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Wednesday, September 12, 2012

When Battery Packs Just Don’t Cut It

When battery pack just don't cut it, consider using a gas generator and power packs! We recently saw this article on the Bron Imaging Blog about power packs and wanted to share this with our readers:

A gas generator can get you power where you need it. While there there are plenty of battery packs available you might think that you don’t need to consider the extra hassle or weight of a gas generator.   Battery packs like the 2400 watt second broncolor Verso pack will work seamlessly between battery and AC power and give you more output than any Elinchrom or Profoto battery pack (Verso=2400 WS!).  And the 1200 ws broncolor Mobil a2r is small and easy to transport  and has 2 heads for about the same price as a single head Profoto 600b and only a few hundred $ more than an Elinchrom Ranger (yep broncolor quality at Elinchrom prices!).  But no battery pack will run all day with full power output and modeling lights cranked up all the way.
Sometimes you just need to be able to plug in your strobes, camera batteries, laptop, a few props, a makeup light , and whatever else you might have -  so you need a generator.Or maybe sometimes you just need to shoot all day (or all night) with the modeling lights on.  And you hate that anxiety about whether your batteries are really gonna make it through the whole shoot.   Running off a generator can get you those extra hours on your shoot using regular AC power packs.  But be careful!  Most packs are not designed for use with a gas generator and not all gas generators are created equally.
Broncolor Scoro packs work on any microprocessor controlled sine wave inverter style generator.  The 3200 watt second broncolor Scoro A4S requires a maximum of 15 AMPs at its fastest recycling setting. This is by far the lowest power consumption for any 2400+ watt second pack.  The Scoro works by using a gentle – but still insanely fast recycling charge system (faster than any other pack out there).    And then on top of that, the Scoro has a power control circuit that is a lot more intelligent, basically analyzing the power coming in and changing its own power control behavior before a spike has a chance to damage the circuitry.
Power pack manufacturers generally don’t publish their pack’s power consumption, but even if you don’t have a power meter, you can do a simple test to get a general sense of its consumption.  Just take any 2400 watt second pack and plug it into a regular 15 amp 110v plug and start banging away.  Some of them will blow your breaker if you fire 2-3 fps at half power for around 20 seconds.  That wil tell you that you are drawing more than 15 amps.  Go ahead give it  try with a non-broncolor pack (but don’t call me if your pack blows up).  Oh, and if your pack cant do 2-3 fps at around 1200ws you should take a look at the Scoro.  You’ll need the power consumption information when looking at taking a pack out in the field on a genny.  Remember that Watts =Volts x Amps (w = va) – therefore the genny you need will depend on how power hungry the devices attached to it.   A Scoro draws 15 AMPS at 110V which means it pulls around 1650 watts.  So you need a generator that is rated for at least that draw.  As an example, check out the Profoto 8a documentation.  Their user manual recommends a 6000 watt generator for a Profoto 8a 2400 ws power pack – more than twice what we recommend for the 3200 ws Scoro!
When calculating the total power requirements for your setup don’t forget to add in the modeling lights.  broncolor heads use a 300 watt modeling light when running at full output.  So for each head you run with modeling lights you need to add a approximately 3 AMPS to your setup.
So how to you select a generator? Not all of them are created equally.  We tend to recommend the Honda EU 3000.  The Honda EU inverter microprocessor controlled generators provide stable sine wave output as long as they are properly maintained.   If you have got a clean one then it can provide you with good clean power without any problems for your Scoro.  Of course there are larger and more powerful generators – I just walked past a Con Edison 40 foot Genny Truck running at full power on 40th street in NYC yesterday.  This thing was running backup power for an entire building – but for the sake of this article we are just talking about what you can fit in the back of a mini-van.
I just read a great article in Pro Lights and Staging News about how generators work most efficiently and how to know if the load you are going to place on a genny is going to actually work.  Richard Cadena covers important issues like calculating load supply for a given generator.  Richard also touches on how to size your genny correctly.  He says that running a genny at around 80% of its load rating will give you the best result. Check out his complete article here:  PLSN.com That’s a Load of Watts
If you are shooting with 2 packs its best to get a Honda 6500 watt generator (or 2 3000 watt generators).  Keep in mind that as you go up in output that the generators get much heavier.  As an example a Honda EU2000 watt model weighs around 50 lbs; a EU 3000 watt weighs around 130 lbs; and a Honda EU 6000 weighs around 265 lbs.   One way around the extra generators is to change the recycle or “charge” speed.  If you set a power pack to recharge more slowly then the pack will pull current through the line at a much slower rate and thus enable the pack to work when less amperage is available.  Remember its always better to have a little more power than what you think you might need.  One of the biggest causes of blowing up a strobe power pack while using gas generators comes from using a generator that is not powerful enough.  Basically what happens is that after you fire your strobes, the pack tries like crazy to refill the capacitors with juice.  When the pack draws all that juice from the generator the power level in the generator drops.  But the generator tries to quickly compensate for the drop in power and drives up the output of current as fast as it can.  A good generator will control the compensation and thus the stabilize the amount of compensation, but a bad one will overcompensate and simply spike up the power to a level that will cause the power control circuit on most strobe power packs to explode – a costly repair.  The Scoro’s power control circuitry is designed to reduce the creation of the spikes in the first place as well as to adjust quickly to compensate for these spikes when they do happen – but any electronics will blow if the power spike is really big.  So while a Scoro gives you you flexibility and forgiveness than other power packs there are limits.  So use a microprocessor controlled generator and you can fire away without worry.
Key Requirements for Generator Selection:
* Electronically controlled (aka microprocessor controlled) sine wave inverter output
* Rated for at least 15amps at 110v (~2000watts or above)
* Look for something that is relatively quiet (but a genny will never be as quiet as a battery)
* Recommend Honda EU series 3000 watt and above

Benefits of Gas Generators Over Battery Strobe Packs:
* You can power other stuff (laptop, backup storage, fans, props, whatever)
* Go all day long (a little extra gas will keep most gennys running all day long)
* No stress about how fast your batteries are being consumed

Drawbacks of Generators:
* Fuel:  It burns explosively and can therefore be a pain in the butt to handle…especially near a city.  Check your local fire codes for rules about handling fuel and generators inside (or even near) buildings and public places.
* You can carry a ton of batteries for the same weight as a genny

For more info about using the broncolor Scoro on gas powered electrical generators see the instruction manual.  Go ask your favorite brand of power pack if you can use their pack on a genny…the answer is usually that it will void the warranty.  Not with Scoro.  The Scoro’s low power draw coupled with an advanced power control circuit will give you great results on a clean power generator like the Honda EU 3000.
In addition to gas powered generators we are also starting to work with some really cool battery packs from LibertyPak .  The Liberty Pak Products put out so much juice that they actually call them Little-Genny and Big-Genny.  These products provide serious battery power.  They are not like the little JackRabbit battery packs – the Little Genny is a serious power supply that can handle powering a 2400 ws power pack.  The Big Genny can actually power Kobold HMI lamps for about 45 minutes.  We will cover the Big Genny and Little Genny more in a future post.