Portable power systems

For all-around performance, Li-Ion chemistry is the winner
Author:
Publish date:


Broadcast RF used an IDX Endura 98Wh Li-Ion battery to power the camera system and COFDM radio at the 2004 Olympics Cycling Time Trial.

Today, many genres of television production depend on the use of untethered cameras and support equipment that let camera operators get close to the action without having to be close to a power socket. All rely on batteries to power their equipment through the working day or night — or both — whatever it takes to get the material shot and onto tape, disc or even solid-state memory.

Just a few years ago, video was analog, formats were either 625/50 or 525/60, free-roaming cameras were predominantly camcorders, and batteries used nickel-cadmium (NiCd) chemistry. What a difference a decade or so makes!

A vital part of that change is attributable to batteries and the service they now can offer. Only five years ago, when virtually all camcorder batteries used NiCd chemistry, the batteries were bulky, heavy and required keen management to maintain reliability. Also, by today's standards, although they could deliver high currents, their capacity was not very large.

Increasing requirements

Some must remember the selection of NiCd batteries taken on a shoot. First, there were a lot of them — fresh out of the charging room that morning to make sure they were fully topped up. Users came to know their batteries, and gaffer tape was often stuck on to show which to use first or last, or as a last resort! Although NiCd batteries remain in use, they are a world away from the power solutions available today.

HD is one of the factors driving the increased demands of batteries; HD camcorders require more power. Digital technology itself has meant more on-camera functions. Other changes include the new breed of COFDM-based digital camera links that have caught the attention of program makers. While every effort is made to minimize power, these links still add to the load.

Another technology now being deployed is disc-based camcorders. The measured power requirement of an XDCAM when recording with viewfinder and LCD screen on is 41W This is a considerable increase from the typical 25W demanded by tape-based SD camcorders.

Chemistries

Cameramen want to be able to concentrate on their prime function. The job of shooting material needs to continue without interruption, so having run times of between one and two hours would be a reasonable target. Better still would be running for a whole session such as morning, afternoon, or the first and second half of a game, so the battery switch can take place in a natural break in the proceedings.

Today, the portable power industry continues to be based on rechargeable chemical batteries. Users have a choice of three types: NiCd, Nickel-Metal Hydride (NiMH) and Lithium-Ion (Li-Ion). Each may have appeal for a given situation to meet the needs of performance and price, but there is a wide divergence between these chemistries. Even then, the performance of a given chemistry may vary depending on its implementation. Here's a closer look at the three types of batteries:

  • NiCd: Many of the old mainstay NiCd batteries continue in use. Five years ago, a regular NP-style NiCd battery provided 28Wh and weighed 700g. These batteries are relatively low-priced and are capable of supplying high currents.Drawbacks include the heavy weight; a high rate of self discharge; and the demon of the ‘memory effect,’ requiring batteries to be fully discharged before commencing a full recharge, at the peril of permanently losing that portion of the capacity. With good care, batteries can last three years. However, be aware of environmental issues relating to the disposal of NiCd batteries.
  • NiMH: Measured against NiCd, NiMH chemistry offers increased capacity — and hence longer run times — from still heavy but relatively compact batteries that today are offered up to 140Wh capacity. NiMH is environmentally friendly and is available in a mid-price range.So far so good, but unlike NiCd, this chemistry cannot recover after use at high currents, and permanent damage is caused. It also exhibits more of the NiCd characteristics, including a high self-discharge rate, a limited battery life and a degree of memory effect.
  • Li-Ion: Measured in terms of capacity and environmental issues, NiMH is a clear advance on NiCd. But for all-around performance, Li-Ion chemistry is the winner. It offers the advantages of light weight and high capacity. The old problem of memory effect is gone, and high self-discharge is very much reduced. All these have a profound effect on ease of use, reliability and general logistics of ensuring the power is available where and when it's needed.


Simultaneous quick chargers, such as the VL-4Si four-channel quick charger shown here from IDX Technology, are ideal for heavy-duty assignments where fast turnarounds are essential.

Using high-grade cells, Li-Ion batteries can be put on charge and removed at any state of charge. Charged batteries can be left on the shelf for days or weeks without losing significant charge. The charging room and ‘topping up’ are no longer required as any battery can be used straight off the shelf — anytime.

Comparing the NP format battery size, the NiCd mentioned before had a capacity of 28Wh, whereas the Li-Ion chemistry now offers 71Wh. Plus, it is lighter — just 460g compared with 700g for NiCd — giving almost a four-fold increase in the capacity-to-weight performance.

The latest high-capacity batteries offer around 100Wh, a figure limited by current airline rules. Li-Ion does not offer as high a current draw as its elders, but there is still plenty to power most on-camera needs. For high wattage tungsten lights, a solution may be to switch to more efficient LED technology. Alternatively, one battery can be docked onto another, doubling capacity and the maximum current.

Chargers

For best sustained performance, Li-Ion batteries need taking care of. Rather than being just a bunch of cells, some include on-board battery management. This logs battery use and status, such as capacity, maximum current, etc., to build a file and accurately predict its performance. This helps to extend their reliable life and keeps them active for longer. Also, with performance only changing slowly, there is little need to differentiate between new and the old. No need for gaffer tape! The benefits were illustrated at a recent athletics championship, where UK company Broadcast RF reports that six RF cameras were in use 12 hours a day — all supported by just one man moving around the stadium with a few batteries in his pockets.

The trend to higher capacity means that more energy is needed to fully recharge batteries. Sequential chargers supply one battery at a time. With capacities of around 100Wh, charging a group of four may take all night. There is a trend towards higher power ‘quick’ chargers that help to bring down the time.

Mounts

The quickest solution is to use a simultaneous quick charger where, for example, a four-channel version is basically four individual chargers in one. Therefore, it is able to give each battery its own charging regime — ideally having first read its battery management data. This intelligent-type of charger should give the best results in the shortest time and is ideal for heavy-duty assignments where fast turnarounds are essential.

Transport

There are several different battery mounts in use. Technically, there may not be much to choose between them, but a pragmatic approach can save weight and money. With Sony supplying a large proportion of cameras, the native V-Mount system is already there on many camera backs. It makes sense to provide V-Mount batteries that mate directly with them, avoiding the cost, weight, space and extra contacts involved with a separate adaptor plate.

Batteries are for people on the move. Locations may be cold, hot, near or far, and the batteries always have to perform. Those making use of airline transportation may be aware of IATA rules regarding the carriage of Li-Ion batteries as they represent a fire hazard. This effectively limits the maximum weight of Lithium in batteries that can be carried as passenger baggage.

Environmental impact

Exceeding the limit means they cannot be put on the aircraft as normal check-in but must be placed in a Class 9 container, labeled “Class 9 - Miscellaneous Dangerous Substances and Articles” and checked-in. In short, it is likely to be easier, quicker and more reliable to use batteries that avoid going over the IATA limit.

At the end of their life, batteries have to be discarded. In the case of NiCd cells, which contain chemicals harmful to the environment, most countries require that these be disposed of in an approved manner. This can cost money. In contrast, Li-Ion chemistry is far more environmentally friendly and can be recycled or disposed of without these costly restrictions.

Kevan Parker is sales manager for IDX Technology Europe.