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Batteries & Chargers Discuss Li-P, Li-Ion, NiMh, Nicad battery technology and the chargers that juice 'em up!

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Old 03-17-2011, 07:22 PM   #1
Swift428
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Default Not All Balanced LiPo Packs Are Equally Balanced

Earlier this morning I replied to a balancing enquiry thread at RCU in that no one either takes the time to really absorb/digest the intent of the poster or they are all following the herd mentality (itís all about volts, volts, volts) whether at WF, RCG or RCU.

Electriceddie
Hi All,
of the 2 listed batteries below. All is the same except for the 20C vs. 30C rating. If all is equal except for the 20C and the 30C what does that mean power wise? What exactly does the "C" rating mean here with a difference of "10C"?
a. FlightPower - EONX30 (Lite) LiPo - 3S, 11.1V, 1200mAh, 30C - wt. 4 oz.

b. Great Planes - ElectriFly LiPo - 3S, 11.1V, 1250mAh - 20C - wt. 4 oz.


Thanks, Ed



Swift427
The difference is the IR=Internal Resistance of the cells. The higher the C rating the less IR so it can be discharged at a higher rate without the cells getting overheated. Thus the thinking also goes that a 2200mAh 45C rated LiPo can be charged at say, 4C(8.8amps), just as safely as a 2200mAh 12C older generation pack at 1C(2.2amps).

The IR of the latest generation 45C LiPo may be as low as 1.3, whereas, the IR of a growing older previous generation pack could be 6.3 or more. If you have an E-flite Cell Checker you can get an idea of the difference in IR from one cell to another. For the sake of an example let's say at a LVC of 9.0v the voltage in each cell of your Electrifly 1250 20C were as follows: 2.65v, 3.23v, 3.12v = 9.00v ... cell1 having less IR is depleted sooner; whereas cell2 has the higher IR. Unfortunately, Cell1 being the better cell from an IR standpoint may also be the cell with a shorter, less lively cycle life if 90%+ of the pack's capacity is always depleted by a pilot that wants to fly as long as possible (until 9.0v LVC).


So, even though you balance charge this Electrifly 1250 20C pack to equal cell voltages of say 4.15v, 4.15v, 4.15v the pack is still not truly balanced because of the IR imbalance difference between cells at the moment of a 9.0v LVC ... Cell1 having the least IR and therefore may actually be closer to a 25C discharge rating; whereas Cell2 may actually be closer to a 15C rating. And Cell3 with a 20C discharge rating ... overall the distributor could rightly label this LiPo pack as having a 20C discharge rating.
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Old 03-17-2011, 10:47 PM   #2
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So, what do you want anyway?
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Old 03-17-2011, 11:47 PM   #3
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More conversation is about it just my guess.
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Old 03-18-2011, 12:18 AM   #4
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The weather here is really windy,but almost hit 90 degrees, cant wait to get sunburn from flying too long!!!
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Old 03-23-2011, 02:29 AM   #5
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I got sunburned today mowing the grass for nearly 4 hours.
Then got in 2 flights late this afternoon.
Henry
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Old 03-23-2011, 02:34 AM   #6
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lol me too again today just doing honey do's, but no flying though 50's mph wind couple hrs ago.

When I seen this thread pop up again...I was like OOOO Nooooo Not Again!!!!!!! forgot to unsuscribe...oops

have a good one
hope you had good flights
cr
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Old 03-29-2011, 05:50 PM   #7
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Actually, if you were paying attention to Swift's post, you might have learned something.
We have a thread going about being too serious, but sometimes I think we can be too frivolous.

This is how you get in trouble. Lazy minds will lead you down a nasty path.

How many of you have ever even thought of the concept of IR in a pack?

You wonder why a pack isn't performing and you say it's balanced.
Kinda like 3 fuel tanks, full of fuel, except one has a 1" fuel line going to the engine, one has a 1/2" fuel line, and the other has a 1/4" fuel line.

Yep they are all perfectly topped off, yet none of them give the same performance.

Hmm, imagine that.

Not to be ugly about it, but this kind of thinking is why you can have problems. And why you will place blame on something without knowing all the facts involved.

Just like the pilots that immediately blame a radio problem on a crash.

Most likely they forgot to mention they are crappy solderers, don't balance their packs, are poor builders using the wrong materials, don't pay attention to placement of electronics, overload their bec's, fly past cut off, can't fly worth a darn, and on and on.

"Nope I had a radio hit, dang faulty rx/tx. Blah blah, blah, so and so's equipment is no good."

Too many folks are stuck in the plug and play mentality, install it and forget it.
Sorry there's more to this then that if you want reliability and safety.

When I die, I want to go like my Grandfather did, in his sleep...... Not screaming like the passengers in his plane.
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Old 03-29-2011, 06:41 PM   #8
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I'm just guessing but maybe you did not see where this all started.

http://www.wattflyer.com/forums/showthread.php?t=60530
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Old 03-29-2011, 09:08 PM   #9
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2 inches of rain in the last 2 days. No flying today. 70% chance of rain tomorrow.
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Old 03-29-2011, 09:26 PM   #10
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No Kidding? Humm...wish we had rain here. I need it for the crops. Cant grow wheat and maize in a desert ya know!
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