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Battery “Memory” Question

Published : 14th October 2003


I have an old Arriflex with a recently re-celled cine60 battery. Should I run this all the way out before charging due to a memory effect? Right now I lose sync at the tail of my rolls possibly due to torque in the mag(?) I'm not sure if I will be doing damage to battery life if I recharge and test this out on another shoot.

Any help would be so nice

Thank you

Rob Vaughn



>Should I run this all the way out before charging due to a memory >effect?

I think that a lot of people misunderstand the memory effect.

[Warning : I may be one of them.]

If you have an application where you repeatedly discharge a NiCad battery to the same partial level, (Like a 14.4volt video cam batt that shows a "low batt" light at 11.9 volts or whatever so that you pull it off the camera when it still has some stuff left) it can develop a "memory" whereby when it discharges to that level, it will then drop to unusable low level of charge at that repeated partial threshold. In the case of rental batteries that might partially discharge on the shelf and then be charged the night before a job, for instance, if they always fade out to the same partial charge on the shelf, they might poop out as soon as they go down that small percentage in the field.

It is not the case that if you recharge a partially charged battery you are automatically inducing a memory or massively reducing its life. The key is in not always draining it to the same partial level before charging it and periodically discharging it fully and letting it charge up fully before reusing.

Note : Smart charges that cycle the cells will do all this for you. Smart chargers that start as fast chargers and then switch to trickle when they are almost full will not.

Two important things to know :

1. The first time you charge a new or re-celled battery, you should absolutely charge it fully beyond a shadow of a doubt...let it sit on the charger for a long time (unless your charger is a fast dumb charger that might cook the battery) The first charge for a NiCad or lead acid (gelcell or car battery) is critical, especially if your device has a high current discharge rate (like starting your car in February in Rochester (either MN or NY))

2. If you use a resistive load (like a car tail-light bulb) to discharge your batteries prior to re-charging them, do not use a load that will discharge them at too fast a rate...if you discharge them much faster than the device that they were designed to work with, you can sharply reduce the working life of the cells by overheating them. (This is also a good warning to consider before you use your camera batteries to run low voltage lighting) You can also blow a fuse or a "pico-temp" which is a thermal cutout doo dad which is wired into some NiCad batteries to prevent them from overheating and doing bad things, especially if they are inside expensive things, like $50k video recorders.

WARNING :

Much of the previous information was learned, some of it the easy way :

Long ago in a city far away where I maintained and re-celled a multitude of batteries that ran everything from Sony BVH500 1" machines to cameras to sun guns to sound equipped etc. at a really cool facility whose initials were FTC.

While the physics has not changed, some of the equipment, and especially the design of the chargers has improved. If in doubt, contact the company that has built or rebuilt your batteries and chargers.

Try to talk to technical people...many sales personnel understand this stuff even less perfectly than I do and I have heard lots of bad advice from well meaning people (such as myself) who think they are saying the right thing.

Mark Weingartner
LA based
If only I could sell this knowledge



Mark Weingartner wrote :

>I think that a lot of people misunderstand the memory effect. [Warning: I >may be one of them.] If you have an application where you repeatedly >discharge a NiCad battery to the same partial level

It is very unusual to develop a true "memory" effect on NiCds. The battery must be discharged to exactly the same degree repeatedly over a long period of time, which almost never translates to real life experience.

(This effect was first discovered when NiCds were used to power early satellites. Solar panels recharged the batteries so they could operate during the night period of rotation. The day/night sequence was pretty constant and after a month or so they had a memory problem.)

However, a similar problem can be created by excessive slow charging, leaving the battery plugged in all the time.

For a thorough explanation, go the Anton-Bauer site at :

http://www.antonbauer.com/handbook/handbook.html

This ought to be in everyone's bookmarks, IMHO.

For the explanation of memory effects, go to the Problems section.

Wade K. Ramsey, DP
Dept. of Cinema & Video Production
Bob Jones University
Greenville, SC 29614


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