As an amateur my equipment sees intermittent use, especially in the winter months. Last week I was asked to do some photography at church. I used my trusty "285" with 2 "charge 15" Ni-Cad clusters. I charged them both, and tested them before the assignment and they seemed O.K. However, after 4 or 5 full power shots they were both exhausted. I believe they should be good for about 40 flashes (on full power).

What does everybody suggest for keeping Ni-Cads in top condition during periods of low usage.

I look forward to your responses, and thanks.

Regards,

-- Alan Purves (lpurves@mnsi.net), February 27, 2002

Answers

How often have the NiCd packs been used previously? NiCds have a nasty habit of building up "memory" if they're not completely discharged before each recharge. What it means is, if you consistently drain them 50% before recharging again, eventually you'll lose that 50% capacity. If this is the case, I'd suggest dumping off your NiCds at your local friendly hazardous-materials recycling center and buying yourself NiMH replacements.

-- Anon Terry (anonht@yahoo.com), February 27, 2002.

Ni-Cad are a poor source of power for occasional use. Ni-Cads depleat their charge over time, they develop memory and do not respond well to not being used which causes loss of ability to build full charge. If you want to use them then try doing this after a prolonged storage period; charge over night and discharge fully then recharge over night and discharge again and repeat charging. This might rebuild capacity. You should also run this routine every six months if you do not regularly use the batteries. However, my advice is to use onetime batteries if your devce is used only on a rare event.

-- Steven Alexander (alexpix@worldnet.att.net), February 27, 2002.

Can anyone explain the physio-chemical reason(s) to this chemical engineer for the urban myth of chemical compounds having a memory?

-- chris chen (chrischen@msn.com), February 27, 2002.

Can anyone explain the physio-chemical reason(s) to this chemical engineer for the urban myth of chemical compounds having a memory?

OK Mr. Chemical Engineer, what we call "memory" is actually loss of cell capacity over time due to repeated overcharging (typically by consumer chargers that use the voltage drop technique to sense peak charge capacity). This slight voltage drop at peak capacity is caused by cadmium hydroxide particles increasing in size, reducing effective contact with the negative plate and resulting in the slight resistance increase. This has a reversible effect on capacity, and such a reversal can be achieved with a periodic deep discharge (aka "conditioning"). But what accounts for what many call "memory"? The secondary conversion of cadmium hydroxide to cadmium metal, also a side effect of overcharging. When this occurs, hydrogen gas is liberated and vented from the cell, reducing the effectiveness of electrolyte. This effect on NiCd cell capacity is irreversible.

Now, some (like chemical engineers) might argue that this is not true memory, but I would refer those people to alt.help.pedantics. In the real world of cheap voltage-drop sensing (over)chargers and overzealous, capacity-crazed, top-off-the-juice battery users (and yes, photographers are a member of this clique), the memory effect is very real and a royal pain in the butt.

-- Anon Terry (anonht@yahoo.com), February 27, 2002.

BTW I may not be a chemical engineer but I have 18 years of experience with NiCd batteries. I used to charge and drain Sub-C cells to "match" them in sets of six for use in R/C buggy racing. In desperate moments I've been known to run my chargers at 15 amps, and following races I'd discharge my packs with literal short outs (typically with a ceramic resistor), so I know a thing or two about overheating and overcharging, most of it learned at the school of hard knocks.

-- Anon Terry (anonht@yahoo.com), February 27, 2002.

Thanks for the thorough answer Anon. Two follow-up questions:

How do we prevent as many problems assoc. w/NiCads?

How is H2 vented from the battery; are they not sealed?

-- chris chen (chrischen@msn.com), February 27, 2002.

BTW, NiMH cells have pretty much killed NiCad for nearly all applications. Greater charge capacity and no "memory effect". They do take longer to charge though (you have to charge them at 1/2 the rate of NiCads).

-- Andrew Nemeth (azn@nemeng.com), February 27, 2002.

I prefer to use NiCads in my flashes because of their shorter recycle time. Also, if I forget to shut the flash off, I haven't wasted a whole set of alkalines. I keep NiCads in the fridge with film and alkaline cells. By keeping them cooler but not frozen, the self discharge is reduced considerably. My oldest set is over 10 years old and seem to be going strong.

I also have a NiCad pack for a Rollei 36RE flash that must be older than that and because it's pretty expensive to replace I want it to last as long as possible. I use it maybe twice a year and it seems to be mostly charged when I take it out of the fridge, something it didn't do before refrigerating.

Cheers,

Duane

-- Duane K (dkucheran@creo.com), February 27, 2002.

Chris, General Electric issued a bulletin some years ago, that I ran across, to the effect that the memory effect was mostly a characteristic of the early NiCads. It said that the then-current GE NiCads exhibited very little memory effect.

This, of course, leaves us without an explanation for the loss of capacity in current or recent Nicads, unless we just assume it's more the result of things getting less efficient when they are older--like me.

-- Bob Fleischman (RFXMAIL@prodigy.net), February 28, 2002.