For the last several years I, and many others, have used the trickle charge
system described by Red Scholefield with great success and little effort.
Batteries seemed to last a very long time and maintained a good capacity.
However, recently several incidents in the local area have raised a question
about the newer Nicad high capacity batteries. It seems that several of us
have had a pack suddenly develop an open cell. In most cases I have asked,
they were the newer cells, but apparently of varying capacity. The latest
one of mine that failed was a 1400 mHr 4 cell pack that was less than 2
years old. It failed while I was starting my plane up at the field one day.
It is the second failure of this nature I have had in the last 90 days.
The implied question is there, but not clear. Are the new technologies
being used in manufacture allowing (or encouraging) sudden failure?
I have had premature loss of capacity of some of the 1100 mAh cells. Like
the man sez, "Nothing's free" -- you get double capacity in the same
package, but don't expect it to last as long as the others.
With an incident that happened to me, you may be on to something. I recently
purchased a HiTec Eclipse 7 computer radio. I've owned many different radios
in the past and have never had an overheating problem of any sort even when
fast charging. About 3 weeks ago, I hooked the Tx and Rx up to my Hobbico
Field Charger at the 1 amp charge rate, started the charge cycle, waited for
about 10 min or so just to be sure all was well and then left. About an hour
later (long after the charge cycle should have completed) my wife heard
popping sounds, the charger alarmed, and my dogs went crazy. We entered the
room which had some smoke and I could hear something frying. I went to the
charge table and the battery pack in the Tx had exploded. The top of one
cell was blown completely off and the formerly square pack was now a string.
The whole thing blew out the back of the Tx but the damage was done. At
first I susptected the charger but upon closer inspection, nothing appeared
wrong. The Rx was still charging normally ( now on trickle) right up until I
shut the thing down.
I tossed the batteries in the outdoor fireplace and closed the covers just
in case there were more explosions but everything had calmed down by that
point. They have since been removed.
I rechecked the charger and it still seemed OK, the fuse wasn't even blown,
so I hooked it up to my HiTec Focus 6 and all charged normally. I've used it
several times since on the Focus (the Eclipse got sent back to HiTec)
without any problems whatsoever.
I'd had the charger for 7 months or so before the incident and had used it
to charge both sytems. I only have HiTec so polarity isn't an issue. I also
checked polarity when the Eclipse first arrived and it matched my previous
About the only thing I can think of is that the system had sat idle for
about 2 months while I was away and the pack went entirely flat and a cell
reversed polarity. I didn't check it before I hooked it up so I can't say
for sure but that's my theory. I've never had anything like this happen
before and I've been in the hobby in one way or another since 1973. Just
goes to show that the Li type batteries are not the only ones that can cause
I was very fortunate that no fire was started and that all I lost was a Tx.
PS, the pack involved was a standard 600mah Sanyo.
HHMMM, I guess that's possible but it has performed flawlessly since the
incident. The electronics I've dealt with either work or they don't. IC's,
transistors, and capacitors don't heal themselves as far as I know. Latent
catastrophic gate leakage could cause something like this but once the
semiconductor does this it usually fails completely. I'll definitely keep an
eye on it from now on though.
Thanks for the info.
Very true, but the peak a given pack reaches and how it reaches that peak
can vary significantly depending on previous cycle, state of charge, age,
temperature, charge rate, etc. The peak "window" on the Hobbico may not be
"tight" enough to sort out these differences. There also could be some drift
in the Hobbico due to temperature variations.
Red's R/C Battery Clinic
| HHMMM, I guess that's possible but it has performed flawlessly since
| the incident. The electronics I've dealt with either work or they
| don't. IC's, transistors, and capacitors don't heal themselves as
| far as I know. Latent catastrophic gate leakage could cause
| something like this but once the semiconductor does this it usually
| fails completely.
You're over-analyzing this.
The peak happens once in the charge cycle, assuming that all batteries
are similar in capacity and state of charge (as they should be.) As
you get close to the peak, the voltage keeps going up, then it drops a
little bit -- that's the peak. If the drop isn't big enough for the
charger to register, then that's it -- no more peaks -- and the
charger just keeps charging, forever, unless something else stops it.
If your pack has cells that are in varying states of charge, you'll
get one peak for each cell or group of cells that peak at the same
time -- but it'll be a tiny peak unless it's from several cells, and
may not be detectable by the charger, as the peak of one cell will
probably be overshadowed by the gradually increasing voltage of seven
Some of the smarter chargers (like the Triton, for example)
periodically stop charging, let the battery settle down, then charge
again. That would let them catch any peaks they missed, because
they'd happen again. The Triton also lets you hook up a temperature
probe to stop things if all else fails.
| I'll definitely keep an eye on it from now on though.
If the batteries get hot, it's past time to stop. If they get
overly warm, it might be past time to stop, or your charge rate might
be too high.
Red responded elsewhere and pointed out (very graciously I might add) that I
used the wrong terminology. The packs had SHORTED cells, not open. DUH,
*I* SHOULD know better. He also pointed out that the separators had to get
thinner to pack more stuff in the same size cell. He used the old 10 pounds
in a 5 pound sack analogy, which just about fits what I have been thinking.
Thank you Red for the answer and the pointer.
The Dymond Super Turbo charger (and others I'm sure) have a setting for the
maximum input into a pack before it shuts down. Just in case it misses the
peak. I usually set it for 2-3 hundred mAh less than the pack capacity.
There are also optional temperature probes that will shut the charger down
if the pack gets too warm.
My experience (34 years) is that the newer, extra-capacity batteries
have a much shorter life expectancy than those I used 20 years ago.
Maybe by a half. The batteries of 34 years ago just plain weren't
reliable. With thinner plates and less electrolyte, you would expect
them (extra capacity) to be more fragile. I have been fortunate not to
experience an explosion or a fire. My guess is that the charger missed
the peak, as others have suggested.
I've had the same problem with the sanyo 1100 mah nicads also. I have found
they have a very short service life. When they are charged at 100-110 mah they
get very warm. In both the Tx and RX the capasity drops off rather quickly.
They seem not to perform to max capasity in service even when new.
I use sanyo 700mah batteries in another system and they perform as you would
think they would.
So I agree. The 1100mah seem to frail.