I needed a precision current shunt to calibrate a recently fixed E3631A power supply. The Agilent 34330A looks nice and is colour coordinated, but at $108 seemed a bit pricey for a resistor in a box.
![](https://ynformatics.com/wp-content/uploads/2020/09/34330A-2.png)
So let’s make a DIY clone…
For the resistor we use an SMD Current Sense Resistor, 0.001 ohm, CSS2H-2512 Series, 2512 [6432 Metric], 5 W, ± 1%. This will give the required 1 mV/A response and can cope with a 30 A current.
![](https://ynformatics.com/wp-content/uploads/2020/09/R001-300x172.png)
A small PCB was cut from a piece of copper clad FR4. The holes are 19.2 mm apart as this is a commonly used binding post separation. Care should be taken to route the sense connections as close to the ends of the resistor as possible.
![](https://ynformatics.com/wp-content/uploads/2020/09/pcb2-300x129.png)
![](https://ynformatics.com/wp-content/uploads/2020/09/IMG_20200906_113237-scaled-e1599396455629-150x150.jpg)
The resistor and sense leads were soldered on
![](https://ynformatics.com/wp-content/uploads/2020/09/IMG_20200906_115039-1-150x150.jpg)
Mounted in a 3D printed box with banana sockets and plugs
![](https://ynformatics.com/wp-content/uploads/2020/09/IMG_20200906_132126-150x150.jpg)
Here is the shunt under test showing we are within 1% tolerance.
![](https://ynformatics.com/wp-content/uploads/2020/09/IMG_20200906_121035-150x150.jpg)
A couple of lessons learned:
- If any solder gets on the resistive part of the resistor it will reduce the resistance!
- The sense connections must be connected as close to the ends of the resistor as possible. A few extra micro-ohms will exceed the tolerance.