Film-Tech Forum ARCHIVE: Rechargeable batteries

This is topic Rechargeable batteries in forum Film-Yak at Film-Tech Forum ARCHIVE.

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Posted by Ken Lackner (Member # 1002) on 09-29-2003, 08:35 PM:

One thing I've never understood is why certain types of batteries behave the way they do. For example, why is it that certain rechargeable batteries (I think either NiCad or NiMH) require a complete discharge before recharging, or else they develop that anoying "memory" feature? Also, I just bought a Nokia 6340i phone. It uses a LiIon baterry, so it does not require a full discharge before recharging. However, the manual does say that in order to get the best performance out of the battery, to go through three complete charge and discarge cycles first. Why??? Why would the battery require anything other than a 24-hour complete charge to get the most out of it?

Posted by Paul G. Thompson (Member # 655) on 09-29-2003, 08:41 PM:

Those batteries have a "memory". If you recharge them when they are not in a complete discharged state, over a period of time the battery will think it is discharged while it is not. As a result, the battery won't perform like it is supposed to because it will be weak even if it supposedly has a full charge.

This is the way it was explained to me.

Make sure the battery is fully discharged before recharging. They will last much longer.

Posted by Ken Lackner (Member # 1002) on 09-29-2003, 09:53 PM:

Paul: Thanks. I have known this for a long time. Basically I am asking why is it this way? What causes that memory feature? Also, why to some rechargeable batteries have memory while some (LiIon) do not?

Posted by Mike Olpin (Member # 1115) on 09-29-2003, 10:53 PM:

First of all, True memory loss in a battery (known as memory effect) almost never happens, and when it does it only happens in NiCd batteries, although many argue that NiMH can also exhibit signs of memory effect.

Memory effect occurs when the battery is discharged to the exact same place every time, then recharged. Even the slightest change in time between when the battery is chargedand then recharged will not lead to true memory effect.
Consequerntly memory effect only occurs in exact controlled conditions such as laboratories.

The phenomanon that everyone refers to as "memory effect" is actually called "Voltage Depression".
If you remove the battery from the device your using, before its finished draining, over time, some of the cells in the battery pack become weaker, and while they sill hold the same capacity , they no longer can hold the same voltage . This becomes a problem for advanced digital devices such as cell phones, palm piolots, and laptops, which monitor thier batery level using voltage as a reference for an expected battery capacity. The device flashes a low battery warning and in some cases executes a timer that will automatically shut off the device after a given period of time after the warning (especially common in laptops). This gives the impression that the battery has become empty, when in fact it has the ability to power the device for much longer. Draining the battery almost compleatly will "re awaken" the dead cells, allowing them to store the correct voltage again, and thus curing this condition. This hapens in all NiCd and NiMH batteries, however some people are recently beggining to report this in Li-Ion batteries as well.

PLEASE NOTE, it is importaint never to compleatly drain the battery, as many people recomend. Drain them to about 1.2 Volts per cell, then charge them. If you go lower, some of the weaker cells will reverse (charge from the other end, if you will). This causes them to compeate with the healthy cells renderring them, and the cells they are compeating with, compleately useless. This is verry bad, and usually results in a battery which appears not to hold a charge at all. Some of the high end chargers, automatically drain the battery to 1.2vpc before charging.

As for Nokia, the manual recomends doing this probably because they want to make sure that all the cells are "fully awakened".

Love the new signature Ken. Anyone who hasn't become aware of the latest craze in internet geekdom should head over here.

Posted by Ken Lackner (Member # 1002) on 09-29-2003, 11:34 PM:

LOL! Thanks for the comment about the sig. Strong Bad rules! Thanks for the info, Mike. How do you know when you're at 1.2 volts per cell? For that matter, how do you know how many cells are in a battery? With my phone, I'm just using all the talk time until it shuts off, then I'm charging it overnight. (Doing this for three cycles, as the manual suggests. Then I will just continue to plug it in at night or when I get home from work, etc., without fully draining it first.)

So I am correct that only NiCad batteries have the memory effect, not Li-Ion, right? But am I reading you correctly that you can undo the effect by completly draining and then recharging a NiCad?

Posted by Brad Miller (Member # 2) on 09-30-2003, 12:28 AM:

Slightly off subject, but not terribly, anyone looking for really good rechargable batteries in the common sizes (AA, C, D, etc) should check out Energizer's ACCU-CHARGE batteries and charger. Besides saving a ton of money, these things beat out regular non-rechargables.

Example: I can take between 20-30 pictures with my Casio digital camera with Duracell or Energizer batteries, saving the display screen as much as possible. With the ACCU-CHARGE batteries, I can effortlessly take at least 50 per set of batteries...then when they are drained I just charge 'em back up again.

I know Best Buy/Circuit City carries these. It's where I got mine.

Posted by Phil Hill (Member # 371) on 09-30-2003, 12:38 AM:

Actually, 1.2V is the nominal voltage of a NiCad cell. Discharged is consider to be 1.0 volts. Charging of NiCad cells is best done at a constant current depending on the battery Amp/Hr rating. When the terminal voltage reaches 1.30 - 1.35 volts, the cell is considered fully charged and should be removed from the charger.

It is always advisable to discharge a NiCad to the 1.0 level before recharging cuz of the "memory" effect.

>>> Phil

Posted by Mike Olpin (Member # 1115) on 09-30-2003, 02:08 AM:

Phill is right, its actually 1vpc, however, from what I understand, in order to prevent cell reversal, one should stop drainage at 1.2vpc to be safe. Mabey it was 1.02 vpc? Oh well, can't remember right now.

Anyway, to answer the cell related question, inside your nokia battery, (or more correctly, battery pack), there are several small cells. If you cross-section the battery pack, oreo cookie style, you will note them inside the battery. About measuring voltage, I guess a standard volt meter should do the trick, but I have never actually done this. The information was more for technical info than for practical application, and the Film-Tech manual dissclaimer (read this and learn -but dont you dare try it) certainly should apply to that. Just use your Lithium Ion battery as the phones manual suggests and you should get 1000 cycles out of it with no problem. After 1000 cycles its best not to try to resurect them. Batterys do eventually die.

quote:
So I am correct that only NiCad batteries have the memory effect, not Li-Ion, right? But am I reading you correctly that you can undo the effect by completly draining and then recharging a NiCad?

Yes, in theory only NiCds suffer from the scientificly correct "memory effect", but it seems that almost all rechargeables suffer from voltage depression. Both can be corrected by a disscharge to near empty, providing that the cells havent reversed.
------------
More pointless ramblings about strongbad

Whenever a film burns at my theatre, I always blame it on Trogdor Inhabiting the booth.

Trogdor the Burninator WITH MAJESTY!

Posted by Joe Redifer (Member # 3) on 09-30-2003, 05:28 PM:

Brad, is that the same charger you had where you cannot touch/remove/insert the batteries as they charge? I remember thinking that as extremely odd.

Posted by Scott Norwood (Member # 30) on 09-30-2003, 07:13 PM:

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?

Posted by Bruce Hansen (Member # 281) on 09-30-2003, 07:26 PM:

Also a note on lead-acid (or gell cell) batteries. Never discharge this type of battery compleatly, it will damage the battery. It is recomended that they be charged after every use.

Posted by John Hawkinson (Member # 1135) on 09-30-2003, 07:56 PM:

This is a sufficiently complicated topic that it's probably not going to reach succesful completion here. But a few comments:

The NiCd memory effect is caused by crystalization within the cells, and a full discharge helps to break down the crystals.

Mike said, "Anyway, to answer the cell related question, inside your nokia battery, (or more correctly, battery pack), there are several small cells." This is generally not true for LiIon. Cells can be manufactured as "prismatic cells", which are basically rectangular extrusions. They are single-cell, and thus have the LiIon nominal voltage of 3.6V.

Ken asked why 3 charge/discharge cycles are necessary. The chemistry of the battery is such that it does not reach its full capacity until it has been used a few times. Some vendors may run these 3 cycles in the factory, or as part of manufacturing, others may instruct the user to do so.

It's also important to remember that all batteries, especially NiCd, NiMh, and LiIon chemistries, have a limited number of charge/discharge cycles, generally "a couple hundred." After that , the battery will stop performing adequately.

For more than you could ever possibly want to know, see the excellent online resource, Batteries in a portable world.

--jhawk

Posted by Ken Lackner (Member # 1002) on 09-30-2003, 08:45 PM:

So, even though my phone uses a LiIon battery which does not suffer from the memory effect, should I avoid just plugging it in at any time (such as over night or when I get home) to reduce the number of charging cycles and thus prolong its life? Or does a charging cycle refer to only a complete discharge and recharge?

Mike: film burns at your theater????

Posted by Mike Olpin (Member # 1115) on 10-01-2003, 02:00 AM:

I was under th impression that most regeargeables can have 1000 cycles before requiring replacement.

Ken: Only twice. 1. brainwrap, 2. bad platter threw the print. But Trogdor got blamed for both.

Posted by Paul Konen (Member # 41) on 10-01-2003, 11:00 AM:

One thing that hasn't been mentioned is that if you are experiencing this effect, how can you safely discharge the battery so that it becomes useful again.

The manufacturers say not to short them out.

Could you build a small circuit that would power a flashlight bulb until drained?

Thanks
Paul

Posted by Mike Williams (Member # 1140) on 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]

Posted by Daryl C. W. O'Shea (Member # 1303) on 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?

Posted by Paul Mayer (Member # 355) on 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.

Posted by Bruce Hansen (Member # 281) on 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.