I installed some 400 watt 120volt hi bay metal halide fixtures in a gymnasium in 1996. In the past two months two ballasts have needed replacement. Both shorted out and tripped the breaker, each at different times. My questions are (1) what is the general life span of this type of ballast, (2) Do they normally short out when they die or is this abnormal. I don't do much with this type of fixture so I am not too familiar with them. Thanks in advance for any help. Scott
Scott '96 seems kind of new for a ballast replacement to be necessary. Were they an "economy priced" fixture? Do they run 24/7? The primary winding is shorting, I think. (the ones I'm replacing are from about '74-'85) ...Another Scott
#11794 - 07/22/0208:26 PMRe: Metal Halide Balast Life
Electricman, we have this problem at the factory where I work. We were using the wrong type of ballast for the bulbs. We had existing sodium ballasts and switched to metal -halide bulbs and the ballasts started blowing out. Also our power is very "dirty" spikes and sags, but a call to the utility fixed some of that, loose pole connection.
#11796 - 07/23/0202:58 PMRe: Metal Halide Balast Life
ElectricmanScott: Heat is the prime killer of HID ballasts. WE do a lot of parking lot/sports lighting, and have ballast failures from <6 months to >15 years. Voltage spikes can hurt too, if they are severe and occur often.. the 120 primary winding is the "weakest" link spike wise. The "other" theory is '96 to '02 is 6 years, the mfg warranty probably was five. You can e-mail Advance/Universal for input also.
Your ionquiry as to normally "short out", it's a 50/50 split...but when the 480 one's short, and the "maintenance" guy resets the CB a "few" times....now that's fireworks..
#11797 - 07/25/0202:47 AMRe: Metal Halide Balast Life
Heat is definitely the most common culprite for Ballast failure. From the description you gave, it is obviously the Autotransformer section which has fried on these Ballasts - due to the breaker tripping from a nearly short circuit.
Running the Autotransformer section in high heat and at the lowest input voltage setting creates even more heat. Figuring 480 VA to drive a 400 watt lamp [apx. 86% P.F.] draws at least 4 amps @ 120 VAC.
Not capping the unused leads will cause trouble also, if any of the leads complete a circuit to the grounded box. It will draw current through all parts of the Autotransformer and make the coil heat up excessively.
Other than terminating to the wrong voltage input and the stuff mentioned above, a typical HID CWA Ballast should last a good 10 years minimum. Lamps, Capacitors and Ignitors fail sooner than frying a coil.
Scott " 35 " Thompson Just Say NO To Green Eggs And Ham!
#11798 - 07/25/0207:19 PMRe: Metal Halide Balast Life
I change ballasts(metal halide) all the time in LSI(brand name) fixtures that are installed in gasoline canopies. Some last years and some don't. The newer ones have smaller boxes to house ballast, capacitor etc, and they die quicker. My guess would be heat build up. Generally they don't short even when the coil is obviously burned up.