MGCC - News (August 96)

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In a recent issue of Safety Fast, reader described the conversion of his Magnette to negative earth and the substitution of an alternator for the dynamo. Whilst this is admirable, I would caution on the ad hoc fitting of alternators as follows:

The change to an alternator provides an increased power output over the 22 amps of the dynamo and heavier cable must be provided. The common ACR output termination is two 0.375 inch blades, of the same polarity, each rated at 35 amps. It may be easier to add a second cable to carry the extra current. This must connect to the battery, or usually the solenoid, via the ammeter. A 28/0.30 mm cable is rated at 17.5 amps. Solder all connectors. Secure the output cables within 6 inches of the alternator to prevent movement. This will spring clip to secure the plug if fitted.

An alternator can provide greater output at lower engine speeds, but only if the pulley ratio is corrected. Maximum speed for a dynamo (Lucas C40) is 10,500 rpm and that for an ACR alternator is 15,000 rpm. A notched vee-belt may be needed to provide enough wrap-around to prevent slippage. Avoid over-tightening the belt, it will only bottom in the vee and the alternator bearings will suffer. Use a premium quality belt. Make sure that the new pulley aligns with crankshaft pulley or the belt will wear rapidly. Don't use a riveted pulley from a dynamo as it will not take the 5 HP needed to drive an alternator at maximum speed and full output!

The ACR alternator has machined faces inboard on the front bracket against which the engine bracketry is intended to fit. The rear bracket has a sliding bush which is normally set in manufacture but may be tapped gently into position to give a snug fit when the unit is offered to the engine brackets. It should not be pulled into position by tightening the bolts as this may fracture the thinner front bracket. Use flat steel washers to protect the aluminium brackets when fitting the nuts and bolts. Ensure that the adjusting strap is flat. Thick ones may have a curved cross- section due to poor manufacture and this can cause bracket failure on tightening. The correct mounting bolt torque is 9 lbs/ft.

There is more to it than you may think!

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