Lotus Elan

Alternator Woes

PostPost by: type26owner » Tue Aug 17, 2004 1:02 am

Well I've done two trackdays now and have managed to kill an alternator after both either that same day or the very next. Usually try to raise the bonnet to let things cooldown after each track session but tend to forget allot. Been using a 3" diameter vee belt drive pulley on the alternator and suspect that it might be spinning up the rotor a tad too much. Normally shift at 6k rpms since my engine seems to fall off in torque by then. What pulley diameter are other folks using on the track assuming you're not using a total loss electrics system? The alternator is a Bosch 65 amp.
-Keith
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PostPost by: john.p.clegg » Tue Aug 17, 2004 10:07 am

Keith
Do you need an alternater driven during the race,couldn't you refit a shorter belt just for the duration of the race?
John
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PostPost by: type26owner » Tue Aug 17, 2004 1:59 pm

Hi John,
I'm actually not racing. Just high speed driving but obeying the strict passing rules. Getting in the better part of 30 minutes of driving at a time with a break of 30 minutes while the second group is out on the track. Lasted 3-1/4 sessions last time before breaking the motor mount and managed to get in 100 miles mostly at speed though. For the very first time was pleased to only get 12 miles per gallon with 92 octane. :D

Not spinning the alternator at all by fitting a shorter belt would be an option and if I had enough room to remove the waterpump pulley to install the belt. The dual electric fan shrouds mounted on the downstream side of the radiator both just clear the pulley by about 1/4" only. By gently tugging on the top of the radiator to pivot it forward I can just pass a fanbelt through the slightly wider gap. Afraid that would require draining the cooling water and removing the radiator each time to install a shorter belt between the crankshaft and waterpump pulleys. Would REALLY prefer to solve this by some other means. Going to install a 4" diameter pulley on the alternator this time instead of the 3" one I've been using. Maybe underdriving the alternator is the fix needed. Surprising since most alternators are rated to 12k rpms supposedly from what I've read.

Wondering if an air deflector scoop added under the alternator area to direct ambient air up towards the rear of the alternator would help cool it down a bit more. Took the alternator in for repairs and have not gotten it back yet so I don't know if it was heat damaged or not.
-Keith
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PostPost by: type26owner » Mon Sep 06, 2004 7:24 pm

Fabricated and installed an aluminum air deflector which sticks down below the chassis vacuum tank by about 1-1/2". This should force feed air to the rearend of the alternator so it will inhale only the coolest air possible. Maybe the volt regulator will last a bit longer when subjected to the maximum heat load from doing a trackday. It'll get tested again soon. :rolleyes:

Also fabricated a larger 4" diameter drive pulley for the alternator to keep it under 10k rpms. Only real danger I've been told from spinning it up too high is having the rotor or fan explode from the centrifical forces.
-Keith
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PostPost by: rgh0 » Tue Sep 07, 2004 1:11 am

Keith

I run a 3 inch pulley on the crank shaft and a Lucas 18 ACR alternator. The same as Lotus originally fitted to later S4's, sprints and plus 2's. This has a 3 inch pulley also. It spins at engine speed of up to 8000 rpm and I have never had any problems.

I also have a heat shield clamped to the front of the exhaust headers as 2 of my pipes run in front of the engine mount and very close to the alternator. This shield protects the alternator from the exhaust radiant heat as well as ensuring the air sucked through the alternator comes from the front of the engine and has not been heated by the headers.

I also modified the alternator so that the connection wires come out the side and not the back so they dont get fried. It also make access to them much easier with fwer burnt fingers, especially if the exhaust is hot

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PostPost by: khamai » Tue Sep 07, 2004 1:29 am

Keith,
My guess is that with the rad shrouds is that headers are cooking it.
Your air deflector or ducting of some sort should help. A shield as suggested is a good idea as well.
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PostPost by: type26owner » Tue Sep 07, 2004 3:44 am

Rohan,
IIRC, my crank pulley is 4.6" in diameter. So I'm turning the water pump and alternator 1.5 times faster than you are. Don't know if that is actually all that bad or not to be truthful. Just know that what has been case in the past kills the alternator.

Assuming I understand correctly are you sure about the inlet air side of the alternator being on the upstream end? Very rare for the flow to be moved downstream through any alternator. The twincam is a left-handed (cw) turning engine so chances are if you examine the fan closely it will be appear to have the vanes pointing backwards if that were true. I was dumbfounded when I realized this the first time. The heat sensitive components like the diodes and the volt regulator are located on the downstream end so they suck the cool air through the housing so it flows upstream to keep that stuff as cool as possible. Makes good sense when one thinks about it but it's not intuitive at all. Unfortunately the alternator is also downstream of the radiator so is bathed in it's warm exhausting air. Not much I can do about that though.

Kiyoshi,
Got the best thermal shield I can buy in place already. It's one of those starter heat shields made out of heavy fiberglass woven cloth which is aluminumized so the emissivity is close to zero. It's doubled up to boot so it's two plys. That only helps to reflect the directly radiated heat though. Any convection or air driven heat will go right around the shielding. Hoping my new air deflector will blow that hot air away from the downstream end of the alternator from now on. It'll get tested at the track soon enough.
Regards,
-Keith
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PostPost by: rgh0 » Tue Sep 07, 2004 8:57 am

Keith

I think you misinterpreted my comments about the air coming from the front.

The Lucas alternator as with all others I have seen has a centrifugal rotor on the front that sucks air out of the front of the alternator. Thus the air flows through the alternator from the rear to the front.

The shield I have installed behind the alternator between it and the headers ensures that air sucked in the rear of the alternator has not come from the header area but is air that has flowed from the front of the motor. Heated by the radiator a few degrees but a lot less than if it had come from around the headers. However I think the protection of the alternator electronics from the header radiant heat is the most critical element. My shield is sheet metal covered both sides with the aluminum faced fibreglass heat shield material.

If you are running a 6500 rpm motor then I dont think its speed that is killing the altenator and a bigger alternator pulley is probably not required. I use the smaller crank pulley to keep the maximum operating speed of both the water pump and alternator near their orginal design maximum of around 6500 rpm for the water pump and 8500 rpm for the alternator when I rev the motor to 8500 rpm.

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PostPost by: type26owner » Tue Sep 07, 2004 3:09 pm

Rohan,
Thus the air flows through the alternator from the rear to the front.

OK, good stuff, we're on the same page afterall. Sorry, my mistake. Surprising how few people are cognizant of that fact about the actual airflow direction. BTW, I started using the Bosch after having having frequent failures with the Lucas unit.

Normally would only do a single modification at a time to the alternator but realized I was spinning my plastic alternator fan a little to fast at 10k rpms and I got nervous. So I slowed it down to 8k rpms by adding the larger pulley. Prefer the plastic fan because with the dipstick along side it's a just (tight) fit. Had an interference at one time with a steel fan and had shower of sparks and had to replace the dipstick. Most driving is 25 mile spurts so the reduced charging rate should not be a problem.

I should stick on one of those temperature strips on the back of the alternator and measure the highest value. Hey, just remembered I bought a cheap digital probe the other day for measuring the engine oil and tire temperatures and could use it there too.
-Keith
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PostPost by: rgh0 » Wed Sep 08, 2004 1:16 am

keith

Your sensible to run a Bosch alternator. I run one on my plus 2 road car for the same reliability reasons.

I only run the Lucas alternator on my Elan as it is a Lotus original setup and the historic racing people here sometimes get fussy if you change components from the original. Also the big cast Ford bracket that matches the Lucas alternator includes a reinforcing arm up the side of the block and is good for a high revving engine as they suffer from vibration problems without a strong rigid mount at around 8000 rpm.

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PostPost by: type26owner » Fri Sep 10, 2004 1:36 pm

Rohan,
My clutch has been slipping lately at WOT so I pulled the engine out yesterday for repairs. Discovered the clutch was slightly wet with engine oil but nothing else was worn out or amiss. New crankshaft seals got installed front and rear.

Hey, to my surprise I found the the front pulley is actually only 4" in diameter. Now all three pulleys are the same size. Electrical system behaves the same as far as I can tell. At idle it would always quit charging but by 2k rpms it kicks back in and indicates 14.5 volts.
-Keith
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PostPost by: type26owner » Thu Sep 16, 2004 1:47 pm

Well my alternator survived the trackday this time. Never had it run so cool before. Cool enough so I could touch it and have no discomfort what so ever after 10 seconds. Didn't bother measuring it but am guessing it reached maybe 50C tops which is probably about the exhaust temperature of the radiator. Made a little change to the heat shielding which I think helped some. Velcroed it onto the top of the alternator housing like usual and for the first time also to the top of the engine mount. This kept the air cooling openings at the rear of the alternator from being obstructed in anyway. Suspect by leaving it draped loosely down between the alternator rear and the engine mount it was flapping around from turbulence and actually impeding the cool air supply from below. At least I can check off another annoying item from my to-do-list.
-Keith
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PostPost by: davidholroyd » Fri Oct 15, 2004 1:34 pm

big pully .. drop its speed .. i rev mine to 8 all the time on tarmac stage rallies for hours at a time and with a big pully no problem with a standard alternator .... this i was told to do by arron electrics ... leeds ... they gave me the bigger pully free with the rebuilt alternator.
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