Originally Posted by tdford

Subbed

Ahhh yayahhhhhh!!

Originally Posted by tdford

Subbed

Originally Posted by T-CAT

Ahhh yayahhhhhh!!

Looks like I need some lessons in RCG literacy here, what was said

Ha-ha, sorry Joe. I know td from speaking with him in many other threads, and I was happy he subscribed to your thread because it's well worth the read.

Lol, nothing really, more of an inside joke

I'll be getting some 90mm EDF's this summer and I'll be shopping for some nice 6s packs in the coming months. So I figured I'd keep more of an eye on this thread.

Welcome aboard td! Very glad to have you.

What brand of fan(s) are you looking at? (that's another testing interest of mine)

Joe

Well the 90mm jets will be Freewing, and I've heard of good results with their newer 12-blade setups. I'm not sure who produces their fans, or if it's Freewing themselves.

In the past I've used XRP/Changesun with good results - though 70mm.

For the price, you can't go wrong with the RCLander's alloy 90mm EDF with 1000kv motor on 10S, as it does a great job at over 4000W. They are also bringing a 12 S version to the market at close to the same amps, but pumping out a good deal more power. Yeehaw

Originally Posted by MCSGUY

Hey Dean, I always wonder the same thing. It's like what's wrong with it that it can't be charged as fast as the other? There's definitely some psychology at work there making me think it's not as good as a pack that can handle a 5C charge.

I wonder if it's just a specification a particular mfgr hangs on their cells or if it's really a chemistry issue? (not that I charge at more then 1C anyway)

...

Joe

I believe it is because of the chemical reaction Li1-xCoO2 + LixC <----> Li1-x+dxCoO 2 + Lix-dxC . When you discharge a cell, you are stripping an electron off of the LiC anode and the Li+ ion zips across to the LiCoO2 cathode. When you charge the cell, you are stripping an electron off the LiCoO2 side which has the potential for you (from too high emf) to cause the crystalline structure of the cathode to break down freeing an O2 and precipitating a Co which neutralizes the Li+ cation into Li metal which then reacts with the O2 to form Li2O + O2 <-- this excess oxygen is the puffiness. There is the potential for the breakdown of the cathode in both the charge and discharge reactions but it takes less energy in the charge process. Since the physics/chemistry of the intercalation process is highly dependent on the composition and manufacturing tolerances, the charge C rating is hard to pin down and not as eye catching like 125C.

Another way to think of it is that when the cell is discharged, it is at a lower energy/stable state than when it is fully charged. Going from a stable to an unstable state usually has a higher potential for things to get mixed up when the transition is quick, compared to going from a unstable state to stable.

Thanks Ian! The chemistry is over my head but I can understand the principles involved because of your clear explaination.

Finally...someone on this tread that speaks plain English! Just kidding...sometimes I feel like Penny...

We have had some discussion about this elsewhere in regard to IR measurement.

My intuitive feeling is that measuring IR while discharging is NOT the same as when charging. Your energy level argument seems to make sense in that regard.

However in practice both methods seem to work.

That is - at least couple of chargers using the "voltage drop when the charge current is removed" (iCharger and Hyperions) give the same result as the "voltage drop when a discharge current is applied" (iCharger and the ESR/IR meter). The FMA chargers give a lower values of IR and measure it during charge with a very brief rest pulse compared with other chargers.

Some people think it doesn't matter, based I suspect on a model of the process as a perfect voltage generator in series with perfect internal resistance. My sense is that you cannot use that model for both charging and discharging . If you could why wouldn't maximum charge and discharge rates be the same?

Be interested in your thoughts on this.

If folks think this is too far off topic we can hop over to the LiPo performance ESR/IR thread here.

https://www.rcgroups.com/forums/show...577989&page=50

John

Originally Posted by E.N.

I believe it is because of the chemical reaction Li1-xCoO2 + LixC <----> Li1-x+dxCoO 2 + Lix-dxC . When you discharge a cell, you are stripping an electron off of the LiC anode and the Li+ ion zips across to the LiCoO2 cathode. When you charge the cell, you are stripping an electron off the LiCoO2 side which has the potential for you (from too high emf) to cause the crystalline structure of the cathode to break down freeing an O2 and precipitating a Co which neutralizes the Li+ cation into Li metal which then reacts with the O2 to form Li2O + O2 <-- this excess oxygen is the puffiness. There is the potential for the breakdown of the cathode in both the charge and discharge reactions but it takes less energy in the charge process. Since the physics/chemistry of the intercalation process is highly dependent on the composition and manufacturing tolerances, the charge C rating is hard to pin down and not as eye catching like 125C.

Another way to think of it is that when the cell is discharged, it is at a lower energy/stable state than when it is fully charged. Going from a stable to an unstable state usually has a higher potential for things to get mixed up when the transition is quick, compared to going from a unstable state to stable.

Thanks John! The ESR/IR thread is definitely a great resource for that.

Originally Posted by daedalusrobert

Finally...someone on this tread that speaks plain English! Just kidding...sometimes I feel like Penny...

LOL! Took me a minute to place the reference. No worries, this is a Sheldon free zone

This thread and your efforts will, already are, prove priceless to anyone with the willingness to invest nothing more than the time it takes to read and understand that presented. KUDOS.

I've been in touch with Buzz Butler who owns the Magnum brand here in Denver. He's been in the hobby a very long time and like many of us has invested time, and in his case money, in coming up to speed with LIPO technology. Over the last year or so I've spent a lot of time talking with him and watching as he developed his line of batteries. He has built a load tester that can draw 100 amps from a battery and measure the voltage drop. Yesterday I watched one of his 6S 5100's put through this test and as has been stated many times already it is nevertheless interesting to watch the voltage rise as the battery heats up. Anyone who has ever wondered at the veracity of some of the high amp claims made by battery manufactures should witness for themselves the temperature rise provided by just 100 amps during ONE minute to both high quality 10 gauge silicone wire and properly soldered EC5 connectors. I told him I appreciated his new labeling on his batteries showing IR instead of C rating. I've used a set of his 6S 5100's on my ALEES heli with good results but one users practical experience is not the same as an instrumented evaluation such as your undertaking. I have an IR/ESR meter from Progressive RC and am trying to see if he will let me use it on a random sampling of his batteries for addition to the objective performance database. I know historically manufactures have been loathe to do this nevertheless the potential marketing value is in the ability to demonstrate minimum and repeatable, within limits, standards to your customers as opposed to the time honored game of who's the biggest liar.

A couple questions for the experts:

What kind of "break-in" if any do you experts feel is warranted before doing baseline ESR testing?

How much correlation have you seen between high current testing and the IR testing done by the FMA/i chargers or the IR/ESR meter?

Hopefully all this work done by a few on behalf of the many will pay dividends for the hobby. I guess only time will tell whether the collective hobby community is smart enough to vote with their discretionary dollars for honesty and integrity over hyperbole.

We all need the Penny's of the world. They remind us that being human is at least if not more important, and fun, than living your life out of a math book.