off and on 120v Metal Halide

[shaunwa75]

[h=6]I have been working on 120v Metal Halide 400w recessed fixtures that keep going off and on at differant times. I have replaced lamps, ballasts both are compatible and thermal protectors RP-B1. The fixtures are switched from 3 locations with 117 volts at the fixture. With no insulation around the fixture the temperture on the fixture housing next to the thermal protector is 233F the thermal protector temp. is 174F, is this to hot? Am I missing something else?[/h]

 

[hillbilly1]

So they are cycling randomly? What is the ambient temp above the fixtures? It's not hot enough in Talking Rock for the normal ambient to be high enough to trip them out, you did not say what kind of building these were in, but if the temp is 233F, and the protector is 174F, it does sound like you have a heat problem.

 

[shaunwa75]

Yes, they are cycling randomly. The ambient temp above the fixtures was 170F. the lights are in a church sanctuary 20' up in a sheet rock ceiling with a tin roof. I see you lived in Evansville Indiana, I grow you north of Terre Haute IN

 

[jeremysterling]

I'm guessing these are F-can ballasts? I've had similar problems with 120V 400W MH troffers in a grid ceiling with no insulation around the fixture. If I replaced the ballast and the lamp together, they last maybe a year or much less and then start cycling or suffer significant dimming. The F-can ballast mounts on stand-offs to ostensibly facilitate cooling air-flow around the ballast.

I think the stand-offs are actually contributing to the overheating. If the ballast is mounted directly to the troffer, the chassis becomes a heat sink to carry away excessive heat. Out in the parking lot, I've not seen this performance degradation with quad-tap core and coil ballasts which instructions normally specify mounting directly to the fixture housing to aid in cooling.

 

[shaunwa75]

They are core & coil multi tap ballast. They are cycling off & on the same day I install the new lamp and ballast and thermal protector, but only in the after noon. I am having trouble convincing the customer that it is heat, if it's heat what are we to do?

 

[hillbilly1]

Yes, they are cycling randomly. The ambient temp above the fixtures was 170F. the lights are in a church sanctuary 20' up in a sheet rock ceiling with a tin roof. I see you lived in Evansville Indiana, I grow you north of Terre Haute IN

Actually I'm just licensed there, we did some work there years ago, we are a nationwide company, so I am licensed in several states. We have done work in Terre Haute too, I put in a 600 kw generator there in a big box store about 10 years ago.

 

[hillbilly1]

They are core & coil multi tap ballast. They are cycling off & on the same day I install the new lamp and ballast and thermal protector, but only in the after noon. I am having trouble convincing the customer that it is heat, if it's heat what are we to do?

They probably need some power ventilation installed in the attic, they probably just recently went with a tin roof which may have changed the thermal characteristic of the attic.