Are HMI's safe to run off diesel power gens?

Daniel Smith · June 14, 2008

Hi.

HMI's are very touchy as to the current they receive, if the current begins to vary then you are essentially putting a HMI on a dimmer, which obviously isn't a good idea as it will blow the ballast.

So what I'm wondering is, what kind of head room in a diesel power generator would I need to make powering a HMI safe?

The reason I'm a little worried is that with diesel, I'm sure it's not going to be a consistent flow of X amount of watts, it will vary, like anything else ran on diesel.

Cheers for any advice.

Dan.

timHealy · June 14, 2008

Most larger generators used on films are diesel. It is only in the small putt putt world that gas seems to main fuel supply.

Basically, it is the electronics and a governor that controls things like voltage and hertz (frequency, cycles), not the fuel supply.

Best

Tim

Matthew Parnell · June 15, 2008

The largest petrol generator I've worked with is a 5kva ages ago, all the rest have been diesel.

What to look for is a well maintained and serviced generator, there are many companies that specialize in silenced film and entertainment generators, ranging from smaller trailer generators, to truck generators, and obviously these guys are the way to go.

If you can, get Electronic ballast HMIs, as they tend to be both more efficient and in my experience have been less fussy about power(ie voltage drops over long cable runs.

Edited June 15, 2008 by Matthew Parnell

June 16, 2008

If you can, get Electronic ballast HMIs, as they tend to be both more efficient and in my experience have been less fussy about power(ie voltage drops over long cable runs.

Also electronic ballasts are generally safer than magnetic ones, and they weigh less :]

Edited June 16, 2008 by Evan Pierre

timHealy · June 16, 2008

Hey Matt,

I don't agree with the voltage drop thing. Though I have never done a side by side comparision, I have never seen anything to suggest that electronic ballasts are less prone to dropping out due to low voltage. Voltage drop to me is more of a matter of physics: voltage, cable length and load and not related to one ballast being better than the other.

If one ballast is designed to run off a lower voltage than the other, well that is a different issue.

Just my 2 cents.

best

Tim

timHealy · June 16, 2008

Also electronic ballasts are generally safer than magnetic ones, and they weigh less :]

Hey Evan,

In what matter do you find electronic ballasts safer other than hernia prevention? I only ask because I have only witnessed electronic ballast exploding and I have never seen a magnetic one doing the same. Not that it has never happened.

Of course most people recommend not sitting on any ballast while they are on to save the family jewels.

Best

Tim

Edited June 16, 2008 by timHealy

Daniel Smith · June 18, 2008

Sorry, should re-phrase that, I mean drop in wattage. ie. If I am powering a 6k HMI on a 6.5k generator, I'm worried that the generator might vary in output, even if it's for a split second, and damage the HMI.

I mean, when you begin a lawn mower it's not always consistent, even just standing still.

timHealy · June 20, 2008

Hey Daniel,

I think you have your terms mixed up.

Wattage is more a component of the draw of a light. Sure a generator can produce a certain amount of wattage. say for example 5000 watts. If you plug in a light that draws 2500 watts the generator will provide enough electric for that. If you plug in a 6000 watt light the generator will try to produce it and rev really high, it will quickly give up and the breaker will trip or the genny will shut down. So a drop in wattage is actually beneficial to a generator so it doesn't have to work hard.

If the voltage dropped while the light is on, the light will simple go out.

The only way you can really damage a light is give it more voltage than it is rated for. A tungsten light with over rated voltage will flash like a camera bulb and an HMI might have internal issues in the ballast with a best case scenario being a blown fuse.

HMI's are used all the time on smaller generators so don't sweat it

Best

Tim

Matthew Parnell · June 21, 2008

Hey Matt,

I don't agree with the voltage drop thing. Though I have never done a side by side comparision, I have never seen anything to suggest that electronic ballasts are less prone to dropping out due to low voltage. Voltage drop to me is more of a matter of physics: voltage, cable length and load and not related to one ballast being better than the other.

If one ballast is designed to run off a lower voltage than the other, well that is a different issue.

Just my 2 cents.

best

Tim

I have been in the situation three or four times where swapping out a magnetic ballast and replacing it with an electronic one has solved problems of lamps not striking. After doing tests, and putting meters across the power situation, voltage drop as a problem is all we could come up with.

Cheers,

Matt.

timHealy · June 22, 2008

I have been in the situation three or four times where swapping out a magnetic ballast and replacing it with an electronic one has solved problems of lamps not striking. After doing tests, and putting meters across the power situation, voltage drop as a problem is all we could come up with.

Cheers,

Matt.

I have not personally come across that situation but OK. I wonder if there is something that is different electronically between lights operating at 50 hertz 220 than 60 hertz 110 or 220 here. In NYC we seem to run into issues where some HMI's powered by square wave ballasts don't fire on certain phases off a generator. The thought is believed to be the way the generator is built and how it operates in single and three phase set ups. Some believe that in three phase one leg is not regulated like the other two. I am not an electrical engineer or a builder of generators so I cannot comment any further than that. Oh I am talking about 1200 or 1400 amp capacity film generators here.

Best

Tim

Edited June 22, 2008 by timHealy

Craig Bowman · June 22, 2008

Its not the generator itself but what's in front of it. If your system is designed properly these days the generator is powering a regulated power supply. Almost like a big UPS but for the purpose of keeping the power at a constant output level despite any minor ups or downs in the generator output which will also have additional circuitry to adjust the speed of the generator.