burning alternator,landrover disco 300tdi

Grrr..... I was wondering if the aircon relay(s) are blowing the charge-lamp circuit.... If smoke is from the back, is it the regulator? Diodes would tend to blow fast (not continuously smoke). But overheating windings would smoke and be fanned out the back. However, standard alternators should be self-limiting with respect to stator overloads. (And regulators should not melt rotor windings.) Besides, what load does an air-con add... not much? Clutches were ~5A which is less than headlights. And the fan(s) shouldn't be too big (whether internal circulation, and radiator booster if fitted). But - the charge lamp circuit.... The charge lamp circuit has 2 modes of operation. First is with IGN on, a "tickle" current flows through the charge lamp & thru the rotor to ensure it is magnetised. The engine then starts and the alternator starts generating. The 2nd mode is when the charge-lamp circuit - aka the "L" terminal on multi-wire systems, or "D+" terminal on single wire systems - becomes a +12V source.     [ The L circuit can be thought of as a change-over (SPDT) relay. The normally closed contact (#87a) is ground, hence L (#30) is ground when the alternator is NOT charging - ie, engine off. IGN +12V is supplied to the charge lamp whose other side is connected to the #30 relay terminal and hence grounded and lit. When the alternator outputs 12V, the "L-circuit relay" energises and flips over to normally open contact (#87) which is connected to +12V. If the alternator stops charging, the L-relay is de-energised, hence grounding and lighting the charge lamp... ] Hence +12V or ground must never be directly connected to the L or D+ terminal - they must always be through some resistance that the L-circuit can handle. IOW, the current must be limited by lamp/s or other relay coils, etc. IE - don't supply raw +12V to the grounded L terminal, nor ground to the +12V L-terminal. Part 2: The L-circuit is often used for other things. EG - older cars used it to control electric fuel pump (so that if the engine stalled, the fuel delivery ceased). Same for fuel stop valves, though these generally applied to carburetted vehicles only. (EFI pumps are (usually) controlled by the ECU.) On newer cars, the L-circuit is often used as a "engine running" signal. This can be used in air-conditioning circuits. Air-cons also often have a cranking interlock - ie, the air-con is normally powered by a NC contact which opens if the starter-motor is cranking. (Often the "starter relay" - the crank/start switch actuates a relay which has 2 circuits: one NC that has the air-con (clutch) feed, and one NO that connects to the starter motor solenoid. So cranking hence supplies power to the starter motor solenoid and breaks power to the air-con.) It is not unknown for these other circuits to be mis-wired. (I was recently across a problem where someone substituted a dual-pole starter relay for an ordinary relay. I don't think they ever understood that the air con is NOT on when that relay is on!) Mis-wiring can mean that the L-circuit is effectively shorted to ground (eg, via the starter solenoid etc), hence SMOKE. Alas I leave you not with a solution, merely a nice simple explanation of complexities of OTHER vehicle controls & wiring. (Yes, I am a bustard!) But I'll try to investigate further (yes - those alternator models ring a bell...). Give me a kick if I seem to delay or forget. Meanwhile, maybe some other checks can be done... Any other wiring changes? Seized relays? Maybe start the engine, then disconnect the L circuit, the turn on the air-con. Mind you, that assumes the alternator still charges without the L circuit (most do, but some don't), and that only the L can be disconnected (some still require other wires to be connected - eg, "S" = Sense to the battery to stop the alternator going high-voltage (though many are limited to ~15.5V anyhow), or the I or Ig terminal for Ign +12V for the regulator).

Yes, I agree that I cant see that aircon makes the load that much more,its simply the 2 facts that a) heavier duty,highe amperage alternators are fitted to aircon cars,and b) thata when the trouble started. There was a little chatter as the air con comp clutch came on but that was a few seconds and cured itself.It was 3 or 4 minutes later that I noticed a burning smell,I thought it was oil burning off the manifold since the head had been on and off,then I noticed smoke from the BACK of the alternator,increasing rapidly.All the rest I have already said. Thanks for getting onto this mate,you are always a suprb source of help. The alt is a magnetti marelli 63340004 high output unit,used on loads of stuff,basically a version of the lucas A127 classic,but is different in that it has stud connectors and a straight through shaft (rather than a cup end bearing) with the brushes outside the bearing.Lots of people advertise the repair kits for the lucas and SAY they will fit a marelli but when cornered admit that they wont.The repair kits that dont actually exist go about £20 whereas the one that does is £78 +VAT+P&P.....I can buy a new one with a years warrantee for under a hundred delivered ! I am off shortly to take the burner off the landrover and put my spare one on,hoping that there isnt a vehicle or battery fault that caused this. If it turns out that it IS the above, I will have 2 to repair and lots more work. I will update as possible. shirker PS is it possible that a old battery could cause this ? One that charges OK and hold that charge...and starts the vehicle ? Is it ? And how ?

NO,no wiring changes at all. The only extra is the caravan tow & split charge system that I have the fuses out of....and anyway they were put in long ago and were always fine.

Put another , identical, marelli 63340004 high output alternator on the vehicle , same battery....no problems. Drove the car around,put lots of electrics on ,though not the aircon,(!) and all seems fine.So far. The unit that came off : had the plastic back cover off for a quick look and cant see any obvious signs of any burnmarks , the brushes and ring look OK. However,the front bearing is squeaking with just hand spinning so I would think that it would not be happy at speed. Have been quoted £25 +,+,+ for bearings but since most alts. use washing machine bearings I will source one elsewhere. Thats as far as it goes for now !

Thank goodness for that. But simply put, washing machine motor = alternator!!

Indeed,both multi pole three phase devices....must look at the mountings sometime ! A washing machine motor with the right controller would seem to be a good replacent for the motor in my bandsaw that runs WAY too fast for metal cutting,which is what I need it for. I shall update as the recalcitrant machine gives up its secrets