Headlight Bulbs Failing

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FundyTides
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Headlight Bulbs Failing

Post by FundyTides » Tue Aug 06, 2019 2:47 pm

I have never driven my 27 T much at night so have never had a problem with bulbs failing. However, our province just implemented a new law that if a car is not equipped with DRL (daytime running lights) then the headlights must be turned on whenever the car is being driven. In the past 2 weeks, 2 of my headlight bulbs have failed on short trips. Is this just coincidence because the bulbs are old? I am running on battery and using a 6 volt battery. With lights on ammeter shows less than 5 amps at road speed.

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Steve Jelf
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Re: Headlight Bulbs Failing

Post by Steve Jelf » Tue Aug 06, 2019 3:48 pm

I suspect you're guessing right about your old bulbs aging out. Six volt bulbs lit by a six volt battery should last a long time. I've driven my 1915 without shutting off the headlights for months, and even those notoriously delicate mag bulbs have lasted pretty well.
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George Mills
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Re: Headlight Bulbs Failing

Post by George Mills » Tue Aug 06, 2019 4:47 pm

It may be coincidence...

But there is a trick. Many/Most old bulbs had the glass attached to the base with shellac. Just the force of putting a lamp in can crack an old shellac seal. Once the seal is broken, the lamp doesn't last too long (But boy does it get bright!)

Cheap hack is to run a bead of superglue around where the glass meets the brass base BEFORE the shellac seal gets cracked in handling.

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TRDxB2
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Re: Headlight Bulbs Failing

Post by TRDxB2 » Tue Aug 06, 2019 5:02 pm

Just thinking (do that now and then). If you haven't changed the electrical system in anyway - then the only conclusion is old bulbs and bumpy roads. time to consider LEDs they are vibration free and if you keep burning the filament ones out - a lot cheaper.


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Re: Headlight Bulbs Failing

Post by J1MGOLDEN » Tue Aug 06, 2019 5:44 pm

I had that problem with a loose wire from the ammeter to the battery.

When the current generated by the ammeter has no path to the battery and does have a path to the lights, the voltage can go up to 36 Volts and the head lights and dash light, along with the tail light go out like the old camera flash bulbs.

That only takes a few seconds and the intense darkness is very hazardous to a night time drive.

LED bulbs are more expensive, but they only require about 20 % of the normal bulb current.


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Re: Headlight Bulbs Failing

Post by Norman Kling » Tue Aug 06, 2019 5:46 pm

If you are showing 5 amp charge with the lights on, it is over using the generator. It should be around zero or just a few amps with the lights on. You might even need to charge the battery while the car is parked. The most common reason that lights burn out is that the path from the generator to the battery is not very good. Clean all the connections between the battery and the generator including the starter switch and the terminal block. Your bad connection could be somewhere between the starter switch and the ammeter. Because the starter is working to start the engine. When the generator does not have a good path to the battery, the charge will go to ground, and the shortest and best path would be through the light bulbs.
Norm

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Re: Headlight Bulbs Failing

Post by Steve Jelf » Tue Aug 06, 2019 5:59 pm

Just the force of putting a lamp in can crack an old shellac seal.

George is exactly right about old bulbs, the only kind available for MAG lights. Last year when I had a bulb go out I thought it was no problem because I had spares. All seven spares twisted apart when I tried to install them. Since then I've acquired more MAG bulbs, but I'll add new glue before I try to use them.
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Re: Headlight Bulbs Failing

Post by Piewagon » Tue Aug 06, 2019 6:18 pm

If you are showing 5 amps of charge with headlights ON then I am going to guess you are using a cutout on your generator and you have your charge rate way too high. Without a voltage regulator then the charge voltage can go very high with that much charge rate. Headlight bulbs have a rather short life when you apply even modest amounts of voltage on them that is higher than normal. Use an analog volt meter only for this test but then check the voltage at the cutout output or across the battery and my guess is you are way higher than 7 volts and that is what is reducing the life of you headlight bulbs.


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FundyTides
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Re: Headlight Bulbs Failing

Post by FundyTides » Tue Aug 06, 2019 8:23 pm

Now that it has been brought up, I did notice lately that the ammeter has been showing a higher reading than normal. It used to run slightly over 5 amps with lights off and near zero with lights on. Now runs 10 amps and near 5 amps respectively. I haven't changed the 3rd brush adjustment. What would do this? Yes I am using a cutout, diode type I think. I changed it several years ago.


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Re: Headlight Bulbs Failing

Post by Piewagon » Tue Aug 06, 2019 9:02 pm

The third brush adjustment is something you have to be careful with since if it comes loose then the adjustment will "self-advance" since you get more output from a T generator when you move the third brush ring in the same direction that the generator normally spins. Thus it will advance itself if you don't have the adjustment well locked down. You may have cooked the battery if you have always had a very high setting. Without a Voltage Regulator the only thing that limits the voltage out of the cutout is the battery and the load. If the battery is not checked and serviced often in those setups it can become a higher resistance due to overcharge and this will allow the voltage to go up. I strongly suggest you get an analog meter and check it out. Don't try to use a digital type meter since you will read nonsense and it does not mattery if the meter is "high quality and expensive" or a $5 Harbor Freight item. The ignition of the model T radiates all sorts of static and the meter picks it up if in the same room with the T.


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FundyTides
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Re: Headlight Bulbs Failing

Post by FundyTides » Wed Aug 07, 2019 5:27 pm

Checked all wiring and connections as suggested. all good except one terminal on starter switch was a little loose. Won't seem to tighten without turning the bolt. I will take the switch off tomorrow and hopefully can fix it. If generator is still charging too high I will attempt to adjust 3rd brush. Never had to do that before in the 50+ years that the car has been in my family.

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