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Power struggle
Pros and cons
Nickel-Cadmium
Smart batteries
Open standards
Power Consumption
Power and Lighting

Power Struggle

by David Fox

Battery manufacturers debate which cell broadcasters should be locked in to....

Nickel-Cadmium batteries have powered portable broadcast applications for more than two decades, but in the last few years new technology has offered an alternative. However, Nickel-Metal Hydride (NiMH) and Lithium Ion (Li-ion) batteries both have their positive and negative points.

"For service life, reliability, ability to handle high current draws, and fast charging, there really is no other technology that can compete" with NiCd, states Alex De Sorbo, president, Anton/Bauer. However, both Li-ion and NiMH weigh less, although this advantages is less marked with the larger cell sizes capable of powering a camera. "A 50 watt NiMH is roughly the same size and weight as a Li-ion and only slightly lighter than a comparable NiCd battery," which will have a "significantly longer product life," he says.

However, Li-ion has "the highest power to weight ratio of any cell; no memory effect (just top up when you like); wide operating temperature; small self discharge; and makes a green environment, as no poisonous material is inside," says Richard Lewis, Sony product manager for camcorders.

Just to complicate matters further, considerations such as smart batteries and chargers, and just what power loading you put on your batteries have to be taken into account.

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BATTERY TECHNOLOGY COMPARED

  NICKEL-CADMIUM NICKEL METAL HYDRIDE LITHIUM- ION
PROS

Inexpensive; Reliable; Resists abuse; Can have high discharge, up to 10C;

Can be used over wide temperature range: -20C to +60C

High headline capacity; Energy density up to twice NiCd No discharge required; Can be recharged in any condition; Almost 40% more power and 50% lighter than standard NP NiCd; No memory effect; Environmentally friendly
CONS Heavy; Can 'die' rapidly and unexpectedly; Requires discharging for long life; Memory effect; Toxic. Poor low temperature performance - can be damaged if charged in sub-zero temperatures; Cannot deliver high load (not suitable with lights); Same weight as NiCd; Low cycle life; Can require new charger or upgrade; Memory effect. Expense; New charger required; Internal resistance approximately double equivalent size and quality NiCd, so poor performance with high current applications (such as a digital camera with light).

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Running Ni-cad

NiCd remains a large market, but "due to environmental and reliability issues its importance is reducing rather than increasing for battery cell manufacturers," says Tony O'Connor, managing director, IDX (Europe). "Nickel-Cadmium is toxic and subject to recycling requirements and also now to new green taxes such as those levied in Scandinavian countries." Lithium batteries contain toxic Lithium metal, but Li-ion uses its ion, which is inherently safer and allows Li-ion batteries to be disposed of in household waste.

O'Connor says Li-ion is "the lightest, most powerful battery available in commercial use." It has been designed to meet professional needs, delivering "consistent reliable power", although he admits it is relatively expensive, but "it is ideally suited to professional video where a premium will be paid for reliability, capacity and light weight." However,what will happen to Li-ion batteries over a long cycle life "has not been determined yet," says Crawford.

Anton/Bauer is happy with NiCd's reliability. Its NiMH HyTRON 50 Watt-hour (Wh) battery has a one year warranty, but its NiCd is twice that and "typically last three or four years in the field," says De Sorbo.

For an average ENG set up with a 25Watt camcorder and 50Watt on-camera HMI light, Crawford says Frezzi's BP-14, a 72Wh NiCd battery, will give up to one hour run time (72Wh/75watts = 58 minutes) because it can withstand high rate discharging from a typical camcorder and light.

Li-ion was primarily designed for cell phones and notebook computers, which have relatively low rates of discharge, and its performance is adversely effected in cold or hot temperatures. "These cells are suitable when you are running only a 25Watt camera. However, if running a 25Watt camera and a 50Watt light from the same Li-ion battery, the performance of the battery will significantly degrade, collapse like a house of cards and die within minutes." For example, with CBS News live coverage of President Clinton in New York, "the cameraman tested his battery, it indicated 100% capacity available. When tape rolled, the battery went from 100% to empty in seconds and died. The shot was lost during the live broadcast." This happened during ideal temperature conditions.

With NiMH, "the 50 Watt-hours claim is based on a discharge rate of a maximum of 10Watts not 75Watts of typical discharge load." You might expect 40 minutes of run time, "but when the NiMH is loaded with a 75Watt draw, it also begins to collapse like the Li-ion." So, you'd be "lucky" to get 28 minutes. The battery will also be stressed, "which will cause permanent cycle life reduction requiring frequent battery replacing. So the pack he thought was going to last 3 years ends up lasting less than 1 year," says Crawford.

Besides, NiMH batteries "can only be charged with the manufacturer's charger and can not be repaired or serviced because they are in a sealed plastic case. The problem with these packs is that the rating system is flawed and misleading," he says.

There is a "need for reliable batteries, whatever chemistry they are. You must be able to rely on them in all weather conditions and charge them reliably. NiCd is undoubtedly the most reliable," says Crawford. For its military systems Frezzi can charge a NiCd battery in ten minutes. "If you have all sorts of heavy kit, saving yourself a pound [weight] on batteries is not worth it. Reliability is all," he adds.

Anton/Bauer sells both NiCd and NiMH, although it is also researching various types of Li-ion and even hydrogen fuel cells and thin plate lead acid batteries. "All these have potential in applications for today's video camera," says De Sorbo.

"We have attempted to develop a system rather than a single battery or single power solution." Although it offers different batteries, they use the same charger, "so users of Anton/Bauer batteries of five years ago don't have to upgrade all their chargers," he says.

"It's important that we have downward as well as upward compatibility in all our products. A battery from 1977 will still fit today's mount. Our mount is in its third generation, but all are backward compatible." He believes battery manufacturers can't afford to leave any of their customers behind, because they'll lose business, which is why its existing chargers can be upgraded with a single chip change.

The same chargers could be used for Li-ion if they offered it. Indeed, it showed Li-ion batteries at IBC 1995, but hasn't sold them because of doubts over reliability, longevity and safety. He says that Li-ion can't be exposed to a high rate discharge. Where a NiCd battery can be discharged safely at four to six times its designated C (capacity) rate, Li-ion is restricted to no more than 1C, so that it can't cope with a camera with an 80Watt light on top. "NiMH can handle higher current draws, but they adversely affect the longevity of the battery," he adds.

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Smart Solutions

He claims Anton/Bauer introduced the first "smart battery" in 1992, which monitors and controls its own charging. With "virtually all cameras", it also means you can look in the viewfinder and see what power remains, whereas with other manufacturers, he maintains that you can only do that if the camera is specifically adapted.

Frezzi's 24 volt NiCd Smart Battery Pack has, "for the first time", advanced battery protection circuitry, so it can be charged from any 30 volt DC power source and will turn itself off charge and discharge. No sophisticated battery charger is required. "This marks the first time in history when the battery has more intelligence then the charger," says Crawford. Frezzi also has smart chargers, which have a reserve mode, so that if no other charger can charge a battery it can recover it (whether it's NiMH or NiCd). It works with any power supply or make of standard battery.

With one make of battery Crawford says the battery monitor learns the capacity of the battery as it diminishes over time, and so always shows 100% at the end of charge, even if the actual capacity has diminished to 80%. Frezzi's Energy Gage system has an LED display, showing exactly how much real capacity is left, so it will show an old battery at 80%, not 100% of 80%.

David Hardy, PAG technical manager, agrees that some "state of charge" meters can be misleading. "It is not uncommon for the display to always indicate 'full' when the battery is charged, even though the battery may in fact be unable to hold even a half-charge." PAG's system shows the precise run time of the battery, under the real loads its experiencing, in the viewfinder. Because of this accurate information, one large news organisation was able to reduce the number of batteries carried on a shoot "from six or eight down to two or three."

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Open Standards

Frezzi uses NP-1 style batteries, which is the most widely used format, and Crawford believes that Sony's NP-1 batteries "outnumber everyone else by about two to one," for video, although Frezzi sells huge numbers to the military.

The original NiCd NP-1 battery was under-powered at only 12 volts at 18Wh, but the latest NiCd version of the NP-1 delivers 27Wh. However, Frezzi's Power Bar delivers 13.2 volts at 50Wh. An on-board micro-controller stops over-discharge and over-charging. Crawford says it is "smaller, lighter, costs less and is not restricted by a proprietary charging system as compared to the mini-brick proprietary 50Wh [NiMH] battery." Also, "for the price of one mini-brick, you can buy three Power Bars."

It can also be used in a hot swapable 3-Pack, so you can have up to three batteries on a camera, giving 150Wh, or "2 hours in a package that's not much bigger than a conventional brick battery. Since the 3 batteries are sharing the load, the batteries will not suffer from the capacity derating as experienced with the mini-brick proprietary 50Wh battery." Users can also swap batteries without turning off the camera. The pack can even use non-Frezzi NP-1 batteries.

"We try to keep open standards," he says, but claims other makers want to limit users to their own batteries and chargers. "Our batteries can also be repaired. Some other batteries are sealed, so if you drop it in the field you can't repair it."

"Everyone wants to standardise their equipment but without the risk of being bound to one manufacturer," says O'Connor, so its 40Wh 14.4v NP-L40 lithium ion battery uses the standard NP design, but delivers more power.

However, "only the camera manufacturers can determine an open system. For many years the NP and to some extent the BP were de-facto standards. Both were non-patented freely available systems. However newer formats such as the Sony Betacam/SX/DVCAM formats are now using a patent unique battery mount system which is naturally meeting opposition and involving the use of unnecessary adapter plates resulting in extra weight and cost. Only a system that is non-patented and freely available to all battery manufacturers can truly become an open standard," says O'Connor.

PAG's batteries can't be used on some other chargers, because to meet Product Liability legislation it has to retain control of how the battery is charged, to ensure its safety, says Hardy. "The new battery technologies present a greater potential hazard unless all the safety issues are fully incorporated into the design," especially during charging, "both for the sake of safety, and to obtain the best performance and cycle life from the product," especially as not all battery chargers are the same.

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Power Consumption

"If there is power available, the manufacturers will find features to use up that power." The larger the tape format and/or CCDs (such as 16:9), the more power they use, says De Sorbo.

"Digital camera technology has seen the average one-piece camcorder moving from approximately 24W to 28W power consumption. This has been adequately served by moving to the higher capacity batteries such as Li-ion which can cope with this increase and still give extra run-time form the same size battery," says O'Connor. "The increase in power is directly related to the number if power consuming ICs in the camera," so Digital S and Betacam SX use more power than DVCPRO or DV, and dockable cameras use more power than camcorders, as some features are duplicated.

For battery manufacturers "the only way to increase run time of the camera is to increase the actual capacity of battery and the reliability of its charging and cell technology so that the full capacity can be extracted each time," says O'Connor.

"To increase run time we are increasing battery capacity," says Lewis. "The BP-L60A Li-ion battery has just increased by 20% from its first introduction. Also, we are continuously developing new LSI chips by increasing the number of gates in one die, which can run on much lower voltages than before, therefore reducing the [camera's] power consumption as well as the number of chips, and the heat produced."

Hardy says that cameramen "generally carry ample battery capacity with them on a shoot, but fail to use much of it because they have no idea of how long their equipment can be powered by a partially discharged battery. Many professionals bring up to three times the battery capacity with them that they actually use. They then fit a 'fully charged' battery at each tape change, so that they can be confident of completing each tape without encountering battery failure."

He has found that "battery indicators on some of the newer cameras are quite inaccurate, and can trigger the low voltage warning when the battery is in fact only half discharged. We know of one camera where a 13.2V battery must be set up in the camera menu as '12V' to avoid a premature warning of twenty minutes."

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Power And Light

Lights are a major power-drain, so, for Betacam SX, Sony has added "a stabilised light output, fed from the camera battery. This provides a soft start (to extend lamp life), a stabilised output (for constant colour temperature) and automatic start-up (the lamp comes on when you go into record and switches off again when you stop recording, to save power)," says Lewis. It has also introduced the AC-DN1 mains adapter, with a V shoe mount, which accepts a battery on the back, to run from mains power and auto switch to battery if there is a mains failure.

"The advances in CCD technology and camera optics have greatly reduced the need for larger on-board lights. Where 50W were the standard 3 or 4 years ago 30W or even 20W are now the most common on-board lights," says O'Connor. HMI and ARC lights are more expensive, but "can produce equivalent of 100W from only 40W actual power."

PAG's new Paglight, has interchangeable halogen and a metal-halide arc lamps - which is equivalent to a 100W daylight-corrected halogen, but consumes a third of the battery power. Also, its PowerMax regulator can replace a standard halogen lampholder, and prevents the lamp (typically specified for 12V) being over-run by a 13.2V or 14.4V camera batteries. "A 100W 12V lamp powered from a 14.4V battery will consume 150W. This results in dramatically reduced run time and shortened filament life," says Hardy. The PowerMax can extend battery run time by up to 25%.

© 2000 - 2010

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MORE....
Battery Technology Update - What's new in batteries for 2001.
A quick guide to taking care of your batteries
Not been looking after your batteries? - help is at hand
For more technical details on batteries the Anton Bauer "Video Battery Handbook" is definitely worth a look.
technical stuff on lithium ion batteries from Sony
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David Fox