I have a 100Watt metal halide ballast (ANSI Code M90 ballast is a Philips/Advance 71A5380) and fixture that I am now using as my room light (I have it in an old FloodPak housing). I have a nice Philips MasterColor CDM 100W/940 Med ED17 CL ALTO (MHC100/U/M/4K ALTO 281352)

I have a few questions about the ballast and capacitor

1. The original Philips/Advance capacitor was cracked so I bought a new one on eBay (12UF/400Volts) I have not used the fixture in awhile and for the first few nights the lamp almost went out every time a big electrical load was turned on/started. (Mostly the refrigerator) but tonight it is fine so did the capacitor just need a time to recharge? and is the capacitor in series with the lamp? I'm not big on electrical diagrams

2. I have been wondering this (I really don't know the answer) ever since I got my first HID fixture
Why does a hot HID lamp have to cool down before being able to be re-lit and re-strike an arc and does keeping a hot lamp powered hurt the fixture components (Ignitor, Ballast, and Lamp)


The ballast is from my apartment complex (They went LED) and my area looses power occasionally or has a brownout long enough to have the lamp extinguish. So the ballast kit I have has a lot of hard hours on it.

1. The original Philips/Advance capacitor was cracked so I bought a new one on eBay (12UF/400Volts) I have not used the fixture in awhile and for the first few nights the lamp almost went out every time a big electrical load was turned on/started. (Mostly the refrigerator) but tonight it is fine so did the capacitor just need a time to recharge? and is the capacitor in series with the lamp? I'm not big on electrical diagrams

That is not the capacitor, but the lamp needed some time to settle (the halide pool has to "move" to the new "coldest spot", corresponding to the new operating position of the lamp).
mainly when the lamp is not really new, it may take longer and in the meantime it becomes a bit more sensitive to voltage dips.

2. I have been wondering this (I really don't know the answer) ever since I got my first HID fixture
Why does a hot HID lamp have to cool down before being able to be re-lit and re-strike an arc and does keeping a hot lamp powered hurt the fixture components (Ignitor, Ballast, and Lamp)

The cause is the pressure inside of the burner:
When the lamp is cold, all fill, except the buffer gas, is solid (halides,...) or liquid (mercury), so the only component in the atmospere is the buffer gas. That means there is rather low pressure inside of the burner, so quite long free paths to accelerate the electrons, so easy to break down (ignite).
When the lamp is hot, the fill is evaporated, so forms a rather high pressure and high density atmosphere, which is then way harder to electrically break down. So unless the lamp/socket/ignitor are especially designated as "hot restart" (automotive HID systems, some projector bulbs,...), the ignitor is not capable to ignite the arc when the lamp is hot.
Consequently the lamp has to first cool down, so the fill material to condense, the pressure drop so the breakdown voltage becomes below the voltage the ballasting system is capable to deliver.

Some lamp EOL mechanisms (lamp cycling) are exactly result of this effect: The pressure rises so high, even the main arc can not be sustained and the lamp extinguishes, cools down, restrikes, heats up again and the cycle is repeating over and over.