Ok I give in..!!

Peter B · 08-21-2006, 05:36 AM

Hi I'm new here. Looks a very interesting and helpful place to be. I need HELP with this one.........

I have a Lucas alternator which has suddenly stopped self-exciting. I put the ignition on, charge warning lamp comes on, start the engine, alternator spins up but the charge warning lamp stays on. I can kick start the alternator by momentarily shorting the + terminal to the IND terminal which I think gives a quick kick of rotor current to start the alternator output, after which it's self sustaining. The alternator then charges normally giving 13.8 volts across the battery.

I've struggled with this for days and drawn a complete blank on why this is happening. I've changed the charge warning lamp several times, trying different wattages from 2 watts to 5 watts - makes no difference. I've even tried to eliminate wiring by making up jumper leads, one with a warning lamp in it, and wiring the alternator directly to the battery - makes no difference.

But here's the killer. My son-in-law has an MG Midget with exactly the same alternator in it, and if I swap them over my alternator works in the MG, but the MG one doesn't work on my engine. So it's not the alternator.

Any thoughts would be most welcome.

Thanks
Peter

Volt-Schwibe · 08-21-2006, 06:20 AM

ok here's my best shot...

do you have any idea if there is a difference in pully sizes across the two motors? i wonder if your car just isn't getting it spinning fast enough. possibly rev it around 2000 rpm and see if it kicks in from that.

also, the only other thing i can wonder, is if there is a ground problem. when you did your tests with the jumper leads, did you connect one for ground also?

Peter B · 08-21-2006, 09:42 AM

Hi, Thanks for your suggestions. The pulleys look about the same size - I haven't measured them, but there's not much in it.

I can rev the engine as fast as I like but the Lucas still won't self-excite. With the jump leads all I did was remove all the original wiring from the alternator, I pulled the small connector off the IND terminal and the large connector off the + terminal. Then I put a jump lead with a 3 watt filament bulb in it from the small IND terminal direct to battery positive, and another jump lead from the + terminal again direct to the battery positive. Ground was made through the alternator case to battery negative as normal. It behaved exactly the same - my jump lead 3 watt bulb lit up as soon as I conencted it, and when the engine spun the alternator up it stayed lit and the battery voltage stayed at 12.3 volts, but when I dabbed the + terminal to the IND terminal with a screwdriver blade the bulb went out instantly and the alternator started charging normally giving 14 volts across the battery.

I should say that I'm an electronics engineer, so I know pretty well what goes on inside an alternator, but I'm completely lost on this one !!

Anyway, just in case it's some quirk of Lucas alternatrors on my engine I've managed to borrow a Bosch alternator to try. It does have a noticably smaller pully on than the Lucas, so it should spin faster too. I'll swap them over tomorrow and it'll be interesting to see what happens.

Thanks again for your thoughts on it.

Cheers
Peter

**Midnight Tech** · 08-21-2006, 07:22 PM

Bad regulator, perhaps?

Peter B · 08-22-2006, 03:15 AM

OK. Got up early today. Put the Bosch alternator on and guess what - worked fine. So it looks like I'm in the market for a Bosch alternator, since the one I have is only borrowed.

Still can't figure out why the Lucas doesn't self excite though, except that the chap in the Lucas shop, (I'm lucky to have a Lucas distributor in the next town), did tell me that Lucas alternators, especially the older ones, don't have good self excitation properties and that they need a real hard kick of rotor current to get them going. But doing a bit of reading up on Bosch alternators I see that the modern ones, which is what I borrowed, are reported to have very good self excitation properties. So that might explain it.

Anyway, problem solved. Thanks for your thoughts on it, but one thing's for sure .... I know a heck of a lot more about alternators now than I did a couple of weeks ago!!

PB

08-21-2006, 05:36 AM	#1 (permalink)
Peter B Registered User Join Date: Aug 2006 Location: Cornwall, UK Posts: 3 OS: XP	Ok I give in..!! Hi I'm new here. Looks a very interesting and helpful place to be. I need HELP with this one......... I have a Lucas alternator which has suddenly stopped self-exciting. I put the ignition on, charge warning lamp comes on, start the engine, alternator spins up but the charge warning lamp stays on. I can kick start the alternator by momentarily shorting the + terminal to the IND terminal which I think gives a quick kick of rotor current to start the alternator output, after which it's self sustaining. The alternator then charges normally giving 13.8 volts across the battery. I've struggled with this for days and drawn a complete blank on why this is happening. I've changed the charge warning lamp several times, trying different wattages from 2 watts to 5 watts - makes no difference. I've even tried to eliminate wiring by making up jumper leads, one with a warning lamp in it, and wiring the alternator directly to the battery - makes no difference. But here's the killer. My son-in-law has an MG Midget with exactly the same alternator in it, and if I swap them over my alternator works in the MG, but the MG one doesn't work on my engine. So it's not the alternator. Any thoughts would be most welcome. Thanks Peter

08-21-2006, 06:20 AM	#2 (permalink)
Volt-Schwibe Asst. Manager, Automotive Forums; HJT Trainee Join Date: Jan 2003 Location: Behind you, watching you as you type. Posts: 7,372 OS: Click "My System" to view details My System	ok here's my best shot... do you have any idea if there is a difference in pully sizes across the two motors? i wonder if your car just isn't getting it spinning fast enough. possibly rev it around 2000 rpm and see if it kicks in from that. also, the only other thing i can wonder, is if there is a ground problem. when you did your tests with the jumper leads, did you connect one for ground also? __________________ <signature> TSF is funded by our Admin's pocket, care to help? Power Tip: Subscribe to your thread (Thread Tools) to receive an instant email notification when you get a reply. New Members: Creating a single new thread in the correct section is the best way to assure your thread will receive a reply. </signature>

08-21-2006, 07:22 PM	#4 (permalink)
Midnight Tech Admin/Head GreaseMonkey/Igor's alter ego/Grand Exalted PoohBah Join Date: Dec 2001 Location: SC Posts: 2,924 OS: Windows XP Home/Pro SP3/Windows 98SE/Fedora Core 6/RH 7.2 with Autopoint/TAMS II	Bad regulator, perhaps? __________________ Please post all questions in the appropriate forum. Questions sent by email or PM will not be answered. Sharing my life...with my Imzadi! Interested in Trek gaming? Check out the Dynaverse! Proud supporter of the Carolinas Aviation Museum. If we have helped you in any way, please donate to keep TSF up and running!

08-22-2006, 03:15 AM	#5 (permalink)
Peter B Registered User Join Date: Aug 2006 Location: Cornwall, UK Posts: 3 OS: XP	Bosch to the rescue! OK. Got up early today. Put the Bosch alternator on and guess what - worked fine. So it looks like I'm in the market for a Bosch alternator, since the one I have is only borrowed. Still can't figure out why the Lucas doesn't self excite though, except that the chap in the Lucas shop, (I'm lucky to have a Lucas distributor in the next town), did tell me that Lucas alternators, especially the older ones, don't have good self excitation properties and that they need a real hard kick of rotor current to get them going. But doing a bit of reading up on Bosch alternators I see that the modern ones, which is what I borrowed, are reported to have very good self excitation properties. So that might explain it. Anyway, problem solved. Thanks for your thoughts on it, but one thing's for sure .... I know a heck of a lot more about alternators now than I did a couple of weeks ago!! PB Last edited by Peter B; 08-22-2006 at 03:20 AM.

08-21-2006, 09:42 AM	#3 (permalink)
Peter B Registered User Join Date: Aug 2006 Location: Cornwall, UK Posts: 3 OS: XP	Hi, Thanks for your suggestions. The pulleys look about the same size - I haven't measured them, but there's not much in it. I can rev the engine as fast as I like but the Lucas still won't self-excite. With the jump leads all I did was remove all the original wiring from the alternator, I pulled the small connector off the IND terminal and the large connector off the + terminal. Then I put a jump lead with a 3 watt filament bulb in it from the small IND terminal direct to battery positive, and another jump lead from the + terminal again direct to the battery positive. Ground was made through the alternator case to battery negative as normal. It behaved exactly the same - my jump lead 3 watt bulb lit up as soon as I conencted it, and when the engine spun the alternator up it stayed lit and the battery voltage stayed at 12.3 volts, but when I dabbed the + terminal to the IND terminal with a screwdriver blade the bulb went out instantly and the alternator started charging normally giving 14 volts across the battery. I should say that I'm an electronics engineer, so I know pretty well what goes on inside an alternator, but I'm completely lost on this one !! Anyway, just in case it's some quirk of Lucas alternatrors on my engine I've managed to borrow a Bosch alternator to try. It does have a noticably smaller pully on than the Lucas, so it should spin faster too. I'll swap them over tomorrow and it'll be interesting to see what happens. Thanks again for your thoughts on it. Cheers Peter