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Regulator Question

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T

TR3AD

Freshman Member
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I replaced the regulator on my TR3A and now the ignition light glows red at idle and goes out upon revving the engine. The amp gauge seems to respond accordingly. Does this mean there is something faulty with the regulator? I haven't had this issue with previous regulators, although the ignition light has glowed at very low idles (under 500rpm).
 
Seems normal to me. Good new ones are rare. I bought a new one in a green Lucas box about 6 years ago from a major US TR parts supplier - to carry as a spare just in case. I tested it in my 1958 TR3A. The new one wouldn't work. So I put back in my original one (now 52 years old) and it still works fine.

There is a company (Cox) in England who repair all kinds of control boxes for all kinds of antique cars and they also do the original Lucas 106/2 voltage regulator (control box) for out TR3As. They do a good job.

https://www.coxautomotiveelectrics.co.uk/

I say that if you have at least two good ones which work like you describe above, don't "fix" it. You are all set for the next 50 years.

I'm sure that Randall will provide some good advice about how to tweak the adjustable settings to make this one even better.
 
The TR2 with 3 supplement has a bunch of info on the control box(regulator). It is in section M of the factory manual starting on page 24. There is also a thread on the control box if you do an advance search in the BFC you might be able to find it. I have it in my "tips" file but did not have any info on the starter of the thread.

Good Luck, Tinkerman
 
Could be the control box, but more likely the generator, IMO. The control box has a "cutout" relay that is supposed to open when current starts to flow backwards into the generator; the light is showing you that the cutout is open.

The cutout relay has two coils, basically the "shunt" coil senses generator voltage while the "series" coil senses current. You know the shunt coil is working, because the cutout closes (light goes out) when you start the engine (there is no current when the cutout is open). To open the cutout, the series coil must oppose the shunt coil (when current starts to flow back into the generator), so it must be working as well.

PS, I have a scan of the Lucas Generator & Control Box Tests booklet; PM me your email addy if you'd like a copy. About 2Mb, PDF.
 
What is your idle RPM?

I'm like Don. Your description sounds like normal operation to me unless your engine is idling at 1500 RPM or something.

The generator has to spin at a certain RPM in order to put out its rated voltage. Typically, this RPM, called generator come-in speed, is not achieved at idle.

That light is in parallel with the reverse current cut-out to which Randall refers. The reverse current relay opens when generator voltage is below battery voltage. At idle, below come-in speed, the generator voltage is lower than battery voltage, so the cut-out is open. Current flows from the battery through the light to illuminate it.

When the generator reaches come-in speed, the cut-out closes. Now the two terminals of the light are at the same voltage, so current stops flowing and the light goes out.
 
I agree, but the drop-out speed is lower than pull-in (since the voltage can't drop due to the battery, and the cutout doesn't open until there is 3-5 amps flowing back into the generator. On my car, that doesn't happen until under about 500 rpm (where my engine won't idle either).
 
That's a good point that I hadn't thought of.

Below pull-in speed, the current is only flowing through the voltage coil to ground. But when the points close, current flows through the series coil and its magnetic field aids the voltage coil field. This holds the points closed harder(?) (can't think of the right word) until the generator voltage falls enough that the battery current flowing backwards through the series coil opposes the magnetic field of the voltage coil. Points open, light on.

My car idles at 600 and the light is illuminated.

I love this stuff.
 
My head hurts :smile:

Cheers,
M. Pied Lourd
 
M_Pied_Lourd said:
My head hurts :smile:

Cheers,
M. Pied Lourd
Click to expand...

That must be how my students felt!

Of course, I had a blackboard, overheads, regulators for show-and-tell, arm-waving and a generator/regulator test machine to further inflict head pain.

One student went home and, after a couple beers, drew the regulator schematic from memory. He got an A.

Take two asprin with a couple of beers.
 
Wish that I had been a part of that class.

Cheers,
M. Pied Lourd
 
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