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Metal Halide MH troubleshooting

BFBOB

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Sep 20, 2011
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:headscrat I hope someone can give me a little guidance troubleshooting a couple of 70 Watt MH lights I have. I built the setup to be portable, installed the ballasts in a metal box just big enough to hold them with nearly no ventilation. I used standard AC outlets to plug in the fixtures. I realize the potential problem of plugging in standard lights, but I'm the only one who uses them. I used them for photographic lighting, so they were on for only a few minutes to maybe half an hour at a time.
Then, one fine day I forgot and left them on for something like 12 hours. When I discovered my error, the lamps were no longer lit and the box was too hot to touch comfortably. The ballast frames were much too hot to touch, not boiling hot (I did the spit test), but probably 130 or so. After cooling down completely, they don't work.
So, not many components to consider, but since these are the only ones I have, I can't do the ol' diagnosis by substitution trick. The ballasts, as I understand it, are just transformers, and I can check continuity easily enough. If they check good, which of the other three components is most likely to have failed, the capacitor, ignitor, or bulb? All components except the bulbs are in the same box.
Thanks in advance, and I think my next investment will be a timer-switch!!
 
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Greatbear

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Most ballasted fixtures have a thermal fuse that is part of the ballast, some are auto-reset, though most are one-shot deals, once they open, it's new ballast time. The thermal fuses open up the supply side, so a simple test with a DMM or continuity tester will tell you the condition of the fuse. If you read an open, the ballast is toast. If there is a nominal resistance the problem can be with the cap or ignitor, but not guaranteed.
 
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BFBOB

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Thanks for the pointer. I tried a search online too, but came up dry. This Forum ROCKS.
 
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BFBOB

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Be very careful as the lower wattage MH lamps are pulse start, & can fry a meter w/ the high voltages produced (400W & smaller HPS are around 2500V not sure what MH is), here is a troubleshooting guide to help.

http://www.hydroponics.net/productdocs/HID_Pocket_Guide.pdf

I Googled "HID ballast troubleshooting".

Thanks to NORCAL and BIGBEAR--I checked things out after reading the Pocket Guide -- loads of good information -- and you ain't gonna believe this. I mentioned this is a portable setup, right? So I made sure to get medium base MH bulbs so they'd fit into ordinary clip lights. And ordinary clip lights have ... wait for it ... SWITCHES!!! I turned the dang things off on the light fixtures, not the main switch on the ballast box. The troubleshooting process led me to that pretty quick, turned'em on, and the whole rig works fine. No harm done!!
 

walrus

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Maine
Pulse start MH use a different socket. It has more insulation around the center contact because of the pulse sent by the ignitor to start the arc. Sooner or later you'll find a regular socket will burn up because it will arc thru .According to an Advance(ballast manufacturer) tech support guy the pulse for a MH175 is 4000 volts.
 
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BFBOB

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Pulse start MH use a different socket. It has more insulation around the center contact because of the pulse sent by the ignitor to start the arc. Sooner or later you'll find a regular socket will burn up because it will arc thru .According to an Advance(ballast manufacturer) tech support guy the pulse for a MH175 is 4000 volts.

Good point. I should be able to find switchless ceramic sockets that will work with these fixtures. Meanwhile, I'll keep an ear out for arcing. I use them rather seldom so they should last a good while. They're 70 watts, not 175. Not sure whether that would indicate a lower ignitor voltage -- even 2kV is way above a standard socket's rating! Very low current, though.
 

Norcal

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If a lampholder is pulse rated it will be marked as such.
 
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