So now that I have my Savage FT-150 monolight I would really like the ability to use the unit on location and away from power outlets. If I could do that then I should have almost all the light I need for a shoot.
The Options for Portable Power
There are 2 possible power solutions for my setup. The first is to get a gas powered generator to provide the needed AC current for the light. That isn't an option because generators are expensive, heavy and loud. There is no way I'd be able to run a generator in a church let's say. The second option is to have batteries attached to a power inverter to transform the DC power into AC for the flash. That solution is better since there is less weight and cost issues and there is little to no noise. The battery solution was going to be my approach, but how to do it without breaking the bank.
Batteries are containers holding potential energy in the form of chemical solutions. That potential energy can be tapped in order to do work like make a fan turn, a light glow or a radio emit sound. Those devices require energy to run their parts and that energy is measured in Watts. When you plug in a fan it needs a certain number of watts in order to overcome friction and keep the fan going, let's say 150 watts.
That rate is usually constant for most devices but flash units work differently than other devices. Flashes release a large amount of energy (light) at one time. Since the flash shouldn't be on all the time and since it would be impractical to drive so much power through the system constantly, flash units store the energy they need until you press the shutter release. The flash draws energy into capacitors on board until they contain the amount needed for the specified flash intensity. This is where the differences between battery solutions comes into play.
A Watt is technically energy over time. The lower the watts a battery/inverter can put out, the less work it can do in a given time. Here is an example:
Since the capacitors on the monolight can charge slowly low wattage supplies can still work but they will take more time to charge the capacitors and will result in longer recycle times when you are shooting. I initially picked up a 400 watt unit but it would take almost 15 seconds to charge even at 1/64th power. When I used an 850 watt power supply my recycle time dropped to near nothing. The higher wattage also means that you can run other devices in paralel with the flash such as a modeling light or perhaps recharge batteries for a flash or camera.
Power supplies for monolights already exist such as the Vagabond II from Alien Bee, but they are expensive. The vagabond unit costs $300 and consists of a battery, inverter (1 plug) and a carrying case. I knew there had to be a cheaper solution that was just as effective.
Some people talk about using a car battery attached to an inverter. While that will provide the power, it is heavy and unsightly. Not to mention that recharging the car battery would be a pain and the thought of exposed terminals on the battery didn't give me any comfort. There are well done and low cost solutions like this around howerver, here is a great tutorial by Jacob the Photographer I found on youtube click here for the homemade vagabond video
I did try a portable power solution, the Xpower 400-Watt Powerpack which has 2 AC plugs, a 12V DC plug, a light and a tire pump. It had a handle and a rugged case and seemed like an ideal solution, but with it the recycle time was something like 15 seconds and the fan was loud.
Since the Xpower didn't work I decided to try out another thought, a computer Uninterruptible Power Supply (UPS). A UPS is a large battery and some electronics designed to keep computers and other electronics running in the event of a power outage or power fluctuations. Their purpose is to allow you to shut down your computer safely in the event of power loss. My hope was that the UPS would be able to charge my monolight. After a brief test on an older UPS I could see that there was enough power to drive the flash. NOTE: Most UPSs do not generate a pure sine wave output, this may charge your capacitors incorrectly and damage your equipment. Be sure to check your gear and see what works and what doesn't. Read this discussion to learn more.
There are several advantages to using a UPS and they can be Voltage Regulation, multiple outlets, detailed status indicators and user replaceable batteries. All of which can help you manage your power during a shoot so that you get the shots you need. Another plus is that UPSs can be found almost everywhere from walmart to Best Buy so you can save a few bucks on shipping.
I decided to go with an APC 1500VA UPS with LCD. The unit puts out 850 watts, has 6 AC receptacles, an LED showing power consumption and remaining battery life and the unit accepts replacement batteries.
Now that I found a power supply I needed a way to take it on site for a shoot. The unit weights 30lbs and measures 14" x 8.5" x 5.25". (A comparable PURE SINE WAVE UPS would be this UPS from APC)I wanted to be able to carry this via shoulder strap so that I could have my hands free for a camera or to cary the monolight. I also wanted to have easy access to the AC ports and, if possible, the ability to read the battery display. Since I was using a UPS in a way that wasn't intended I knew there would be nothing out there that exactly matched my needs so I started figuring out how to make what I needed.
Carrying Case Construction
Here is how I built my carrying case.
I started off with a Jeep brand diaper bag from walmart ($18) which had extra pockets and a shoulder strap. Don't worry, no butterflies or flowers on this bag, it's black and rugged. I tested it out to see if it would handle the weight and the unique cross-bag strap design gives it that strength.
I then measured where the LCD display would be once the UPS was inside and proceeded to cut out a square with scissors and a box cutter.
I then cut a 6" by 6" square of 1/16" clear rubber that I got in the fabrics department at walmart for $.48. I slid the rubber in between the inner-lining and outer-lining of the bag and proceeded to sew the 3 layers together with a standard needle and thread covering the edges twice to ensure strength and durability.
Next I measured and cut the other side so that I had a flap accessing the power plugs area of the UPS. Since there was a pocket there I just cut into the pocket and folded it over the outside. I sewed the inner/outer lining closed again and then placed velcro on the flap so that I could seal it shut.
Well, that's it. I'm not sure if anyone has done this before and I'm not 100% sure how effective or safe it is. The unit takes 16 hours to fully charge it's battery and I still need to do a full shoot test to determine how many flash releases I can get from a full charge. When I find out I'll post the results here. (update, a review of effectiveness in the field can be found here)
The UPS cost me $130 after $30 mail-in rebate. The bag cost $20 to make and took about 3 hours to build, mostly due to the hand-sewing.
If you have any questions or comments, leave them below or shoot me an email.
I imagine hooking up an oscilloscope to the power output would tell you immediately whether you were getting true sine waves out of the UPS or not. Happen to know any electronics hobbyists with good kit? ;-)
Posted by Garth Wood @ 02/12/2009 12:27 PM
Just a followup, I have used this in the field with great results. I am working on the blog post for that experience. This doesn't mean the solution will work for every monolight, but it performed flawlessly with my Savage FT-150