Rectifier block valve testing schemes
A - checking both "positive" and "negative" valves simultaneously; B - checking "negative" valves; B - checking "positive" valves; 1 – generator; 2 – control lamp; 3 – battery
A working valve only passes current in one direction. A faulty valve may not pass current at all (chain break), or pass current in both directions (short circuit).
A short circuit of the rectifier block valves can be checked without removing the generator from the car, after disconnecting the wires from the battery and the generator. You can check with an ohmmeter or with a lamp (1–5 W, 12 V) and a battery, as shown in Fig. Schemes for checking the rectifier block valves.
Attention! In order to simplify the fastening of the rectifier parts, three valves have a "plus" of the rectified voltage on the body. These are "positive" valves and they are pressed into one plate of the rectifier block. The other three valves are "negative", have a "minus" of the rectified voltage on the body and are pressed into another plate of the rectifier block or into the generator cover.
First check if there is a short circuit in both the "positive" and "negative" valves. To do this, connect the "plus" of the battery to the "30" terminal of the generator, and the "minus" through the lamp to the generator body (see fig. Test diagrams of rectifier block valves, position A). If the lamp is on, then some of the "negative" and "positive" valves have a short circuit.
A short circuit of only the "negative" valves can be checked by connecting the "plus" of the battery to the plug of the central terminal of the stator winding (12 in the figure (see Fig. Generator G-221, this plug is unmarked), and the "minus" is through the lamp with the generator housing (see fig. Schemes for testing rectifier block valves, position B).
If the lamp is on, it means there is a short circuit in one or more "negative" valves.
It should be remembered that in this case the lamp burning may also be a consequence of the short circuit of the stator winding turns on the generator housing. However, such a malfunction occurs much less frequently than a short circuit of the valves.
To check for a short circuit only in the "positive" valves, connect the "plus" of the battery to the "30" terminal of the generator, and the "minus" through a lamp with the plug of the central terminal of the stator winding (see fig. Test diagrams of rectifier block valves, position B). The lamp lighting up will indicate a short circuit in one or more "positive" valves.
A break in the valves without disassembling the generator can be detected only indirectly when testing the generator on a bench by a significant decrease (by 20–30%) in the value of the output current compared to the nominal value.
If the generator windings are in good condition and there is no short circuit in the valves, then the reason for the decrease in the output current is a break in the valves.