Disassembling the Soviet variable resistor SP3-16V (10 photos)

Good day, friends. Today we will get acquainted with the design of the Soviet variable resistor SP3-16V. The appearance of this resistor is shown in the picture below.





Appearance of the resistor SP3-16V

Our sample belongs to the variable resistors, trimmer, non-wire shielded, small-sized. Designed to work in DC, AC and pulse current circuits. Designed for volumetric installation.

Let's try to figure out the marking of this variable resistor:

C - resistance;

P - variable;

3-16 - design - shielded small-sized for volumetric installation;

Resistance value from 0 to 1 kOhm.



Fasteners and adjusting shaft on SP3-16V

In the upper part of the SP3-16V resistor body we can see a thread on which there is a nut and a washer. These elements are used to mount the resistor in the housing of the finished product. Next, we can see the shaft, by rotating which the resistance value of this resistor is adjusted.





Three terminals of the variable resistor SP3-16V

This part has three terminals for the possibility of connecting a variable resistor as a voltage divider, as it is most often used.



SP3-16V contact assignment

SP3-16V has 3 legs (contacts). The resistance between the outer legs (1 and 2) is constant (if you look at the product marking with your face) and in this case is approximately 1 kOhm. This is the nominal resistance of this resistor. The resistance of SP3-16V between the middle (3) and outer legs (1 or 2) is variable. It changes from zero to the nominal value of 1 kOhm. In this case, the resistance between the middle and outer legs changes in antiphase. If we turn the resistor shaft all the way in one direction, the resistance between the middle (3) and right leg (2) will be zero, and between the middle (3) and left leg (1) will be the nominal 1 kOhm. If we turn the knob all the way in the other direction, everything will be exactly the opposite. If we put the knob in the middle position, the resistance between the central leg and the right leg will be approximately equal to the resistance between the central and left legs. Both resistances will be equal to half the nominal value, and in our case, this is approximately 500 Ohm.

Let's try to open the case of this resistor and see what's inside. As the name suggests, this variable resistor is not wire-wound, so we will most likely find some resistive films inside.



The base of the resistor SP3-16V with its contacts

Having opened the resistor case, in its lower part, we can see three contacts. Two of them are connected with a resistive film (As expected =)) . The third contact is highlighted.



Contacts of the resistor SP3-16V

Now let's look at the upper part of the product from the inside.



A movable contact inside the SP3-16V resistor

We can see a movable contact in it. This contact is connected to the shaft of the product, which extends beyond its housing. By rotating the shaft, we rotate this contact around the axis of the shaft on which it is fixed.



Continuing to pick at the base of the resistor

If you continue to pick at the base of this resistor, you can establish a correspondence between its terminals and internal contacts.



Variable resistor contacts



Continuing to break the resistor.

Having dismantled the base, we come to the following conclusion. The two outer contacts (1 and 2) of the resistor were connected to two contacts inside the resistor, located on its outer edge. They are constantly connected to each other by a resistive film, and the resistance value between them is not exactly and is approximately 1 kOhm. The middle contact (3) of this resistor is connected to the central internal contact. The connection of this contact to the outer contacts is carried out by a movable contact inside the resistor and a section of the resistive film that it manages to capture. The longer the length of the conductive film that gets on this circuit, the greater the resistance value between these contacts.

That's all for today. I hope you weren't bored =) Bye!