Sunday, 25 March 2012


While preparing Patience for the summer boating season, we noticed that the red warning light on the control panel was 'on' when the ignition switch was off, and vice versa. One of the potential causes of this is a failed diode in the alternator, allowing battery voltage from the battery terminal to feed back through the diode to the field coil terminal and hence to earth via the warning light and the ignition switch. Some investigation with a multimeter confirmed that this was almost certainly the problem, rather than the alternative possibility of a faulty ignition switch. A replacement alternator was bought from Unipart at a cost of £57.23 (£24 of which is refundable when the old one is returned). The first photo shows the old one on the left and the new one on the right.

The only challenge then was to transfer the pulley and fan assembly from the old alternator, as these weren't supplied with the new one. The only way of undoing the 7/8 in AF shaft nut was to use a pneumatic impact wrench, which fortunately a friend just happened to have in his very well equipped garage. With the fan and pulley transferred to the new alternator, it only remained to instal it on Patience, adjust the belt tension and check its operation. With some relief, we discovered that this had cured the problem and the new alternator seems to be working fine and charging the battery bank. The second photo shows the new alternator in place on Patience (top right).

It's just as well that we spotted the problem when we did, as the failed diode would have discharged the batteries when mooored up overnight with the main power switch on. It shows the importance of keeping an eye on the instruments and investigating anything unusual as soon as you spot it.

With the sun shining and some spare time, we took the opportunity of cleaning the domestic water system and refilling the freshly painted bow tank with about 650 litres of clean water, ready for the first cruise of the season.

No comments:

Post a Comment