MikeP
Legendary Member
- Joined
- Apr 12, 2005
- Messages
- 8,674
- Status
- OTHER
- Hatteras Model
- Not Currently A Hatteras Owner
Had one of the dual-bulb circline florescent fixtures go out the other day. Since there are two bulbs with an individual socket to attach each bulb to the ballast, I assumed that the ballast was bad since I could not imagine that two bulbs failed at exactly the same instant. But to be sure I did some voltage checks at the ballast sockets. They showed 5.5V or thereabouts. I didn't know what the voltage should be but I ASSUMED the 5.5 couldn't be right. So I was convinced the ballast was bad.
Luckily, while getting into the car to go buy a new ballast - 75 bucks! - I thought about it some more and went back to do some more checking. I learned two things via the internet re florescent fixtures that I didn't know. First, in these circular fixtures it is common to have both bulbs go dark if one fails. Second, the ballasts cannot be successfully tested for proper operation using a multimeter - the voltage applied depends on the load. I re-attached the ballast and installed two new bulbs and presto!
I was totally embarrassed that I didn't know any of this. My assumption that each bulb was powered independently was totally in error. I don't know if the circuit inside the ballast for the two bulbs is a series circuit or not but that is how it acts. NOTE that this is re the circular dual-bulb fixtures only, not other types of florescent fixtures - it MAY apply to others but the info I was reading specifically mentioned this re the circulars but not the straight tube dual bulb fixtures.
Obviously, had I just replaced both bulbs immediately, I wouldn't have wasted the time involved. OTOH, I wouldn't have learned anything.
Luckily, while getting into the car to go buy a new ballast - 75 bucks! - I thought about it some more and went back to do some more checking. I learned two things via the internet re florescent fixtures that I didn't know. First, in these circular fixtures it is common to have both bulbs go dark if one fails. Second, the ballasts cannot be successfully tested for proper operation using a multimeter - the voltage applied depends on the load. I re-attached the ballast and installed two new bulbs and presto!
I was totally embarrassed that I didn't know any of this. My assumption that each bulb was powered independently was totally in error. I don't know if the circuit inside the ballast for the two bulbs is a series circuit or not but that is how it acts. NOTE that this is re the circular dual-bulb fixtures only, not other types of florescent fixtures - it MAY apply to others but the info I was reading specifically mentioned this re the circulars but not the straight tube dual bulb fixtures.
Obviously, had I just replaced both bulbs immediately, I wouldn't have wasted the time involved. OTOH, I wouldn't have learned anything.
