With that in mind, I took the tip off my Weller 100 watt soldering gun and
measured the AC voltage (I'm not sure whether or not the voltage is rectified).
I measured it at .604 VAC. That would provide 165+ amps at that voltage. Now
since I don't understand voltage drop under load and all that, I'm not sure
this measurement is valid, but that's what the math yields.
It seems to me using a soldering gun for a base to build an RSU would work. Can
anybody offer evidence to the contrary?
>>asked the question of whether or not a soldering gun could be used as the
>>transformer for an RSU. We
Heat generated by the heating unit does not work in the same way as an rsu. The
rsu has instant heating and cooling and the carbon rods do not stick to the
soldered joint.The rsu is also capable of generatig greater heat than the gun
and of concentrating it in the area needed. I feel that rsu soldering is
As an aside, I found a set of bamboo food tongs are an excellent basis for
making rsu tweezers.
I think you missed my point. My point is this: You want high amps at low volts.
The soldering gun by my estimation gets the job done. You simply substitute
8-gauge wire with carbon tips for the heat tip. No long heating times
necessary. I'm no electrician, but my supposition is that metals don't care
what's pushing the current, whether it's an RSU transformer or a soldering gun
performing the same function, it's all low volts and high current. Am I missing
something here? Is there some electrical law of which I'm not aware that would
make this dangerous or not work? My understanding is that the reason a
soldering gun tip gets hot is that you're trying to cram too many amps through
a small space. Resistance causes heat. Replace the tip with 8 gauge wire and
graphite tips, you simply move the point of resistance to the joint.
I have this: 60W = 12V @ 5A AC - works most of the time for an RSU.
I could rewire the above to:
60W = 1V @ 60A AC - works better as RSU.
I also have this:
100W=165A @ .604V - soldering gun. Why wouldn't it work for an RSU with
appropriate substitutions of equipment for the tips?
The difference is the tip of the gun gets hot, then by conduction transfers
that heat to the joint. In RSU, you let the metals on either side of the joint
conduct juice. The air gap at the joint causes resistance, and thereby, heat. I
see no difference. It's high amps low volts either way.
If you replace the tip with a large gauge wire with graphite tips, wouldn't it
The air gap would stop the resistance unit from operating,
The heat is produced by the resistance of the part and requires complete
electrical contact to work at all.
You do have a good idea, and it would be easy to try it.
Why is there an Ozone Hole at the South Pole but Not at the North Pole?
Somebody's been lying to you!
Thanks, Bob. That's the kind of answer I was looking for.
In other words, I'd be better off rewinding my 12V 5A transformer down to
something like 3-4 volts to push 15-20 amps, rather than trying to re-rig a
soldering gun to do the job.
This is a follow up to a rather old post, but the definitive answer is,
I had a couple of parts half soldered together, and I wanted a better
joint. I didn't want to use an iron because I didn't want to heat the
surrounding areas. Sounds like a job for a resistance solderer, which I
I took the tip off the gun, then took a couple of pieces of #14 copper
wire about 4" long, and bent about 1/2" over double at one end of each
piece, and twisted that end so the tip clamp screws would hold. I bent
the free ends around to form a sort of pincher, and caught the parts to be
soldered between the wire ends. I pulled the trigger for a few seconds
and the solder melted and flowed to make a better joint.
So, a soldering gun can be used for resistance soldering. The major
drawback of the way I did it was that it was pretty inconvenient. It took
three or four hands and a couple of elbows to hold everything in place to
solder. It didn't happen this time, but the copper wire tips could have
easily been soldered to the rest of the pieces.
Now that people know that it can be done, maybe somebody will come up with
some better ways to do it.
There are three ways to do a job: good, cheap, and quick.
You can have any two.
A good, cheap job won't be quick.
A good, quick job won't be cheap.
A cheap, quick job won't be good.
How about bits of nichrome wire for the tips? That's what my commercial
resistance rig uses in the tweezers.
>JCunington (jcuni...@aol.com) wrote:
>> Some time back in my thread "Built my own resistance soldering unit", someone
>> asked the question of whether or not a soldering gun could be used as the
>> transformer for an RSU. We never definitively answered that question.
>This is a follow up to a rather old post, but the definitive answer is,
>I had a couple of parts half soldered together, and I wanted a better
>joint. I didn't want to use an iron because I didn't want to heat the
>surrounding areas. Sounds like a job for a resistance solderer, which I
>I took the tip off the gun, then took a couple of pieces of #14 copper
>wire about 4" long, and bent about 1/2" over double at one end of each
>piece, and twisted that end so the tip clamp screws would hold. I bent
>the free ends around to form a sort of pincher, and caught the parts to be
>soldered between the wire ends. I pulled the trigger for a few seconds
>and the solder melted and flowed to make a better joint.
>So, a soldering gun can be used for resistance soldering. The major
>drawback of the way I did it was that it was pretty inconvenient. It took
>three or four hands and a couple of elbows to hold everything in place to
>solder. It didn't happen this time, but the copper wire tips could have
>easily been soldered to the rest of the pieces.
>Now that people know that it can be done, maybe somebody will come up with
>some better ways to do it.
Can't remember *exactly* where on the Web I found this.
HOW TO BUILD AN ECONOMICAL RESISTANCE SOLDERING UNIT
These instructions were a clinic handout at the 1992 NMRA National
Convention given by Don Thomas, Train Specialty Co, 11540 Auburn Rd,,
Chardon OH 44024-9310
The applicable bit to the above problem is :
"Carbon rod 1/8" in diameter by about 4" long. The rod is called Arch
Gouging Carbon and is available at most welding supply or hardware
stores. It comes in 12" lengths and is easily cut into 4" pieces using
a fine razor saw. Sharpen the end using a common pencil sharpener."
I got some of this rod (it's cheap), I've tried it, and it works !
I've still got the problem of "finding" a suitable power supply,
anything I have lying around here kicks out too high a voltage.
-- The Despicable Stewart
-- Perfidious Alban
Copper melts at FAR too low a temperature to be useful as electrodes in
a resistance unit. You are usually soldering brass, and it's easy to
melt small pieces of THAT too if you're not careful. While resistance
units are GREAT for structural soldering, and more controllable than
even an iron, it is still possible to make a big mess with one.
That was one of the web sites I worked from. I've seen it. Hit if from
altavista advanced search, "resistance soldering". It comes up near the top of
the list, maybe the 5th or 6th one when I tried it last.
My preference for tips (due to cost and availability) is graphite. I use 1/4"
rod and it works great to anchor rail to PC ties. I just place the rail, hold
it down with one probe, place the other on the tie and hit the footswitch. Two
to three seconds does the trick for me. I tin both pieces before soldering.
Like painting, thin coats work best. A little paste flux in between doesn't
seem to hurt things either.
>I've tried it, and it works !
>I've still got the problem of "finding" a suitable power supply,
I got the 12V 5A transformer from American Science & Surplus (sciplus.com).
They're 10 bucks and have a breaker built in. No fuse needed. The voltage is a
bit high, but the 5A nominal output (actual trip current is somewhat higher)
works great. Once I moved the breaker out of the transformer case and used
paste flux in the joint, it hasn't tripped yet (used to when I first built it).
So either the flux is limiting the current just enough, or I'm finally getting
the touch for using the thing. The nice thing is, I was able to use 16 gauge
lamp cord for the conductor. It's a bit light perhaps, but flexible. The duty
cycle is short enough the cord doesn't heat up. But those graphite tips get a
C&NW/CNS&M in 1940-1955
remove "moner" to reply
>>HOW TO BUILD AN ECONOMICAL RESISTANCE SOLDERING UNIT
>That was one of the web sites I worked from. I've seen it. Hit if from
>altavista advanced search, "resistance soldering". It comes up near the top of
>the list, maybe the 5th or 6th one when I tried it last.
Thanks but I had copied and pasted all the data from the website as a
Word document for future reference.
>My preference for tips (due to cost and availability) is graphite. I use 1/4"
>rod and it works great to anchor rail to PC ties.
These rods I got (welding supply shop for anyone in the UK, Ł8.00 for
about 50 rods) are graphite with a thin coating of what looks like
foil. Used a pencil sharpner to get a point as suggested.
>I got the 12V 5A transformer from American Science & Surplus (sciplus.com).
>The voltage is a bit high, but the 5A nominal output (actual trip current is somewhat
>higher) works great.
I only played around with what transformers were to hand,
I've yet to see what's available to buy. Buy ?? The last resort !
>The nice thing is, I was able to use 16 gauge lamp cord for the conductor.
>It's a bit light perhaps, but flexible.
I used fairly heavy (2.5 mm) twin core copper audio / speaker cable
which I had lying. One big advantage is that it's very flexible.
The tips of the TWEEZERS are usually tungsten. These have to remain
STRONG even at red heat, or the tweezers will bend or collapse during use.
All 'resistance soldering' means is that a high current is passed
through the part(s) being soldered, such that their electrical
resistance (Ohmic heating) causes enough INTERNAL heat to melt the
solder and complete the joint. The key here is INTERNAL HEAT. The parts
heat themselves! The soldering tools should NOT get very hot.
This is one reason for the success of resistance soldering ... a 'cold
soldered joint' is near impossible to make. In ALL soldering one should
first heat the parts, then allow the hot parts to melt the solder.
Often, however, beginners melt the solder and just sort of drip it on
the parts like hot-melt glue. This, or variations, is what is meant by a
'cold soldered joint'. It is NOT a good thing. Both structurally and
electrically it makes a VERY poor joint.
Heating the parts by conduction from an iron or gun is not always easy.
'Heat Transfer' is the key. If the soldering tips are not clean and well
tinned you can't get efficient heat transfer to the parts. The tool gets
hot, but the work does not. Oxides and dirt on the metals can reduce
heat transfer. A good flux can aid heat transfer (one of several
purposes for flux).
Now, the tips of soldering tweezers may get RED hot, or near that, at
times. This is not in itself desirable, but passing a LOT of current
through anything will cause it to heat up. Even the heavy probes will
get hot after extended use. The point is, however, that all heat in the
TOOLS is wasted, and undesirable (but some is unavoidable). What is
WANTED is adequate heat to be generated INSIDE the parts being soldered.
As for the transformer the best solution is to wind a special one. You
need low voltage at high current. I've measured 80A on my RSU.
A nice easy way to make a tweezer probe is to use bamboo serving tongs and
attach a conductive tip of your choice to each arm.