Magneto headlights question - bulbs burning out at high speed ?

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Model T Ford Forum: Forum 2012: Magneto headlights question - bulbs burning out at high speed ?
Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank Harris from Long Beach & Big Bear on Tuesday, May 29, 2012 - 09:58 am:

I know this has been asked before but it is our first time dealing with this issue. The headlights on our son Bill's 1915 Touring car burned out at speed. He has stock gearing and a Ruckstell so the engine turns over a lot at highway speeds. The highway roadside radar detector said he was going 45 miles an hour. We believe that we were using the correct bulbs so the question is, Can we place a resistor in the circuit to stop this situation ? Or, is there a better bulb ?


Top of pagePrevious messageNext messageBottom of page Link to this message  By William Harper - Keene, NH on Tuesday, May 29, 2012 - 10:08 am:

Hi Frank,

I use # 1142 bulbs (12v double contact single filament) in my magneto powered headlamps. I have not blown out any but then I may not achieve the RPMs that your son does. Good luck with your project. Bill


Top of pagePrevious messageNext messageBottom of page Link to this message  By William Harper - Keene, NH on Tuesday, May 29, 2012 - 10:12 am:

I forgot to mention that my lamps are wired in series so it would take 24 volts to burn them out. Bill


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Tuesday, May 29, 2012 - 10:17 am:

A bulb that will survive gives less light - specially at low rpms. Ford had a better idea in 1918 with the dimmer coil - they arn't reproduced, but can usually be found used. Introduce a dimmer coil in Bill's wiring and the mag bulbs will last longer. With a more modern switch with three positions you'll be able to dim the lights too. http://www.mtfca.com/discus/messages/257047/277943.html?1332701995
dimmer coil

Still a bit unsafe in the dark though, since both lamps are wired in series. A good mag should be able to give some charge to a 12 v battery with Fun Projects mag charger - not to run with 12 bulbs on for several nights, but to get out in the dark in the morning and get home a little later at night :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By bill harris on Tuesday, May 29, 2012 - 10:20 am:

Actually, I was only going about 10-15 MPH when one blew last night. I had reached the 45MPH speed earlier in the day with lights turned off. The bulbs are old "FORD" script and it is a shame that one blew out. I have more in the supply that came with the car. We won't be doing much night driving but it is necessary to have lights available when needed. They are wired in series, thus both went out. There is a white cloud on the top of the burned out bulb.


Top of pagePrevious messageNext messageBottom of page Link to this message  By George_Cherry Hill NJ on Tuesday, May 29, 2012 - 10:45 am:

Frank,

Solutions at hand above....regular 9V/10V bulbs for mag service are rated for maybe 200 hours of avg. life, some at 100. At 45mph with a well gapped mag, his car may be putting out up to 30V or above on mag! Thats 15V each, on a 9V lamp! the normal derate for this says maybe a nano-second of lamp life...lol

If 30V at mag the 12V lamps are the best bet but thats still 15V+ so that changes projected average lamp life even at 12V lamp Rating to about 2 hours of use...lol. Better but not a win since he is a Harris and 45 is min speed :-)

As Roger said, Ford even eventually gave up trying to find a lamp that worked and lasted and went to a reactor coil feeding 6V lamps in series during 1917.

The only problem with using higher rated lamps is that lamps don't change from red glow to real illumination until they see about half voltage, so two 12's in series won't fire themselves up until about 4.5 MPH in low, and maybe 11MPH in high. No easy answer unless there is a way to shed voltage output from mag, and thats what the reactor block eventually did. Nobody makes them today but a good source told me easy to find at 'swaps'. I don;t know...lol...I NEVER turn the lights on in my 15 :-)

Now slap 12V combi of dry cells or even a wet cell at 12V, go 6V lamps, take lamp power off of mag...and Bill can still stay single wire outside and have great lamp life...lol


Top of pagePrevious messageNext messageBottom of page Link to this message  By George_Cherry Hill NJ on Tuesday, May 29, 2012 - 10:49 am:

Bill I was too busy proof reading my rotten typing skills and English use since it was going to Frank :-):-) I just noticed my time stamp it lots later than yours....geez Frank, see what this grammar thing does? LOL

Bill. at 15 MPH it should have just died a natural death...the white cloud says hmmm...but can happen, the other lamp will still be good maybe. 1 goes out they both go out, but one can still be good


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Tuesday, May 29, 2012 - 11:06 am:

If you have a dead T ignition coil it will make a superior ballast. I used one on Mike Robison's "No Dollar" speedster. As I recall, I used two 6 volt bulbs in series and pulled off windings until I got to the point where the bulbs dropped 12 volts when in series with the ballast. Then at any speed above where the mag put out 12 volts, the bulbs would stay at virtually the same brightness.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Tuesday, May 29, 2012 - 11:19 am:

Here is a link to that thread.


http://www.mtfca.com/discus/messages/179374/248579.html?1322449173


Top of pagePrevious messageNext messageBottom of page Link to this message  By ROBERT BERGSTADT on Tuesday, May 29, 2012 - 12:55 pm:

I have some of those dimmers if you need one, Bob


Top of pagePrevious messageNext messageBottom of page Link to this message  By JohnH on Tuesday, May 29, 2012 - 11:56 pm:

lights


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