Electronic Ballasts and Genies

[Matt Workman]

I was under the impression that you needed a crystal synch (read: rented from a grip/elec company) generator for HMI's regardless of the ballast type.

 

For HMI's with electronic ballasts can you use a cheapo put-put from Home Depot?

 

Thanks.

 

Matt

[Rob van Gelder]

Electronic ballasts have often a switch for 50 or 60 Hz and Flickerfree. In the last state, the input frequency is less important, as it is internally controlled .

 

Your main problem is the start-surge that many ballast have, this will often throw your cheap genie into an off-speed cadenze, e g. it will fall down suddenly in speed, trying to recover, and together with the demand of the ballast this might result in an oscillating effect, which could damage the ballast,generator or both.

 

a 575 W on a 3.5 Kw genie might do, and even 2 or 3 if you start them with some interval, but a 2,5 KW on the same genie might not work.

 

Also keep in mind that the there are 2 types of electronic ballast: with or without power correction. With power correction, the wattage taken from the generator is only slightly higher than the rated load, but without power correction it can be a lot higher, and even though your total load is less then the rated output, the actual power demand might be a lot higher.

When using old style magnetic ballast is is true for sure!

 

 

In general, i think it is only safe to use Tungsten lighting on Home-Depot style genies.

[Ryan McMackin]

For what it's worth...

 

I've successfully used a 3000W Honda generator (http://www.hondapowerequipment.com/ModelDetail.asp?ModelName=eu3000is) to power an Arri 1200 HMI Par w/ electronic ballast. The light output was consistent and the genie seemed to handle the load fine---maybe I was just lucky!?

[Matt Sandstrom]

i've run one 800w redhead and one 575 hmi on a 2k honda, which worked as long as i switched on the redhead first. the other way around caused the hmi to die.

 

/matt

[timHealy]

For HMI's with electronic ballasts can you use a cheapo put-put from Home Depot?

 

Basically, yes, as long as the generator is large enough for your load. The Honda EU series of generators (2000, 3000 etc) are really terrific and quiet. And you can use two 3000's synced to gether to use smaller 220 volt HMI's

 

Best

 

Tim

[Barry Cheong]

Is it still possible to get flicker using a electronic square wave ballast on a cheaper genny? Or does the fact that's it's a flicker free ballast negate all that? I've heard that some people won't guarantee flicker free operation on certain gennies regardless of the ballast.

[timHealy]

It is possible to get flicker with any generator and any HMI when something is not operating properly. But you can get away with using an electronic flicker free ballast on genny without crystal sync.

 

As I was told from a techician with one lighting manufacturer, an electronic flicker free ballast is flicker free all the time in a small range from say 20 to 30 frames per second in silent mode at 50 or 60 hertz. When you switch to flicker free mode it is flicker free at all other shooting speeds but you get that high pitch wine from the head when the additional sine wave clipping occurs.

 

But check with the manufacturer of whatever brand you are using just to get the specifics on that brand.

 

Best

 

Tim

 

PS the honda Eu series are great generators for film shoots. True sine wave, 12 volt DC and they are really quiet. I just saw an EU 7000 watt generator yesterday that you can run a small 220 volt HMI off of.

 

http://www.hondapowerequipment.com/gensup.asp

Edited September 23, 2006 by timHealy

[Rob van Gelder]

I would not trust the technician too much and it might not be applicable for all brands as well. As I know it, the silent position on electronic ballasts gives you true 50 or 60 HZ output, and then you need to shoot at certain speeds only, combined with a shutter angle you can have a few possibilities:

 

20 fps/180/50 is ok, 24fps/172.8/50 is ok, 25/180/50 is ok, 33.333/180/50 is ok and there are similar positions for 60Hz too.

 

Look in the American Cinematographer Manual and you can find a list of what is checked and confirmed/safe.

[Rob van Gelder]

I just got confirmed by the instruction manual from the ARRI electronic ballasts, in this case the 6/12 K version, but the specs are the same for their whole range of electronic ballasts.

 

in the 50/60HZ position you can ONLY USE SPECIFIC FRAMERATES, there is no margin from 20 to 30 fps or so.

That is only valid in the flickerfree position, but then from 0 to 10.000 FPS.

[Joseph Carney]

When planning on using portable genies, either from Honda or Kipor, just make sure you get the ones where model numbers end in 'i'. These are rated for sensitive electronice equipment. I think the 'i' stands for inverter and provides consistant voltage,amps and wattage within spec. On the Hondas', sustained power is 80% of peak (ie 2000i is 1600 continuous). Kipor which has similar models and are less expensive, uses a slightly different scheme, so you can't depend on their model numbers to indicate sustained and peak output. So check the specs on Kipor before purchasing. Their 3500ti is becoming very popular.

 

The sustained vs peak is because of their use in the RV market. When you turn on an Air Conditioner in a Travel Trailer or something similar, there is a sudden increase in demand until the AC gets ramped up. These gens were designed to handle that sort of sudden increase without hurting other equipment. Turns out they work great for film/video too.

[timHealy]

I would not trust the technician too much and it might not be applicable for all brands as well.

 

Why would you not trust the technician I spoke of? He worked at Lightmaker and if I remember correctly, was one of the first to have electronic flicker free ballasts. So he was the one who told me about the way their ballasts worked.

 

Basically electronic ballasts are flicker free all the time except that in "silent mode" one would have to be in the 50 or 60 hertz setting. But you do get a small window of a flicker free frame rate at those settings. That is why you can use an electronic flicker free ballast on a non crystal generator. The sign wave is still clipped as it is in flicker free all the time mode except one doesn't get the wine in the head during sound takes.

 

I did mention one should check with the manufacturer of the lamps you are using just to be sure. You said you read the Arri specs but I called Arri's US headquarters in Blauvelt NY, and spoke to Andre who manages the lighting repair department. He confrimed that Arri ballasts do have a flicker free window at 50 to 60 hertz of approximately 20 to 30 frames per second. And then there is the flicker free all the time setting.

 

But if one is shooting offspeed, even just a little, it never hertz to go to the flicker free all the time setting.

 

Best

 

Tim

[Rob van Gelder]

Tim, if the Arri manual clearly states that in the Silent (50/60 HZ) the ballast is working similar as a conventional (magnetic) ballast, only it has a "Active Line Filter" that cancels the negative things from a magnetic ballast.

 

these are the exact words, and you may choose to ignore them, but Arri has a reputation to maintain:

++++++++++++++++++

1) in the position flicker free (yellow LED indicating light)the electronic ballast will operate flicker free up to 10,000 fps, the lamp gives out a constant light.

 

2) In the position "50 Hz" and "60 Hz" (red LED indicating light) noise will be substantially reduced, the amount depending on the lamp, in some cases even to almost zero.

 

The light, however, is NOT flicker free any more.

 

When operating in this mode, the same limitations for speed of camera and/or shutter angle apply as for magnetic ballasts. All other adventages of the electronic ballast will apply as before!

 

If in doubt: (i.e. remote from ballast) with flicker analyser P.R.O.F. light can be checked to be flicker free or not.

++++++++++++++++++

 

Anyway, I am off to Germany next week where i will attend a workshop about maintenance and use of Arri Electronic Ballasts and Lamps. I will certainly put this debate on the table there and inform you about it.

 

It's better that technicians really know what they are talking about and in 2 weeks I will certainly have the answers from the very designers of these ballast.

Then I stand corrected, or you have to correct your source, seriously!

 

Best, Rob

[timHealy]

This is getting stupid. Two people in two different lighting companies told basically told me the same thing and you don't believe me or them. So please do talk to the Arri guys and anyone else you need to.

 

But I really don't understand why you don't understand that a flicker free electonic ballast is electronic all the time. It does not miraculously turn into a magnetic ballast while in the 50 or 60 hertz mode. Electronic ballasts are square wave all the time, period. They just work a little harder in the flicker free all the time mode.

 

I am in no way suggesting you should keep the ballast in 50 or 60 hertz if shooting off speed or ignore safe HMI shooting speeds. I am just saying that there is a flicker free window of approximately 20 to 30 fps in those modes. That seems to be the only point we disagree on. Or else one would get flicker while using a non crystal generator (but I don't know anyone who wouldn't put an HMI in a flicker free all the time mode while on such a generator)

 

I would love to hear what the Arri guys in Europe have to say. I wish I could attend such a class as well because HMIs are so damn sensitive and troublesome.

 

 

best

 

Tim

[Rob van Gelder]

No need to get personal Tim.

I only tell you and everybody else what is in the manual. and I am sure it is written there for a reason.

 

The big difference between the flicker free and the 50/60 HZ position is that you have a square-wave pattern on the current output that goes through "0 volt"and therefore the light output falls down considerably. In other words, in the 50/60 HZ position you have a lot of "dark" time between the "light" time.

 

however in the flicker free position the electronic ballast runs on 75 Hz and also fills the "dark" periods, giving a constant light output, in fact it is like DC-current, with only very minor dips between the square waves.

 

Looking at the ASC manual, there are some nice graphs that make things more clear, at least to me. :)

I want to attach it here, but that would infringe on the copyright.

 

another graph shows that there is a certain range in varying the shutter angle, as long as the frequency from the supply AND the camera speed are constant 50 or 60 HZ.

 

I will tell you later what the factory's opinion is

[Rob van Gelder]

Or else one would get flicker while using a non crystal generator

 

 

Tim, this is exactly what I experienced once at a shooting, when I was a camera assistant. We were shooting on location, after the first day we get a call from the lab that they notice a real flicker/pulsating problem in the highlights/glare in shot (tennis court, indoor, rubber floor).

We were using magnetic ballast at that time, shooting high speed (50 fps, 100 fps).

We discovered that the generator was running a bit faster, like 51 Hz.

 

The graphs in the ASC manual also show that you have a very limited tolerance in the frequency.

This seems to be even smaller when shooting high speed .

 

Magnetic ballast and electronic ballast in in 50/60 HZ mode have a similar output on the lamp.

The electronic is only lighter and often is phase-corrected on the mains side

[timHealy]

No need to get personal Tim.

 

Did I say something that you may have interpreted as personal? I just find it odd that you seem to doubt the very technicians who work and built the ballasts and equipment for the two companies that I mentioned.

 

Best

 

Tim

Edited September 29, 2006 by timHealy

[timHealy]

We were using magnetic ballast at that time, shooting high speed (50 fps, 100 fps).

We discovered that the generator was running a bit faster, like 51 Hz.

 

That was your problem there. They used a magnetic ballast with a non crystal generator. That was a dumb mistake. Nothing but a sure recipe for disaster. Who on the crew thought that would work? The electricians? The DP? A cheap producer? Experienced electricians would have known better. If you were the AC it would not have been your job to ensure the generator was crystal. I think your responsibilities as the AC would have ended with ensuring the camera was utilizing an HMI safe shooting speed which I assume you did because at 50 hertz 50 and 100 fps are safe.

 

If you had an electronic square wave ballast, the footage would have been fine. Or if they had a crystal generator the footage would have been fine. With a square wave, at 50 and 100 fps it would be necessary to shoot in the flicker free all the time mode.

 

But why would you want to use an example of what occurred with a magnetic ballast in a discussion about square wave ballasts? That is a rhetorical question.

 

I look forward to hearing what the Arri technicians tell you.

 

Best

 

Tim

Edited September 29, 2006 by timHealy

[Matt Workman]

Good info. I would expect the newer Arri-Sun HMI's with Flicker-free ballasts to be fine with ungoverned power.

 

I'm trying to figure out if some 1980's Lee HMI's with electronic ballasts would have a problem. The do not have different settings like 60hz/50hz/FlickerFree. They just have on and off.

 

I'm hesitant to just try it out, for obvious reasons. If anyone knows their specs or can ask their grandfather if they know I'd be interested.

 

Matt :ph34r:

[timHealy]

I don't recall Lee making electronic ballasts in the 80's. But I could be wrong. The first ones I became aware of were Lightmaker in 1992 or perhaps it was 1993. I do have to say they were very troublesome back then and asked for magnetic backups for all HMI's when doing a job that had been supplied with Lightmaker ballasts.

 

Best

 

Tim

[timHealy]

PS the honda Eu series are great generators for film shoots. True sine wave, 12 volt DC and they are really quiet. I just saw an EU 7000 watt generator yesterday that you can run a small 220 volt HMI off of.

 

http://www.hondapowerequipment.com/gensup.asp

 

 

Oops I made a mistake. The Honda 7000 is an EM series not an EU. The nice and quiet EU's only go up to 3000 watts and the EM series are louder. But a 7000 is a nice size nontheless.

 

Best

 

Tim

Edited October 3, 2006 by timHealy

[Hal Smith]

Cheap test: look at the HMI through any ac rotating fan. If you see fan blades slowly rotating, it's not flickerfree, if you don't see fan blades, it's flickerfree. I just tested this with my magnetic ballast MSR stage lights - I saw fan blades.

[timHealy]

that could be an expensive test if you don't get it right if one needs to reshoot.

 

best

 

Tim

[Hal Smith]

that could be an expensive test if you don't get it right if one needs to reshoot.

best

Tim

Maybe you needed to take one of my stroboscope labs from me when I was a Physics Teacher at the University of the South?

 

The principle is that AC fans use induction motors which will rotate at a slightly slower speed than a synchronous motor would. If the fan is driven by a known frequency from either a commercial power source or a crystal generator, then if you look at a pulsating light source you'll see slowly rotating fan blades. If you look at a square-wave flickerfree or incandescent source there won't be visible fan blades, just a blur. There really isn't much different logically between a camera shutter and a rotating fan blade.

 

What I've suggested is a good, low budget test that is better than guessing. I agree that anyone on a high dollar shoot should have a real flicker tester with them and/or be renting gear that can be trusted absolutely. But there is a world where a ten dollar fan could save someone a lot of grief. Maybe I should repackage cheap Chinese fans, call them "Professional Gaffer's Flicker Testers" and sell them for $250.

[Matt Workman]

Tim: I bought the Lees from good ol Visual Products, so I'm not sure when they were made. But they are electronic and they are old. If you are saying they are from the 90's then I feel better already. Though I'm selling them pretty soon.

 

Hal: Fan test sounds good. But I don't think I'd diagnose any lighting problems with it. It may have worked with for your sample: magnetic ballast vs. newer Arri Universal Ballast, but unless you have a Lee to test too then I'm still out an answer.

 

It may be easier to use a 2k or 5k (tungsten) and just get a huge generator. Tungsten lights are so easy.

 

Thanks.

 

Matt

Edited October 4, 2006 by Matt Workman

[Hal Smith]

Hal: Fan test sounds good. But I don't think I'd diagnose any lighting problems with it. It may have worked with for your sample: magnetic ballast vs. newer Arri Universal Ballast, but unless you have a Lee to test too then I'm still out an answer.

It may be easier to use a 2k or 5k (tungsten) and just get a huge generator. Tungsten lights are so easy.

Thanks.

Matt

The test should work as a fail-safe with the Lee's, I'll guarantee that if you see moving fan blades on the Lee's that they're not safe unless on crystal or commercial power with safe shutter speeds. If you don't see moving fan blades then it's probably worth a test with some cheap short ends.