8mm Forum: Immediate bulb burn out

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Posted by Drew Durazo (Member # 1391) on January 08, 2009, 08:39 PM:

I have an Elmo ST-600DM. It is in great "new like" condition, however it blows out the bulb in a second. I've made sure the bulbs were new, free of skin oils, at room temperature and handled with a clean cloth. The bulb is a EFP 12volt 100 watt. I metered the bulb socket and measured 13.8 volts (a/c). Any help is greatly appreciated.

Posted by Steve Klare (Member # 12) on January 08, 2009, 09:44 PM:

I guess that's 13.8 VAC with the bulb out so it's probably sinking down closer to 12V with the bulb in circuit.

If it's really 13.8V with the bulb in circuit I could see the lamp burning out faster, but not in a second.

I'm tempted to ask if the cooling air is blocked, but I don't see that causing bulb failure in one second either.

If I were in your spot, I'd cobble together some sort of a dummy load with wirewound resistors of about 1.5 Ohms total that can take a multiple of 100W and run the operational cycle while monitoring the voltage. Ceramic wirewounds are not as touchy about over-power as a tungsten bulb filament. You could cut off the pins of a dead EFP to interface with the socket.

Something is telling me, at some time, for some reason, you are actually seeing a lot more than 12V.

Good Luck!

PS: How many bulbs?

Posted by Drew Durazo (Member # 1391) on January 09, 2009, 01:19 PM:

Thank you for the info. I ran the projector without a bulb while monitoring the current of the socket and the voltage maintained a 13.8 vac. I even monitored it while switching the light switch on and off thinking it might show a surge, but there was none. I have another bulb (not a EFP) that is rated for 21 volts, thinking of trying it. Think that is a good idea?

Posted by Martin Jones (Member # 1163) on January 09, 2009, 01:49 PM:

Check the transformer tapping.... if it is set to 100 volts and your mains is 115 volts, then the lamp voltage will be 13.8 volts ! 13.8 volts is not good for a 12v lamp. Your actual mains could be higher; have you measured it?
If in doubt, set your transformer to it's highest setting (120 volts ?; I'm not familiar with US machines) and measure the voltage across a new bulb when switched on. Better to have a little less than 12v than 1.8 volts (15%) more.

Martin

Posted by Drew Durazo (Member # 1391) on January 11, 2009, 02:35 AM:

Martin, thank you so much. I checked the transformer setting and it was set at 115 volts. I then checked my AC current and it was 125 volts. The next setting on the Elmo transformer was 125 volts. After setting the transformer to 125 volts I checked the bulb socket current and it was now 12.5 volts. I put in the last of the three new bulbs I had and shazzzzam, it worked. Just 1.3 volt may be a small difference, but it made a big difference. Thank you again.

Posted by Steve Klare (Member # 12) on January 11, 2009, 07:00 AM:

Wow!,

Your line voltage is on the high side! Mine runs around 117.

Do you have to replace your regular light bulbs very often?

I'm still surprised at how fast the bulbs were going: 13.8V gives about 133% of rated power. If you'd said 5 minutes it would have sounded reasonable. I guess these lamps are being run pretty close to the limits of their capacity.

Posted by Paul Adsett (Member # 25) on January 11, 2009, 11:08 AM:

Surprises me too Steve.
One thing I found out recently is that projector transformers are not held to very close manufacturing tolerances. I was getting what I thought was a dim picture from my Eumig 938. I checked the mains voltage and it was 117 volts. When I checked the lamp voltage (with the lamp running) it was only getting 13.8 volts instead of the required 15 volts. So I set the transformer tapping back from 117 volts to 110 volts and the lamp voltage came up to 15.2 volts and gave me a much brighter picture. I've been running the machine at this setting for months now with the same lamp.

Posted by Drew Durazo (Member # 1391) on January 11, 2009, 04:20 PM:

I purchased this projector from Central California and the seller said it worked great. I live in Southern California, so I didn't even consider voltage settings. I have been educated.

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