Trickle charging NiCd pack?

I don't use my cordless drill all that often, and often when I need it for something it's only half charged. I hate not being able to top it off after nearly every use like I've got in the habbit of with everything li-ion. I was thinking about putting a DC jack on the drill, which I could plug into a trickle charger made out of an LM317 in constant current mode that would charge the battery very slowly...like over the course of a week or more.

I am conflicted as to whether this is a good idea or not. My first thought is NiCd batteries should not be recharged without discharging to around 1v, which is what I normally do.

My second thought is that cordless phones almost always have NiCd packs charged exactly as I suggest...and they last a long long time.

What effect exactly would this have on the life of my cells?

Hi there,

Charging constantly at the normal rate isnt a good idea.
What many people do (including myself) is plug their charger into a wall timer
set to turn on for one hour and then turn off, once every day. You may even
get by with only 30 minutes.
What this does is turn the charger on for a short time which allows the cells to
be charged up again replacing the (self discharged) charge in the cells. This
works pretty good as the cells dont have much time to overcharge if they
dont need the whole hour.
The wall timers are available everywhere from WalMart to HomeDepot and are
only about $5.00 or so. Even the cheap ones work ok.
This means you dont have to build up a special trickle charger too.

Take care,
Al

Many NiCd products from 2-way radios to Magchargers are left continuously trickle charging without ill effect; this is the one main advantage of NiCd over NiMH. You only need to drain to 1v once per month to prevent memory effects so feel free to top them up anytime.

I read recently somewhere (probably a link obtained from here) that NICD memory effects are a myth derived from issues in very controled charge/discharge enviroment, where a battery is continuasly discharged to the same capacity, and then recharged, over an over again, and that developing memory effects in batteries requires many cycles to the exact same point of discharge. So, as long as your cells recieve a veriety of charge cycle sizes, with occassional cycles down to the "dead" area (1Vish), then you should never have to worry about developing memory effects.

Proof should be simple: look at your cordless phone. Almost all of them have NICD batteries and see varying discharge cycles every time you pick it up. Some conversations lasting minuts, others lasting hours, each time, going back onto the charger to top up without any significant ill effects or memory developments. Cordless phone batteries often see thousands of cycles at varying depths before needing to be replaced.

So- try not to worry too much about having perfect charge and discharge cycles all the time, just don't overdischarge, or overcharge the batteries, and they should give plenty of cycles.

a timer for the charger sounds like a good idea to me., just flip it on once and awhile for an hour or so to top em off.

Hi again,


Just a reminder...

Trickle charging means charging at a pretty low current level, while 'normal'
24 hour charging is usually done around 100ma or so. It's the 100ma that
isnt good for the cells if left on indefinitely, while the correct trickle charge
will simply replenish the cells self discharge. Getting the trickle charge right
isnt all that easy, but the one hour timer method seems to work ok.
The trick is, most simple chargers put out 100ma or more and if left on for
only one hour per day (maybe even a half hour) they act as a trickle charge
for the cells even though the charge puts out 100ma. It's still 100ma but
only for one hour per day.


Take care,
Al

Somewhat related...perhaps someone smarter than me can figure it out.

I have 4 Golden Power NiCd 4000mah D cells (bought from Real Goods a long time ago). I used these things in a blowup mattress. After a few uses, the batteries run low, and I charged them up. It seemed like they were developing a memory effect, so I put them (two at a time) in a toy motor (from a hotwheels kit) and ran them until they were drained. Ironically, it ran over 24 hours (and remember, these weren't fully charged to begin with!) each time.

Ok, so now I had four pretty much depleted D-Cells (I'll assume the motor had no real voltage cut off, so it ran them down). So I stick them into my accumanager 20. Lo and Behold, I run into the voltage problem that the accumanager is infamous for. So I try the power cycle trick many time, and that, coupled with sticking them into my Battery Manager, I eventually get to revive them, and they charge back up.

If there was a memory problem, should that have cleared it? (I'm now using these newer 11,000mah D-cells in my mattress, so I haven't tried the original ones yet)

-Mike

Hmmm...I like the idea of just using the stock charger for 1/2 hour a day...

The charger says it's output is 200ma, and it's supposed to be a 3 hour charger. The battery doesn't have a capacity listed, so those numbers make it sound like it's under 600mah. Does that sound ridiculously low for a 9.6v drill to anyone else?

Anyway, if my numbers are correct, that means it would overcharge by 500% every month. (assuming I don't use it in that month) Will that be a problem?

Hi there BatteryCharger,

Wow, that does sound low or they made a mistake.
Most drills i've seen have at least 1.2 Ahr cells, but perhaps you can
open up the pack to read the side label of one of the cells to know for sure.

I think lots of people use the 1/2 hour (or one hour) timer idea because they
dont have to buy a new charger that does trickle charging, or build a new
charger that only trickle charges (actually not that hard but it's still work).
Buy a simple wall timer and that's it

What do you mean that it will overcharge by 500 percent every month?
How did you get that number? Did you mean with constant charging?

If you like you can test the pack by connecting a known load resistance and
monitoring the voltage and recording that voltage and time. We can then
calculate your pack Ahr rating. You have to start with a well charged pack though,
by assuming it's maybe 2.2 Ahr when you charge it.

Can you tell if the cells are Sub C size, or smaller than that?


Take care,
Al