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Battery Powering of Studio Flash
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PostPosted: Thu Mar 15, 2007 1:08 pm 
Battery Powering of Studio Flash

In the past, using high-powered flash systems in the field required the photographer to buy two separate lighting systems: an AC powered one for the studio and a battery powered one for location use.

In the past couple of years, it has become practical to power AC studio flash systems with battery power converters that produce 120 Vac. Thus, the photographer can easily take his entire studio setup anywhere without buying another lighting system. But there are some special considerations in doing this:

Professional flash systems are somewhat unique in their power requirements and cannot be used with the ubiquitous “Modified Sine Wave” or “Quasi Sine Wave” power invertors often sold as accessories for cars and boats. These inverters are notorious among pros for damaging either the flash units or the inverters themselves, and most of these won’t work at all.

The reason is that studio flash units convert AC power into high voltage for the flashtube using capacitor based voltage multiplier circuits. These circuits require a Pure Sine Wave similar to that you receive on your household powerlines. Thus, proper operation of flash units demands a Pure Sine Wave Inverter from a battery supply as well.

Beyond this, studio flash units exhibit another powering obstacle. While their long-term average power requirements aren’t severe, there is a very high initial inrush current to deal with. This can be from 16 to 60 amps or more. While this does not usually cause household breakers to blow because it is of short duration (like a motor-starting circuit on a refrigerator), conventional power inverters often cannot supply this sort of current and simply shut down.

For reference, conventional circuit design would require on the order of a gigantic 7000W inverter and a 100lb battery to supply this much current directly. Indeed, many photographers have lugged gasoline-powered generators around to fill these requirements.

In order to create a battery inverter system more in tune with the needs of the traveling photographer, we have taken a different approach to things in our pioneering Vagabond System. We use a Pure Sine Wave inverter of modest size and power that is capable of limiting its output current to a safe value during the initial stages of recycle instead of shutting down.

>> Click Here for more info on the VAGABOND Portable Power System

A feature of the Vagabond inverters is their ability to deliver current-limited output on nearly a continuous basis. This allows a single battery and inverter to power multiple studio flash units with an aggregate of up to 5000WS when very high amounts of flashpower are needed.

The requirement of the flash units attached to such an inverter system is that they be capable of operating in the presence of the dramatically lowered AC input voltage necessitated during the initial recycle period (“Brownout”). All Paul C. Buff, Inc. flash units are fully compatible with these conditions as are most competitive studio flash products. But in some digitally controlled flash units, the designers have not allowed for this sort of operation and the microprocessors used can “crash” under brownout conditions. This can cause such units to work improperly with small Pure Sine Inverters, or to not work at all.

Thus, while we guarantee our Vagabond system to be fully compatible with our flash units, we cannot make a blanket recommendation for using Vagabond with competitor’s flash units.


Recycle Times

The current-limiting methods above of necessity place constraints on the recycle time of the attached flash units. The more flash units attached, and the higher the WS rating of the flash units, the longer the recycle times.

The base rate of the Vagabond 150 system is 150 Ws per second. This means that if an aggregate of 600 Ws is used, at Full Power settings, the recycle time will be approximately 4 seconds. Add another 600 Ws of lights (using standard multi-outlet extension cords) and it becomes 8 seconds and so forth. The Vagabond 300 contains two Pure Sine Wave invertors sharing a battery and can deliver 150 Ws/Second to each of two outlets and thus can recycle a multi-light 1200 Ws system at Full Power in about 4 seconds. We are currently in the design stages of Vagabond systems that can allow considerably faster recycle rates from a single inverter.

As for battery life, either the Vagabond 150 or 300 can supply about 400 full power flashes at 650 Ws, 200 at 1300 Ws per battery charge and so forth. While it can power 200W of modeling lamps, this will drastically reduce battery capacity.


*One safety note that should be observed:
For safety against shock hazard when using inverters or generators it is always advisable to use some form of grounding rod or attachment to a grounded object. The use of a ground fault interrupter (available in extension cord form at Lowe's and Home Depot) is also advisable.

A further precaution is that use of equipment that is intended to be grounded (all studio flash units) can possibly result in erratic function and possible damage from static discharge in dry climates if used ungrounded.

Use in wet locations requires particular concern for safety and should avoided if at all possible.


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