Alternator System Modifications

Over the last year or so, our domestic alternator system has not been causing problems but it has been irksome. In the mornings after the three “leisure” batteries have spent the night supplying power to the fridge, TV and the rest of our modern paraphernalia, the engine sensing battery management system, the Adverc, makes sure the batteries get charged up rapidly and uses high current. The drive system is similar to that found on many classic-engine boats. It consists of a large drive wheel (330 mm diameter) mounted on the main crankshaft driving a 60 mm diameter pulley mounted on the alternator driven through two V-belts. This used not to cause difficulties but recently, despite new drive belts, we have become aware of “early morning drive belt squeal”. Looking at the system we operate a couple of points came to mind.

Original Domestic Alternator System

The first point that occurred to me was that looking at drive pulley the gap between the two belts on the drive pulley was closer than on the alternator (3 mm and 6.5 mm respectively) so the alternator belts were misaligned. Secondly, the contact area on the alternator pulley was small, particularly since the centres of the two pulleys were quite close together (200 mm). This contact area is, I gather this is known as wrap around. The drive ratio of the pulleys was 5.5 so at modest canal cruising speed (say 550 rpm) the alternator should have been working at around 3,000 rpm which is considered optimum.

I decided to contact the helpful people at Adverc about the issue. When I described the system the size of the alternator mounted pulley caused a sharp intake of breath at the other end of the phone with the comment that it is small pulley and your wrap around (or lack of it) may the problem. The upshot was I arranged through Adverc to get a new alternator pulley manufactured. It has a larger (75 mm diameter) and with the appropriate gap between the belts (3 mm). Adverc were able to ensure it was manufactured with the correct profile for the belts and shaft specification to fit the 90 A Bosch alternator. The new pulley design was intended to increase wrap, remove the belt alignment problem, and reduce the drive ratio of the system. This would of course reduce the speed of the alternator (to around 2,500 rpm) and that would marginally decrease alternator performance although within the acceptable range. The changes would also reduce the load on the system and the engine, again reducing the chance of belt slip. I must point out in all these considerations I did not want to make a new large pulley or to change the position of the alternator.

Putting the theory into practice meant removing the old pulley and replacing it with the new. This meant removing the alternator from its mounting because it was not possible to remove the pulley with the alternator in place. The nut holding on the pulley was set back in a tight recess and, although there was a helpful Allen key slot to restrain the shaft, it was impossible to put an Allen key on the shaft and use a ring spanner on the nut. There was only sufficient clearance in the pulley for a simple socket and meant an Allen key couldn't be used. I called in at by favourite garage in Milton Keynes (Arden Park Garage) with the alternator and they took one look at said “we use a special tool”. Half-an-hour later, they fitted me in between jobs, I had the new pulley mounted on the alternator.

New Domestic Alternator System

On Sunday, I fitted the new system and over the last couple of days I have been testing it out. So far there has been no evidence of the “early morning” belt squeal and the charging rate after the overnight battery drain is a very reasonable 45 – 50 A. The wrap angle is a respectable 120 degress - I understand that 100 degrees is considered the minimum. Unfortunately I didn't measure the original wrap angle but I doubt if it approached 100 degrees.

I am pleased how the job went. Let’s hope the new arrangement remains reliable. I am also pleased with the personal touch I got from both Adverc and Arden Park Garages.