Kitbashed Resistance Soldering- Ideal for N scale

[Kentuckian]

Peteski,

Can you give an example of a "commercially made auto transformer"?  I had to take circuits twice when I was in college, and not because I wanted to!

[mmagliaro]

The Staco 171KW is a commercially-made auto-transformer.
And unfortunately, even though you CAN buy it "off the shelf", I priced them.  Allied Electronics wants $176 for that puppy.
So even not counting the un-buyable second transformer with the 3v 83A secondary, this would be an expensive
thing to build yourself.

I think of an auto-transformer as a transformer with a "movable tap" on the secondary.  So unlike sticking a rheostat in there,
you get any stable secondary voltage you want (from 0 -120 in this case), and it doesn't vary with load, like it would
with a rheostat.

If nothing else, Peteski, showing the insides of that thing gives me new-found appreciation for how American Beauty makes their products and why they are so expensive.

[C855B]

(Max kinda beat me to it, but here goes anyway...)

Variable transformers, at the top: www.mouser.com/catalogviewer/default.aspx?page=2172.

Technically, I think what we're talking about here is a "variable transformer". An "autotransformer" is a step-down transformer with a single winding (versus separate primary and secondary windings), with taps for voltage reduction, although it is certainly possible - maybe even likely - that these variable transformers are actually autotransformers with a variable tap.

As you can see from the link, the variable transformer is not super-expensive, tho' not cheap. I think the pricey part of the commercial resistance setup is the step-down transformer, which I suspect is custom.

[mmagliaro]

(Max kinda beat me to it, but here goes anyway...)

Variable transformers, at the top: www.mouser.com/catalogviewer/default.aspx?page=2172.

Technically, I think what we're talking about here is a "variable transformer". An "autotransformer" is a step-down transformer with a single winding (versus separate primary and secondary windings), with taps for voltage reduction, although it is certainly possible - maybe even likely - that these variable transformers are actually autotransformers with a variable tap.

As you can see from the link, the variable transformer is not super-expensive, tho' not cheap. I think the pricey part of the commercial resistance setup is the step-down transformer, which I suspect is custom.

Mouser has a Hammond  165Z3, 3V secondary 50A.  It's not 83A, but it's getting there, for about $57.  Looking at Hammond's website and complete product list, 50A is the highest-current secondary transformer they make.   Clearly, it is not cheap or easy getting
or making these components.

Still, we are now into the $200+ cost range, and still need case, jacks, probe, heavy wire. 
If I could buy a used or discounted American Beauty for under $300, it would not be worth building my own.

[peteski]

I shoudl have provided better explanation of the autotransformer (variable transformer), but it looks like at this point it has been very well explained.

I also underestimated the current prices (I have not really looked around for pricing).  That does better justify the pricing of the American Beauty units. They are pricey, but powerful and should be very reliable.

The 3V 50A transformer (along with the autotransformer) would make a fine 150W resistance soldering station. 150W would be more than adequate for our N scale needs.  But (like also already mentioned) adding the cost of other things like a case and heavy-duty connectors would make its price close to the price of commercially available units.

I forgot to mention the foot switch. It simply controls the main 120V power going to the entire unit.  Again, it is easier to control higher voltage at low current than low voltage, high current.

Ron's unit obviously works for him (even if it works more like a super-hot conventional iron).  The decision with what do do has to be made by the person desiring to have the ability to do resistance soldering.  I just wanted to provide some additional info to assist one on their their design for a home-brewed unit, or to get the real thing.

Second-hand units are out there, often available for a cost lower than new unit.

I bought my American Beauty back in 1992, after reading an article about resistance soldering in the April 1992 issue of MR magazine.  Back then I contacted American Beauty (via snail mail), and I still have the reply letter.  My 250W base unit cost back then $211.  The hand-pieces and the foot switch (I bought at that time added more than a $100 to the total cost.

[Kentuckian]

Thanks to all for explaining this, and especially to Ron for bringing it up.  As usual, I learned a lot from everyone.

[alhoop]

Ron:
try this - clamp your ground lead to a small piece of brass wire and wrap another piece of brass wire around the first
piece and touch and hold your electrode to the the piece of wrapped wire and activate your foot switch( your are using a foot
switch right). The resistance between the two wires is what gets hot instantly - not your electrodes - and it only takes a second.
When you remove your electrode it should be cool to the touch. If you don't deactivate  the foot switch immediately after the solder flows
then the electrode will get red hot since where it is touching the work piece is now the point of highest resistance.You could also solder a brass bell to a locomotive shell the same way without loosening other solder joints. Now this is resistance soldering.
 I don't think the small tweezers can carry 83 amps.

Al

[u18b]

Alhoop, I'm feeling a little dense.  Sorry.  But I'm not picturing what you are describing.
Can you provide a drawing?

[u18b]

As Peteski has said,  what I built may not be true resistance soldering, but actually it does work for a limited purpose.  Given the wisdom of what some have said, it might be best not to put such a device through heavy use.  But for needing an intense heat source for a specific problem (especially if space is a bit tight) this device seems to work for that purpose.

Since I have built two of these, I'm going to try a couple of changes.
First, I'm going to drop the 5 volt red wire- it could now power an LED.

And I'm going to the 3.2 volt orange wire.
Instead of using one and clipping the other two, I'm going to solder all three to the same spot for higher amperage if it might be a problem.

Then I have ordered a part from China (ebay was very convenient).  Even though some have mentioned a load issue with a variable resistor, it won't hurt to try something.  I'm going to install a huge potentiometer.
Here is an ebay link. ( Mods, if this is a problem, I understand if you need to remove it.  But since it is not trains, I'm assuming this might be OK and even helpful).
http://www.ebay.com/itm/130697154306?ssPageName=STRK:MEWNX:IT
This is a huge 100 watt power rated pot.

I'll put this on the 3.2 volt source to drop the voltage and and see if I can move in the direction of true resistance soldering.  Obviously, there will be a few other changes that need to be made.

As has been demonstrated in the last few posts, the commercial set-ups are actually not that outrageously expensive, once you understand how they work and what is in them.

However, if there is at least a possibility a much cheaper home brew might work, I'm open to trying.

[alhoop]

Alhoop, I'm feeling a little dense.  Sorry.  But I'm not picturing what you are describing.
Can you provide a drawing?

This describes it better: Click on 'watch the video'

http://www.micromark.com/microlux-resistance-soldering-unit-with-single-electrode-handpiece,10952.html

Al

[rodsup9000]

  Wow, I've learned some stuff here. Thanks

Peteski Thanks for the pics of yours.

I've seen some made out of battery chargers and now I'm wondering if the really work like the one Ron has made.

 Now I'm wondering, I have a 10 amp variac (0 to 140 volts) and if I buy the 3V transformer that Max points to, if I can make a true resistance solder station. A few years ago, I bought a set of PBL tweezers with nicrome wire tips and I've made a foot petal.

 The question I have is with the 3v transformer. How many amps would you need on the input side to get the 50 amp on the output???

  Rodney

[peteski]

  Wow, I've learned some stuff here. Thanks

Peteski Thanks for the pics of yours.

I've seen some made out of battery chargers and now I'm wondering if the really work like the one Ron has made.

 Now I'm wondering, I have a 10 amp variac (0 to 140 volts) and if I buy the 3V transformer that Max points to, if I can make a true resistance solder station. A few years ago, I bought a set of PBL tweezers with nicrome wire tips and I've made a foot petal.

 The question I have is with the 3v transformer. How many amps would you need on the input side to get the 50 amp on the output???

  Rodney

If the primary winding is designed for 120V, then it would consume about 1.25A (not considering the transformer losses). Basically, 3V times 50A is 150 Watts.  120V times 1.25A is 150 Watts.  In real transformer. the primary current consumption would be a bit more than 1.25A.

[rodsup9000]

Thanks Peteski.
I think my variac will be overkill then. I'll look around for a smaller one just to use for the solder station.

Rodney

[LV LOU]

I think this whole thing is an exercise in cost,and what you really NEED..Sure,Ron's setup isn't an American Beauty,but then,he's only working on N scale trains for the most part.Looks like it will,in fact,be able to actually perform true resistance soldering on small stuff,just needs a few "tweaks"..The real setups with solder BIG stuff,I've seen the American beauty video,they're soldering 1/4 inch thick stuff..That's 20X what you need here.I think Ron's has more than enough output to solder say,N scale track,and locomotives.
  Ron,I'm gonna work up some updates,and a stepped variable resistor setup,should wake it right up.I have a 40 Amp 5V power supply,I want to build one myself,as I'm gonna be doing a pile of trackwork soon.If I can't get this thing working,then it won't,LOL!!

[mmagliaro]

Ron,
Are all three of those 3.2v wires coming off the same physical connection inside that power supply?
They aren't separate, are they?  I ask, because, if they are separate, you should not tie them together to get more
current capacity.  You have to start worrying about the phase of the
rectified wave on each of those 3 wires.

If they are all physically connected together inside the case, then no problem.