underwater Photo Course :: (2) Equipment Guide :: Underwater Camera Housings :: Underwater Strobes :: Power Supplies

Underwater photography requires a lot of light and strobes must keep up with fast recycle times, which dictates efficient power supplies. It is not necessary to know exactly how the electronics work in a strobe in order to use one, but it is useful to understand the idiosyncrasies of the batteries you put in it!

It is especially true when buying a strobe that the number, and size, of battery cells a particular strobe takes will determine its performance. The ideal battery should allow the unit to be able to deliver many firings and recycle quickly. The main types of battery used in strobes are (1) alkalinestandard non-rechargeable batteries (2) Nickel-Cadmium (Ni-Cad) (3) Nickel Metal Hydride (Ni-MhNickel Metal Hydride batteries are very efficient and offer about 40% more capacity than NiCD plus they dont suffer from memory effect. However they only last 500 charge and discharge cycles. NiMH batteries lose about 3% of their charge daily.) (4) Lithium Ion.

• Alkalines are extremely efficient in that they give many firings and do not fail abruptly, but have the disadvantage of their limited life-span, which makes them costly. The travelling underwater photographer needs a power source that will shoot a roll of film (at least) twice a day for every day of a two week vacation. You would need to carry 14 packs of Alkalines for such a trip (one for every day of your holiday with most strobes). Apart from the inconvenience of carrying that little lot about with you, just think also of the effect on the environment of producing those 14 packs of Alkalines!
• Nickel Cadmium (Ni-cads) can be recharged hundreds of times and are therefore the most cost effective power supply. They are ideal for the travelling photographer, as you only need to take two sets with you (one in use and one to keep on charge). Ni-Cads offer faster recycling times, but less firings than alkalines and fail more abruptly (usually without warning and usually in mid dive!). They normally require 14 hour charging times and can develop a 'memory'. You must discharge them fully before recharging otherwise they 'remember' and will only take a part charge next time.
• Nickel Metal Hydride (Ni-Mh) batteries were originally devised as power sources for laptop computers. They deliver more power, quicker, and with no memory problems. They are also re-chargeable and can accept a charge in an hour!
• Lithium Ion are rechargeable batteries with negligible memory effectNi-Cd (NickelCadmium) cells had a reputation for losing capacity if they were not discharged fully during each cycle of use. This was dubbed the memory effect i.e. the cell remembered that you didnt use it to the full and changed accordingly. and offer about twice the capacity of Ni-MH batteries. They require dedicated chargers.

Rechargeable batteries only survive limited charge and discharge cycles. However this may amount to many 1,000's of cycles so are the most cost effective

Most strobes have removable batteries and can use either Alkaline, Ni-Mh, or Ni-Cads. Some strobes however, incorporate integral Ni-cads which cannot be removed but which usually are industrial grade and of high capacity. Some models boast sealed battery compartments, this is a useful feature in the event of a flood as the internal electronics are protected.

Do not use rechargeable batteries in your camera. Use standard, Alkaline (or lithium) only. The voltage is lower, and this can throw off your meter!