Kitbashed Resistance Soldering- Ideal for N scale

[up1950s]

If the female part is the power source when you stick in the male part it supplies a double neg or double pos or double AC to one side of the unit the plug is wired to . Could be bad .

If the male part is the power source , when you stick it in the female part it shorts the tip to the sleeve or ring / (then after that , the ring to the sleeve if stereo is used ) . This is what I did . Bad bad Bad

[Lemosteam]

Ron, I am Geeked about this because I have been fruitlessly trying to build some great brass etched models from Allen Eck and traincat, having to continuously resort to using CA, not that there's anything wrong with that. 

I just really want to build these awesome models without getting CA all over the place. 

So this idea comes at a welcome time for me.

[u18b]

Maybe we should call this....

Precision Hybrid Soldering Station

It is sort of a hybrid between resistance soldering and traditional irons.


I appreciate the moderators leaving this here for a while before moving it to the electronics section.  It is the high precision that makes this so helpful for smaller scales.

[u18b]

Lemo, this would probably work well for you. 

What I might do is-- with the parts held together....
Place the ground alligator clip on the solder ribbon itself.
Flux parts.
Then touch the carbon tip to the spot you want to solder. 
Push the foot pedal.

Then when you touch the solder to the soldering spot, electricity flows, the tip heats up.  Almost instantly.  Then remove the soldering ribbon.  It would only take a little touch I think.

I would be curious to know how that procedure works.

[u18b]

I don't know why I didn't think of this before....

Several people wondered what kind of amps we are dealing with.

But if  V = I * R

Then if we know that V = 5 volts

Then if we knew the resistance of the carbon electrodes, we could figure out I.

So I inserted 1/2 a pencil lead as I described in that article.  I then measured the resistance from the brass holder to the tip of the carbon.  The digital reading jumped between 1 and 2 ohms.
So it is probably about 1.5 ohms.  But as it burns off and get shorter, the ohms would drop.  Let's say 1 ohm.

V = I * R........ 5 = I * 1 .....  I = 5.
 
So by the math, we are dealing with about 5 amps.

Actually, I'm thinking about trying this with the orange wire.  It was measured at 3.2 volts.

[mmagliaro]

That's using your noodle, Ron.
So 5 amps, 5 volts, a total power of about 25 watts.

That means that there is no need to be buying 100 watt, or higher powered, stations, especially if they
cost more money.

[peteski]

That's using your noodle, Ron.
So 5 amps, 5 volts, a total power of about 25 watts.

That means that there is no need to be buying 100 watt, or higher powered, stations, especially if they
cost more money.

The problem is like Ron stated - this is not really a resistance soldering unit (in the original sense of the defintion). Those "real" units pass dozen's of amps (at very low AC voltages) through the pieces to be soldered. That high current heats up those parts instantly. The total resistance of the parts being soldered themselves, and the electrodes is in milliohms.

Ron's soldering device is more like conventional iron - that white-hot glowing graphite rod is the main source of heat (just like a conventional iron).  It then just passes the 5A of return current through the parts being soldered, which doesn't, much contribute to heating them up.

[LV LOU]

I don't know why I didn't think of this before....

Several people wondered what kind of amps we are dealing with.

But if  V = I * R

Then if we know that V = 5 volts

Then if we knew the resistance of the carbon electrodes, we could figure out I.

So I inserted 1/2 a pencil lead as I described in that article.  I then measured the resistance from the brass holder to the tip of the carbon.  The digital reading jumped between 1 and 2 ohms.
So it is probably about 1.5 ohms.  But as it burns off and get shorter, the ohms would drop.  Let's say 1 ohm.

V = I * R........ 5 = I * 1 .....  I = 5.
 
So by the math, we are dealing with about 5 amps.

Actually, I'm thinking about trying this with the orange wire.  It was measured at 3.2 volts.

Ron,I think the actual lead is what's limiting it to 5 amps..A heavier lead will flow more current..

[peteski]

Ron,I think the actual lead is what's limiting it to 5 amps..A heavier lead will flow more current..

It absolutely is, but looking at the overall design, it is probably a good thing.  I use thin steel electrodes on my American Beauty unit.  Much lower resistance.  But I suspect that passing 20 or 30 amps through the phono jack would not be the safest thing to do.

[mmagliaro]

The problem is like Ron stated - this is not really a resistance soldering unit (in the original sense of the defintion). Those "real" units pass dozen's of amps (at very low AC voltages) through the pieces to be soldered. That high current heats up those parts instantly. The total resistance of the parts being soldered themselves, and the electrodes is in milliohms.

Ron's soldering device is more like conventional iron - that white-hot glowing graphite rod is the main source of heat (just like a conventional iron).  It then just passes the 5A of return current through the parts being soldered, which doesn't, much contribute to heating them up.

Hmmm... interesting, and I understand the difference.  I was wondering about the wattage.  It seemed to me that
if American Beauty's smaller stations are 100 watt, they wouldn't be doing that just for laughs, so how could this work
with only 25 watts of power?   Now I see. 

So.... does this rig accomplish the end goal that a resistance solderer does?  Namely, does this cause a big, rapid
heat build-up at a very precise location, hot enough and quickly enough that it can flow solder and finish a joint before
the surrounding metal starts to heat up?  Is the only difference between using this and, say, a really high-powered soldering iron or a small torch that this is able to focus all that heat into a little pin point?  (Not that that is a small accomplishment, by the way.
That may be the whole key to making this work!)

[Lemosteam]

It absolutely is, but looking at the overall design, it is probably a good thing.  I use thin steel electrodes on my American Beauty unit.  Much lower resistance.  But I suspect that passing 20 or 30 amps through the phono jack would not be the safest thing to do.

A phono jack was his plug of choice at the time.  One could use a traditional two blade plug to accomplish the same effect with a lower resistance tip, no?

[u18b]

Hmmm... interesting, and I understand the difference.  I was wondering about the wattage.  It seemed to me that
if American Beauty's smaller stations are 100 watt, they wouldn't be doing that just for laughs, so how could this work
with only 25 watts of power?   Now I see. 

So.... does this rig accomplish the end goal that a resistance solderer does?  Namely, does this cause a big, rapid
heat build-up at a very precise location, hot enough and quickly enough that it can flow solder and finish a joint before
the surrounding metal starts to heat up?  Is the only difference between using this and, say, a really high-powered soldering iron or a small torch that this is able to focus all that heat into a little pin point?  (Not that that is a small accomplishment, by the way.
That may be the whole key to making this work!)

Max.  You have hit it precisely, I think.
In my ignorance, I called this what a lot of other people on the web call it- resistance soldering.
I see now that it is not.

However, as you pointed out.....at least to some degree, I think it does accomplish the same thing.  High, quick, pinpoint heat in a precise location.  With cooling of the "iron" being quick as well.

I guess that's why I suggested the term- Hybrid Soldering.  It is not one or the other (though it is probably closer to traditional soldering).

One major difference I see is carbon/polymer residue.  This adds a bit of impurity into the solder mix.  Not much but some-- depending on the brand.

[u18b]

A phono jack was his plug of choice at the time.  One could use a traditional two blade plug to accomplish the same effect with a lower resistance tip, no?

Exactly right.  I wrote the paper showing that these are the choices I made--- but if you understood what the wiring was doing, you could go a different direction.

There is no reason at all that someone could not use other plug/socket combos.

Suggestions are welcome.

[peteski]

Ron,
for the benefit to all interested members, I hope that you won't mind if I post this info here (instead of a PM).

First, let's examine a real resistance soldering unit - the one I own: an American Beauty 250W unit.  The design is an exercise in simplicity: including the power switch and the fuse, it has only 4 electrical components.  All the components are really basic electrical devices, which would be right at home in laboratories of 19th Century inventors like Tesla or Edison.    Basically, there are 2 transformers.  There are no transistors, resistors or capacitors.  Just the transformers and bunch of wires.  This means that the unit will be very reliable - nothing really to break, fry or blow up.

The first component is an autotransformer. Specifically, Staco Energy Products Type 171 KW.


Autotransformer is a special type of variable transformer (controlled by the knob on the front of the unit). In this setup, it is simply used to vary the voltage feed to the 2nd transformer. It supplies from 0-100% of the input voltage (or 0-120V AC). It is sort of like a high-power rheostat in an old model power pack, but since it is a transformer, the output voltage is stable, independent of the load on it.

The variable AC output is then fed to the 2nd transformer.  This is the transformer which provided the high current/low voltage needed for resistance soldering.

Notice the 6 turns of big-a$$ wire visible on that transformer.  That is the actual secondary winding (the 120V primary winding is under the insulating layer).  That winding is then connected directly to the hand-piece connector socket using a really heavy-duty braid-like wire (inside the black tubing).  That is all there is!

The output specs are: Voltage: variable 0-3V AC at 83A  Yes, 83 Amperes!  The 0-3V output is directly proportional to the the voltage feed to the primary side.  So, when the autotransformer is set to maximum (120V AC), the output will be at 3V AC. Lowering the input voltage will proportionally reduce the output voltage.  Since the current flowing through the circuit will depend on the total resistance of the load (the leads, hand-piece electrodes and the resistance of the parts being soldered), controlling the voltage gives you control of the current.

The voltage control is done on the 120V AC side, because it is much easier (and less expensive) to control up to 2A of current (that is 250W at 120V), than controlling the current on the low-voltage 83A side.

Since this device is capable of producing 83A of current the connectors are chosen to be able to handle that current. Here is a view of the rather hefty sockets.


The plugs are simply cone-shaped lugs which fit tightly in the sockets.  The wire used on the low-power tweezer (with thin steel electrodes) is 14 AWG. That hand-piece handles only up to 100W of power. The higher power capacity grounding strap, and the larger hand-piece use 10 AWG wire.  The carbon electrode I have has a layer of highly conductive copper on the outside and the resistance of the carbon itself is less than 1 ohm.

The total resistance of the wire, electrodes, and the soldered parts is in milli-ohms. The 0-3V adjustment gives a wide range of current adjustment (remember, the unit is always capable of supplying 83A of current- at any output voltage).  How much current is consumed is strictly related to the total resistance of the circuit.

As you can see, this is a very simple and robust design. No transistors to fry, no electrolytic caps to explode. It would be a breeze to build at home, except for one problem: The high current transformer is something that is custom made by the manufacturer. If such transformer was available off the shelf, it could probably be purchased for about $40 in single quantity. But since it is not available, American Beauty can charge whatever they want for their unit.

Now we get to your unit.  You are using a small part of a very complex electronic switching power supply.  It is designed to precisely filter regulate many output voltages and supply them to a computer circuit.  While it has short-circuit protection, it was never designed for someone to simply take one of the outputs and start basically shorting it out!  There are literally hundreds of components in there, ready to blow up from it being used in such a brute way.

I would compare this to the real resistance soldering unit being a dirt-bike being driven on a unpaved and rutted road, at a high rate of speed. The bike is very simple (not many parts in it) and it has a suspension designed to take abuse. Your power supply would be like a Porsche (highly complex, high-performance) car being driven on the same road. Both vehicles can be used, but the chances are that the Porsche will not survive the trip undamaged. 

Then you chose the 5V output. As you see, that is a bit high for "real" resistance soldering, where the total resistance should be in milli-ohms.  That would instantly short out the 5V output, and hopefully trigger the circuit breaker.  Using the 3V would probably make sense if you insist on using a computer power supply. But you would still need to beef-up your connectors and hand-piece wires.

Then there is another possibility for building a home-brewed unit. As you mentioned, a soldering gun utilizes the same low-voltage/high-current method as a resistance soldering unit (except it has a fixed loop  formed as a soldering tip).  If you were to remove the tip and use the 2 terminals for a high-current low voltage output for your hand-piece, that might do the trick.  The only possible problem might be that the voltage might be too low to make it work properly with the total resistance of your hand-piece and the item being soldered.  For adjustment I would recommend to do it on the 120V side (using a commercially made autotransformer rated at the max wattage of the soldering gun).

I hope that this sheds some lights on the resistance soldering process. I'm no expert by any means, but I own and use my commercially-made unit and I do have electrical/electronic background.  So I do have at least half a clue. 

[u18b]

This has been very educational.  Thanks.