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what are possible causes and solutions for low output voltage on a HID ballast?

HV starting pulse is normal, but then output voltage drops to around 1.5-2VAC.  no obvious damage to PCB or components within.

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Is that against a real HID lamp  ? Or a simulated load ? Or no load ? 

jhvh.one (author)  steveastrouk7 years ago
that's with no load, just the multimeter.....do i need to check the output voltage with the lamp connected?   
Yes, you have presented the PSU  with a fault condition ! Its whacked the tube with the starting pulse, fully expecting the thing to conduct and demand a lot of current at a low voltage ( I don't know what the tube parameters are), and you've not given it anything. Its probably shut down as a safety measure, but the lamp is pretty low impedance when its on as far as I can remember, so 1.5-2V might be nominal for all I know,
jhvh.one (author)  steveastrouk7 years ago
checked output voltage with the lamp connected, similar results, voltage was fluctuating around 1.84VAC....there's a brief blue flash in the arc tube when i power the ballast on.  the lamp only has about 200 hours on it... 
ballast2.jpg
I assume the ballast strikes as soon as its powered ? Any way of testing it against another tube ? 200 hours may not be long, but it may still be screwed....

Steve
jhvh.one (author)  steveastrouk7 years ago
aha! i guess it was the lamp after all.... i didn't have another 400W metal halide to test but figured it wouldn't do too much damage to briefly connect a lower wattage lamp.  so i used a 175W mercury vapor lamp and it fired right up.  
for $30 my projector will be back in business....

thanks for your input steve! 
Fix ! AND you now know how a HID ballast works.
Result !

Steve
jhvh.one (author)  steveastrouk7 years ago
thanks for the info! i'll have to test this a bit more, i see... and i will report back 
lemonie7 years ago
Is this something that has stopped working after a long/short period in use, or something you're adapting for another purpose?

L
jhvh.one (author)  lemonie7 years ago
This is the ballast for the 400W metal halide in my homemade video projector that has stopped working after maybe a year and a half of minimal use. I used it infrequently until 3 months ago when i used it for approx 12 hrs/week.  Just the other day, i powered the projector on, and noticed that the arc tube had a brief, faint blue flash before going dead.  I figured with not much more than 200 hours on  the lamp, that the problem was not there, but with the ballast.  So I checked the voltage at the ballast output and found it incredibly low.  I would like to try to repair the ballast, or else i'm out $140 for a new one...although perhaps i could fit a low cost ballast kit into this one's heatsink/enclosure.....