Manganin Shunts are widely used for energy meters, electric bicycles, cordless tools, and so on. A shunt is a precision resistor made of copper and manganin. Manganin is an alloy of typically 84% copper, 12% manganese, and 4% nickel.
Manganin is used in the manufacturing of resistors, particularly ammeter shunts, because of its low TCR (temperature coefficient of resistance) value and long term stability.
The most common manganin materials in China are 6J13 and 6J12. Accordingly, there are two kinds of shunt: 6J13 manganin shunt is precision enough for most applications, 6J12 manganin shunt is rarely chosen as the high price.
Shunts usually consist of manganin and pure copper. The copper usually used is electrolytic copper, and the model is T2. There’s no need to choose oxygen-free copper, as the purity of T2 copper is high enough. Some products, like current bar or U Type Bar needs only T2 copper.
Here we introduce the production process of a typical manganin shunt resistor as below.
Electronic Beam Welding
First, we should prepare for the material. Nowadays, some shunts are spot welded by copper and manganin, but others are made by EBW strips. EBW stands for Electronic Beam Welding. Usually, the EBW strip contains three parts: manganin strip in the middle and copper strip at the sides. As the EBW strip is not thick, rarely > 3.5 mm, we always wound the strip to make a roll. Then, it will be easy to handle and move.
Stamping
Once the material is ready, we’ll stamp them to make required parts, like EBW plates, maganin plates, or copper lugs. Although EBW manganin shunt plates are semi-products, some customers purchase them for further processing themselves. Some of Xianyu’s stamped parts can also be used as the intelligent battery sensor for cordless power tools and so on. We can also produce the shunts which serve as critical parts in the magnetic latching relays.
For pilot production, we choose simple stamp die, as the cost of tooling is low, maybe a few hundred US dollars. But there’s a drawback, i.e, the production effectiveness is not so good. So, for mass production, we always use progressive stamp dies, although it will cost more than 2000 US dollars to make a set of progressive stamp die.
Wire Cutting
For some manganin shunt resistors, not only the stamp parts, but also some wires are required. There’re two kind of wires: sampling lines, and multi strand copper wires or braided copper wires. Usually, we should use automatic cutting machines to get these wires of required length.
Sampling lines, used for small current, are welded to the sampling points of a shunt. After the welding, one kind of shunt, i.e, EBW manganin shunt resistor, which consist of an EBW shunt plate and two or three sampling lines, is finished.
Multi strand wires or braided wires are used for connecting two or more metal stamp parts. As they are flexible, we can apply such kinds of shunt to may different products. They are the main parts of neutral multi strand copper wires, which are brazed by wires and copper lugs.
Spot Welding
After the required parts are ready, we should combine them to get a final product. The method is spot welding. Then, two or more metal parts and multi strand wires were brazed together, and sampling wires were brazed to the sampling points too. As a result, we get C type shunts, primary wire shunts, terminal block shunts and so on.
Degreasing & Plating
During the process of stamping and welding, the surface of shunts is very dirty. So, the processes of cleaning, degreasing and anti-tarnishing treatment are required. After that, some shunts should be plated according to customers’ requirements. Usually, nickel, silver, and tin are the most popular material for plating of shunts. Nickel plating will protect the copper from oxidation, and make the surface very smooth. Silver plating makes the surface resistance low, as silver is the best conductor among all the metals. Tin plating is used to improve the soldering of solder points.
Resistance Value Test & Adjustment
The resistance value is the most important parameter of a shunt. So, we must test the value before packing. The resistance value of a shunt is only a few hundred micro ohms. Micro ohm is the unit equal to 0.000001 ohm, which is a really very tiny value. So, normal multimeter is not suitable. We can only get such small value by precision shunt test machine. Usually, only the tolerance of resistance value less than 5% is accepted. For some special requirements, we can make the tolerance less than 3%, or even less than 1%. If the customers want safe galvanic separation, they can choose the current transformer.
Packing & Shipment
Now, all the shunts has been tested and defected ones are removed. We’ll pack them by plastic bags, paper box or cartons. When all is ready, we’ll ship them to customers.