c-grain

hI all,I have about $1200 worth of LIPO packs that have no taps for balancing the individual cells.Since all the manufactures of these packs have known from the begining that it was very important that ALL the cells in a pack must stay within a tight tolerance to last a reasonable time,why didn't they include the tap's in the first place?Well,I contacted Apogee and asked if they could add the taps to all my existing packs---kinda like a "recall" like the auto dealers do with cars,and they said -no,they were not set-up to do that!I have lost 3 packs due to "bulged" cells in the past 1.5 years and get this---I have never pushed a pack past it's advertised peak.I have allways allowed for "headroom"!For example,if the pack is rated @ 10.5C,I will prop to 10C max-- not the 14C burst rating!The only reason I can think of for the bulging is because of IMBALANCE.I have tried to add my own taps,but most ot my packs can't be soldered.Even if I had the special solder to do it,it's a scary proposition!!Emagine if you short one out by mistake[X(]Does anyone know if there is anyone out there that can offer this upgrade service to all of us that bought these packs in good faith?Also,I have never charged over the 1C rate on any of the packs even though I have read that some people have had success charging the newer "high C " packs @ 2-3 C.

GWR

My Feedback: (31)

Didn't I just read this elsewhere?[sm=punching.gif]

exeter_acres

My Feedback: (2)

not that I am aware of...now go fly

Greg Covey

Although one reason for a bulged cell in a pack is due to inbalanced cells, it is not the only reason.

We (electric flight enthusiasts) are typically on the cutting edge of technology. We see technology changes in our hobby faster than we can digest them. It is, in part, our responsibility to move forward with some sense of caution when a new technology is introduced. In fact, it is the R/C user himself that actually helps push the technology to new heights.

With this pioneering spirit in mind, look from FMA for the leading technology in Lithium-safe products that will help protect your future investment. The three systems below offer true cell balancing on charge and true cell protection on discharge.

Scorpion (2-cell) packs for R/C car racing
Balance Pro (2-cell) packs for R/C airplanes
Skyvolt (2-12 cell) packs for R/C airplanes

GWR

My Feedback: (31)

I don't have any. They are a recent development. All my packs are at least a season old. Soon all replacement batteries will have them.

Matt Kirsch

My Feedback: (21)

Frankly, I don't believe for a second that LiPoly suppliers knew about the imbalance problems "from the beginning." I've worked in R&D and you wouldn't believe the kinds of things that end users could "break" on us that no amount of lab testing could reveal beforehand. Sometimes the testing environment becomes too ideal, too sterilized, and it takes an end user not quite following the directions in a way never thought of to reveal an issue, like the cell imbalance problems.

As Greg said, though, cell imbalance is only ONE of the possible causes of "silver sausage disease." Unless there's concrete proof that the cells were out of balance prior to the silver sausaging, you can't really say with 100% confidence that cell imbalance was the problem. You can suspect, but until/unless you can prove, it's still only a suspicion. I do quite a bit of root cause analysis for a living, and my bosses don't accept explanations for problems without some form of concrete proof.

xrboss

What are the oter reasons for the cells to bulge??

dwilco1001

I have just joined rc universe and also started to use Li-Po batteries, so I hope the following is of interest and that I am not breaking the rules of the forum in any way.

I bought a couple of 3S2P 2200MAH packs from ebay which were fitted with a balance lead and connector. However, as I could not find a socket in the UK to match the connector I dis-assembled the packs carefully and replaced the supplied balance connector with a Flight Power lead, which I couple to a Flight Power balancer. I worked carfully and managed the soldering, but it was stressful based on what one reads about packs catching fire etc!

I have been surprised to see that the balancer always has some work to do when I plug it into the packs - at the end of a charge, at the end of use and during storage. So, based on my little experience so far it appears that cells do get out of balance. As I have a balancer, I hope it will keep my packs in good condition.

Like the first contributor, I charge my packs slowly (10% of C in my case) and prop up to just under 5C (10 amps). I have only carried out bench test so far as it will be some time before I build a plane to flight test this set up.

I think Li-Po cells will open up a great many opportunities for more eficient electric flight and I am sure we will all become more comfortable with the cells with experience (as we have with Ni-Cads and Ni-MH cells over the years).

DHG

My Feedback: (7)

Greg,

This thread reminds me of the old saying, "Never ascribe to malice that which can be adequately explained by stupidity." But anyway ... Let's say I have some very new (less than 20 cycles) Thunder Power 3s 1320 packs, a couple of which I suspect are out of balance. And let's say I would consider it a prudent investment to try to retrofit them with balance taps. And finally, let's say I don't know diddly about soldering aluminum and have no interest in splattering myself with napalm while trying to learn.

Who can I send these to? Does Thunder Power, FMA, or some garage-shop entrepreneur that you know of offer this service?

Thanks!

Duane Gall
RCPRO

Greg Covey

Hi Duane,

At this point in time, nobody will re-wire your packs that I am aware of. It is simply a matter of liability as well as the fact that few cell-balancing chargers have hit the market yet. Several manufacturers have started selling packs with taps as a preemptive move to position their readiness for balancing the pack in the future. I feel that this is a good move on their part.

The reason that FMA Direct has not made big packs until now is the fact that there was a real danger of failure and therefor plenty of liability at stake. Much of this is coming out now against ThunderPower over on the RC Groups "Batteries and Chargers" forum.

Keep in mind that we'll have another round of tap connector incompatibilities and the smart users will simply make their own adapters so as to not void any warrenty. Only the Skyvolt system will provide high performance 20C discharge and 3C charge rates due to the Kokam cells used and the charge/discharge algorithms that protect the weakest cell and only charge to 90%. Other systems, will have the added safety benefits but will unlikely match the increase in pack longevity.

For those folks looking for smaller cell balancing, non-Kokam cell selections, and a wide range of new capacities, stay tuned because 2005 will be another bombardment of new products for electric flight!

DHG

My Feedback: (7)

Greg,

Thanks, I suspected that might be the answer. It's expensive and sometimes frustrating to try and stay on the "cutting edge" of anything, but IMHO this whole e-flight phenomenon is worth it!

D.