7.4 Powering Your Flash Unit

As mentioned previously, external flash units have an insatiable appetite for AA batteries.  The four AA’s that fit inside my flash unit’s battery compartment provide enough power for relaxed shooting, but for intense shoots I require the use of an external pack that holds an additional eight AA’s.  The external pack allows me to take more shots before needing to swap out the batteries for a fresh set.  It also reduces the recycle time of my flash.  This is the amount of time that it takes for the flash to recharge its capacitor after a shot.  If you try to take another shot before the capacitor is fully re-charged, the flash unit will either fire at a lower intensity (resulting in slight under-exposure) or may fail to fire at all (possibly resulting in extreme under-exposure).  By shortening the recycle time of the flash head, the external battery pack allows me to take successive shots closer together in time, without risking under-exposure.  Most flash units have a pilot light on the back of the unit, which indicates when the capacitor is fully charged.  If you take a photo before the pilot has re-lit, the flash may or may not fire at all, depending on the settings of the flash unit (and the capabilities of that particular model).  On some models you can instruct the flash to fire at lower power if a photo is taken before the pilot has re-lit, or you can instruct it to not fire at all until the pilot lights up.  Not all flash units offer the ability to fire before the capacitor is recharged, however.




    Keeping your flash unit well-fed with AA’s can be a challenge, especially when traveling.  Rechargeables are obviously the most cost-effective solution.  However, most chargers will fit only four AA’s at a time, and some chargers are so bulky that using two chargers in one dual-socket wall outlet doesn’t work.  The popular six-socket power strips aren’t ideal either, because they’re generally spaced too closely to allow more than two or three chargers to be plugged in simultaneously.  As mentioned in section 4.3, I’ve found the Power Sentry “Squid” to work well, since it can easily accommodate five chargers all at once (see the figure below).




As already discussed in section 4.3, the use of high-voltage battery packs, such as those available from companies such as Quantum and the like, are generally not recommended for use with flash units in the field, since they may void the flash unit’s warranty and may damage the flash by providing more voltage to the flash’s circuitry than the flash was designed to handle.  Although others have had success with such third-party battery packs, I’ve had several flash units destroyed this way.  In addition to the potential for dangerously high voltage, the use of external packs (even those made by the camera’s OEM) can potentially cause a meltdown (see section 7.10 for tips on avoiding a meltdown).