# Building a Resistance Soldering Unit



## bnsfconductor (Jan 3, 2008)

To those who have built a resistance soldering unit do you have any tips or tricks to suggest to me? I recently acquired a 13v 20amp car battery charger to use in the construction of such unit. I've got all the parts (including a 10amp push button switch (I think that should be fine?)) now except a piece of carbon rod. I called the local welding shops and they have a box of 50 for around $20. I'm hoping to get carbon rods on Saturday so I can start putting all the pieces together. 

Thanks in advance,
Craig


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## xo18thfa (Jan 2, 2008)

Hi Craig: Here's a couple documents on home built units. On my list of "to-do's" as well.

Vance Bass Soldering Machine

NMRA Soldering Machine


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## bnsfconductor (Jan 3, 2008)

Thanks for the links, but I've already read both of them. I post some pictures when I get it finally built, but I was wondering if anyone else had built one. I've been looking for a 5-10 amp transformer for about 2 months now when I found a 20 amp transformer at a antique store last week. It's a pretty easy project except finding carbon rods.


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## Greg Elmassian (Jan 3, 2008)

Contact Vance directly, he may have a few. I got a couple from him a long while ago. A heck of a nice guy. 

Greg


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## bnsfconductor (Jan 3, 2008)

Well yesterday I finnally was able to build the unit, and get a 50 pack of carbon rods from the welding supply place. But when I went to fire up the unit, I blew the fuse on the transformer (like I expected) so I had to tear apart the transformer unit to bypass the fuse. In the process I managed to break on of the leads of the bridge rectifier. Off to radio shack for a replacement, and thankfully they had one! So after installing the new bridge rectifier, and reassembling the unit I proceeded to make my first joint. Well I go the unit way to hot, and proceeded to melt the original wires on the soldering iron! So I know it works, but now I'm having to replace the wiring. I think I might have to high of voltage, or I may not be fast enough with the on/off switch. I was using 10 gauge wire from the transfomer into the switch, and then to the original soldering irons wire (I'm thinking it was maybe 14 gauge?) so I'm going to keep the 10 gauge and replace the melted wires with 12 gauge and hope that everything works out. When I get it finished I post some pictures. I just used scrap styene to make the foot switch along with a 15 amp push button switch. 
Craig


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## xo18thfa (Jan 2, 2008)

Craig. There are always "bugs" in things like this. It sounds like you are getting them worked out. Request you do a little write-up with pictures of the final product. I would be interested.


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## bnsfconductor (Jan 3, 2008)

Ya I'm sure I can make something up when I get it done. It's actually a fairly easy project to do.


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## bnsfconductor (Jan 3, 2008)

A question to all those who have more electronic experience then me follows. After rebuilding my wiring and replacing a bridge rectifer I attempted to test the resistance soldering unit again. It worked, for a while until I both tripped the house fuse, and the destroyed the new bridge rectifer. So I need to reduce the voltage (currently its a 13.6 volt transformer and 20 amps) from 13.6 to something in the 6-8 volt range I was thinking. So here's my question. Were should I add resistors? On the 110 side prior to transforming from AC to DC or should I reduce on the DC side (not sure on the exact voltage but the unit says max of 13.6 volts at 20 amps. I was thinking about adding a potentiometer but again I'm stumped at were to put it. I could buy a household light dimmer switch for around $5 at the hardware store and wire it in line with the transformer (on the 110 side), but my basic electronic skills are stumped.
Craig


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## Greg Elmassian (Jan 3, 2008)

Can I ask the amp rating on the bridge rectifier you destroyed? 

I was not aware RS had 20 amp bridges. 

to trip the house breaker, you needed to be pulling over 15 amps ac... that is roughly 150 amps at the dc side, since you say the output is about 1/10 of the input. (so the amps are 10 times more)... 

That would have been a nice short. 

In any case, a dimmer switch that can handle 15 amps is going to be interesting, I would not do this... also on the DC side you would need something with an amp rating ten times as high. 

Resistors better be large and calculated for the power output... 

I think the key is picking the right transformer in the first place... 

Regards, Greg


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## bnsfconductor (Jan 3, 2008)

Posted By Greg Elmassian on 11 Feb 2011 09:26 PM 
Can I ask the amp rating on the bridge rectifier you destroyed? 

I was not aware RS had 20 amp bridges. 

to trip the house breaker, you needed to be pulling over 15 amps ac... that is roughly 150 amps at the dc side, since you say the output is about 1/10 of the input. (so the amps are 10 times more)... 

That would have been a nice short. 

In any case, a dimmer switch that can handle 15 amps is going to be interesting, I would not do this... also on the DC side you would need something with an amp rating ten times as high. 

Resistors better be large and calculated for the power output... 

I think the key is picking the right transformer in the first place... 

Regards, Greg 

Greg, 
The bridge was a 20 amp bridge. I was kind of suprized myself that RS had one (in stock no less). After speaking with my brother in law (an EE) he suggested that I use a dimmer switch on the AC side, and then proceeded to ask me if I wanted one. I replyed sure, so we go out into his garage and he gives me an industrial grade 1500 watt dimmer switch. So I think that should work. But speaking of transformers in retrospect I would should have gotten one with a lower voltage output, but lesson learned. 
Craig


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## Dansgscale (Jan 9, 2010)

Reading this reminds me that I need to go pull my old Resistance solder rig I built 25 years ago out of storage. I'll be needing it for a couple of projects I have on the drawing board. I used to use it to build Sn3 and On3 C-16 Brass locomotives. You can't beat one of these to solder brass detail parts to a brass bolier. I was lucky enough back then to get my hands on a pair of soldering tweezers are a real low price, I think it was like $10.00, now I see that Micromark has them for almost $100.00. 

The unit I built has a 20amp transformer, to convert the 110V to 12V DC, I use a standard Household Dimmer switch on the input side of the transformer and put and 15V voltage meter on the output side so I could see what the setting was that worked best. There is also a Pilot light so I know when it is on, along with a toggle switch to turn it on and off. I found an old electronic instrument case that had a handle on top of it to put everything in. I replaced the front panel of the case with a 1/4 think plexiglas and painted the back side black so the outside was nice and shiny. The dimmer switch, pilot light and on / off switch are mounted in to the plexi glass. I also installed 4 banana plug jacks in the front as well along the bottom edge. Two of them are where I plug in my soldering tweezers or the carbon rod and grounding clip. The other two are for hooking up the sewing machine foot switch that I use to activate the tweezers or carbon rod. I made a rod holder out of a wooden dowel that was drilled through the center. After I solder the lead wire to the copper covered rod, I slide it into the dowel and the sand the end of the rod to a nice point. 

Once I dig it out of storage I'll take some pics and figure out how to post them here. 

Dan S.


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## wonkytock (Mar 21, 2012)

Hello, 
I was wondering if a transformer for a resistance soldering iron needs to output DC? 
Thanks!


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## Amber (Jul 29, 2011)

Transformers only work on AC, you need a rectifier to convert the AC output of the transformer to DC. The size of the rectifier depends on the amount of power that will be going through it.


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## ralphbrades (Jan 3, 2008)

I personally do not like resistance soldering units as you have to pass so much current through the thing... BUT speaking as a (retired) computer designer you do have to massage the design of the PSU to match the requirements. If this was one of my designs I would use an E+I transformer rather than a toroid as this prevents "cold inrush" as the device is connected to the mains -thus blowing the fuses. You would be looking at a transformer of mains to 9 Volts at 200VA rating thus giving you about 7% regulation. 

If we accept 4.5 Amperes at 12 Volts as the wattage flowing across the tips then the PSU has to capable of supplying at least 7 and preferably 10 times this figure. The diodes I would specify at at 8 times load, a Fairchild 100V 35A bridge rectifier costs £2.18p (UK). This I would couple with a bank of capacitors at around 10,000uF with a summed ripple rating of around 7 Amperes (preferably more). This is just a rough run through -it is far easier and cheaper just to plug in an AC soldering iron and not bother with all the maths! 

regards 

ralph


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## spincaster (Mar 10, 2012)

AC works fine for resistance soldering. I use a 15A variac to produce variable 0-115VAC voltage. A 20amp transformer with an output of about 6VAC max is plugged into the variac. So you end up with the transformer output of about 0-6VAC 20A which works fine. Dead simple set up and I use the variac to control other tools like a router and a soldering iron. I figured this out from various articles and seeing a variac in a Brass model locomotive mfgs work shop. I did buy a trashed commercial unit cheap at a flea market for the tweezers and carbon holder but both can be made easily.


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## lotsasteam (Jan 3, 2008)

Sorry ,just noticed that post! Go to your local Dental lab and ask for the framework(partial department)almost all dentallabs using laserwelders and the resistance welders are obsolete ,you might get one realy cheap around $ 80. or so! These are powerful units (current adjustable)and you are able to silver solder steelparts together! 

Manfred


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## Rbrbr (Nov 26, 2020)

bnsfconductor said:


> Thanks for the links, but I've already read both of them. I post some pictures when I get it finally built, but I was wondering if anyone else had built one. I've been looking for a 5-10 amp transformer for about 2 months now when I found a 20 amp transformer at a antique store last week. It's a pretty easy project except finding carbon rods.


Just go buy a heavy duty 6 volt flashlight battery and take the carbon rod outofthecells inside,they are the same size as a pencil so u can sharpen them in a pencil sharpener


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## Pete Thornton (Jan 2, 2008)

Rbrbr said:


> Just go buy a heavy duty 6 volt flashlight battery and take the carbon rod outofthecells inside,they are the same size as a pencil so u can sharpen them in a pencil sharpener


Sorry, but that thread dates from 2011. I doubt he is still around.


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## Greg Elmassian (Jan 3, 2008)

Yes, the OP (original poster) last posted in 2018...

I did go to some youtube pages and saw a breakdown of a 6v cell, with the 4 large 1.5v cells in it, and saw the carbon rod. Nice tip.


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## Nick Jr (Jan 2, 2008)

Didn't know this was an active subject till I went to post about my find this morning. Over the years made several hand rails and steps soldering brass, the last was most frustrating so looked into Resistance Soldering. Found Micro Mark is offering a Resistance Soldering Set Super Value #87726. Has maybe all that you woud need to do small jobs. Received it yesterday and played with it a little to become familiar. It even came with scraps of brass and copper to learn the art. Sorry I didn't decide to go this way long ago. If anyone wants to offer any suggestions how to make my learning curve easer, please do so. Thank You
EDIT; I have no affiliation with Micro Mark, just an old dog learning a new trick.


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## Greg Elmassian (Jan 3, 2008)

Not an active subject... read back a few more posts, it basically ended in 2012, 8 years ago... not active in my book.

Greg


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## fredlub (Feb 7, 2010)

bnsfconductor said:


> I blew the fuse on the transformer (like I expected) so I had to tear apart the transformer unit to bypass the fuse.
> Craig


It is an old thread but still I had a good laugh with the mentioning of bypassing the fuse. It is like removing brakes from your car because the squeak. 
Regards
Fred


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## Nick Jr (Jan 2, 2008)

I don't subscribe to your book, doesn't have to be immediately active to be interesting or informative. Old saying about HISTORY still true.
EDIT: 'Played' with it some more, no buyers regret here.


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## Nick Jr (Jan 2, 2008)

I like it so much purchased a Grounding Vice to help hold the item I am working on, needed more hands than I was issued.


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## Greg Elmassian (Jan 3, 2008)

Sigh... Nick, I was responding to you in your post#20, where you say:



Nick Jr said:


> *Didn't know this was an active subject *till I went to post about my find this morning. Over the years made several hand rails and steps soldering brass, the last was most frustrating so looked into Resistance Soldering. Found Micro Mark is offering a Resistance Soldering Set Super Value #87726. Has maybe all that you would need to do small jobs. Received it yesterday and played with it a little to become familiar. It even came with scraps of brass and copper to learn the art. Sorry I didn't decide to go this way long ago. If anyone wants to offer any suggestions how to make my learning curve easer, please do so. Thank You
> EDIT; I have no affiliation with Micro Mark, just an old dog learning a new trick.


It was *not *an active subject.... that's *all *I was saying, not rejecting the content of the thread, just responding to you that it was not an active subject, someone commented out of nowhere, and then you took that to be "active"... and I disagreed... he commented on something that had been inactive for quite some time.

I like the thread, I was a commenter on it in 2011 and 2012 (8-9 years ago).... 

So I apologize if I confused the case, I just was making the sole point about active vs inactive, not demeaning the content of the thread as it was and continues to be informative.

Greg


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## Nick Jr (Jan 2, 2008)

I found the soldering tweezers, while useful, just didn't grip the part well enough. Going to use a small needle nose pliers and 14 gauge wire to make one I can apply more pressure to. While waiting for the Grounding vice to arrive been using the Soldering Pad and pins that came with the kit. Found that to be helpful, even if I were using the 750W hand iron I use. Still havin' fun.


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## Nick Jr (Jan 2, 2008)

Received the grounding vice. It was a big help, not only holding the item securely, but was also able get an accurate 90' angle on the step to the side. AND the adjustable table made making the distance between steps as simple as turning a screw. Still on the bottom of the learning curve, but encouraged to continue. No buyers remorse here.


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## OldNoob (Apr 30, 2016)

I made a poor mans soldering Jig some years ago. I'm guessing it wouldn't work for resistance soldering?


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## Nick Jr (Jan 2, 2008)

Noob, looks fine to me. Anything that will hold the parts you are connecting secure, that works. I used to use a piece of wood and brads to make the small parts. Looks like you are making hand rails?


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## Nick Jr (Jan 2, 2008)

I successfully used the Resistance Soldering unit to repair the brake rigging on my G5. As can be seen from the pics, brake and line not only came off the loco, but bent. In attempt to straighten, it of course broke. Now I have 3 pieces that need to be soldered for this repair to be successful. I used the soldering pad which has the constitution of heavy styrofoam. I pressed the parts into it to hold them in line, then applied the acid flux and silver solder. The final connection was made when the parts were afixed to the truck. It does need to be cleaned up and painted, but am happy with the results.


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## OldNoob (Apr 30, 2016)

Very neat.


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## Nick Jr (Jan 2, 2008)

Noob, thank you. I wasn't sure pressing the parts into the soldering pad would allow the solder to flow. Held them better than the pins. In the future will carve out the pad to hold other things while soldering, it is expendable with the low price.


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## Rbrbr (Nov 26, 2020)

bnsfconductor said:


> To those who have built a resistance soldering unit do you have any tips or tricks to suggest to me? I recently acquired a 13v 20amp car battery charger to use in the construction of such unit. I've got all the parts (including a 10amp push button switch (I think that should be fine?)) now except a piece of carbon rod. I called the local welding shops and they have a box of 50 for around $20. I'm hoping to get carbon rods on Saturday so I can start putting all the pieces together.
> 
> Thanks in advance,
> Craig


I know I'm late but u can find carbon rods in any heavy duty battery I like the ones out of the 6volt flashlight batteries


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## Rbrbr (Nov 26, 2020)

bnsfconductor said:


> Thanks for the links, but I've already read both of them. I post some pictures when I get it finally built, but I was wondering if anyone else had built one. I've been looking for a 5-10 amp transformer for about 2 months now when I found a 20 amp transformer at a antique store last week. It's a pretty easy project except finding carbon rods.


Carbon rods are in batteries that say heavy duty,the best carbon rods I found are in those 6volt flashlight batteries they are the size of a pencil so I can sharpen them in my electric pencil sharpener


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## Rbrbr (Nov 26, 2020)

Rbrbr said:


> Just go buy a heavy duty 6 volt flashlight battery and take the carbon rod outofthecells inside,they are the same size as a pencil so u can sharpen them in a pencil sharpener


They are about 10 ohms


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