Klas Strandberg wrote:
>
> Walt,
>
> I speak with filmmakers, cameramen (film and video) and lightcrew almost
> every day. They use the best of chargers and very expensive accus. They
> report ongoing problems. Every time they throw away a 150 dollar 12V pack,
> they waist 9 cells just because 1 is blown out completelly. Very troublesome
> for the users and very good business for the pack-makers.
>
> I make new cellpacks for them, with loose 6Ah D-size cells and a very simple
> current limited slow charger. (say 6-15 hours) With loose cells and 2
> chargers, they can even charge a 12v set from the car battery.
>
> I believe in battery packs and fast charge when I see it work on my bench. I
> admit though, that it works okay when the load is fairly low and the charge
> is fairly slow. Perhaps you can thank your HHB for your good experiencies?
>
> I use fast chargers only to my cell-phones. I have to buy new packs 2-3
> times per year.
I use fast charge for everything, except the 9 volt batteries though
there is a fast charge specification for them too, and the cells that
I'm now replacing are 5-6 years old or older, with extensive use. I've
not yet replaced any NIMH batteries, just some of the older Nicads. And
my oldest NIMH are 3-4 years old. I went to fast chargers several years
ago when the first of the microprocessor controlled ones came out. Since
then I've had less cell failure, not more, in fact I tried the new
chargers on the batch of "dead" batteries I'd accumulated, and quite a
few the new charger had no problem getting to work again. I keep my
batteries in groups and charge them in groups, which is equivalent to
having a bunch of battery pacs. I mark the date on every battery when I
get it, so I know exactly how old everything is. The HHb uses a battery
holder for 8 AA's, but it's not a pac, takes loose batteries. Though I
do keep them in sets of 4 and have two batches of 8 just for it. And the
HHb is only one of quite a variety of things that I run off
rechargables. It's not my major battery eater, my lights are.
I actually trust the built in charger in the HHb less than the fast
chargers. It's a slow charger, but the batteries stay warm even when
charged, indicating it's trickle charge may be too high. My fast
chargers the batteries cool to near room temperature after charging when
left in the charger. Though they are in battery maintaining mode.
I expect that the pacs you make could be fast charged reliably using a
new charger made for the job. In any case replacing a cell would not be
a problem on the ones you made. It would be nice for the pac makers to
put out pacs designed for cell replacement. Older pacs often were held
together by screws making it easy. Newer ones are more often locking
tabs and glue to fight.
Part of the problem is that there are many fast chargers that are not
properly designed, often they are simply timed and little more. Many of
these fast chargers have settings that are critical, or if they lack
them they are depending on the operator. That's even more true of the
elaborate, expensive ones. I don't trust timed charging for fast
charging, and manual ones you sooner or later forget. It only got
reliable for me when they added microprocessor control, I used some of
the older fast chargers, but they had to be watched through the charge
cycle to be safe, and immediately disconnected from the batteries when
it was done.
The latest pulsed fast chargers look like they may be even better. Gas
buildup at the plates is the biggest problem with fast charging, and
these break up the gas formation. Slow charge produces gas too, but at a
rate it does not normally build up. This latest style of fast charge may
eliminate the last bit of physical difference in what happens with the
two styles.
I certainly agree, if you fast charge at the fastest allowable rate I'm
not sure you do as well as I do. The folks that run R/C cars and so on
are the ones I know around here who charge at that rate. While my
chargers are considered fast chargers, they still take about 2-4 hours
to charge (depends on the capacity of the battery), considerably slower
than the high speed fast charging that takes less than a hour. My sons
had a R/C truck that they charge the main battery pac on a super high
speed charger, and several of those nicad pac's are several years old
and still going strong. They get charged in 20 minutes! That charger is
not microprocessor, but has a settable timer and always discharges the
batteries first, you have to be careful using it and set the timer for
less if it's a older pac that's not holding a normal full charge. It
would be easy to damage the pacs by simply setting a few extra minutes
on the timer. That sort of overcharging would give exactly the sort of
symptoms you are experiencing. Particularly when combined with something
else, which is to chronically drive the batteries right down flat when
using them. Sooner or later you will reverse a cell doing that.
Note that both my sons and I pay attention, follow the instructions,
understand what's going on. I'm wondering about the folks you are
dealing with. I'm thinking they are rushing around thinking about
anything but proper battery care. The most expensive chargers I know
about are designed primarily for use by someone who's job it is to
maintain a large set of batteries for some company or such like. They
are all manually settable, very capable machines, and results depend on
both correct setting and correct understanding of the process. They are
tools for battery pros. Fairly inexpensive microprocessor controlled
fast chargers designed for the characteristics of the pacs they use
would be a better choice for your folks. The kind that will do all the
thinking necessary and adapt to the varying capacity of pacs as they
age. And learning to not run them into the ground in use would probably
help a lot too.
Walt
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