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Striking loads for HMIs

hmi strike load initial

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#1 Ella Huovinen

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Posted 20 February 2014 - 06:39 AM

I was wondering what kinds of striking loads do different HMIs have (1,2 kW, 2,5 kW.. and so on). I have been taught that, for instance, 4kW HMI needs a 6 kW power source because of its initial spike in drawing electricity. Can one calculate the initial strike load? I understand that older ballasts use more power when striking than new ones. Also, if one cannot calculate the initial load (for some reason or other) is there a general rule of thumb to go with?

 

Cheers,

Ella


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#2 Matthew Parnell

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Posted 20 February 2014 - 04:28 PM

That is true of older induction HMIs. They draw more load at strike and the load decreases as the lamp comes to temp.

Electronic HMIs draw less at strike and the load increases as the lamp comes up.

Always allow some headroom when working with HMI. Because of power factor, older ballasts without Power factor correction tend to draw significantly more current. If you have a look through the posts by Guy Holt you will find an extensive amount of information on maximizing what you can do small power sources. Alternatively you can run a larger genset, have lots of headroom and fewer headaches.
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#3 Guy Holt

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Posted 20 February 2014 - 06:35 PM

If you have a look through the posts by Guy Holt you will find an extensive amount of information on maximizing what you can do small power sources. 

 

This is a complicated question, and given the amount of mis-information out there, it is hard to know where to begin. What makes it so complicated is that when it comes to running HMIs, Fluorescents, and LEDs on small portable generators, it matters not only what type of generator you use but also what type of power supply (ballast) the light uses. These issues have been vexing set electricians for years.  Use this link for an informative newsletter article I wrote that explains the electrical engineering principles behind these issues and how to resolve them. 

 

 

BoxBookLinkGenSetFP.jpg

 

 

This article is cited in the just released 4th Edition of Harry Box's "Set Lighting Technician's Handbook" and featured on the companion website "Box Book Extras." Of the article Harry Box exclaims:

 

 

"Great work!... this is the kind of thing I think very few technician's ever get to see, and as a result many people have absolutely no idea why things stop working."

 

"Following the prescriptions contained in this article enables the operation of bigger lights, or more smaller lights, on portable generators than has ever been possible before."

 

The article is available online at http://www.screenlig...generators.html

 

Guy Holt, Gaffer, ScreenLight & Grip, Lightng & Grip Rental in Boston


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#4 Ella Huovinen

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Posted 21 February 2014 - 11:11 AM

Thank you for replies and the link!

- Ella


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#5 Eric Wobma

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Posted 23 February 2014 - 11:55 AM

Only in Theorie can you calculate how much the ballast of an HMI draws, and yes, it ALWAYS spikes when starting up, even though the brand new electronic ballasts do that a bit less than the previous generations of electronic ballasts.

 

The reason any calculation will be somewhat or a lot of in the Real World is: there are too many unknown factors.

How much cable do you have on the floor before reaching the ballast.

What kind a cable ?? (ALWAYS continue as long as possible with the most powerful cables, before splitting them up !!)

 

How old are the cables ?

How well maintained are they ?

Is it freezing or rather warm/hot on location ???

 

European Power is different from North America, so maybe it is different for you over there (although I did not ran a mock in Montreal, Quebec, when shooting there…), but I always TRY to stay at a 2/3 load of the full capacity.

Of course, sometimes that is not possible, money wise.

 

The Link Guy Holt provided is great !!

 

many Greetings from Amsterdam !!


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