Resistance Soldering

A guide to resistance soldering basics.

How resistance soldering works, choosing a resistance solderer, about DIY resistance solderers,  and about making solder joints.

Advanced Resistance Soldering Guides

We have two other pages that provide more advanced information

Resistance Soldering Unit – A guide to making your own Resistance Soldering Unit.

DIY Resistance Solderer – Shows two types or resistance solderers and a simple approach to making them.

How Resistance Soldering Works

Resistance solderers take advantage of a materials resistance to electrical current flow.

An incandescent light bulb does the same thing.  When the filament in the bulb has a certain resistance to electrical current flow.  When voltage is applied to the light bulb, current flows through the filament. It gets hot.  The heated filament throws off light.

If you substitute two pieces of brass with some solder between them, the brass will get hot, the solder melt and a join made.

By using probes we can focus the path of the current to a very small area.

The pinpointed area gets very hot very fast and cools quickly.  Other solder joints near it stay unchanged.

In short, with a RSU you can make a soldered joint which would be impossible by any other method. This is method is particularly useful when making joints in close proximity to each other or where you need to avoid overheating the surrounding materials.

A carbon tip on the probe gives a high speed, concentrated spot of heat just where you want it.

Choosing A Resistance Solderer

If you are a dedicated brass modeler, you may wish to make the investment necessary to add an RSU to your bench. Most are so expensive that they deter people from buying them.  But there are some that are quite affordable.

Hobby modelers generally need low power units.  Too much power can cause arcing that results in pitting of the brass. And there is no need to spend the extra money that unneeded higher power costs.  Some companies recognize this and offer units for the hobby modeler.

Here a couple that a hobby modeler might consider.

If you are in the US or any other location that uses 115v , this is a fine unit from a fine company.  Click here to learn more.

In Europe or any other country that uses 230v , this is a low cost unit that we have tested and found it to be good.  Click here to learn more.

But for most flexibility, go DIY.  And it saves you money.  Click here to learn more.

About DIY Resistance Solderers

A DIY RSU saves you money and gives you flexibility.

You can find on the web many pages and videos describing how to make a resistance soldering unit. Most start with modifying a microwave transformer.   We consider that hacking and dangerous.

We recommend that you use a commercial product that is specifically made with the exact primary and secondary windings you need.  And we recommend  0-115 v  0-115v primary, 0 – 6v  0-6v secondary  50 VA.

Your RSU will be able to be powered by either 115 v AC or 230v AC

You can get either  such a transformer  or complete DIY resistance soldering unit kit here.


About Making Solder Joints

An RSU is used in conjunction with your normal soldering iron.

Fluxing and tinning the pieces to be joined assures you of fine clean joints. That is done with your normal soldering iron.

You can avoid that process by using a good solder paste such a Koki. It has an embedded flux and is easy to use.  Don’t use off the shelf plumbers paste. If you want a quality joint, use a quality paste.

The video below shows many examples of how to make the joints.

Guide To Resistance Soldering

Guide To Resistance SolderingIf you click on the image to the left, you will go to a video that is a must watch for anyone interested in resistance soldering.  So that you do not lose this page, it will  open in a new window.



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