Volvo Service Bulletin 3-32-11

Product Section Group No. Date Title
B 3 32 11 02.79 Alternator CAV 80 A

Supersedes SB B-3-32-11, of Dec. 77.

Wiring the regulator and shunt for the 80 Amp alternator

The regulator and shunt must be properly connected up to ensure that the alternator supplies the correct current and voltage, otherwise the alternator, regulator and shunt can be damaged. Incorrect wiring can also cause the batteries to "boil".

The shunt is a fixed resistance via which a voltage drop is obtained. This drop is registered by the regulator via M1 and M2. In this way, the regulator limits the alternator charging current to max. 80 Amps.

The following sketch shows the correct wiring.

Volvo B10M 80A alternator wiring diagram
Figure 1. Wiring diagram

The problems that have arisen have been due partly to the fact that the B- on the shunt has not been properly earthed, and partly because the cable from the alternator terminal has been connected directly to B- on the shunt. It has also happened that the M1 cable has been wired where the M2 should have been wired, and vice-versa.

If there is poor contact between B- and earth, this will bum out the shunt.

B- must, therefore, be properly earthed.

B- must be earthed directly to the chassis by means of a cable of the same area as that for the D- alternator cable.

Cables that have to be earthed in the electrical distribution box, must be wired to B- on the shunt.

The regulator will stop function entirely if the earth terminals B-/D- are mixed up on the shunt or if the M1 and M2 cables are mixed up. A regulator that does not function can result in damage to it, the alternator and batteries.

Checking the shunt calibration

It can happen in exceptional cases that the shunt is not calibrated, that is, that the resistance has not been adjusted via the drillings as shown below. This will result in the alternator supplying current in excess of 80 Amps. The higher temperature consequently generated could then damage the alternator. This applies to vehicles which have equipment that can require more than 80 Amps during long periods. In such a case, the non-calibrated shunt should be replaced by one that is calibrated.

Check to make sure that the cable terminals are correctly wired and properly tightened. Use wavy washers. Resilient washers or toothed washers must not be used.

Volvo B10M Checking the 80A alternator shunt calibration
Figure 2. Checking the calibration