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Old May 21, 2012, 12:20 PM
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I challenge you to find a higher energy density battery

Flight times for all RC aircraft are a function of the energy density of the battery. In engineering terms, this is typically represented as energy/mass. Units are most typically watt-hrs per kilogram (Whr/kg). To calculate this for any given pack, multiply the number of cells times the nominal voltage, times the capacity, and divide by mass. For a lithium-polymer for example, if it's a 3-cell, 2200mAh and weight 200g, the energy density would be:

3*3.7*2.2/.2 = 122 Whr/kg

This is a pretty typical energy density for a pack with 30-40C discharge rating. As the discharge rating goes down, the pack can be made less massive yet retain the same energy storage capability, meaning it's energy density will go up!

So I've been cataloging various Lipo batteries, to find the highest energy density pack. The best I've found is this:

Thunder Power 6-cell 8000 mAh, 932 g, 16C discharge, for 191 Whr/kg
http://thunderpowerrc.com/html/docum...st08242011.pdf

Is there anything better?
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Old Jun 01, 2012, 08:19 AM
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It turns out maxamps has a pack that gets 200 Wh/kg:
http://www.maxamps.com/Lipo-11000-111-Pack.htm

I found the cells they're using in those packs however, and they are NOT rated for 40C. I can't believe they are advertising 40C for this pack. This is impossible. If someone were to attempt 40C from this, they'd have a failure on their hands...
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Old Jun 01, 2012, 08:28 AM
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Quote:
Originally Posted by rogue277 View Post
It turns out maxamps has a pack that gets 200 Wh/kg:
http://www.maxamps.com/Lipo-11000-111-Pack.htm

I found the cells they're using in those packs however, and they are NOT rated for 40C. I can't believe they are advertising 40C for this pack. This is impossible. If someone were to attempt 40C from this, they'd have a failure on their hands...
Your surprised? Look at the packs that MaxAmps claims 150C on lol. Even the 100C ratings are a joke. Just do a search here on rcgroups and you'll find all the BS. They refuse to provide a sample battery to any of the people here who do independent testing and refuse to provide a discharge graph to support their claims.
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Old Jun 01, 2012, 08:53 AM
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I refuse to accept any company's published specifications unless they're substantiated by empirical evidence. I'll add that a lot of the "empirical evidence" (both good & bad) comes from end users instead of the manufacturers themselves, but the bottom line is most published specifications are simply unsubstantiated propaganda seasoned with a LOT of hyperbole.

I will say this, though: I've been using Thunder Power packs almost exclusively since I began using LiPos in 2004 and my personal experience has been that their specifications are and have always been among the most accurate in the industry.

Pete
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Old Jun 01, 2012, 09:19 AM
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Look at the packs that MaxAmps claims 150C on lol. Even the 100C ratings are a joke.
Lets see here: A 150C 2100mAh pack can theoretically supply 315 amps for 24 seconds. If we apply the 80% discharge rule that becomes 315 amps for 19 seconds.

Let me start by saying I just don't believe it. Assuming that you could even put that kind of load on the pack without it becoming a fire bomb, what would the voltage drop be? That, and how many times could you do that before the pack was toast?

Then there's the simple question of how practical a 19 second run time is.

Not only do I not believe it, but I wouldn't be impressed if it was true.

Pete
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Old Jun 01, 2012, 09:27 AM
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I just want to see someone put it to the test and show the empirical evidence for everyone to see just how full of #&%$ maxamps is.
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Old Jun 01, 2012, 12:50 PM
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16C will not do the job in a lot of applications

so comparing a 25C 6s 5400mAh of TP 710g to a 6s 30C 5300mAh Gens ace, 734g. I will go for the gens ace, they cost a lot less and still very light.

Bart,
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Old Jun 01, 2012, 05:01 PM
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16C will not do the job in a lot of applications

so comparing a 25C 6s 5400mAh of TP 710g to a 6s 30C 5300mAh Gens ace, 734g. I will go for the gens ace, they cost a lot less and still very light.

Bart,
That depends on what you're trying to do with it. If you need a lot of power density, then you'll need high C. These types of applications include fastest transit, or most aggressive flying. To maximize flight time, however, you'll need to maximize energy density. In the case of a modest quadcopter, I've found that max flight time will occur with a 3S 30Ah pack. Since this is such a large, pack, you don't necessarily need a high C rating to get the necessary current (and power). 1C out of a 30 Ah pack will give you 30A! 2C will give you 60.
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Old Jun 01, 2012, 07:37 PM
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A fuel tank the same size full of 100 octane petrol would have a much higher energy density.

But seriously, I keep hoping for better batteries in the near future.
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Old Jun 01, 2012, 09:44 PM
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Quote:
Originally Posted by rogue277 View Post
1C out of a 30 Ah pack will give you 30A! 2C will give you 60.
Isn't a 30Ah pack a 30,000mAh pack?
That will give you 30Ah alright.
Now where do you get one of these?
It would be too heavy for anything I fly.
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Old Jun 02, 2012, 06:14 AM
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Originally Posted by BillzillaAus View Post
A fuel tank the same size full of 100 octane petrol would have a much higher energy density...
Yeah, but then you have to figure out how to effectively and efficiently use it to do what you want. My electric motors don't run on petrol very well.

By the way (while we're off the subject), check out the energy density potential of antimatter.
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Old Jun 02, 2012, 08:33 AM
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Quote:
Originally Posted by BillzillaAus View Post
A fuel tank the same size full of 100 octane petrol would have a much higher energy density.

But seriously, I keep hoping for better batteries in the near future.
Yes, but brushless motors are around 70% efficient. I thought the best efficiency you could get from combustion engines was 30%?
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Old Jun 02, 2012, 08:50 AM
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The next thing in the works is Lithium air batteries.
The max energy density of lithium-air batteries is theorized to be around 12 kWh/kg, some 15 times greater than li-ion — and more importantly, comparable to gasoline.
http://www.extremetech.com/computing...um-air-battery

But I understand they are many years away yet...
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Old Jun 02, 2012, 08:54 AM
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Another related question is cost per w/hr.

for example :
http://www.hobbyking.com/hobbyking/s...idProduct=9176
22.2V at 5AH so 111wh

Cost: 0.37$/wh (pack at 41.82$)
Weight: 140wh/kg (pack of 793g)
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Old Jun 02, 2012, 10:30 AM
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Isn't a 30Ah pack a 30,000mAh pack?
That will give you 30Ah alright.
Now where do you get one of these?
It would be too heavy for anything I fly.
I found a few places that sell large capacity cells. Other than that you'd just have to put packs in parallel. Multicopters can lift these size packs. A 3s 30Ah pack can be as light as 1.3 kg.
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