Magnetic ballast problem...

[Woodstock]

Help! One of my two 250 watt SE MH bulbs won't light up. The ballast humms really loud for about 30 seconds, the bulb barely lights, then the ballast shuts off.... it repeats this cycle every 5 min or so trying to fire the bulb....over and over and over Is it a bad capacitor, or a bad ballast?

This is the same one that I have had dimming issues with before but replacing the capacitor fixed it.

Here is a pic of the ballast...

 

[liveforphysics]

Help! One of my two 250 watt SE MH bulbs won't light up. The ballast humms really loud for about 30 seconds <this is the low voltage cathode warming stage> , the bulb barely lights <inductive flyback from stored flux upon the thermal switch opening the circut for the cathode heater> , then the ballast shuts off.... < unable to maintain kernal of plasma arc to get adquate temperature into the walls of the arc tube> it repeats this cycle every 5 min or so <cool down period before the bi-metal temp switch can reset to begin the cycle again> trying to fire the bulb....over and over and over Is it a bad capacitor, or a bad ballast?

This is the same one that I have had dimming issues with before but replacing the capacitor fixed it.

Here is a pic of the ballast...

Ok, the frequency and the cap size are what control the current that the bulb sees. The freq isn't going to be something you can change on this balast (at least without being REALLY clever). This means, your cap is likely whats limiting the current. Its also possible but unlikely that a failure inside the transformer (internal winding shortage) could be limiting adquate voltage to do the job, but from experience with how durable these suckers are (if installed correctly), my best bet would be on the cap being the cause.

If you are local I can test your test your cap and voltage etc for you.

*EDIT* I just saw that you are on the east coast, so I would look for some other local geek to help you.

 

[Woodstock]

Thanks for the reply

So, for us non-geeks, does a bad cap mean I need to get a new ballast?

 

[Woodstock]

It is the bulb!!!!!! I had a brain storm and switched the bulbs... the problem is that the bulb won't fire. It isn't the ballast at all...which is good news.. I think LOL~ Atleast I know how to change out a bulb

I've never had a bulb to stop firing. These Sun Aquatics are only about 8 weeks old too...