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Topic: Rechargeable batteries

Mike Williams
Master Film Handler

Posts: 255
From: Knoxville, TN
Registered: Feb 2002

posted 10-01-2003 01:00 PM

quote:
Brad--you need to change batteries for every 30-50 pictures? Ouch! Remind me not to buy one of those cameras. I'm accustomed to using (film) cameras that either a) don't require batteries or b) use so little power that the batteries only need changing once per year, if that. What is it about that camera that consumes so much power?

Because it is Digital.... and digital is better [Wink]

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Daryl C. W. O'Shea
Film God

Posts: 3977
From: Midland Ontario Canada (where Panavision & IMAX lenses come from)
Registered: Jun 2002

posted 10-01-2003 02:02 PM

You'd want to be careful with that Paul. If you drain Lithium Ion cells that way they can catch fire if you drop below their critical voltage or above their critical current (which is somewhat dependant on the cell design).

Brad -- would ~300 pictures out of a single CRV3 not be a lot more convenient (if your camera uses 2AA or a CRV3 of course) -- although a little more expensive?

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Paul Mayer
Oh get out of it Melvin, before it pulls you under!

Posts: 3836
From: Albuquerque, NM
Registered: Feb 2000

posted 10-01-2003 03:27 PM

Makita put out a paper a while back claiming that memory effect in NiCad batteries has been largely eliminated (at Makita anyway) by improved manufacturing techniques. Tighter control of the manufacturing process has led to less contamination of these batteries' Cadmium and Nickel-coated plates. Another area of improvement was in the lamination seals used between the plates in these batteries. Failures in these areas are the primary contributors to memory effect.

In another life I worked as a spacecraft controller for Hughes Commuications, flying several Hughes-built communications satellites (HS376 bus--Galaxy's 1-3 plus HS393--Leasat's 1-4). All of the spacecraft I flew used NiCad batteries and battery management was and is a big part of what a spacecraft controller does.

To reduce the potential for NiCad memory effect, spacecraft are provided with internal discharging loads to be used for battery reconditioning. Prior to the start of each eclipse season the spacecraft's batteries are switched off of trickle charge (normal state with healthy batteries) and put on to the reconditioning load in order to discharge down to 1.0V per cell (we had telemetry for every cell's voltage, and temperature from selected cells). As soon as any cell hits 1.0V the reconditioning load is disconnected and the battery is put on a high charge rate. High charge would be terminated (and trickle charge restored) when any of several voltage (especially voltage rollover), current, or temperature limits were reached. This deep discharge and full recharge once per eclipse season ensured that we'd have full amp-hour capacity for that season.

The recommendations for running a NiCad battery down to some minimum voltage before charging it came from this industrial practice of battery reconditioning. When battery performance suffers from low endurance, it is almost always due to premature termination of charging after a deep discharge, i.e. not enough amp-hours are being put back in. By design many chargers are conservative and either cut off charge current too soon or provide too low a charge current. Either occurrence will result in reduced battery capacity and endurance. The better chargers use a combination of high and low-rate charge currents and employ temperature, current, and voltage-rollover monitoring to ensure a full charge. Vivitar for one made a charger for their flash unit batteries that used these techniques to quickly "burp" batteries up to a full charge.

Note that this practice of deep discharging and recharging is specifically not recommended by Makita for their batteries. Makita claims that modern NiCads do not need to be kept in condition this way--in fact they claim that modern NiCad batteries can be damaged using this technique.

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Bruce Hansen
Jedi Master Film Handler

Posts: 847
From: Stone Mountain, GA, USA
Registered: Dec 1999

posted 10-01-2003 04:39 PM

NiCads should never be stored in a charged state. If they are, they can develope internal "shorts", that will cause the battery to self discharge quickly. If this happens, you may be able to bring them back to "life" by charging a large capacitor, and "poping" it across the battery several times. At times this will burn out the "shorts". It is a good idea to discharge NiCads before storing them for any length of time.

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