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Eye-opener Zippy Compact incident

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Eye-opener Zippy Compact incident

Old 08-09-2013, 07:02 AM
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Astropattern
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Default Eye-opener Zippy Compact incident

I thought this might good to share this, since I’ve never seen anything this dramatic with LiPos.

This pic shows a 2013 Zippy Compact 10s5000 battery that I took out of my Episode/Contra last week, moments after a Masters practice flight. The first two cells in the pack had swollen to such an extent that they actually spit the shrink-wrap. The battery was quite warm after the flight and the swollen cells felt like they were rock-hard with pressure.
I think I was lucky.

This battery was one of three Compacts I bought at the beginning of this season to replace some standard Zippys I was flying. The other two Compact batteries are still going strong while this one is, for obvious reasons, off-line.

As background, this battery is one of many batteries my son and I have owned/flown/tried in 4-1/2 seasons of flying electric so far. We’ve lost two in flight (long story), and three were defective on arrival, but otherwise we've had good, long, service from our batteries. One of the Zippys Adam flew at the Nats this year was from his first season.
Specifically, these three new Compacts were “broken in” with two flights at 25 Amps with 1800ma drains. After that, this particular battery was flown 20 times. As I periodically “amp” my flights with a WattsUp meter, I have never seen more than 67Amp peaks nor more than 3800ma drains on any of my flights. I put back in 4000ma on one very windy day. Last week was dead calm. Also, I have never charged any of our batteries at greater than 1C.

The only odd or unique thing about this battery was that cells #1 and #2 were showing roughly 8 mOhms IR while the other cells in the pack averaged 4 mOhms. All three Compacts get warmer than my Thunder Power packs and might show a little “softness” in the sides after flying, while the TP's are invariably “hard and flat”.

Not sure this means anything except that the battery was defective or became defective after a small number of flights, but it is a hint that perhaps a 2-to-1 difference in cell IRs within the same pack may be a leading indicator of a potential problem.

John


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Old 08-10-2013, 12:50 AM
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I got some zippy compacts recently and 1 of the 5s packs had a cell at 14 mOhm compared to the other cells at below3 mOhm . I refuse to use the pack as it will do like your one. Hobby king offered me 14$ refund as the voltages were good, they don't deem IR's a reason for replacing a pack..
Old 08-10-2013, 02:01 PM
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Even after sending them this pic, they refused any warrantee service.

John
Old 08-10-2013, 02:24 PM
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Jetdesign
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Rethinking this post while I'm writing it: If I were a betting man, I would wager that there was some small physical issue with the first two cells, so they were working harder during charge/discharge. We know vendors similar to the ones that sell Zippy batteries are notorious for selling products with reduced quality control. My first thought however was regarding the break-in and usage of the packs.

I wonder if break-in/discharge has much to do with it. Technically a proper break-in would be a charge at 1C and a discharge at something like 0.2C, and would discharge the battery down to somewhere around 3.4v/cell. I know none of us do this, and the batteries don't come with instructions telling you specifically how to break them in. People use the 80% discharge rule - also a common rule of thumb for breaking in. Seems this pack was discharged the full 80% only once or twice.

The point of breaking in the batteries is to arrange the ions inside so that they are not biased toward or away from the battery poles. The higher charged ions will fight their way toward the anode or cathode depending on the state of the battery. They will be the first ones to start working during charge/discharge. When this kind of discharge isn't done and the battery sees a higher current draw during use, the biased mix of ions don't get the residence time they need to find their way to the pole and end up reacting with whatever is around them (the electrode).

The puffiness in lithium batteries is usually a byproduct of the ions reacting with the electrode - it is a chemical reaction that results in the release of a gas. It usually happens when batteries are over discharged. Over discharging could be drawing a current higher than the battery's C rating - discharging a battery that is not broken in would have the same effect as either way you get a rush reactive ions without the proper residence time to get to the poles).

Again my bet is probably something mechanical in the battery - loose connection, cheap solder, etc. I don't think there was any fault, except for the lack of the lipo battery industry properly educating the end users how to properly handle their product.
Old 08-10-2013, 06:16 PM
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I usually charge the battery at 1C after receiving. If all the cells take the charge equally well, then I will go fly with the pack. If any one of the cells shows sign of taking the charge much slowly than the rest, I would usually stop right there and negotiate an exchange.

So far, the practice serves me well and none of the packs surviving the first test charge die prematurely. I have been using Zippy Compact, Turnigy, F3A Unlimited and other packs.
Old 08-12-2013, 07:49 AM
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I am using 5 cell Zippy compacts, two packs in series. I bought the first 4 packs last year. When I was preparing them with connectors and Velcro, I noticed one of three packs was 1/8" narrower than the other 3. It also had a cell with much higher internal resistance. I made no attempt to return it, I purchased a replacement pack. I purchased another set of 4 packs this year and they were OK, but it looks like you need to check them carefully when you get them.
Old 08-12-2013, 08:21 AM
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Just a thought.

The specifications indicate a 5000mAh rating. It’s possible the pack is “overrated” by the manufacturer and the mAh capacity is actually lower than specified. If that’s the case, you would be overcharging and over-discharging the same battery many times unintentionally.

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Old 08-12-2013, 05:32 PM
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He would know that based on the battery voltage after a flight, if he were to look at the charger or use a little lipo meter.

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