Alternators

<Archived> Even supercars have their flaws..
Guest

Alternators

Post by Guest » Sat Dec 07, 2002 5:58 pm

Well we all know that Exiges seem to eat alternators for breakfast and there seems to be much speculation as to why!!! Most seem to quote heat as the main reason for failure,Absolute rubish!! Having done extensive reserch on a certain X111 FLY (brothers car)which managed to kill one after just 200 miles we have found that if you use your car particuly on the track at high RPM then it won't last long!!Doing the maths of crank pulley/alternator pulley we found that at the max 8000rpm (rev limiter)the alt. is doing 23000 rpm. Having checked this against a spec sheet for it found that the max continuous rating is 18000rpm.Putting it another way if you do more than 6500rpm then your alternator is beyond is design spec. It phisicaly shakes itself to bits.Ever wondered why the ignition light goes out on cranking, because the alternator is allready up to charging speed just on the statrer motor!!!Two choices Bigger alt. pulley (guess 80mm should do it) OR smaller crank pulley.Yes we all know that it's close to the exhaust but one of the lowest of the maximum alowable temps. (See specs below) relates to the bearings in the alt. of 150 c, surely if temp is a problem then why do we not hear about bearings breaking up?? Failures of bits falling off inside, badly damaged brush tips, broken copper brush wire, broken diode leg are all far more consistant with a vibration problem!!!Max continuoes rpm: 18000 rpmDiode pack: max continuous-190 deg, max for 30 mins-200 deg.Regulator: cont-140 deg, 30 mins-150 deg.Stator windings: cont-220 deg, 30 mins-240 deg.Bearings: cont-150 deg, 30 mins-150 deg.Charge rate for 85A alt: @10000 rpm = 75A, @80000 rpm 65A, so WHY do lotus run it up to 23000 rpm???? funny that red line on your average Rover 200 is 6500ish, oh that just puts the alt upto its max!! Could it be they just bought the engines as a unit including alternator and didn't twig that they were going to run them upto 8000 rpm?? No surely not!!!Any body else have any thoughts on this???Lets try and get this expensive problem sorted once and for all.Belive me one of the first thing I'm gonna buy is a differant pulley for mine!!!!!Dave[This message has been edited by Dave Kelly (edited 07 December 2002).][This message has been edited by Dave Kelly (edited 10 December 2002).]

Guest

Re: Alternators

Post by Guest » Sat Dec 07, 2002 9:15 pm

DaveInteresting ...What I read so far about alternator failure was charging problems rather than bits falling off inside.That tends to be an diode pack/regulator etc failure rather than a bearing failure ?? and that seems to be heat related - I mean we used to fry the diode packs on road rallies becuase of the power the lights pulled !! and then no charging ( red light flickering at high revs ) - I'm sure external heat can cause the same problems ?? However have to say slowing the speed down a bit cant do any harm ...Now what about the air con compressor - I guess its not good to rev to 8K with the air con on ??

Guest

Re: Alternators

Post by Guest » Sat Dec 07, 2002 11:30 pm

It has been debated a lot in the past but due to the cost of alternators, i've seen them for �39 (http://www.sales.bestofbritishrover.bti ... /index.htm) most people just put up with it and hope for the best.The Lotus ECU will kill the air-con when full throttle is applied so it shouldn't be a problem.

Guest

Re: Alternators

Post by Guest » Sat Dec 07, 2002 11:43 pm

Miniman, PhilProbably not to good for the A/Con but it is running a much bigger pulley than alt so obviously wont't be spinning at circa 23K rpm so prob be ok.The last 2 alt failures we had was 1. Copper wire on brush broken and tips badly chipped and damaged through vibration.2. Mounting lug to which one of the legs of one of the diodes was attached to snapped off (again vibration)The first failure happend just out of warrenty and cost some �400 to replace, at that time we didn't realise there was going to be a problem so didn't get to pull it apart to find the fault.At 23K it would need some seriously carefull dynamic balancing to prevent the shakes setting in!!!Was that �39 for the alt suitable for the air con car cos they're different, �155 was the best I could get through the trade and that was for the 65amp one not the 85A one that it should be???Dave[This message has been edited by Dave Kelly (edited 07 December 2002).][This message has been edited by Dave Kelly (edited 07 December 2002).]

Guest

Re: Alternators

Post by Guest » Sat Dec 07, 2002 11:56 pm

quote:Originally posted by Dave Kelly:The first failure happend just out of warrenty and cost some �400 to replaceDaveEh? [image]ubb/NonCGI/images/icons/shocked.gif[/image]When mine went at 21K miles, I fitted a recon. unit for �85. Okay, that then packed up after 1K miles, but it was replaced FOC & is still okay after another 2K miles including 1 trackday!!!Demon Tweeks now sell uprated & lightweight alternators - have you checked these out for the Exige?

Guest

Re: Alternators

Post by Guest » Sun Dec 08, 2002 1:38 pm

Mine has lasted ONLY 4300 miles found out last week. With no track day outings !Pesky thanks I will check Demon Tweeks ?[This message has been edited by SPEEDY (edited 08 December 2002).]

Guest

Re: Alternators

Post by Guest » Sun Dec 08, 2002 9:58 pm

Last time I checked they only did one for the non air con cars, but that may have changed. Be sure to check the max rpm, most seemed to be 16000rpm.The crank pully on our cars is approx 132mm so dependant on the alt pully size work out what yours is likely to be. Brise suggested a max of around 12KDave

Guest

Re: Alternators

Post by Guest » Sun Dec 08, 2002 10:03 pm

Not sure if the �39 one is suitable as i have not had any problems yet to warrant any investigation, What is the difference between the two as i thought they were the same ?Cheers

Guest

Re: Alternators

Post by Guest » Sun Dec 08, 2002 10:18 pm

No unfortunatly they are mounted differently, the A/C is fixed and mounted up high with seperate tensioner and the non A/C lower down and has no seperate tensioner.We only found this out when Lotus Motorsport sold us a �300 unit that was reputed to cure the problem but when it came it was compleatly differant and not fittable to the A/C car. The one they sent was a Brise unit (as Demon tweeks I think) but after speaking to Brise they were very concerned about the high rpm and told us to get it down to a sensible 12K rpm.Dave

Guest

Re: Alternators

Post by Guest » Mon Dec 09, 2002 1:42 pm

I think that there is probably something in the high rpm theory, but mine went, finally, at the end a hot summer's day drive from the Midlands to the West Country. Although I was having fun, there was no way that the engine held revs over about 6500 for any length of time. The demise was accompanied by smoke in the engine bay which was what caught my eye as there was no indication of a problem through the instrument panel. The car then started and ran normally on aseries of short journeys for over 24hrs before the battery ran out of juice and I had to be recovered. A new unit was fitted by my local dealer.I had done a few track days in the car so it had received the high rev treatment in the past - perhaps it's accumulative?Funny thing is though, if it was bearing failure I would have expected colateral damage so any of Mimimans and Dave Kelly's diagnosese could have been the culprit. If Dave is right then slowing the thing down must help reduce vibration surely?Anyway, I agree with Dave - it's time Lotus came up with a solution, perhaps a replacement pulley on a general recall, to sort out this ridiculous and utterly predictable failure.Mike[This message has been edited by 83man (edited 09 December 2002).]

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