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What are the odds of 4 alternators being defective?

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macgregw Greg Williams
Boyertown, PA, USA   USA
Hi all, I feel like we’re chasing a ghost here... any insights are welcome! Driving home in my ‘74 TR6 after having LiteZupp LED lights installed by a reputable LBC mechanic, I noticed my volt meter spiked all the way to the right. Checking voltage at the battery confirmed 16 volts being charged (no switches were on, just my electric fan running). Sure sounds like the voltage regulator is bad in my 2 yr. old refurbished Lucas 43 amp alternator (3-wire plug), right?

I unplugged the alternator and drove it back to my mechanic (only a 15 min. drive) to have it replaced. They had 4 refurbished alternators on hand. The 1st was installed and we checked the voltage at the battery with the engine running (& briefly revved). 11.99 volts, so not charging. Same thing with the next 3 alternators. The mechanic checked everything possible (wires, plug connections etc.), except for testing the alternators on a bench. We even reinstalled my alternator, which also showed no charge. As a side note, all lights, switches etc. are working.

I should mention that the mechanic has been sorting out electrical issues on LBC cars for 30+ yrs. and is an electrical engineer by trade. He’s stumped. I guess it’s possible that all 4 alternators are bad, but what are the odds of that? I’m taking the car back in next week so he has time to try to figure this out. Just hoping that maybe someone on this forum has had a similar experience and can help us get to the bottom of this!

Thanks for any input,
- Greg

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kansanbrit Avatar
kansanbrit Phil H
Bonner Springs, KS, USA   USA
1952 MG D-Type Midget
1964 Morris Mini-Minor
1980 Triumph TR8
1980 Triumph TR8 "TR8 Holley"    & more
Very unlikely to be all bad. What is the ignition light doing? They won't charge if there is no ignition bulb present to supply initial field current.

Nemo74 Emile Bergeron
Falmouth, MA, USA   USA
You didn't by chance replace all your dash lights with LED's including the ignition
light ? If the ignition lamp is replaced with an LED the alternator will not charge
it must be an incandescent type otherwise you will get no field excitation voltage
for the alternator.

Emile

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Nemo74 Emile Bergeron
Falmouth, MA, USA   USA
You may want to check that the bulb isn't burnt out or has a broken filament, also make
sure that it's properly plugged into the gauge. I know that on my TR the lamp socket
tends to fall out at the least provocation.

Emile

tapkaJohnD Avatar
tapkaJohnD John Davies
Lancaster, Lancashire, UK   GBR
Engine earth strap intact and connected?
John

macgregw Greg Williams
Boyertown, PA, USA   USA
Emile, I didn’t realize that the ignition warning lamp needed an incandescent bulb! I bet that’s the issue... will try it tomorrow and report back. Thanks!!
- Greg

TR3driver Randall Y
Confusion, Los Angeles, USA   USA
In reply to # 1531105 by Nemo74 You didn't by chance replace all your dash lights with LED's including the ignition
light ? If the ignition lamp is replaced with an LED the alternator will not charge
it must be an incandescent type otherwise you will get no field excitation voltage
for the alternator.

Emile
The other alternative is to add a resistor.



Randall
56 TR3 TS13571L daily driver
71 Stag LE1473L awaiting engine rebuild
7? Stag awaiting gearbox rebuild

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macgregw Greg Williams
Boyertown, PA, USA   USA
So we swapped the LED ignition bulb with an incandescent bulb and... still not charging. The ground strap seems secure, too. Back to the drawing board. Any and all thoughts are welcome!

- Greg

macgregw Greg Williams
Boyertown, PA, USA   USA
Randall, where would the resistor need to be placed?

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dicta dick Taylor
Downey, Callifornia, USA   USA
In reply to # 1530998 by macgregw Hi all, I feel like we’re chasing a ghost here... any insights are welcome! Driving home in my ‘74 TR6 after having LiteZupp LED lights installed by a reputable LBC mechanic, I noticed my volt meter spiked all the way to the right. Checking voltage at the battery confirmed 16 volts being charged (no switches were on, just my electric fan running). Sure sounds like the voltage regulator is bad in my 2 yr. old refurbished Lucas 43 amp alternator (3-wire plug), right?

I unplugged the alternator and drove it back to my mechanic (only a 15 min. drive) to have it replaced. They had 4 refurbished alternators on hand. The 1st was installed and we checked the voltage at the battery with the engine running (& briefly revved). 11.99 volts, so not charging. Same thing with the next 3 alternators. The mechanic checked everything possible (wires, plug connections etc.), except for testing the alternators on a bench. We even reinstalled my alternator, which also showed no charge. As a side note, all lights, switches etc. are working.

I should mention that the mechanic has been sorting out electrical issues on LBC cars for 30+ yrs. and is an electrical engineer by trade. He’s stumped. I guess it’s possible that all 4 alternators are bad, but what are the odds of that? I’m taking the car back in next week so he has time to try to figure this out. Just hoping that maybe someone on this forum has had a similar experience and can help us get to the bottom of this!

Thanks for any input,
- Greg

Greg --- My experience with over or undercharging has found that the battery ground strap must make solid connection with both the engine block/head and the body of the car. No paint interference.

Dick

Nemo74 Emile Bergeron
Falmouth, MA, USA   USA
Another thing to check, make sure that the smaller gauge brown wire is making a
solid low resistance connection directly to the battery. This is the 'sense' lead for
the alternator, if disconnected or of questionable connection the battery will overcharge.

Emile

tapkaJohnD Avatar
tapkaJohnD John Davies
Lancaster, Lancashire, UK   GBR
In reply to # 1531347 by dicta
Greg --- My experience with over or undercharging has found that the battery ground strap must make solid connection with both the engine block/head and the body of the car. No paint interference.

Dick

I'm with you, Dick, (POst 5)
John

kansanbrit Avatar
kansanbrit Phil H
Bonner Springs, KS, USA   USA
1952 MG D-Type Midget
1964 Morris Mini-Minor
1980 Triumph TR8
1980 Triumph TR8 "TR8 Holley"    & more
In reply to # 1531339 by macgregw So we swapped the LED ignition bulb with an incandescent bulb and... still not charging. The ground strap seems secure, too. Back to the drawing board. Any and all thoughts are welcome!

- Greg

So what does the ignition light do? Come on with ignition, stay on after starting? Going dim? Going out? Not coming on at all?

kansanbrit Avatar
kansanbrit Phil H
Bonner Springs, KS, USA   USA
1952 MG D-Type Midget
1964 Morris Mini-Minor
1980 Triumph TR8
1980 Triumph TR8 "TR8 Holley"    & more
In reply to # 1531358 by Nemo74 Another thing to check, make sure that the smaller gauge brown wire is making a
solid low resistance connection directly to the battery. This is the 'sense' lead for
the alternator, if disconnected or of questionable connection the battery will overcharge.

Emile

Some Lucas alternators have this need but most don't, they have internal voltage sensing, depends on model and the regulator.

macgregw Greg Williams
Boyertown, PA, USA   USA
OK, thanks Dick... I’ll check it out.

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