Flat Eric Posted June 25, 2005 Share Posted June 25, 2005 Flipping Fan belt. Turns belt upside down. Have checked that it is alligned. Think problem is alternator is spining too fast. Having looked at vauxhalls which are running this alternator, their crank pulley is a relatively small size. However on my V8 crank pulley is 150mm (previously 170mm) with the alternator pulley of 58mm Ratio of 2.59 :1 Which means when I hit 6,200 revs - alternator is spinning at 16,058 revs Think this excessive speed is causing belt to flip, what is an acceptable speed for alternator to run at. (I have 2 other alternator pulleys 100mm (reduces speed to 9,300 rpm) + 133mm (reduces speed to 7365 rpm) Which is most suitable Quote Link to comment Share on other sites More sharing options...
pistonbroke Posted June 25, 2005 Share Posted June 25, 2005 AFAICR altinators are good for c 10,000 rpm plus will comfortably run up to 20k intermittant not sure with ratios as this needs to be matched to the A/C power curve of your own unit Usual around 3:1 ratios for road cars ? Quote Link to comment Share on other sites More sharing options...
Flat Eric Posted June 26, 2005 Author Share Posted June 26, 2005 Perhaps another way of looking at it is, at what speed will will a 1.3 Charade alternator start charging. Idle speed is at 900 rpm Alternator speed with car running at idle 2,331 rpm (58mm) 1,350 rpm (100mm) 1,015 rpm (133mm) Quote Link to comment Share on other sites More sharing options...
Kevin Wood Posted June 26, 2005 Share Posted June 26, 2005 Perhaps another way of looking at it is, at what speed will will a 1.3 Charade alternator start charging. Idle speed is at 900 rpm There's an easy way to find out. Turn on a bit of electrical load (e.g. headlights, fan). Put a voltmeter across the battery terminals, start the engine. Wind the idle speed down as low as it will run and give it a minute or two for the voltage to stabilise. You'll need to see about 13v for the alternator to hold its own, and 13.8 - 14.4v for it to be charging the battery. If this isn't satisfied at a slow idle increase the rpm until you see the above voltages. Having found the RPM the alternator needs, calculate new RPM values based on the ratios between the different wheels. You really want the voltage to be within the 13.8 - 14.4 range at your normal cruising RPM so the battery is being charged well. It's probably not going to cause you an issue if it then drops to 13 or so at idle. The alternator is still powering the electrics but just doesn't have anything in reserve to charge the battery. Also bear in mind that the alternator must start up by "self exciting" . This means it will need a few RPM before the warning light goes out and it starts to charge, so a blip of the throttle may be required on start-up. If the ignition light comes on at idle when it has previously been charging you have gone too far and the alternator has stopped providing any power. Sit in traffic for a while with the fan running and it will deplete the battery. HTH Kevin Quote Link to comment Share on other sites More sharing options...
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