Resistance Soldering Unit

How to build your own DIY resistance soldering unit.

This page covers materials that you will need and takes you step by step through the process to make a dual power 50 VA resistance soldering unit.

This DIY FinePoint RSU is ideal for Hobby Modelers working from N scale on up.  Use a FinePoint |Resistance Soldering Unit for Fine Scale modeling.

It is designed so that you can quickly and easily change probe types in order to be able to make the best joints possible on the project on your bench. Probe types are shown below.


Materials Required


We recommend the FinePoint Resistance Soldering Transformer that is wired  0 – 115v 0-115v primary, 0-6v  0 -6v

You can power it with either 115 volts or 230 volts.

It allows for two 6v power settings.  The low is for most soldering that an etched brass kit builder would use. The high is for the occasional job that requires a bit more heat.

Use a FinePoint |Resistance Soldering Unit for Fine Scale modeling.

Available here.





Available as part of a kit  here.




power cordPower Cord

A 3 prong plug that fits the receptacles in your locale.





Switch x 2

One is for the unit input power and the other is to switch between high and low power.

Available as part of a kit  here.





Used for probe and ground.  These allow you to easily change to the best probe to use for your job.

Available as part of a kit  here.



Plastic Box For RSUContainer

An electrical junction box is fine.

Available as part of a kit  here.



insulating sleeveInsulating Sleeve

Things do get hot.  Cover all your internal connections.


Available as part of a kit  here.



Foot SwitchFoot Switch

Available here.




3 amp circuit breakerCircuit Breaker  3 amp

Available as part of a kit  here.



Copper Clad Carbon Rods

Carbon Rods

Available here.






Thransforer pinout


Wiring Diagram

FinePoint RSU Wiring Diagram






Making The RSU

Use internal wiring capable of 8 amp current.

Install the connectors and switch on the top of the container.

Insert the power cord into the side of the container.

After applying thermal sleeves, solder the power cord wires to the proper tabs.

Solder probe and ground jumpers to the proper tabs.

After applying thermal sleeves, solder probe and ground leads to the tabs.  Measure your wires long enough that you  will be able to open the box and turn the cover upside down.

Solder the resistor in place along with the wires that will connect to the switch.

Connect the switch, probe and ground wires.







We hope that you found the information in this page useful. The internet is all about getting and giving. And giving back is the best. Please donate $1 or more to aid us in our continuing quest to add to and polish the information in our site.

Scroll to top