18W 12V lamp issue

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1793 said:
Yes I can do that, good idea. I spoke with my customer today and I asked him if the other lamps were turning black and he said there is a slight "blacking" near the base of the other lamps.
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This might, paradoxically, be because the base is cooler than the rest of the bulb envelope because of heat conduction through the socket and so the halogen scavenging action is less there.
 
Amazing amount of thought going into this.

It seems to me if he is using the lamp that the fixture is designed for and using the fixture as intended, and the voltage is correct it has to be an issue with the lamps.

I don't buy into loose rivets shortening the life of the lamp due to heat. I also don't buy into a loose connection cycling the lamp shortening the life as you would see the lamp pulsing.
 
iwire said:
Amazing amount of thought going into this.

It seems to me if he is using the lamp that the fixture is designed for and using the fixture as intended, and the voltage is correct it has to be an issue with the lamps.

I don't buy into loose rivets shortening the life of the lamp due to heat. I also don't buy into a loose connection cycling the lamp shortening the life as you would see the lamp pulsing.
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It doesn't seem to make any sense, I agree. But I can't tell you how many times I have had complaints about short lamp life and replacing a bad socket did improve lamp life, so something is happening to effect the lamp. I have never been able to figure out just exactly what is happening to shorten lamp life - but never put much effort into finding out either.
 
iwire said:
Amazing amount of thought going into this.



I don't buy into loose rivets shortening the life of the lamp due to heat. I also don't buy into a loose connection cycling the lamp shortening the life as you would see the lamp pulsing.
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I have seen it myself, on one of my own fixtures. I have a ceiling fan with three sockets. In one particular socket, the bulbs, no matter if incandescent or CFL, would only last a short time, then burn out. I found loose rivets in the socket. I replaced the socket with a new one over a year ago and no more bad bulbs.

I don't have a theory, but it really does happen.
 
K8MHZ said:
I have seen it myself, on one of my own fixtures. I have a ceiling fan with three sockets. In one particular socket, the bulbs, no matter if incandescent or CFL, would only last a short time, then burn out. I found loose rivets in the socket. I replaced the socket with a new one over a year ago and no more bad bulbs.

I don't have a theory, but it really does happen.
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Thats cool, I remain unbelieving.
 
K8MHZ said:
I have seen it myself, on one of my own fixtures. I have a ceiling fan with three sockets. In one particular socket, the bulbs, no matter if incandescent or CFL, would only last a short time, then burn out. I found loose rivets in the socket. I replaced the socket with a new one over a year ago and no more bad bulbs.

I don't have a theory, but it really does happen.
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It seems to happen the most often with aluminum shell lampholders. There is often signs of stretching the aluminum shell from over - torquing the lamp during the installation.

Bob never sees aluminum shell lampholders is why he doesn't believe:happyyes:
 
iwire said:
Thats cool, I remain unbelieving.
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Why unbelieving? We certainly aren't making this up. We also admitted we did not know why the poor connections related to shorter lamp life.

It's not all that far fetched to think that the bulb may be compromised by the loose connections. The base is where the wires enter the bulb and is the most likely place for oxygen to enter as well.

I wonder if others have done any forensics or autopsies on burned out light bulbs.

Not going so far as to do autopsies, issues like the OP's are very interesting to me. Multiple bulbs failing in rapid succession in the same manner surely must have something in common.

If new make and supply cure the problem, we know the fix, but not the fail. Hopefully the OP will let us know that info when he gets the lights to stay on for while.
 
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Look closely at the pic.

The wires meant to be used as base contacts are black, not copper colored.

Are those cracks just above the wedge?

The obvious is why, if due to an O2 failure, there is no yellow oxide (I have seen this in 194 bulbs).

Maybe there was another bad connection that we can't see. The one that connnects the filament to the support. That would cause some metal vapor to deposit.

So I'm thinking.....poorly made bulbs. Bad connections both inside and out.
 
Straight from Malibu's FAQ Section:

"At least 50% of the power pack?s rated wattage should be used. Using a small fraction of the power pack?s wattage may lead to an ?in rush? problem. The resistance of the bulb filament is lowest when it is cold just as the light is turned on. This is made worse by having just a few fixtures on a power pack. Per Ohm?s law, the current is the voltage divided by the resistance. If the resistance is low, the current is high. The filament gets a short time when the current is higher than normal and this is when incandescent bulbs usually blow. "

They also have these amazing suggestions::blink:

"1. Reduce the resistance of the cable if your lights seem dim. Change it from 16-gauge to 14-gauge, and so on. Even if you are well within the limits for the cable gauge, number of lights and transformer power, this is worth a shot.

2. Use the full capacity of the transformer. If your transformer can handle 100 watts, use 10, 10-watt lamps, for example. Always use at least half the capacity of the transformer to reduce premature bulb failure.

3. Reduce load on the transformer. If the lights blink on and off all the time, the transformer is overloaded. The total lamps wattage must not exceed the transformer's rating.

4. Replace the bulb if the fixture doesn't illuminate. Also check that the connectors are squeezed together as tight as possible.

5. Change the cable if you get lower light output at the end of the cable. The transformer's wattage determines minimum cable gauge. 217-300 watts needs 12 gauge; 157-216 watts needs 14; 121-156 watts needs 16 and 0-120 watts needs 18.

6. Verify that you have at least 10 feet between the transformer and the first light if bulbs keep burning out."
 
LJSMITH1 said:
Straight from Malibu's FAQ Section:

"At least 50% of the power pack?s rated wattage should be used. Using a small fraction of the power pack?s wattage may lead to an ?in rush? problem. The resistance of the bulb filament is lowest when it is cold just as the light is turned on. This is made worse by having just a few fixtures on a power pack. Per Ohm?s law, the current is the voltage divided by the resistance. If the resistance is low, the current is high. The filament gets a short time when the current is higher than normal and this is when incandescent bulbs usually blow. "

They also have these amazing suggestions::blink:

"1. Reduce the resistance of the cable if your lights seem dim. Change it from 16-gauge to 14-gauge, and so on. Even if you are well within the limits for the cable gauge, number of lights and transformer power, this is worth a shot.

2. Use the full capacity of the transformer. If your transformer can handle 100 watts, use 10, 10-watt lamps, for example. Always use at least half the capacity of the transformer to reduce premature bulb failure.

3. Reduce load on the transformer. If the lights blink on and off all the time, the transformer is overloaded. The total lamps wattage must not exceed the transformer's rating.

4. Replace the bulb if the fixture doesn't illuminate. Also check that the connectors are squeezed together as tight as possible.

5. Change the cable if you get lower light output at the end of the cable. The transformer's wattage determines minimum cable gauge. 217-300 watts needs 12 gauge; 157-216 watts needs 14; 121-156 watts needs 16 and 0-120 watts needs 18.

6. Verify that you have at least 10 feet between the transformer and the first light if bulbs keep burning out."
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The wire is 12 gauge
The distance to first fixture is 14'
There are 159 watts on one 300 watt
There are 213 watts on the other 300 watt
The pictured bulbs look like they have been coated, inside, with copper

I'm planning on getting out to the house tomorrow to drop off a different make of lamps to try in these lights.
I'll post results as they roll in.
 
Yesterday I was able to check voltage as the lights were turned on. When turned on voltage went up to 10.5V, there was no spike or inrush of current at any point along the line of lights.
 
1793 said:
The wire is 12 gauge
The distance to first fixture is 14'
There are 159 watts on one 300 watt
There are 213 watts on the other 300 watt
The pictured bulbs look like they have been coated, inside, with copper

I'm planning on getting out to the house tomorrow to drop off a different make of lamps to try in these lights.
I'll post results as they roll in.
Click to expand...

also most 18 amps (17.9).... what is the total distance of the run ????
 
A maximum distance of 5.76 feet will limit the voltage drop to 3% or less with a #12 Copper conductor delivering 18.0 amps on a 12 volt system.

For Engineering Information Only:
20.0 Amps Rated ampacity of selected conductor
1.9029 Ohms Resistance (Ohms per 1000 feet)
0.054 Ohms Reactance (Ohms per 1000 feet)
0.36 volts maximum allowable voltage drop at 3%
0.9 Power Factor
 
AllCircuitsElectrical said:
A maximum distance of 5.76 feet will limit the voltage drop to 3% or less with a #12 Copper conductor delivering 18.0 amps on a 12 volt system.

For Engineering Information Only:
20.0 Amps Rated ampacity of selected conductor
1.9029 Ohms Resistance (Ohms per 1000 feet)
0.054 Ohms Reactance (Ohms per 1000 feet)
0.36 volts maximum allowable voltage drop at 3%
0.9 Power Factor
Click to expand...

Under voltage would make the lamps last longer, the problem is the lamps are burning out quickly.
 
Malibu lights came with the # 921 automotive (18W) lamp. However, the GE miniature lamp catalogue specifically states that this lamp is "excessive wattage for bulb size". Try using a 922 automotive lamp. Not quite as bright, but runs cooler, and lasts longer. Available at any place that sells automotive lamps. You might also want to look into 904, 906, and 912 autolamps, lower wattage, but they last longer, and do not darken.
 
ka6chp said:
Malibu lights came with the # 921 automotive (18W) lamp. However, the GE miniature lamp catalogue specifically states that this lamp is "excessive wattage for bulb size". Try using a 922 automotive lamp. Not quite as bright, but runs cooler, and lasts longer. Available at any place that sells automotive lamps. You might also want to look into 904, 906, and 912 autolamps, lower wattage, but they last longer, and do not darken.
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Thank you for a totally reasonable sounding explanation of the problem at last! I bet nobody can say why, other than greed, that Malibu chooses to use those bulbs. It makes the lights a lot brighter while they last.
Am I right in guessing that the 921 is normally used for stop lights or turn signals that are only used intermittently and also need to be bright to be visible in daylight?
 
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