MarkB Posted September 7, 2012 Share Posted September 7, 2012 Hi AllI have an alternator fitted to my Mk3 Spit and have done for the past 10 years. On tick over at about 800-900 RPM it will happily idle for a few minutes but then the revs drop to around 500 rpm as if about to stall but the engine continues to idle for a couple of minutes and then picks up again to 800-900 rpm. I initially thought this was to do with fuel air leak etc. but then it dawned on me it must be when the alternator is cutting in to charge the battery. I put a meter across the battery and without the engine running the battery is showing around 13 volts. At idle the meter reads about 14.5 volts at 800-900 rpm. When the rpm drops to 500 rpm the meter reads 17.5 volts. I am wondering if the alternator is faulty and over charging as I always thought the charge was around 14 volts. This is a new battery as the last one died after about 6 months and I put this down to lack of use as the car often stands for weeks unused. Any advice appreciated.Mark Quote Link to comment Share on other sites More sharing options...
Rich_s Posted September 7, 2012 Share Posted September 7, 2012 sounds like a duff alternator to me, my old mini did that, all of a sudden it would jump to about 17volts and the headlights went bright, was great as was in middle of sinter and driving around i could see the road for the first time :D after a few weeks though it cooked the battery so had to get a new battery and an alternator, next time i'll know to stop and change the alternator straight away.rich Quote Link to comment Share on other sites More sharing options...
RedRooster Posted September 7, 2012 Share Posted September 7, 2012 Agree duff alternator. Just gone to change mine on the 1380 & the bl**dy shaft diameter is 19/32 instead of 21/32 so the pulley doesn't fit the new alternator. Worth checking what you have before you order.RR Quote Link to comment Share on other sites More sharing options...
MarkB Posted September 7, 2012 Author Share Posted September 7, 2012 ThanksYes very bright lights, infact like day light 8). I'll change the alternator and see how it goes. RR I didn't realise you don't get a new pulley with the alternator. To be honest never bought a new one before.Mark Quote Link to comment Share on other sites More sharing options...
Rich_s Posted September 7, 2012 Share Posted September 7, 2012 some alternators you do, i did with my last 2, ask before buying as saves having to swap them over or buy new bits Quote Link to comment Share on other sites More sharing options...
junkuser Posted September 8, 2012 Share Posted September 8, 2012 Denso alternators have very reliable regulators so may be worth considering.Seems, from posts on this forum, that some Lucas not so good in this area.Over-voltage will quickly destroy the battery as Rich said.I have fitted old style Bosch alternators with external regulators to many vehicles over the years and they have never given any problems. (All old ones picked up at swaps and refurbished)Fitted a Denso to the Spitfire a year or so back, just for the heck of it, as I happened to have one in my junk from an early Cherade and had read how good they were.Mounting was simple and can be changed back to take Bosch by shuffling spacers on the original generator bracket.They do appear to be well built. Quote Link to comment Share on other sites More sharing options...
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