• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

TR2/3/3A Headlight bulb rating

Share this page

CJD

CJD

Yoda
Country flag
Offline
Spent some time on the headlight assemblies last night. The first step was to test the bulbs that came with the cars. It turns out that they all worked, but...

Some were stamped with "6v" and had nice, bright lighting characteristics. Others were stamped "12v", but were dingy yellow when lit with 12 volts. So, was it common to use 6 volt bulbs for better light back in the day? The 12 volt bulbs are pretty sickly looking. Also, are the 6 volts going to fry quickly?
 
Last edited:
Are we talking sealed beam units or bulb-in-reflector (i.e. home market spec.)? Either way, the cars were 12v, so I can't really imagine a 6V bulb is going to last all that long. As for brightness, that's more related to good power wiring, good grounding and (depending on which lamp you have) a good reflector and clean glass.
 
These are old style sealed beams. I'm just testing, so it's just hot wired directly to the battery. I'm like you, Andrew, in that I would not think a 6v bulb would last...but they did come off the car, so they had to last for at least some time with 12v input. I also held the connection for over a minute to see if they would burn out. The light output looks normal for an average old sealed beam. The 12v bulb looks unusably dim.
 
CJD said:
...but they did come off the car, so they had to last for at least some time with 12v input...
Click to expand...

But that 'some time' would have only occurred when the car was driven with the lights on. Depending on the owners habits this may have been rare. I'm guessing they would not last long.

Is there a wattage shown on the old 12V? Originals were far from blinding but many upgrades are available - some look fairly correct until you turn them on.
 
Come to think of it, the original tungsten-filament sealed beams never were all that bright to begin with, and by nature of how the tungsten filament works, they got dimmer over time. Meanwhile, depending on what brand and vintage any of those units are, they might be worth a few bucks to originality-obsessed collectors!
 
I've heard of using 9 volt bulbs, but never 6.
If it was just one bulb, I'd blame the bulb. But, have you checked that your battery is actually getting something close to 12v to the bulb? Sometimes the internal resistance goes up, such that it puts out normal voltage with just a voltmeter attached, but the voltage droops badly under load.

The correct 12v tungsten bulbs do look a little yellow compared to modern technology bulbs. That was done in part to increase their life. If you jack the voltage up until the color matches a modern quartz-iodide bulb, the life will be severely shortened.

But hey, it's your car. Install those 6v puppies and tell us how it goes!

Oh yeah, one other little problem, the stock generator isn't going to be able to keep up with the increased current draw. Mine just barely keeps up with my 55 watt halogen bulbs, and only at higher rpm. And that's without running the heater or wipers.
 
Last edited:
First, I agree with TR3driver's comments.

Sounds like the dingy yellow bulb you are talking about may be an old pre Halogen bulb from the 1950s or 60s.

I am not sure how old you are, but the headlights back in the 1950s were not what they are today and to be honest with you they really did not need to be brighter since the roads were inferior to today and the speeds people drove where much slower also.

The other thing was drivers would tend to use their high beams a lot more when they needed the extra light and their was no oncoming traffic, so the trick was not to drive beyond the capabilities of your headlights and use the high beams when their was no oncoming traffic. Now days the general public wants their normal headlights to have better brightness as the older headlight high beams used to put out. Better optics have allowed manufactures to focus the beam a lot better as compared to the old sealed beam to compensate for the increased light while not blinding that oncoming traffic. If you remember when the blue-ish lights first came out the rice burners would put them in their older cars and basically blind all the oncoming traffic and increase the probability of a head-on accident.

Like others have said, try the 6V lights, but I would turn the lights on at night and stand out in front of the car to see if you are going to blind oncoming cars which could cause an accident.

The pre Halogen bulbs tend to have a yellow tint, and as the bulbs improved over the years so did the power requirements.

You want to see bad lighting, you should see the lights on my 1933 Chevrolet, which originally had 21 candle power (cp) headlight bulbs. I have upgraded to 32 cp bulbs and if I use the high beams the amp meter shows the battery is discharging. I drive this car with the normal beam headlights on all the time, but the state law says I am restricted to day light driving only with this car.

Visit my personal website at: www.jakegingervila.wix.com/bobs-vintage-cars-

Vila
1933 Chevrolet
1962 Triumph TR4
1984 BMW 633 CSi
 
Thanks all for the input. When I studied the bulbs for chips and other flaws it came down to 1 usable 12v and 2 usable 6v. So, I built the bulb assemblies with the 2 good 6v's...boxed them and sent them away to storage for final assembly in a couple years or so. I decided I already had the bulbs, so I have nothing to lose if they burn out quickly.

More to follow in a couple years!
 
Here we are...almost 3 years later!

The 6V bulbs give out a beautiful bright and almost white light. It's almost like LED light, but with more coverage. All the LED headlights I've seen are much narrower spread of light.

But...yep I did discover a down side.

The TR2 generator only puts out 19 amps. Apparently the 6v lights draw more than that, because the ammeter sits at a slight discharge no matter how high the engine revs. I'll have to put 12v bulbs on the to-do list, as I don't want to overheat an already marginal generator. Oh well, that should close out my 6v bulb thread. I still gotta wonder why the PO bought them. Must have been confused, thinking most '50's vintage cars were 6 v systems?!?

Cheers!
 
Too late. I ordered 12v bulbs from TRF, but tonight I drove the car back from the fabric shop in the dark. By the time I turned into the neighborhood the generator was gone. Bummer!

When I installed the 6v bulbs I figured the filaments would be the thing to go first. I was wrong.

So...don't use 6v bulbs!
 
I doubt that the generator failure was caused by the bulbs. The battery supplies what the generator can't; that's how the system works. If the battery is weak, though, it's remotely possible that the high load might have damaged the generator, but I still think it's not likely. Check your brushes; they might have worn out. Also, check the windings on the field and armature, and see if they look burned, or if there are other signs of overcurrent.

Still, I'd get rid of the 6V bulbs and, if you really need more light, go to halogens or LEDs. If the generator can't provide the power, there is always the option of an alternator conversion. My Bugeye Sprite had halogens, and the current drain at idle, with the generator, was astonishing. When I installed an alternator, the ammeter showed a nearly perfect balance between charge and discharge. It was only 55 amp alternator; I was impressed.
 
Fixed it up today. The armature was fried.

I have not measured these lights for amperage, but the last 12v headlights I measured were 10 amps. Assuming 6v bulbs at 12v input, I figure they may be pulling 20. That's the bulbs alone, not including the running lights, ignition, and instrument lights. So it had to be pulling 25 To 30 amps. You are right, the battery was maintaining the load, but the generator was locked at full power trying to make up for it. It got so hot the solder was spinning off and was splattering the inside of the housing.

We'd have to ask Randall to see if the regulator has any max load protection....but in my experience what I got is exactly what I've seen for these generators at full amperage for an extended time. So I have no excuse...I knew better.

I checked the armature on a growler and it had multiple internal winding shorts, in addition to missing solder on the commutator. I swapped in a new (55 year old!?!) armature with the same brushes and field windings and all is good again. Of course, no more headlights until the 12volters show up!
 
The control box is definitely supposed to limit max current.

But it's somewhat primitive, so voltage and current do interact to some extent. A sustained load in excess of generator capacity will eventually sap the battery down and possibly allow excess current.

That said, I've run my battery flat many times and let the generator recharge it without issue. The main problem IMO is getting it adjusted properly and keeping it that way. In my experience, that means cleaning and readjusting every few years.
 
Thanks Randall. I did have a thought that I very likely have a newer voltage regulator, and those were for slightly higher amperage generators...21 or 22 amps? If so, is the max power limiting adjustable on the regulator, or is it inherent in the generator?
 
Its inherent in both of them, the only relevant adjustment is the voltage adjustment.
Lucas specifically warned against mixing control boxes and generators. IIRC, the 19 amp box has an extra half turn of heavy wire on the regulator relay,and a different value for the resistor.

As you've noticed, the current regulation is very important. Otherwise the generator will happily put out enough current to destroy itself. I like to keep an eye in the ammeter every time I start the engine. If it goes above 20 for more than just a few seconds, there is something wrong that must be addressed immediately.

Last time it happened to me, it turned out to be a bad connection inside the control box. The voltage (shunt) winding on both coils is connected through a brass sleeve around the center post. Corrosion had crept in and prevented a good connection, allowing current (and voltage) to go way high. Fortunately I caught the problem and disconnected the generator for the ride home.
 
Thanks, Randall. It's starting to come back. I was thinking I had a newer regulator, but when I started shopping the big 3, I saw that the later, higher amperage generators used the control box with spade terminals. Since my box has the original screw posts, I'm tending to believe I have the "correct" 19amp control box. With your information I dove back into the manual. It says the "split series coils" aid to cut the field power at a lower voltage to prevent overloading the generator. Interesting, as it even notes that could happen with a discharged battery and the lights on. Of course that was written assuming the standard 12v lights too!?!

That leads me to think that maybe I have the voltage setting too high on the regulator. Is there a way to set the regulator to ensure when the series windings kick in the generator output would prevent overloading? Alternatively, should I just assume the protection is there...but I just dumped too heavy of a load for what the protection is able to protect...if that makes sense?
 
In searching for other info, I came across this old thread when I was rebuilding the generators 3 years ago. Out of 5 armatures I am now down to 1 good one. I'll have to take care of this one! I did buy one more junk generator...I know, I need another junk generator like I need another hole in my head...but this one is date coded correctly for the car.

I am still interested in investigating what, if any protections are inherent in the control box. When I catch up on all the projects, I plan to test different voltage settings vs. the voltage step-down when overloaded. I'm thinking there may be an optimum voltage setting to also protect the generator from overloading. The 14 volts I am using now "aint it"! I'll need a decent induction ammeter, so another excuse to buy a tool!?!

https://www.britishcarforum.com/bcf/showthread.php?97573-Generator-Configurations
 
Only solution I know of is to use a more sophisticated regulator, with separate controls for current and voltage. I'm not certain when Lucas started making the 3 bobbin boxes, but early Spit, GT6 and Vitesse had them.

Tony Rhodes offers an electronic conversion that fits inside the old RB106 box and should do nicely.

I was thinking about trying one myself just to see how much difference it made; but when the field opened on my original generator, and my spare turned out to have a short in the field (plus I burned my finger on the overheated relay), I got mad and put an alternator on instead.

PS the correct setting is actually higher than 14 volts, namely 15.6-16.2, but must be done with the generator output disconnected from the battery and the regulator coils at 20C. Easy way to do that is to stick a bit of paper into the cutout contacts.

I don't have it handy, but somewhere I've got an article where someone worked out the equation for how the current affects the voltage. But basically the more current, the lower the voltage. So it winds up putting a few amps into even a fully charged battery, plus the few amps for the ignition, and regulating voltage around 14.5.
Then as you add more load (like headlights) the voltage drops farther. With 55 watt headlights it actually leaves the battery slightly discharged.
 
I played with the regulator for a couple hours this evening. You're absolutely right, Randall...it's simple and limited. I just set it as the book says and will live with it.

One thing I learned...the Lucas ammeter spring can get tweaked. I messed up putting the bolt into the generator, so it tied the field to the armature output. The generator became self energizing! I only ran it for a few minutes that way, but the ammeter pegged on charge. Now it sits about 1/4" left of center, so shows a little discharge even with no load at all. One more thing to take care of.
 
Back
Top