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#1
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Electrical problem!
So the aft-most two dome lights (12 volt) on a 4 light circuit have been
giving me the blues for a month or so. Intermittant most of the time but now dead, sort of... Bill replaced the switch on one and they both worked until he left town...After another day of meters and torn up galley seems he's getting 13 volts through the wires but it won't light the bulb...He's thinking there is some sort of resistance somewhere. Any ideas? Experience? Jokes?? The Taiwanese in their infinite wisdumb epoxied the wires into the deck beams and cabin sides!!! Seahag (Dinner's on before dark!) |
#2
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Measure the resistance of the bulb alone. Then measure the resistance of the
wires with the bulb in the socket from the circuit breaker or power connection. If the bulb is, for instance, 12 watts, it draws 1 ampere. If the wire resistance is 5 ohms in addition to the bulb resistance, you're looking at a five volt drop in the wires, which is almost the power of the bulb. Report the resistances of the wires back to me and I'll walk you through this. Magnum "Seahag" wrote in message ... So the aft-most two dome lights (12 volt) on a 4 light circuit have been giving me the blues for a month or so. Intermittant most of the time but now dead, sort of... Bill replaced the switch on one and they both worked until he left town...After another day of meters and torn up galley seems he's getting 13 volts through the wires but it won't light the bulb...He's thinking there is some sort of resistance somewhere. Any ideas? Experience? Jokes?? The Taiwanese in their infinite wisdumb epoxied the wires into the deck beams and cabin sides!!! Seahag (Dinner's on before dark!) |
#3
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Thanks, sounds like you have a clue! We're just having coffee so it will be
awhile before we start tearing out stuff. Seahag "Magnum" wrote: Measure the resistance of the bulb alone. Then measure the resistance of the wires with the bulb in the socket from the circuit breaker or power connection. If the bulb is, for instance, 12 watts, it draws 1 ampere. If the wire resistance is 5 ohms in addition to the bulb resistance, you're looking at a five volt drop in the wires, which is almost the power of the bulb. Report the resistances of the wires back to me and I'll walk you through this. Magnum "Seahag" wrote in message ... So the aft-most two dome lights (12 volt) on a 4 light circuit have been giving me the blues for a month or so. Intermittant most of the time but now dead, sort of... Bill replaced the switch on one and they both worked until he left town...After another day of meters and torn up galley seems he's getting 13 volts through the wires but it won't light the bulb...He's thinking there is some sort of resistance somewhere. Any ideas? Experience? Jokes?? The Taiwanese in their infinite wisdumb epoxied the wires into the deck beams and cabin sides!!! Seahag (Dinner's on before dark!) |
#4
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use your meter, don't tear anything apart unless the meter indicates the
need to tear out! Scout "Seahag" wrote in message ... Thanks, sounds like you have a clue! We're just having coffee so it will be awhile before we start tearing out stuff. Seahag "Magnum" wrote: Measure the resistance of the bulb alone. Then measure the resistance of the wires with the bulb in the socket from the circuit breaker or power connection. If the bulb is, for instance, 12 watts, it draws 1 ampere. If the wire resistance is 5 ohms in addition to the bulb resistance, you're looking at a five volt drop in the wires, which is almost the power of the bulb. Report the resistances of the wires back to me and I'll walk you through this. Magnum "Seahag" wrote in message ... So the aft-most two dome lights (12 volt) on a 4 light circuit have been giving me the blues for a month or so. Intermittant most of the time but now dead, sort of... Bill replaced the switch on one and they both worked until he left town...After another day of meters and torn up galley seems he's getting 13 volts through the wires but it won't light the bulb...He's thinking there is some sort of resistance somewhere. Any ideas? Experience? Jokes?? The Taiwanese in their infinite wisdumb epoxied the wires into the deck beams and cabin sides!!! Seahag (Dinner's on before dark!) |
#5
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Thanks. Just what I was thinking. The new 20w. halogen bulb alone is 0.9
average. The resistance on the ground side is 1.5 ohms. The ground side got interesting today, I had the terminal strip unhooked to do these tests when Haggy went to take a shower and there was no water. Why do they use only one ground circuit for the whole boat? Well I hooked back up... ah marital bliss restored! The positive side gives me 255K ohms! I guess we know where the problem is. Too bad the wires are forever berried in epoxy. I have the saw out. Stay tuned. Mr. H. "Magnum" wrote: Measure the resistance of the bulb alone. Then measure the resistance of the wires with the bulb in the socket from the circuit breaker or power connection. If the bulb is, for instance, 12 watts, it draws 1 ampere. If the wire resistance is 5 ohms in addition to the bulb resistance, you're looking at a five volt drop in the wires, which is almost the power of the bulb. Report the resistances of the wires back to me and I'll walk you through this. Magnum "Seahag" wrote: So the aft-most two dome lights (12 volt) on a 4 light circuit have been giving me the blues for a month or so. Intermittant most of the time but now dead, sort of... Bill replaced the switch on one and they both worked until he left town...After another day of meters and torn up galley seems he's getting 13 volts through the wires but it won't light the bulb...He's thinking there is some sort of resistance somewhere. Any ideas? Experience? Jokes?? The Taiwanese in their infinite wisdumb epoxied the wires into the deck beams and cabin sides!!! Seahag (Dinner's on before dark!) |
#6
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"Seahag" wrote
The new 20w. halogen bulb alone is 0.9 average. ..9 Ohms? If so, something is wrong here, perhaps with your meter. At .9 ohms, given a 12 volt supply, that bulb would draw 13.3 amps (or 160 watts). A 20w bulb should have an ohm reading of about 7.2 ohms. The resistance on the ground side is 1.5 ohms. from where to where? from the grounded terminal strip to the ground side of the bulb socket? That should be closer to zero, but again, I don't know how accurate your meter is. The positive side gives me 255K ohms! Again, measuring from what point to what point? One way to double check this before you rip anything apart, is to take a new piece of clean, adequately sized wire (14-16 gauge), long enough to reach from the fuse or breaker panel that feeds the lights, and do the following: 1. check the resistance of the new wire (it should be very close to zero ohms). 2. disconnect the positive wire from the light fixture and twist one end of the new wire to the now disconnected fixture wire. make sure they are clean and tight. 3. run the other end of the new wire back to the fuse or breaker panel. 4. disconnect the suspect wire from the fuse/breaker and connect your ohm meter to these two free ends. 5. if you show high resistance now, break out your saw or find an alternate route for your new wire. I hope this helps. If nothing else, it can confirm suspicions before ripping apart anything. I'm a bit concerned about that meter though. Scout Too bad the wires are forever berried in epoxy. I have the saw out. Stay tuned. Mr. H. "Magnum" wrote: Measure the resistance of the bulb alone. Then measure the resistance of the wires with the bulb in the socket from the circuit breaker or power connection. If the bulb is, for instance, 12 watts, it draws 1 ampere. If the wire resistance is 5 ohms in addition to the bulb resistance, you're looking at a five volt drop in the wires, which is almost the power of the bulb. Report the resistances of the wires back to me and I'll walk you through this. Magnum "Seahag" wrote: So the aft-most two dome lights (12 volt) on a 4 light circuit have been giving me the blues for a month or so. Intermittant most of the time but now dead, sort of... Bill replaced the switch on one and they both worked until he left town...After another day of meters and torn up galley seems he's getting 13 volts through the wires but it won't light the bulb...He's thinking there is some sort of resistance somewhere. Any ideas? Experience? Jokes?? The Taiwanese in their infinite wisdumb epoxied the wires into the deck beams and cabin sides!!! Seahag (Dinner's on before dark!) |
#7
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Perhaps resistance increases with temperature as it does with almost all
metals.? Unless the bulb element is made with germanium. Good going Mr. Hag! Watch out for ground resistance. Daisy chaining ground wires can give you high ground resistance, or large voltage drops especially when other circuits draw a big current. If you use multiple devices on the same ground wire make sure the ground wire is rated for the sum of all the currents from each device. "Scout" wrote in message ... "Seahag" wrote The new 20w. halogen bulb alone is 0.9 average. .9 Ohms? If so, something is wrong here, perhaps with your meter. At .9 ohms, given a 12 volt supply, that bulb would draw 13.3 amps (or 160 watts). A 20w bulb should have an ohm reading of about 7.2 ohms. The resistance on the ground side is 1.5 ohms. from where to where? from the grounded terminal strip to the ground side of the bulb socket? That should be closer to zero, but again, I don't know how accurate your meter is. The positive side gives me 255K ohms! Again, measuring from what point to what point? One way to double check this before you rip anything apart, is to take a new piece of clean, adequately sized wire (14-16 gauge), long enough to reach from the fuse or breaker panel that feeds the lights, and do the following: 1. check the resistance of the new wire (it should be very close to zero ohms). 2. disconnect the positive wire from the light fixture and twist one end of the new wire to the now disconnected fixture wire. make sure they are clean and tight. 3. run the other end of the new wire back to the fuse or breaker panel. 4. disconnect the suspect wire from the fuse/breaker and connect your ohm meter to these two free ends. 5. if you show high resistance now, break out your saw or find an alternate route for your new wire. I hope this helps. If nothing else, it can confirm suspicions before ripping apart anything. I'm a bit concerned about that meter though. Scout Too bad the wires are forever berried in epoxy. I have the saw out. Stay tuned. Mr. H. "Magnum" wrote: Measure the resistance of the bulb alone. Then measure the resistance of the wires with the bulb in the socket from the circuit breaker or power connection. If the bulb is, for instance, 12 watts, it draws 1 ampere. If the wire resistance is 5 ohms in addition to the bulb resistance, you're looking at a five volt drop in the wires, which is almost the power of the bulb. Report the resistances of the wires back to me and I'll walk you through this. Magnum "Seahag" wrote: So the aft-most two dome lights (12 volt) on a 4 light circuit have been giving me the blues for a month or so. Intermittant most of the time but now dead, sort of... Bill replaced the switch on one and they both worked until he left town...After another day of meters and torn up galley seems he's getting 13 volts through the wires but it won't light the bulb...He's thinking there is some sort of resistance somewhere. Any ideas? Experience? Jokes?? The Taiwanese in their infinite wisdumb epoxied the wires into the deck beams and cabin sides!!! Seahag (Dinner's on before dark!) |
#8
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"Magnum" wrote
Perhaps resistance increases with temperature as it does with almost all metals.? Yes, but they most likely have tungsten elements, and will not see such a *dramatic* increase in resistance (i.e., .9 to 7+ ohms). That drastic behavior in an incandescent bulb would be very unusual; methinks the .9 ohm reading is an error. Scout |
#9
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Have you read his post carefully? He has stated the high resistance in the
other line, not the ground leg. Scout "Magnum" wrote Good going Mr. Hag! Watch out for ground resistance. |
#10
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ahh, yes. I stand corrected on that point. Thank you.
Scout "Magnum" wrote in message Perhaps resistance increases with temperature as it does with almost all metals.? Unless the bulb element is made with germanium. |
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