Choosing Extension Cords for Plug-In Strobes
Before considering an expensive battery pack or generator for your big lights, don't overlook the obvious. Extension cords are a cheap and reliable way to get power to your studio strobes.
A couple hundred feet of power cable and a little advance scouting will solve the vast majority of your location needs. But be careful not to skimp. Here's how to choose a good extension cord for your strobes.
The Short Version
For those not into the technicals, here's the cheat sheet: Buy the thickest cord you can, and don't run longer spans than necessary. Also, don't combine splitters with long cord runs.
Cords are pretty cheap. I bought the 12 AWG, 100-foot stinger (meaning, the female end lights up when the cord is live) above from Costco for ~$25. A small price to pay for remote power, and safe for even my juice-hungry Profoto Acutes.
Way better to be safe than sorry.
The Detailed Version
Note: All units below are expressed in US terms. Your voltages and power requirements may differ in other countries.
There are actually a few variables to consider when using AC extension cords to power big lights remotely. Four things you'll need to think about when choosing a cord for strobes are:
1. Strobe power requirements
2. The gauge of your extension cord
3. Distance you need to cover
4. Safe operating voltages for your flash
Strobe Power Requirements
This will be expressed in amps, and will loosely track with the maximum power rating of your flashes. For instance, AlienBees only need 6 amps continuous, while a Profoto 8A can draw 8 amps just to run two modeling lights -- the flash itself will add to that considerably.
And even the 6 amp draw of the AlienBees is a little deceiving. When the flashes are recharging, they will momentarily draw much more power. Long story short, make sure you understand what your flash need to drink so you can get a straw (extension cord) thick enough to feed it.
Gauge of the Cord
This is the thickness of your straw. A smaller number represents a thicker wire, i.e., 12 gauge is thicker (and better) than 16 gauge. In the U.S., an extension cord will say something like "12 AWG", which stands for 12 American Wire Gauge.
The wire should note a safe amperage level, too. If it does not, you can look up safe amperage levels for different gauges of wire easily.
For instance, my 12 AWG extension cord will safely carry the 20 amps that my Profoto Acutes need. But If I were shooting AlienBees, I could get away with a 16 AWG or even an 18 AWG cord.
The distance you are going to transport the electricity comes into play. Wire has resistance, and for a given thickness a longer wire will have more resistance. Thinner wires (say, 18 AWG vs. 12 AWG) also have more resistance.
Some of the voltage of your AC outlet will be lost across this resistance. A long run of thin wire can leave you with significant voltage drops, which could be harmful to your flash. How much current you are running will also factor into the drop. The more current needed, the more voltage drop over a given line.
There is a great online calculator for this, here. (Many thanks to reader Gary Nach for the link.)
So technically, you can run 13 amps through a 16 AWG cord. Meaning it is safe for the cord. But doing that over a span of 200 feet would rob you of about 22 percent of your voltage. Which could be very risky for your particular model of flash.
That calculator is a very neat tool, and it especially shows the dangers for your big flashes when running power excessive distances.
Speaking of that, pay special attention when combining long cord runs with splitters. You have to add up all of the current requirements of everything plugged into the splitter. So use short cords with splitter, or go with multiple cords.
The technical data in your strobe's manual will list the safe operating voltages. Most are designed to account for less-than-ideal voltages. For instance, your flash might be happy down to 90 volts.
But you have to remember that your mystery meat AC outlet on location might not have ideal voltage levels. And any voltage drop issues from long cord runs would exacerbate that problem.
Long story short, invest a few more dollars to get a nice, thick extension cord for your AC strobes. Cords are cheap and strobes are expensive. And when you are not using them for location power, your cords will also be versatile enough to handle other heavier current uses.