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Old 30th Nov 2022, 11:32 pm   #1
Phil G4SPZ
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Default Soldering iron bit temperature

I hope this will be considered an acceptable topic for this section.

I’ve been thinking about how a conventional soldering iron maintains its bit temperature with a constant wattage element. The bit temperature remains reasonably constant once it’s up to temperature, even without any fancy electronic or magnetic temperature controllers. I did wonder whether the element resistance rises when hot, thus reducing the power drawn, but some resistance measurements on my 15 watt Antex show that this is a very marginal effect: 3.7k cold, 3.8k hot.

So I conclude that the bit temperature stabilizes at a temperature where it, and the other hot parts of the iron, are losing heat to the environment at the same rate as heat is being supplied by the element. Any thoughts?
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Old 30th Nov 2022, 11:39 pm   #2
Herald1360
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Default Re: Soldering iron bit temperature

I think your thought is correct.


Ever tried soldering outdoors in even a slight breeze with a small low powered iron? The "forced air" cooling is very effective
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Old 30th Nov 2022, 11:57 pm   #3
Restoration73
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Default Re: Soldering iron bit temperature

The original irons are called "thermally balanced" and I started using Henley and
Litesold irons of this type. As they did not have iron coated bits, they could become
pitted and some irons stands were designed to absorb some heat.
(Some had a bit saver switch that inserted a single diode rectifier).
I have a 100W Henley still ideal for metalwork.

Later I used thermostat irons (Weller) mains and 24V with iron coated bits which I
prefer for speed and maintenance in use. Bits can be selected from a range of temperatures.

Last edited by Restoration73; 30th Nov 2022 at 11:59 pm. Reason: typo
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Old 1st Dec 2022, 12:32 am   #4
Bazz4CQJ
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Default Re: Soldering iron bit temperature

I cannot really comment on the question Phil, but I hope you will take this comment in the spirit it is intended.

Up until I was in my 50's (and working as a chemist), I was content with a fixed temp iron at home; first Henley then Antex. Then I got a job in a small company where I too needed to do some soldering and was given a temperature-controlled iron.

Very quickly, I had to go and buy my own temp-controlled iron .

B
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Old 1st Dec 2022, 1:44 am   #5
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Default Re: Soldering iron bit temperature

I remember my Adcola iron of which thousands were sold.
I also remember filing the rotten tip down every 20 mins- half hour as it burnt away.
To add insult to injury the smaller/shorter the bit got, the hotter it became. So another $1.00 for a new tip, depending on how much soldering I did.
BAD because my pocket money was six bob a fortnight.
I then worked in Canberra on BIG computers and was given as part of my kit, A Weller temp controlled station.
I have two now, but have graduated/ changed to Hakko. Tips last about 12 months, even if I haven'tt soldered a single joint.

My old Adcola was superb though, because I didn't need borrow dad's. AND I could solder at night when I was supposed to be sleeping .

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Old 1st Dec 2022, 2:05 am   #6
Al (astral highway)
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Default Re: Soldering iron bit temperature

Quote:
Originally Posted by Phil G4SPZ View Post

So I conclude that the bit temperature stabilizes at a temperature where it, and the other hot parts of the iron, are losing heat to the environment at the same rate as heat is being supplied by the element. Any thoughts?
I can see why it could appear that way. The bit temperature might have a ceiling on ‘manual standby’ , if you like , but it may vary critically fast while you’re applying heat to a component or assembly.

I like to know the temperature, which I vary for different alloys and thicknesses of solder and bit and with what I’m doing. I’d rather a quick blast of 450C for a second than holding a too-cold bit to something until it overheats. I go higher for heavier pieces or desoldering.

I found with the unregulated types that heat would eventually spread up into the handle and start to cause discomfort to me , or I’d be anxiously saying ‘hurry up and melt’ while trying to solder something fragile.

Not a problem of course with the huge, 1940 era brazing iron that was my grandfather’s. I used it to teach myself to solder, age 13, using those little strips once available from Tandy. . That fella had to be heated with a blow torch first l.
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Old 1st Dec 2022, 7:47 am   #7
Phil G4SPZ
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Default Re: Soldering iron bit temperature

Thank you all, some wonderful reminiscences there and some very pertinent comments.

I agree that ‘thermally balanced’ irons cause bits to burn away. This was more of a problem to me back in my youth when I was doing a lot of construction and leaving the Solon powered up for hours at a time. Now I do mainly repairs and restoration, so the iron gets switched on and off again relatively quickly. I confess I tend to choose the largest iron/bit that will do the job. The heat flow into the joint seems to come mainly from the heat stored in the bit, rather than the element.

I also do metalwork soldering copper, brass and tinplate (repairing old oil lamps) and still regularly use old-fashioned irons with large copper bits, heated by a paraffin blowlamp.

I did use temperature-controlled irons at college decades ago, and still have them available to me at the Repair Cafe, and find them easy to use. I’ve nothing against them, but haven’t yet found the need to invest in one!
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Old 1st Dec 2022, 7:02 pm   #8
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Default Re: Soldering iron bit temperature

Quote:
Originally Posted by Herald1360 View Post
I think your thought is correct.


Ever tried soldering outdoors in even a slight breeze with a small low powered iron? The "forced air" cooling is very effective
Yes! When trying to solder the centre pin of a replacement type N connector at the end of the cable from a mast-head VHF antenna on the roof my late brother-in-law's boat. My trusty Antex 15W wasn't up to it, and we had to visit a local DIY shop and buy a more powerful soldering iron. There wasn't much of a breeze either, and improvising a windbreak was useless.
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Old 1st Dec 2022, 8:43 pm   #9
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Default Re: Soldering iron bit temperature

Quote:
Originally Posted by Herald1360 View Post
I think your thought is correct.


Ever tried soldering outdoors in even a slight breeze with a small low powered iron? The "forced air" cooling is very effective
Yes. In my younger days I often worked on things that needed soldering, outdoors. Way too big to bring inside. The Weller 60W mains temperature controlled iron was a revelation. Had it for my 18th Birthday and still have it (though rarely used these days).

EDIT: BTW before I got my Weller, I was using my Dad's Henley Solon. That's back with me now though I don't know what to do with it!
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Old 1st Dec 2022, 10:02 pm   #10
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Default Re: Soldering iron bit temperature

I think that most ‘Dads’ have at least one Henley Solon kicking around in the shed or workshop. I have at least two - one bought at a discount price from Staff Sales when I was an AEI apprentice in 1960.

If properly connected, the bit should be earthed via the 3-core mains lead, so no leakage current should reach any components being soldered.


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Old 3rd Dec 2022, 9:36 am   #11
Phil G4SPZ
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Default Re: Soldering iron bit temperature

It’s true that the handles of Henley Solons tend to get hot in prolonged use. I find that if you hang the iron by its hook with the bit pointing upwards, the effect is lessened. Presumably the heated shaft and tip induce a flow of cooler air vertically past the handle. I have two Solons, one kindly donated by a Forum member, and a 110 volt model which I run from a double-wound isolating transformer.
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Last edited by Phil G4SPZ; 3rd Dec 2022 at 9:39 am. Reason: Clarity
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Old 3rd Dec 2022, 12:57 pm   #12
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Default Re: Soldering iron bit temperature

One of my mobile-radio-business's competitors was a nototious skinflint who sent his techies out on jobs with inadequate equipment; I remember watching one such trying to solder the centre of some coax outside in the wind using a car-battery-powered non-thermostatic soldering-iron of deeply inadequate power.

The techie had clearly come across the problem before because he had a jam-jar with a hole punched into the lid; he stuck the iron in through the hole to shield it from the wind and waited a while for the heat to build up.

Thermostatically-controlled soldering irons are brilliant in the field-service world; I'm sure their fast heat-up-to-soldering-temperature, saving several minutes per call and so letting the techie do more calls per day, soon pays for their greater cost over clockwork irons.
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Old 3rd Dec 2022, 1:30 pm   #13
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Default Re: Soldering iron bit temperature

Once you have a decent thermostatically controlled iron, you won't go back! The Metcal iron is amazing - fast heat-up, and as soon as heat is sucked away, more is fed straight straight in.

Failing that, a big chunky copper bit, as a good heat reserve, is important especially when soldering large items. A bit sitting at 400deg C is no good if it sags to 200deg C when you try to solder to a screening can!

What temperature, anyway? 350deg C is usually fine... 420deg C for stripping solderable enamel winding wire. For small surface-mount devices, as low as possible (250 deg C) to avoid thermal shock.
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