I have been trying to get 575w to run for awhile. First I got a 600w eballast pretty cheap on ebay, but it had a low voltage shut off and liked to shut off once the ballast warmed up.

Now, I have been trying to run the 575w lamp on a 400w s51 ballast. I got the ballast, and the extra 13.5uf caps (Natural Newbie's suggestion). I wired it up and it worked flawlessly for about 10 lights. Then one time it wouldn't light, I could see the "blue spark" jumping the arc, but it wouldn't actually light. So, I unplugged it. Now I get no blue spark. So, I left it plugged in for 10min to see if it would eventually light. No change.

I assumed that since I was using a 400w ignitor that it was broken because I was trying to overdrive it too much. So, I ordered a new 600w ignitor and wired it in. I still get no light. The ballast does hum. Maybe it is a problem due to the capacitor. I know the lamp is still good because I tried it on my 600w ballast and it lights.

Anybody now what might be the problem?

Thanks in advance.

Lay it all out for us. What's the total effective capacitance you're using with the S51 setup? Now you're using a 600W ignitor with the S51 and some capacitance, correct? And you get no start-up spark. Were/are you using forced cooling on the S51 ballast when overdriving 400W to 575W? I use a dual S51 ballast setup and have stubborn start-up of my 575W lamp at times. I start on one ballast and then cut in the second after the lamp fires as per ArizonaVideo's recommendations. I cannot say with certainty how one may mix and match ignitors as you've kinda done.

Total capacitance: 68.5uf

Ignitor: 600w hps

I did not have cooling on it. I will when I run it for long periods. But so far, I have only been running it for about 10min at a time.

Beyond me. I'd caution against short duty cycle runs of the lamps we use though. Supposedly it's not good to run lamps multiple times for 10 minutes only. I think like 30 minutes or more per burn is recommended. It escapes me why I just remember not to do so. My brain is too full to remember all the nitty gritty details. Some will say it don't matter but . . .

ArizonaVideo schooled me on the details of using an S51 and there was something about the increased capacitance necessary to properly drive the 575 meaning startup could potentially be more touchy. IIRC he suggested starting with a lower capacitance and then switching in the extra capacitance required beyond the typical uF value used for a 400W lamp. Mayhap that is the problem you are now experiencing in full or in part. You could try taking out the extra cap just to see if your lamp then magically ignites??? Just a thought.

Edit: Note that switching a cap into an energized circuit introduces its own set of potential problems because the switch used can deteriorate due to excessive arcing. But switches are relatively cheap and plentiful and easy to replace if one plans ahead.

I tried it without the extra caps. It still doesn't work. Is it possible that my 55uf cap is dead? I regret running it for short duties now, I just hope I can fix it.

Got any electronic experience? Google "testing a capacitor" or similar for advice on determining whether you have a bogus cap. Do you think you ever overheated the ballast? Smoking or stinking? Shouldn't have since you only ran short durations.