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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 09-22-2012, 08:09 PM   #1
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Default Gens Ace LiPo versus A123's

OK
After five years, I finally bought two Gens Ace 2200 3S1P batteries rated at 25 C. These LiPos will be used in a foamie picked up a few weeks ago.

Note that this is the first discharge test on the Gens Ace battery, further tests might improve things a little bit.

Basic info, the Gens Ace battery weighs 6.38 ounces, and measures 4 3/8 by 1 3/8 by 1 inch. My Cellpro Powerlab 8 charger shows its internal resistance at 9.5 milliohms.

Compare that to my 4S1P A123 pack. It weighs in at 10.4 ounces, measures 5 1/2 by 1 by 2 inches. The '8 charger shows its internal resistance at 6.8 milliohms per cell.

The A123 battery pack would then add four ounces to a model that weighs in at about 18 ounces.

Take a look at the discharge curves generated by the Western Mountain CBA battery analyzer.


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Old 09-22-2012, 09:25 PM   #2
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A the A123 looks pretty good in that test but to make it fair it would be interesting to 'normalise' the graph on a discharge per ounce basis, or simply test the A123 against liPo's of the same weight (a 3s 3600mAh would be about right). I'm sure that the comparison would look a lot more LiPo favourable if done that way.

Also cost being taken into account would be interesting, though I do appreciate that a simple 'cost new' comparison could be misleading as A123 should have longer life.

It's interesting that the Gens Ace falls well short of it's claimed capacity, maybe few cycles on the LiPo may also improve it slightly, as you say. I take it that it was charged fully to 4.2v per cell?

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Old 09-22-2012, 11:23 PM   #3
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If I read your graph correctly, the A123 is putting out about 112 watts at the roughly 50% capacity point versus 99 watts for the lipo. However, when you look at the watts/oz. the lipo is about 40% more powerful by weight. That's similar to what I've found.

The lipo is probably a better choice for the foamy. Adding over 20% to the AUW with likely cause a noticeable decline in performance. I've found A123's useful for scale models where you often can use the nose weight. The ability to build the pack in the shape you need, and even build it into the model (due to the inherently safer charging and high rate) are also useful.

BTW, there is a thread on RCG that compares batteries under a defined protocol that shows Gens Ace has one of the most honest C-ratings in the industry but they also fall somewhat short of their rated capacity.

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Old 09-23-2012, 01:14 AM   #4
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Originally Posted by pmullen503 View Post
If I read your graph correctly, the A123 is putting out about 112 watts at the roughly 50% capacity point versus 99 watts for the lipo. However, when you look at the watts/oz. the lipo is about 40% more powerful by weight. That's similar to what I've found.

The lipo is probably a better choice for the foamy. Adding over 20% to the AUW with likely cause a noticeable decline in performance. I've found A123's useful for scale models where you often can use the nose weight. The ability to build the pack in the shape you need, and even build it into the model (due to the inherently safer charging and high rate) are also useful.

BTW, there is a thread on RCG that compares batteries under a defined protocol that shows Gens Ace has one of the most honest C-ratings in the industry but they also fall somewhat short of their rated capacity.
Yeah, 9 Amps was the limit of my CBA battery analyzer. The A123 cells advertise very high "C" ratings on their cells, but for me, any value of C over about 20 or so results in to much voltage drop on their output. That translates to about 35-40 Amps per cell.

There is another thread in www.wattflyer.com where a LiPo supplier indicates their batteries have a 150C rating. With the battery rating of 8000 Mah, that's 1200 Amps. The battery uses #12 wire, a wire size that will melt at much over 350 amps. Let the buyer beware.

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Old 09-23-2012, 01:19 AM   #5
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Originally Posted by JetPlaneFlyer View Post
A the A123 looks pretty good in that test but to make it fair it would be interesting to 'normalise' the graph on a discharge per ounce basis, or simply test the A123 against liPo's of the same weight (a 3s 3600mAh would be about right). I'm sure that the comparison would look a lot more LiPo favourable if done that way.

Also cost being taken into account would be interesting, though I do appreciate that a simple 'cost new' comparison could be misleading as A123 should have longer life.

It's interesting that the Gens Ace falls well short of it's claimed capacity, maybe few cycles on the LiPo may also improve it slightly, as you say. I take it that it was charged fully to 4.2v per cell?

Steve
The LiPo battery was topped off at 4.2 Volts DC per cell on my Cellpro Powerlab 8 charger.

The A123 pack does look pretty good in that test. But, they would add some 4 ounces of weight, and their much larger physical size limits use in a foamie airplane. They simply won't fit.

The bottom line, IMHO, these A123 cells are more suitable for the larger models, perhaps 1KW in size or larger.

I paid $9.00 each for $36 for the four A123 cells from www.voltmanbatteries.com, versus $20 for the 3S1P Gens Ace 2200 Mah battery.

Note that even the A123 cells never match their claimed 2300 Mah rating. Just about every one I've tested comes out at about 2100 Mah at currents of 30 Amps or so.

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Old 09-23-2012, 03:26 PM   #6
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I would prefer to "normalise that graph by increasing the lipo current (maybe double it)
IN a sense pretending to "prop UP" for the lipo to make up for the lower voltage. The voltage is kinda relevant when viewing the graph , but to make things fair the wattage should really be the same thus making the lipo run out of capacity first. Maybe an even closer comparison would be a 4s , maybe the weight would also be close?

ps. I can tell by the graph that 10 C is just fine for this lipo pack.
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Old 09-24-2012, 02:33 AM   #7
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Originally Posted by nidly View Post
I would prefer to "normalise that graph by increasing the lipo current (maybe double it)
IN a sense pretending to "prop UP" for the lipo to make up for the lower voltage. The voltage is kinda relevant when viewing the graph , but to make things fair the wattage should really be the same thus making the lipo run out of capacity first. Maybe an even closer comparison would be a 4s , maybe the weight would also be close?

ps. I can tell by the graph that 10 C is just fine for this lipo pack.
Yeah, I'd like to have discharged those battery packs at 20 or 30 Amps, but with the 100 Watt limitation on my Western Mountain CBA battery analyzer, that was not an option.

The main point of this thread was to show that a 4 cell A123 pack will outperform a 3 cell LiPo with similar Milliampere Hour ratings, but at a severe increase in weight of 4 ounces for the battery pack.

IMHO, these A123 packs are just not suitable for powering these very popular foamies because of the weight and physical size issue.

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Old 09-24-2012, 03:04 AM   #8
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Originally Posted by nidly View Post
I would prefer to "normalise that graph by increasing the lipo current (maybe double it)
IN a sense pretending to "prop UP" for the lipo to make up for the lower voltage. The voltage is kinda relevant when viewing the graph , but to make things fair the wattage should really be the same thus making the lipo run out of capacity first. Maybe an even closer comparison would be a 4s , maybe the weight would also be close?

ps. I can tell by the graph that 10 C is just fine for this lipo pack.
Just ran another quick test on these batteries.
I've built up a resistor load box consisting of six two ohm, 50 watt resistors, with each resistor on a toggle switch for adding or removing.
Both tests were conducted right off the battery charge cycle.

The LiPo battery put out 11.07 Volts at 31.6 Amps.
The A123 battery put out 11.34 Volts at 33.2 Amps.

Note that the LiPo battery voltage will drop off during the discharge cycle, where as, the A123 battery voltage discharge curve is much more flat.

And, that 10C is an appropriate discharge value. With a constant 10C discharge rate, that will give six minute flights.

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Old 09-24-2012, 03:39 AM   #9
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I'm surprised that the a-123 voltage fell off that much. Do you think at 20C the lipo may hold higher voltage than the a-123? One thing is for certain and that is that "around" the MAX current the lipo graph will be just about flat.

I'm really afraid of something here.

I'm afraid that you will buy more lipos and never look back. (powering even your larger models with lipos as well)
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Old 09-24-2012, 03:49 AM   #10
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Originally Posted by nidly View Post
I'm surprised that the a-123 voltage fell off that much. Do you think at 20C the lipo may hold higher voltage than the a-123? One thing is for certain and that is that "around" the MAX current the lipo graph will be just about flat.

I'm really afraid of something here.

I'm afraid that you will buy more lipos and never look back. (powering even your larger models with lipos as well)
One thing about those wild "C" ratings on some of these LiPo batteries. Like one supplier is claiming 150C. Running a battery at 150C will result in a flight time of about 24 seconds. Totally unrealistic.

IMHO, flight times on the order of four minutes are a little more reasonable, and that represents C=15, the value I tested both the A123 and LiPo's at. I've got some 1000 watt resistors, but really don't want to push my "cheap" Gens Ace battery that much.

As far as going LiPo, not likely! IMHO, the advantages of these A123 cells just outweighs the Lipo batteries in the larger models that are in my hanger. They can be charged in 15 minutes, and mine are lasting five years with little or no loss of performance. They can be stored fully charged, half charged, doesn't make much difference.

Yes, my same models will likely perform better with a Lipo pack, but they'd likely need lead in the nose to balance them. And pulling a liPo pack out for charging in my models is a real head ache. The A123 batteries are pretty much built into the model. And, my models will fly straight up out of sight, including the giant scale Big Stick that weighs in at some 16 pounds. No they won't hover, but that's not how my models are flown.

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Old 09-24-2012, 06:21 AM   #11
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I totally agree that the 150c claim is totally ridiculous but there is IMHO a perfectly good basis for batteries with discharge rates far higher than 10-15c.

For instance, my 3D models run 4 cell 2200mAh batteries. I get about 7 minutes of mixed flying from them which is an 'average' discharge rate of about 10c. However my peak amps in these planes which I use during some aerobatic manoeuvres is 60A, which translates to a little over 27c. The batteries are actually rated 30c.

So my point is you cant simply take the flight time in minutes and divide that into 60 to get your required C rating, unless that is you fly the entire flight on constant power, and where would the fun be in that?
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Old 09-24-2012, 06:28 AM   #12
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Originally Posted by JetPlaneFlyer View Post
So my point is you cant simply take the flight time in minutes and divide that into 60 to get your required C rating, unless that is you fly the entire flight on constant power, and where would the fun be in that?
Exactly
If you've got a Castle Creations ICE ESC, you can graph out the current pulled for the entire flight.

I've set my Giant Big Stick at about 90% power levels, and put the model in various attitudes, from gentle climbouts to gentle descents, all without moving the throttle.

The graphs show that just doing gentle climb outs and dives can vary the current pulled by the motor by a very wide margin. Some graphs show currents on the order of 55 Amps during climb out, and only 4 or 5 amps on a gentle descent. All at the same throttle setting.

The Hacker A60-16M with a 19X12 prop and 12S2P A123's pulls 75 amps at full power on the ground. During take off, that current increases to about 82 Amps or so.

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