| Yes, you can use rechargeable batteries
in your SB103 strobe. As a matter of fact, "rechargables"
can be used to power virtually any underwater strobe using
replaceable batteries—and they’ll also work in
just about any non-water strobe that I’ve heard of.
Yes again, all things considered, I believe that using reusable
batteries is a good thing to do. And what all were the things
considered? First of all, currently, when you say "rechargeable"
you’re talking NiCad. Tomorrow, who knows, but today
it’s NiCad. A far as I’ve been able to determine
the new nickel metal hydride, so-called "green"
batteries, don’t deliver current rapidly enough, don’t
mix with water well enough and are too unstable during charging
(they sometimes explode) to be serious considered by underwater
strobe manufacturers as a power source for their products
in today’s litigious society. Rechargeable lithium batteries
may likewise be dangerous when in contact with water. It’s
bad enough to lose the strobe when it floods, never mind your
mask—or the thing it’s mounted on.
NiCad (nickel cadmium) batteries are not all created equal,
but just about any decent manufacturer’s rechargeable
cells will deliver current more rapidly than virtually any
alkaline battery. Since strobes draw current in great humongous
gulps when recharging their capacitors during the recycling
phase after firing, the ability to deliver current quickly
is paramount and can be the limiting factor in recycle time.
The simple fact that a strobe powered by NiCads will recycle
considerably faster than the same strobe powered by alkalines.
You’ll get more flashes out of a fresh set of quality
alkalines than out of a set of NiCads, however.
A battery’s capacity is rated in ampere hours by the
manufacturer—not always accurately, to be sure! It would
be nice of none of us had to pay taxes again until the day
that a manufacturer understates the capacity of his battery
to deliver current. Some brands’ ratings are more overstated
than others. Rechargeable AA cells deliver around 300 milliamp
hours (30/1000 amp hours) to around 800 milliamp hours. NiCad
D cells deliver about 1.8 amp hours to about 5.7 Ah. Notice
a difference here? There are D cells out there that have the
smaller C cell inside, and although the D cell configuration
allows the battery to be used in applications where a D size
is the only one that will fit, the battery has the capacity
of only the smaller C size.
NiCads can be divided into a consumer class and an industrial
class. Consumer batteries tend to be of lower capacity. These
are the types that you can buy in stores. Industrial batteries
are manufactured for use in appliances, power tools, and the
like. Battery manufacturers believe that there is little demand
among consumers to pay two or three times as much money for
a battery that delivers two or three times as much power.
I don’t know about the general public, but underwater
photographers would—or at the very least should—be
willing to pay the higher price for the more powerful cells.
Changing batteries underwater is problematic; you’d
just have to be awfully fast! A notable exception is the Gates
Millennium Battery. This is an almost full-blown industrial
type NiCad which can be purchased "over the counter"
at your local hardware store.
Alkaline batteries, when fresh, measure about 1.75 volts
although they are specified at 1.5V. As they’re used,
the voltage drops in a fairly linear relationship to the amount
of power remaining in the cell. Performance drops in a simple,
predictable way with the drop in measurable voltage. Recycle
times gradually increases as the battery is depleted, and
if you’re paying attention to this fact, you’ll
be able to predict when the batteries won’t deliver
enough power to get you trough another roll of film. Somewhere
just before this point, the alkaline batteries will not charge
the capacitor or capacitors in the strobe to their full-rated
voltage, and the result is that the guide number of a full-power
flash will be lowered by so much as a quarter-stop or more.
If you don’t account for this, you won’t get consistent
exposures. This is rarely a consideration in normal TTL flash
photography. You’ll discard alkaline batteries around
1.4 volts.
NiCad batteries are rated at 1.2 volts. A good NiCad with
a full charge measures about 1.35 volts; at about 1.0 volts,
it’s done for. Performance doesn’t suffer much
over most of the useful charge life of the battery. If alkaline
performance decreases along a gentle slope, NiCads drop off
a cliff! You’ll notice an increase in recycle time over
several flashes...then nothing! You must know the condition
of your batteries and how many rolls you can expect them to
deliver.
How many flashes they’ll deliver depends on how you
use your TTL (how close to full power you push the strobe)
and how much of the capacitor is therefore discharged. How
much a fully charged battery can deliver depends on its rating
and its proper use, abuse, or disuse. A cell that has been
allowed to discharge over months of disuse may be damaged,
as will a cell that has been overheated during charging or
that has been shorted. Be conservative—there are no
pints for getting an extra roll out of a set of cells, and
there are few things more aggravating than seeing your strobe
go in the dumper after a half-dozen shots and screwing up
your dive because you took a gamble to win no points.
But what about memory? Everyone knows that if you partially
discharge a NiCad, then recharge without completely discharging
it first, it will lose some of its capacity and will deliver
only as much power on the next cycle as was demanded of it
on the previous cycle. Right? It, like, develops a "memory"—right?
Actually, this isn’t anywhere near as right as it was
only a few years ago. M The latest NiCad technology allows
the manufacturer of a cell that, for all practical purposes,
has virtually no memory at all. When you get your new batteries,
fully charge them in a proper charger, then discharge them.
Charge them again for twenty-four hours. After this procedure,
you can use, charge, and reuse them in just about any manner
that you might normally desire. And what’s a proper
charger? Ideally, the battery charger should charge the batteries
to about 75 percent capacity at a fast rate, then finish the
charge at a slow "trickle rate" in order to avoid
destructive overheating of the cell.
Although, ideally, you would want to give your batteries
a full charge every time (anywhere from about four to seven
hours for the "quick" models and up to about fourteen
for the slow types, depending on the type of charger), you
could yank your batteries off a quick charger at somewhere
around 30 to 50 percent of the suggested time if you needed
only about 75 to 80 percent capacity for a roll or two.
You can have a pretty good idea of the status of your batteries
at any time if you pick up a tiny multimeter (smaller than
a checkbook) at Radio Shack for about twenty-five dollars.
This little treasure is the absolute first item that I pack
when I’m going on a dive trip.
Please don’t be intimidated by this device. Not to
worry. I assure you that you don’t have to be an engineer
to use it, and it will make your life much easier. You don’t
even have to get the negative and positive leads right. Just
set the meter to DC volts, and touch one probe to each end
of the battery. If you get them reversed, you’ll get
a minus reading but the numbers will be correct. Ignore the
minus sign. If your batteries have been out of service for
a while, they’ll have probably developed a "surface
charge" that will usually cause the voltmeter to give
a false fully charged reading.
The NiCad battery charge decays at about 20% per month. If
you are in question, then charge them. If you’ve been
using the batteries, simply read the DC voltage. You may find
on of the cells in the set is a couple of tenths lower than
the rest. This is an indication that that cell is either not
fully charged or is damaged or worn out. If you just charge
the setup and never measure the cells, you’ll have some
severe performance problems. I wouldn’t recommend starting
a dive with NiCad cells measuring less than 1.2 volts. You
might get by, but there’s a good chance those batteries
will eat your lunch.
Now that you’ve learned to use the voltmeter scale
on the multimeter and have a superpower second only to x-ray
vision, you can check the condition of the batteries of your
camera, the batteries in any video light on the video camera
itself, the boat generator output... But alas, you can’t
determine another person’s intelligence or sexual prowess
from the DC volts reading on your new multimeter!
A final consideration. If you dive twice a year on one-week
trips and shoot a dozen rolls of film each trip, you’ll
have used approximately 186 alkaline batteries during the
average six-year life of a set of NiCads. If you are a semi-heavy-duty
diver and average twenty-five rolls of film on each of three
trips a year, our favorite planet will eat about 600 of your
discarded alkaline cells during the life of a set of NiCads.
There’s a clue in there somewhere!
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