt. The 60 watt looks a little cheaper in quality but not too much cheaper. Which one do you purchase?

If you answered "The 60 watt iron" to either question above, you probably paid too much for that iron because guess what, they are all about 40 watts !!

In various ad's on the web we see 60 watt irons that are the exact same model as the 50 watt irons, yet they are both really only 40 watts. This means they cant solder as well as a real 60 watt iron for somewhat larger metal joints.

First we see the 60 watt rating, which appears in ads for companies that dont seem to care about what they say about their product as long as it sounds good. Then we see the 50 watt rating, where the company is a little more responsible about their rating because they take their rating directly from the heating element which is stamped "50 watts, 24 volts". So we cant blame the companies that advertise 50 watts.

Measuring the DC resistance, we see that the "50 watt 24 volt" element resistance really measures 16 ohms. The power delivered to a 16 ohm resistance with 24 volts DC is:
P=24^2/16=36 watts.

So the elements are not even up to 40 watts yet !

The way it looks is every time the product changes hands the receiver tacks on another 10 watts, so that by the time the ad gets posted it's up to 60 watts in some cases.

That's quite deceptive because we purchase items based on what we need, and sometimes we need the higher power iron but we dont get that, when if we knew the actual rating we would get one that really fit the job.

You'll note that many soldering stations use AC not DC, but that only makes matters worse if there is any inductance because that can only lower the wattage not increase it.

One manufacturer that was contacted actually said that the "60 watts" came form the "input power to the station". But that's not accurate either because the input power with only the iron running is not anywhere near 60 watts. It's also very unlikely that a small control board and transformer would consume 20 watts of power when powering a 60 watt device on full power.
When informed about this, they simply state that you can return the entire station for a refund.

Please note that this doesnt mean that the irons dont work at all, they do, but they wont be as high powered as expected. For example, i had no trouble soldering a #24 gauge (AWG) copper wire end to a 10 turn Bourns potentiometer terminal, which is about 1/8 inch wide and about 1/8 inch long and thin metal. Didnt try #12 AWG wire yet though.

If you have any comments that would be nice to hear, or if you have any experience with these irons. The elements themselves are often advertised as "50 watts 24 volts DC".
Great Post. Thanks

how did you measure the resistance of the soldering iron without the circuit board exactly? sorry for the n00b question

An example:

Pin connections for the desolder gun 8 pole are:
Pin 1 red and pin 2 Grey+yell = element.
Pin 3 blue and pin 5 black = normally open vac switch. (always on for iron)
Pin 4 brown= case ground.
Pin 6 green and pin 7 white = ‘K’ thermocouple.
Wire colors may vary, but this is the info to transpose their 5 pole to 8 pole connectors.

The element would likely have a resistance <100 ohms.
The thermocouple would read a short, BUT it will also read in mV. and vary with temperature. The hotter the tip is, the more voltage.
My tool, you can remove the element and search for the pins with the same resistance.
I have a solder/desolder station also with hot air, but solder and desolder are separate tools.

At a minimum you have a sensor, and a heating element and likely a shield. With de-soldering, you need a switch as well.

Thermocouples are just one way of measuring temperature.

wow thank you so much for the breakdown of a solder iron and how it actually works in terms of a wire diagram.

I feel extremely stupid for saying this... but you would touch which two pins of the above described example with your multimeter testing resistance? 3 and 5?

ty so much, really!

yes. But in my example 3 and 5 are a switch or permanently on. On a de-solering tool there is a switch, so the resistance would go from infinate to near zero with the switch depressed or not.

Some reverse engineering isn't hard. Usually the element is removeable so you can check the resistance of just the element and "find" the pins where it appears in the cable plug.

The element and shield should be easy to identify.

Then for a soldering iron in my example, two sets of pins would have nearly zero resistance. They would be the always on switch and the thermocouple.

Which one is the thermocouple. The pair that also measures a few mV. Put a match to the tip and they should increase. The thermocouple polarity is a little harder.

A thermocouple is probably the best choice for temperature measurement. To measure temperature, you need the mV reading and the temperature of the terminals at the other end, a lookup table and a reverse lookup table. Solid state sensors and thermisters are typically used to measure the terminal temperature.

If a thermocouple measuring device is shorted with a wire, it will usually read the temperature of the terminals (room temp) or the lowest temperature the instrument can measure. There are different types of thermocouples too.

You can also look for a diagram of your specific iron. You may find a complete pinout so you dont have to guess which pins are for what.

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