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Jul 21, 2017, 09:58 PM
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Discussion

# Batteries - Performance

There is so much to cover about batteries , I always find something I left out , so sorry about that .

Lets talk performance .

Batteries are not created equal , just like there might be variance in car engines coming of an assembly line , there is variance in the cells that make up a battery pack . So many variables here .

Anyhow , are these individual cells tested and graded and then matched for battery packs ? ( I really don't think so - certainly not the cheaper ones ) So depending on where the pack builder sources there cells could seriously affect the over all quality . Lets get to performance ..

Batteries are graded by Capacity / number of cells / and discharge ... We are interested in discharge .

Now you may notice batteries have 20C / 25C / 30C and so forth on the labels ..
This is the discharge rating .. It means ( 20C ) 20 times capacity .
So lets say you have a 1000mAh 20C battery that is 3s with a nominal voltage of 11.1 volt

1000 x 20 = 20 Amps lets multiply that by the nominal voltage 11.1 ( Lets call it 11 ) 11 x 20 = 220 Watts
So on paper , we have established that this battery might be suitable for applications where the motor ( ? ) might produce around 200 Watts
So what just happened is we matched the battery pack to the power needs ..

Do you have to do this ? ( Well that's up to you ) The battery pack might be able to do better than that , but you also might run into issues where the batteries are maybe not that great a quality and the extra power drain might be too much for them . And batteries can fail when pushed beyond their limits , which in turn can cause serious problems ( Think Fire ) .

What is written on the label is often optimistic .. That 1000mAh battery might be more like 800mAh when discharged in a hobby charger . And without testing ?
Well lets see ..

800 x 20 = 16 Amps and 16 x 11 = 176 Watts

So if you were looking to power a 200 Watt application , this battery would fall a little short . Maybe not the end of the world if the batteries are quality ones , but are they ? So it might be better to aim a little higher than what you plan on using . That way if reality falls short of the advertising it's not the end of the world .

So depending on what batteries you buy , one really needs to wonder how much poetic license was put into the printed label ? There is this very unfortunate trend to print something on a label that has no real basis in reality and how much of that has filtered into the RC battery market ? So could I dare to suggest paying a little more to get better quality batteries that last longer and are safer ? ( Might be an idea )

Anyhow , back to performance .
So it can be some what important to try and match battery performance to the real world needs of the application ( RC car - boat - plane - helicopter ) so as to maximize fun and safety . One merely has to have some idea of the power needs ( motor ) and then acquire a suitable battery that meets or exceeds those needs .

Wow , these things can suck a lot of juice ..
Anyone watching the speed records ?
Apparently the batteries were bursting into flame at a certain speed point .. ( single battery pack )
So to go faster , they are using two batteries to share the power load ..

What is happening ? Well my guess would be that the power drain is so high that the cells are failing , and when one cell fails dramatically - the pack goes up in flames .. And this folks was apparently happening on a regular basis , so its not fantasy - it's reality . It simply is what can happen when you push batteries harder than they were designed for and when you push them to the extreme - extreme things happen .

Be safe / be happy

Last edited by old4570; Jul 22, 2017 at 01:38 AM.