HMI - electrical failure with restrike

[emilian]

Hi guys, just a quick question about a situation with an HMI fixture.

We were using a 1200w arri HMI with a 3rd party (chinese) electronic ballast and osram bulb. Both the lamp head ignitor and the bulb are designed to withstand a hot restrike. Not sure about that 3rd party ballast, but it survived.

Unfortunately, there were 2 consecutive power downs of the whole electrical outlet. After the 1st power-down, the HMI started to pulsate, but was still on. 10sec later, after a second power-down, the HMI died. Even though the electricity came on, the lamp was still dead.

We pulled the plug off, after 2 minutes of it still sending voltage to the ballast, while the lamp was dead. Were these 2 minutes doing any harm to the ballast?

So then we waited 10 mins for the bulb to cool off, then switched it back on and miraculously, it started! Ok life was good again.

I am just worried that we were frying the ballast, although it worked.

 

[dwiener]

Older (more hours of use) bulbs may not do a hot restrike without some cool down. It's pretty hard to fry a ballast. I'd worry more about why you kept tripping the circuit breaker.

 

[paulears]

HMI lamps are an open circuit when not struck - so sending the running voltage and current to them when n to struck doesn't do anything, including make them light up. If your ballast cannot do a hot restart, then you must wait for it to cool down - which isn't long really - maybe a couple of minutes? When you press the start button, do you hear it arcing in the lamphouse - that nasty buzzy sound? If you hear that, and the COOL lamp doesn't strike, then normally that's down to a lamp that has failed. Occasionally, it can be the ballast failing and not producing enough HT to strike the arc. The only real test is a new lamp (which is of course wasted, if the new one doesn't strike either.

One thing to check on the Chinese ballasts is the wiring in the connector at the light end - if you open it up, short out all the pins with a screwdriver before touching them, residual charge can really hurt! Often the connectors have been arcing inside the connector - and this could be the problem.

After the 1st power-down, the HMI started to pulsate, but was still on. 10sec later, after a second power-down, the HMI died. Even though the electricity came on, the lamp was still dead.

So the HMI pulsed, as in flickered? Was this when you tried to restart? The flicker is quite normal on a hot lamp with a non-hot strike ballast. You said it was still on, so do you mean the lights/power died and immediately restored, and then it flickered? It's possible the ballast tried to restart the lamp when it was already lit, which could damage it - but that's rare.

Chinese ballasts can be rather unpredictable and variable on the life span front. I have 3, and only one still runs properly.

 

[emilian]

Thanks for the info, paulears!

Yes, the lamp flickered after the 1st restrike, which now I know, was normal. The lamp could not re-strike for a 2nd time, I guess, because the voltage needed to go even higher and the ballast was not designed to do that.

My only worries were of the ballast switch/circuit left ON running, even though the bulb was already off. So that was not damaging anything right?