New battery questions.

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 set up.

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 a fire.

I was very fortunate that no fire was started and that all I lost was a Tx.

Jim W

PS, the pack involved was a standard 600mah Sanyo. "Six_O'Clock_High" wrote in message news:6tFEc.430$ snipped-for-privacy@newsread2.news.pas.earthlink.net...

My best guess (99.9%) is that the Hobbico Field Charger missed the peak and kept on charging at 1 amp. Hobbico electronics equipment should not be used unsupervised.

-- Red S. Red's R/C Battery Clinic

us out for "revolting" information.

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.

I've had my Hobbico Mark II miss the peak on packs it has successfully charged before and since. Don't trust them! [at least for NiMh]

remove my-wife to reply :-)

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. Red's R/C Battery Clinic

us out for "revolting" information.

| 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 other cells.

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.

SNIP

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.

John VB

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.

John, In the cases where I have experience failure, there was NO FAST CHARGER, peak detecting or not. You echoed what Red said, so we are in agreement.

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.