Electronic Ballasts and Genies

Barry Cheong · October 5, 2006

If a twistlock plug on a generator puts out 30A and you get an adapter cable to go to 3x 15A household plugs that 30A gets shared over the 3x 15A plugs?

An adapter cable like this:

http://www.nooutage.com/g01912.htm

timHealy · October 5, 2006

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.

I certainly don't doubt your abilities as a physics teacher and I understand your point, but you did get the meaning of my sarcasm. I doubt there is any DP in the world who would be shooting a larger motion picture or a high profile commercial and trust a 10 dollar fan to check flicker. My question to you is how does one explain to a producer that may be spending hundreds of thousands of dollars a day, that the days work, no matter how well founded, was checked with a ten dollar fan?

Best

Tim

Edited October 5, 2006 by timHealy

timHealy · October 5, 2006

If a twistlock plug on a generator puts out 30A and you get an adapter cable to go to 3x 15A household plugs that 30A gets shared over the 3x 15A plugs?

An adapter cable like this:

http://www.nooutage.com/g01912.htm

So this is a 120 volt 3 pin twistlock?

You can make an adapter and put as many 15 amps plugs on it as you wish but the breaker will trip at it's capacity rating which in this case is 30 amps.

Any practical electrician would make an adapter with two 15 amp edison plugs on it as 15ax2=30a. If you wanted to get really fancy you could put a 15 amp breaker on each line, but hardly anyone does that if it is for your own use. In a worst case scenerio, you could overamp one 15 amp plug to 20 or 25 amps, but the 30 amp breaker would not trip. Eventually it would burn up. So always check the amps of the equipment being plugged in and do the math.

best

Tim

Barry Cheong · October 6, 2006

So this is a 120 volt 3 pin twistlock?

You can make an adapter and put as many 15 amps plugs on it as you wish but the breaker will trip at it's capacity rating which in this case is 30 amps.

Any practical electrician would make an adapter with two 15 amp edison plugs on it as 15ax2=30a. If you wanted to get really fancy you could put a 15 amp breaker on each line, but hardly anyone does that if it is for your own use. In a worst case scenerio, you could overamp one 15 amp plug to 20 or 25 amps, but the 30 amp breaker would not trip. Eventually it would burn up. So always check the amps of the equipment being plugged in and do the math.

best

Tim

Thanks Tim! Now in the case of the Honda EU3000is genny the twistlock is a 30amp plug outputting 23.4 amps at 120V. If you made an adapter with 1 15A edison on it would that edison be able to pull the full 23.4 amps but subsequently eventually burn because the plug is only designed to take 15A? Additionally if you broke it out to two edisons instead would it be split evenly to 11.7amps on each plug?

timHealy · October 6, 2006

If you made an adapter with 1 15A edison on it would that edison be able to pull the full 23.4 amps but subsequently eventually burn because the plug is only designed to take 15A?

Right. But the chances of having something (a light or piece of equipment) that draws 23 amps but only has a 15 amp edison plug on it is probably not likely unless someone did an after market change which wouldn't be a very good idea.

Best

Tim

Additionally if you broke it out to two edisons instead would it be split evenly to 11.7amps on each plug?

No. Electricity on its own doesn't work like that unless you have some sort of fuse or electronic limiter on it. If you had two 15 amp plugs and one light draws 15 amps then you could only draw 8 one the other for a total of 23 before the breaker tripped. You could draw 20 amps off one and have something that draws 3 on the other before the breaker tripped. But the one plugged into the 20 amp device would burn up.

You can learn alot of basic electricity in many how to books, but then film technicians use some different things that can be found in the Harry Box Set Lighting book.

Best

Tim

Rob van Gelder · October 13, 2006

Hi all,

I just have finished the ballast training at Arri Munich and talked tot the designer from it, regarding the topic in the first part of this thread: flickerfree shooting even on Low Noise position.

According to the engineer, the claim that you can should from 20 to 30 fps in this mode was made by Lightmaker.

Lightmaker is not in the market anymore, to my knowledge, so ......

The Arri ballasts are indeed lower in flicker percentage then magnetic ballast, but definately not safe to shoot other speeds then those originally calculated.

The designer of Arri ballast does not recommend shooting off-speed on the low noise setting!

Sunlight= no flicker

Tungsten = 3-8% flicker

Flickerfree Arri = 2-3% flicker

Lownoise = 15-30 % flicker

Tube light = 30 - 60% flicker

Magnetic ballast around 50-60% flicker

Also: its always better to use maximum power on the light, don't dim more then 80% is recommended, though you can go down to 50%. But then the arc in the bulb might be a bit more unstable, giving more flicker and also a green tint, though the color temp stays the same.

There was much more to learn there, a great course!

:)

timHealy · October 14, 2006

Regardless of whether Lightmaker is out of business or not, I guess Harry Box is wrong too then:

"In the silent mode, most. square-wave ballasts provide flicker-free light at frame rates up to about 34 frames per second (fps), and In flicker-free mode, up to 10,000 fps"

The whole article:

http://www.lightlineelectronics.com/HMI.html

I never advocated shooting off speed within the 10 fps window, but I was commenting on how most square wave ballasts work and how they may have saved someones ass when using a non crystal generator. I mentioned in an earlier post that one has to check with the brand you are using. If you want to be safe, one should always be in flicker free all the time mode when shooting off speed. Perhaps ARRI and the engineer you met don't have that sort of window, but even if they did, would an engineer start telling people you can shoot off speed in silent mode? Once that genie is popped open they would be getting all sorts of calls about their ballasts not working when people shot outside that window. So if I was an engineer I wouldn't tell anyone either.

Best

Tim

PS Just in case you don't know, Harry Box is a Los Angeles gaffer who has written the most comprehensive film electricians equipment handbook that is available.

Rob van Gelder · October 15, 2006

No, i don't know the guy but are really interested in his book. Not only for me but for the people that i have to train in the country i work, Thailand. I am sure there is plenty of other usefull tips in it.

Can you give me the full title of the book and number please?

Besides that, I know from experience that you can sometimes get away with some irregularities in the exact shooting conditions, it doesn't show up always.

But I like to advise people to go with what is true and tested.

On the course were many people, maintenance technicians, from many countries, from Holland to Kazachstan, India, Thailand to Spain.

Everyone had many different brands of lamps and ballast in their inventory. The general feeling was that the Arri stuff has the best performance and design, the others are either not supported by their original manufacturer anymore (but still working in the field) or of lower quality/ copies from older electronic designs of Arri/B&S

Arri also sells a Flicker-meter, with that you know precisely your margins.

timHealy · October 15, 2006

the Harry Box book:

Set Lighting Technician's Handbook, Third Edition: Film Lighting Equipment, Practice, and Electrical Distribution (Paperback)

http://www.amazon.com/Lighting-Technicians...8864134?ie=UTF8

I didn't realize there was a third edition.

The book covers the electrical lighting equipment and practices in the US and Los Angeles specifically. But generally the issues and theories can be applied to all film shoots no matter how lighting gear and distribution vary around the world.

A friend describe the film business in LA as an "industry" (as opposed to an "art form" where some things are figured out each time) so there are many things that anyone else might not make use of because there isn't as much work where you may be, in comparision to how much work there is in LA. So some things there are streamlined.

A great book though for the electrcian and DP alike.

Best

Tim