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Bradley Mowell

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Posts posted by Bradley Mowell

  1. On 6/20/2015 at 8:06 AM, Guy Holt said:


    Since the advent of electronic HMI ballasts, measuring hertz is not as important as it was when HMI ballasts used magnetic ballasts. In those days you had to make sure the generator was spinning so that the frequency was +/- a quarter cycle of 60Hz (59.75-60.25Hz) to avoid flicker. By squaring off the waveform to the globe, electronic ballasts eliminate flicker except at very high speeds in which case you need to use 1000Hz high-speed ballasts.


    If you will be using electronic HMI ballasts, you want to make sure you get a meter that reads true RMS. In an introductory workshop my local, IATSE Local 481, offers for set electrics we do an exercise where the students meter the voltage and current on a putt-putt generator (non-inverter type) while running a non-pfc 2.5kW HMI light. Since, invariably, the meters brought by the students range in quality, the readings they get range from being 84% over to 40% under what they should be. We then so the same exercise with tungsten lights and they all read the same. The discrepancy in the results is a good jumping off point for a discussion about how meters work and that they can be mislead by the distorted waveforms drawn by some electronic HMI and Kino ballasts. Since the consequences of under measurement can be significant - overloaded cables may go undetected, bus-bars and cables may overheat, fuses and circuit breakers will trip unexpectedly - it is important to understand how meters work and why only meters based on "true RMS " techniques should be used on power distribution systems supplying nonlinear loads. To see why that is the case use this link: http://www.screenlightandgrip.com/html/emailnewsletter_generators.html#anchorMeters


    Guy Holt

    ScreenLight & Grip

    Lighting Rentals & Sales in Boston

    What particular True RMS meter would you recommend, Guy?

  2. 35 minutes ago, Ed Conley said:

    Interesting. The Harry Box tech handbook states that all 12k and above are now PFC but this is  Fourth Edition 2013 Edition.

    How old is the ballast?

    The ballasts are all retired rental stock. I’d guess they’re about 20 years old…definitely pre-4th edition. I bought 1st and 3rd edition copies of Box’s book to try to find more info about these particular ballasts. 

    35 minutes ago, Ed Conley said:

    the  "excess" power returning on the neutral matters because in a normal load if all phases are balanced then there should be no load on the neutral but w/o PFC things get weird and the neutral will see excess load and you need to factor in this extra load when sizing the cables and the generator.

    It still maters when using house power too.

    On 240v the excess power still exists.

    I’ve read the section(s) on power factor correction in each of the three editions of Box’s book, but what I don’t understand is this:

    On 240v single-phase house power, how can excess power return on a neutral wire when the ballasts don’t have a neutral wire? 😂

  3. 1 hour ago, Ed Conley said:

    I believe that is a PFC ballast though.


    I wish it was, Ed. Unfortunately, the plate shows 0,7…and emails with Arri confirm it’s non-PFC (no active line filtering). Unless I’ve misinterpreted what I’ve been told, which is entirely possible. 

    BTW, thanks a bunch for the advice about a year ago. Worked like a charm, sir. 


  4. I have four Arri 6/12 electronic ballasts that are non-PFC ( power factor correction ) that operate at 190-250v. Each ballast has a green ground, black hot, and red hot. 

    I’ve read that non-PFC ballasts return a lot of excess current on the neutral wire because of low power factor (these are rated at 0.7 PF) but how does that apply to ballasts that operate at 190-250v that have no neutral wire? I’m using 240v location power rather than a generator, so how/where does the excess current from a non-PFC ballast return on a neutral wire in the distribution system?  I’m assuming all current is “cancelled out” at 240v between the black hot and red hot. But if, somehow, there IS still excess current, where does it go?




  5. What should one watch out for when buying a used, larger HMI par without a warranty?

    If the unit strikes fine, what would it be a good idea to check before making the purchase?

    Lens and reflector condition? Cable damage? Any particular issues with ballasts? Bulb condition? Etc.


  6. Hi,

    I purchased a used Arri True Blue T5 tungsten fresnel wired for 220v w/a new 220v bulb. The lens and wire screen are fully intact, and the unit itself appears to be in very good condition.

    Do I simply strike it using the inline switch or should I power it up gradually from a dimmer? 

    Thank you!

  7. 19 minutes ago, Joseph Tese said:

    The other option, is to invest in step-down transformers, which has more advantages.
    http://www.screenlightandgrip.com/html/emailnewsletter_generators.html#anchorTransformer/Distros on Wall Outlets

    Thank you. I contacted them a few days ago, and a transformer certainly does have its advantages, but I was shooting for something more portable and less pricey. I think you're suggestion about contacting someone local to build an adapter is a good idea. As I mentioned to Ed, I'm overly-cautious and hesitate to do electrical DIY projects without clear directions and step-by-step pictures. 😆

  8. 4 minutes ago, Ed Conley said:

    making an adapter is easy enough.

    You start by purchasing a Dryer 4-wire power cord and then attaching female connector on the other end that matches your connectors on the lights.


    for 120v: Hot ( Red or Black wire) , white, ground.


    Thanks, Ed. Joseph probably has the right idea about consulting with a local electrician to build something for my needs. I'm the cautious type, and without a tutorial or book I'm hesitant to mess with anything electrical (I've installed many a breaker, wired for 240v in my garage, and other electrical projects, but I've always had a clear tutorial to work from - complete with pictures 😂). Unless you know something I could reference, probably best to leave it to someone more in-the-know.

  9. 1 hour ago, Joseph Tese said:

    Thanks, for the link, Joseph. However, wouldn't doing it that way mean that each 20amp Edison outlet would only supply 2400 watts to a light? I'm seeking a way to be able to access the full 3600watts from 30 amps to power 2.5k to 3k lights. I apologize for all the questions.

  10. 1 hour ago, Joseph Tese said:

    Are you wanting to power 240v lights? Or, do you want to split the phases so you have two lines at 120v?

    Either is possible.

    If your dryer plug was only three prong, and had no neutral, then it is unsafe to split the phases because your load will probably not be perfectly balanced.

    Thanks, Joseph. Looking to build (or buy) an adapter (the dryer outlets are four prong) to be able to access 30 amps (or 40 amps from the range) for 120v lights. Splitting phases for two lines would be great, but one line would suffice. The dryer outlet is 30 amp / the range is 40 amp.

  11. I've read until I'm blue in the face - both here and elsewhere - and still don't understand. Trying to accomplish this:

    "There are 220V plugs on dryers. They are similar to our genny connectors here. The dryer connectors have 4 prongs on them. You have a ground and a neutral and then a hot and a hot. You do need to build an adaptor that eliminates one of the hots. You separate the hots out so you have 2 hot connectors on the end of that. That way, you can access all 30 amps... Back in the day, when I was doing a lot of music videos, we made our own connectors that we could tie into these dryer circuits. I was maxing out homes all over in my music video days of the 90s."


    How does one go about making/buying an adapter?

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