DIY Interturn short circuit tester for anchor or stator of electric motors

With this simple tester, you can find an interturn short circuit in the anchor or stator of an electric motor, even if one turn in the windings is shorted.

A transmitter is assembled on the VT1 transistor, a receiver on VT2, a detector on the diode, and a signaling device on VT3-5. Coils L1-L2 are in the same plane at a distance of 3 cm from each other and are well fixed. If you bring the anchor with a closed turn to these coils from the side, the LEDs will switch and show in which groove the coil with a closed turn is wound.

Coils L1-L2 are wound on ferrite dumbbells 10 mm long with an unknown ferrite. You can wind the coils on the dumbbells that you have, the magnetic permeability of the ferrite can be different. I took ready-made chokes. Choke L1 with an inductance of about 990 μH, L2 - 9.8 mH, a difference of ten times. This inductance can be different, there is no clear data on these coils here. The transmitter coil must emit a signal of sufficient strength, and the receiver coil must also receive it with sufficient strength. A diode of the 1n4148 type can be used, etc., but the voltage drop on silicon will be greater. It is advisable to use transistors VT2 and VT3 with a high gain.The device can be tested, adjusted and configured in a cascade by surface mounting. First, you need to assemble a signaling device on transistors VT3-5 and a diode. The anode of the diode is not connected anywhere. When power is supplied, the LED on the right according to the diagram lights up. Touch the anode of the diode and the power plus with your finger, the LEDs will switch, the transistor VT5 will be open by the closed transistor VT4.

The transmitter on VT1 can be checked with a long-wave radio receiver; by bringing the receiver to the L1 coil, the hissing will be quieter. This is a generator of a sinusoidal signal with a frequency of approximately 30-35 kHz and a peak-to-peak amplitude of about 8 volts.

The device is adjusted by the trimmer resistor R4. The operating mode can be set in different ways. If you check closed turns without a core, then you need to make sure that the LED on the right side of the diagram initially lights up. Bring one closed turn to the coils L1-L2, the device will respond by switching the LEDs. If you check closed turns with a magnetic circuit, that is, an anchor or stator, you need to set the LED glow on the left side of the diagram with a resistor, and the LED on the right side should not light up

Now, slowly rotating the anchor near the coils, you can find the short circuit of the turns in the anchor. When the turn is closed, the LED on the right will go out, and the left one will light up. In this case, you can determine in which slot the winding with the closed turn passes. Since the winding passes through two slots, the LED on the left will light up twice.