May 21, 2012, 12:20 PM Registered User Joined Dec 2010 115 Posts Discussion 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?
 Jun 01, 2012, 08:19 AM Registered User Joined Dec 2010 115 Posts 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...
Jun 01, 2012, 08:28 AM
Registered User
United States, MN
Joined Feb 2011
4,385 Posts
Quote:
 Originally Posted by rogue277 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.
 Jun 01, 2012, 08:53 AM Low AltiDude United States, CA, Costa Mesa Joined Jun 2004 8,527 Posts 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
Jun 01, 2012, 09:19 AM
Low AltiDude
United States, CA, Costa Mesa
Joined Jun 2004
8,527 Posts
Quote:
 Originally Posted by grimbeaver 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
 Jun 01, 2012, 09:27 AM Registered User United States, MN Joined Feb 2011 4,385 Posts 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.
 Jun 01, 2012, 12:50 PM Bart Netherlands Joined Oct 2010 298 Posts 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,
Jun 01, 2012, 05:01 PM
Registered User
Joined Dec 2010
115 Posts
Quote:
 Originally Posted by dirtyballs 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.
 Jun 01, 2012, 07:37 PM My cat moderates better Australia, QLD, Worongary Joined Apr 2011 784 Posts 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.
Jun 01, 2012, 09:44 PM
RC Helicopter Pilot
United States, CA, Westminster
Joined Mar 2010
1,696 Posts
Quote:
 Originally Posted by rogue277 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.
Jun 02, 2012, 06:14 AM
どうもありがとうミスターロボット
United States, IL
Joined Jul 2009
3,063 Posts
Quote:
 Originally Posted by BillzillaAus 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.
Last edited by Wrend; Jun 02, 2012 at 06:58 AM.
Jun 02, 2012, 08:33 AM
PEMAC
Australia, New South Wales, Penrith
Joined Jul 2007
756 Posts
Quote:
 Originally Posted by BillzillaAus 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%?
 Jun 02, 2012, 08:50 AM PEMAC Australia, New South Wales, Penrith Joined Jul 2007 756 Posts 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...
 Jun 02, 2012, 08:54 AM PEMAC Australia, New South Wales, Penrith Joined Jul 2007 756 Posts 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)
Jun 02, 2012, 10:30 AM
Registered User
Joined Dec 2010
115 Posts
Quote:
 Originally Posted by TheWoodCrafter 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.