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Hot Striking - HMI


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#1 gregory mandry

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Posted 17 August 2005 - 05:03 AM

I was recently trying to use a 6 k HMI from Arri and had problems with what I thought was a tempremental HMI. sometimes the lamp would go on, sometimes not. I wondered if it was a ballast problem. Arri said it was more likely a problem called 'hot striking' evidently a hot 6k HMI bulb often does not light can any one explain this and does anyone have a sollution other than just leaving the lamp on.

Gregory Mandry
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#2 Phil Rhodes

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Posted 17 August 2005 - 06:35 AM

Hi,

I've frequently used HMIs up to 2.5K and they always seem perfectly happy to hot strike; can someone confirm if the rules change with bigger ones?

Phil
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#3 Robert C. FIsher

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Posted 17 August 2005 - 01:35 PM

Hi,

I've frequently used HMIs up to 2.5K and they always seem perfectly happy to hot strike; can someone confirm if the rules change with bigger ones?

Phil

<{POST_SNAPBACK}>


The hot strike problem has more to do with using old bulbs, larger HMIs don't last as long as the under 1200 watt bulbs. As the bulb gets older the anode and cathode (it is an arc light so there is no filament) wear and get farther a part so when you switch off hot it takes more voltage to start the lamp again. Typical hot restrike voltages are 20-35,000 volts. To start a cold lamp the voltages aren't as high. A lot of this also has to do with lamphead design in which interior cooling makes a big difference. The cooler the lamp operates at the longer the bulb lasts.

I hope this helps.
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#4 Frank Barrera

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Posted 17 August 2005 - 07:53 PM

Like the man said- the age of the bulb and the design of the head are the culprits. The solution is to let it burn all day. But if you need to attempt a hot strike we usually tilt the head up just a few degrees and swing the door open. Heat does rise and this position will accelerate the cooling process.

I had a how strike problem last year during the day that ended with the Great Northeast Blackout. The air temp where I was was about 100 degrees F. There was no cooling down that bulb. It was a disaster.

Have fun.

Frank Barrera
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#5 Riku Naskali

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Posted 17 August 2005 - 09:14 PM

You could also check the microswitch, the head won't strike if the switch "thinks" the door is open. It's the black pin-like button somewhere, yank it a couple of times and see if it helps.

On the other hand, you know, they aren't supposed to be striked and restriked constantly... But usually no one cares about rented equipment.
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#6 gregory mandry

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Posted 22 August 2005 - 12:07 PM

thanks

guess i'll just leave them on in the future, makes tweeking them a little tricky.
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