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Old 8th Sep 2017, 5:21 pm   #1
mark_in_manc
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Default 'Transformer' type soldering gun - transformer spec?

Hi folks

A friend had a heavy-duty and slightly off-topic job to do with his transformer-type soldering 'gun' - the kind of thing with two big prongs coming out, a wire element between them which heats up, and a trigger to turn it on.

Unfortunately, before I could measure it, he cooked it. I wonder if anyone knows what kind of voltage one is looking for at the secondary - this application merits looking for a big transformer to mount remote from the device, with a fan on it maybe. Power dissipation of the iron is likely to be about 100W.

cheers
Mark
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Old 8th Sep 2017, 6:32 pm   #2
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Default Re: 'Transformer' type soldering gun - transformer spec?

I seem to remember that our friend in Cuba, Miguel Lopez, made his own homebrew soldering gun. Looking up his posts on that might give some good info.
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Old 8th Sep 2017, 7:59 pm   #3
Ed_Dinning
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Default Re: 'Transformer' type soldering gun - transformer spec?

Hi Gents, from memory the "home job" / apprentice solder gun used about 2500 turns for the mains and 3 turns of copper strip for the LV,.

I've still got mine and it heats the 16SWG "bit" pretty quickly.

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Old 9th Sep 2017, 1:33 am   #4
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Default Re: 'Transformer' type soldering gun - transformer spec?

Some years ago a mate of mine made a new bit for a Weller one out of a wire coat hanger.
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Old 9th Sep 2017, 10:08 am   #5
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Default Re: 'Transformer' type soldering gun - transformer spec?

Mark..not many volts if my Weller on 140W setting is representative!
Meter is on 2v ac setting.
Also tried it with the illumination bulb removed ,it made no difference.
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Old 9th Sep 2017, 10:53 am   #6
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Default Re: 'Transformer' type soldering gun - transformer spec?

Some years ago as an impulse buy, I bought a cheapo 100 Watt 'Parkside' (Lidl) solder gun, which I've never used, so I've taken it out of the box, taken it apart and taken some pictures. First thing to say is that the transformer isn't very heavy. I removed the tip and checked the voltage, which is 0.55V. The secondary of the transformer is flat copper strip, 5mm wide x 2mm thick. The solder tip leads which connect into the gun are 3.5mm diameter, (about 9.6 sq mm), with the tip itself being flat, 3mm wide x 1.5mm thick (4.5 sq mm), hence, the higher resistance of the tip causing the heat to be concentrated there. (540C!).

My knowledge of transformer technology would fit on the head of a pin, but it seems to me that the secondary, with vitually zero resistance, almost amounts to a shorted turn and will saturate the transformer in no time at all. Not surprising therefore that the label says: 'On 12 Seconds - Off 48 seconds' - a duty cycle of 1:5. I dare say that's often ignored and as the transformer doesn't have a thermal cut-out, I can well understand why so many transformers get smoked and end up as landfill (or should I say 'electrical waste'?).

A few pics might be of interest:

First shows the complete iron.
Second shows the data label.
Third the transformer.
Fourth the secondary winding.
Last is the tip.
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Old 9th Sep 2017, 11:30 am   #7
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Default Re: 'Transformer' type soldering gun - transformer spec?

Many years ago a friend of mine built a soldering gun in the school metalworking shop. He acquired a mains transformer (probably from an old radio) and replaced the secondaries with a couple of turns of thick copper strip. The heating element was something like 18swg (or 16swg?) tinned copper. Given the short duty cycle the transformer could be massively overloaded.

Shorted turns (which this almost is) do not cause core saturation - they prevent it. What can happen in an underrated transformer is that saturation occurs if the secondary goes open circuit, but these guns always use a primary switch as the 'trigger' so that should not be a problem.
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Old 9th Sep 2017, 12:12 pm   #8
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Default Re: 'Transformer' type soldering gun - transformer spec?

Quote:
Originally Posted by David G4EBT View Post
My knowledge of transformer technology would fit on the head of a pin, but it seems to me that the secondary, with vitually zero resistance, almost amounts to a shorted turn and will saturate the transformer in no time at all.
Shorted turns don't cause core saturation. Pretty much the exact opposite, in fact: the low resistance causes energy to be taken out of the core as fast as it can be supplied.

Note that the transformer design calculations are of the form
Code:
Teslas = Volts * seconds / (turns * square metres)
and don't mention current anywhere. The practical limit on current is the resistance of the transformer wire, which determines the amount of self-heating. Also crucially unlike a real shorted turn, most of the heat energy liberated by the secondary current is being dissipated at the soldering tip, not into the transformer itself.

If the manufacturers were being really cheap, they could even get away with using less steel in the transformer -- but then it would tend to saturate if you switched it on without a soldering bit fitted, once there were no more little compass needles not lined up with the applied field and nothing else trying to twist them away from it. Then the only limiting factor will be the (DC) resistance of the primary winding; which could get very hot, very quickly,
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Old 18th Sep 2017, 5:55 pm   #9
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Default Re: 'Transformer' type soldering gun - transformer spec?

Quote:
Originally Posted by davidw View Post
Mark..not many volts if my Weller on 140W setting is representative!
Meter is on 2v ac setting.
Also tried it with the illumination bulb removed ,it made no difference.
The older Weller soldering gun is still the best one made in the US or anywhere else. The models like yours, use the tip nuts that make a better connection to the tip, where the newer models use set screws to hold the tip.
The cost of the replacement tips have gone to the sky!! $7 USD for a pack of two! Not long ago, they were two for a buck!
I even checked the Internet, not much cheaper.
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Old 21st Sep 2017, 1:59 pm   #10
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Default Re: 'Transformer' type soldering gun - transformer spec?

As I have mentioned previously..... when I was an apprentice TV engineer in the early 60's our workshop exclusively used PICSTONE soldering guns..... these were obviously hand made, as the handle / case was made from aluminium in a very hand made way. The Tip was a length of 16SWG TC wire, and as has been rightly said the secondary was approx 3 turns of copper strip. These possibly predated the Weller guns, with their penlight bulb,
We bought a later Picstone gun which.. by then... had been commercialized with a Handle / case which was stamped and folded by machine...these were not as good as the originals, but were "ok". One of my jobs as an apprentice was to make the tips and ensure there were spares in the van. I wonder what happened to the original guns..nearly 60 years on.
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Old 22nd Sep 2017, 8:15 pm   #11
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Default Re: 'Transformer' type soldering gun - transformer spec?

Hi Folks, here is a picture of the somewhat battered soldergun I made at Reyrolle some 50 odd years ago. It still works well after all this time.
from memory there were wooden patterns available to form the handle from sheet brass.

If anyone fancies trying to make one I have the copper strip.

Ed
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Old 22nd Sep 2017, 10:28 pm   #12
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Default Re: 'Transformer' type soldering gun - transformer spec?

There are several videos showing the construction of homemade solder guns on YouTube. Just putting 'solder gun' into the search should bring up various examples.

Just one example: www.youtube.com/watch?v=TIW6P7Du-CY

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Old 22nd Sep 2017, 10:59 pm   #13
mark_in_manc
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Default Re: 'Transformer' type soldering gun - transformer spec?

I got my mate's one apart-ish - the primary is burnt out, but the stack of laminations looks like it might come apart easy enough. Now there's another reason to make a coil winder. Primary wire is 10 thou dia.
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Old 24th Sep 2017, 9:47 am   #14
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Default Re: 'Transformer' type soldering gun - transformer spec?

Have you checked the thermal fuse that's attached to the primary's winding, my old weller had this fuse that failed after using it incorrectly, not allowing cool down after every use.
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Old 28th Sep 2017, 12:38 pm   #15
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Default Re: 'Transformer' type soldering gun - transformer spec?

I had one of these soldering guns for a while but it has been sat in one of my tool boxes for a few years. It hasn't been used for many years because I lost one the the tip retaining nuts for which I could never find a replacement. I think the trigger switch also failed or broke as a part of it is missing. I think that is probably why I removed the mains lead and just kept the body and TX in case it came useful for anything. Anyway, I just connected it up to the mains for a few seconds and the bulb lights up brightly and the element gets hot. Given your requirement for a separate transformer maybe this is not suitable, but if you think the TX might fit and you would like a parts donor then I am happy to send it to you for the cost of postage as I have no further use for it anyway.

BTW, I measured the output voltage on a Fluke 6062, which showed that the AC voltage started at about 2.00v, and then dropped rapidly to about 0.77v after 3-4sec with the tip removed, 0.57v with the tip in situ. The Brymen did not seem to pick up the initial surge, just recorded the lower voltages so I also tried the AVO and this also just settled at around the same lower voltage with no indication of an initial surge.
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