I just don't get the whole battery thing...why can't you use all the available power?

mmurfitt

mmurfitt

Member
As will become apparent I'm new to the whole world of RC and as such I just don't get why you can't use all the available power in your battery.
In normal life you charge a battery, you then use it/discharge it and when flat, you charge it again.
Why are the Lipo batteries different?
Why can you only use part of the available charge?
I've bought a 14.7v 5000mAh however from what I've read I can't really use it if the voltage falls below 10.7v, why is that?
What happens if you do use the remaining voltage?
Does it drop off super quick or something?
 




kloner

kloner

Aerial DP
and it starts at 16.8 total....... if you take a 4s pack to 11 volts, it's done, smoked, no more, junk

You have a modern cell phone, ever see it say low battery and shut off? That's a lipo being protected by a computer. same things happen with anything lipo, cause if not it will cause a fire, it will destroy the battery instantly, it does alot of things. Don't hate technology, embrace it, follow the normal use train of thought......

why do we put up with this kinda stuff, easy,the energy that comes out of these things is incredible and the weight is almost non existent. if you had been around 6-7 years ago and went to fly this thing and found out you needed 130 cells of nimh or nicd that weighed 10 lbs to get a 2 minute no power flight. now with brushless and lipos, EVERYTHING has changed.
 

mmurfitt

mmurfitt

Member
Thanks Bartman.

Is it me, being a naive RC newbie, but with a battery which has a capacity of 14.8 volts, isn't it an awful waste of 13.2 volts??

As I said in my original post I'm clearly completely new to the whole RC thing, but isn't it about time the guys who make batteries sort something out where the drop off doesn't mean you waste the energy of the majority of your battery?

I know it's probably going to be something to do with physics or some other dark art, but not being able to utilise 80% (or more) of your battery seems criminal to me...
 

kloner

kloner

Aerial DP
mmurfitt said:
Is it me, being a naive RC newbie
Click to expand...

to be blunt, yes. if your gonna whine about your rc battery, you better get on the phone with apple, sony, norelco, anything you got cordless today and tell em there ripping you off only letting you at 80% of the battery in your razor/phone, laptop. when the guys with the white suits show up with a straight jacket, you know what to do. It's not just rc this is being done to you. it's probably a conspiracy

if you got a chevy volt, your really gonna be pissed
 

mmurfitt

mmurfitt

Member
Ok, I see your point. I stand corrected and instructed.

BTW, I love technology, only a geek (like me) will take a transmitter manual to bed for some light reading.. :)

:nevreness:

kloner said:
and it starts at 16.8 total....... if you take a 4s pack to 11 volts, it's done, smoked, no more, junk

You have a modern cell phone, ever see it say low battery and shut off? That's a lipo being protected by a computer. same things happen with anything lipo, cause if not it will cause a fire, it will destroy the battery instantly, it does alot of things. Don't hate technology, embrace it, follow the normal use train of thought......

why do we put up with this kinda stuff, easy,the energy that comes out of these things is incredible and the weight is almost non existent. if you had been around 6-7 years ago and went to fly this thing and found out you needed 130 cells of nimh or nicd that weighed 10 lbs to get a 2 minute no power flight. now with brushless and lipos, EVERYTHING has changed.
Click to expand...
 

ChrisViperM

ChrisViperM

Active Member
You get something mixed up here....Volts is not the capacity, it's the voltage. One LiPo cell has a nominal Voltage of 3,7 V and a maximum charge Voltage of 4,2 V
The capacity of a Lipo is measured in Milliampere hours. A milliampere hour (mAh) is 1000th of an ampere hour ( Ah ). Both measures are commonly used to describe the energy charge that a battery will hold. As your motor (for example) is consuming mAh from your LiPo, the LiPo starts to get down with it's Volts, and that is used as an indication how full - or empty - your LiPo is. If you take a bucket and fill it with 10 liters of water, you can go and water your plants with exactly 10 liters of water. If you have a LiPo with 5.000 mAh you cannot use the full 5.000 mAh, otherwise your LiPo dies and in many cases can catch fire. This has to do with the internal chemical reactions within the LiPo. See the remaining mAh in a LiPo as the safety structure to prevent the LiPo from collapsing.

Here is some more reading to shed some light:
Here the easy ones: http://science.howstuffworks.com/environmental/energy/question501.htm http://www.electricwingman.com/guides/lithium-polymer-battery-guide.aspx
Here some advanced stuff: http://www.mikrokopter.de/ucwiki/en/LiPo, http://en.wikipedia.org/wiki/Lithium_polymer

Chris
 

kloner

kloner

Aerial DP
i've woke up more than once with papers thrown about

the main thing is you get a pack, it is at a low voltage storage setting. You go hook it up to your charger and put in 3000 mah lets say. You still get that 3000 mah back out of it, you just leave what it came with. It's not like you put in 3000, only get 80% back out then put in another 3000 and only get 80% out of that again, that would be a legitimate problem to complain about.

The nicer you treat lipo the longer it will last, never over discharge it, never charge it at a rate too high for the pack,,, usually 1c charge rate unless anything says different. a 5000 mah pack will be a nax charge rate of 5 amps at 1s. it is safe to discharge it to 4000 mah, you should see nothing higher than that on your charger after a flight. if you did, it damages the internal resistance of the pack, that is like heavy metal in a body, it just builds and builds till it's too high, pack doesn't last as long as it should, doesn't charge right. A good indicator you done everything right is a nice cool pack after a flight and after a charge. Any heat indicates damage... little warmth is alright, i'm talking you grab it and go, hmmm, that's a hot pack
 

ChrisViperM

ChrisViperM

Active Member
If you buy a 1.000 mAh LiPo, it's actually a 800 mAh Lipo...but they don't write that on the label. So a 1.000 mAh will alway give you 800 mAh. If you do some serious flying one day you will find out that your investment in LiPo's will easily be higher than your flying machine....that's why we all treat LiPo'S like brand new girlfriends....

PS: Rule No. 1: kloner knows his stuff about LiPo's.


Chris
 

G

Gump

Member
mmurfitt said:
Thanks Bartman.

Is it me, being a naive RC newbie, but with a battery which has a capacity of 14.8 volts, isn't it an awful waste of 13.2 volts??

As I said in my original post I'm clearly completely new to the whole RC thing, but isn't it about time the guys who make batteries sort something out where the drop off doesn't mean you waste the energy of the majority of your battery?

I know it's probably going to be something to do with physics or some other dark art, but not being able to utilise 80% (or more) of your battery seems criminal to me...
Click to expand...

look at it a different way. voltage is not what drives the circuitry. its amperage. And there's a relationship between amperage and voltage (and heat as well). Low volts and high amp draws produce heat.
Modern lipo's have a LOT of amperage to give compared to the heavy and large batteries of yesteryear. Some of the batteries of yesteryear were much more chemically stable, and handeled heat WAAAYYY better (nicads).... but their performance levels were lack-luster.
Modern high performance r/c with brushless and lipo will draw a LOT of amperage, and when the voltage drops to a certain level it simply can't deliver the 'oomph' (amperage) any more. This turns up the heat because the pack is now struggling and can chemically damage the cells. Chemically damaged cells don't like being charged or discharged any more and will protest in the form of a nice little lipo fire (look up lipo fire on youtube), which may consume your model, or your desk, your car or your home..... or may just snuff out in the lipo bag you purchase.
Regardless, looking at the voltage cutoff as a waste is just the wrong way to think about it. Voltage is just the indicator of when the pack has delivered over 80% of its internal capacity.... or its AMPERAGE.
 
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plingboot

plingboot

Member
…on the subject of safety, it' worth getting a few used ammunition cases to store your lipos in, there's loads of sellers on ebay with them - i picked up 3 x .50cal cases for about £30.

they lock tight and are a better option than just leaving lipos sitting around on shelves, in drawers or other combustable locations.
 

kloner

kloner

Aerial DP
one note about cases,,,,, if you do that remove the seal in the lid. You want to contain the fire, not the smoke..... I'e heard of cases blowing up during a fire. it's like a house fire and why they cut em open to vent the gasses so they don't backdraft...... pelican cases should have there screw removed

if you can find a plastic can it'd be a little safer just to keep from anything shorting out...... I've stuck a deans to a ammo can before not even trying, it pushed through that heat shrink like it wasn't there and arced a fatty. By the same token plastic melts so keep that on concrete away from walls, rags, life
 

usnooz

usnooz

Member
On this note. whats the safest way of dsposing of used batteries that no longer hold charge? I probably have about 8 dead ones kicking around that i need to get rid of?
 

kloner

kloner

Aerial DP
i cut the main wires back to the case, make a saltwater bath and dunk em a few days.... it makes something in your bucket to be careful what you do with it, but after that it is drained to the core

left with anything in it and disposed can easily light a fire in the trash truck

if you ever get in the position of being in a fire situation, always worry about what it's lighting and don't worry about putting the battery itself out... contain the brush, wood, whatever it's lighting and don't touch it... consider it like grabbing a solid fuel rocket motor... it is really hot
 


mmurfitt

mmurfitt

Member
kloner said:
the main thing is you get a pack, it is at a low voltage storage setting. You go hook it up to your charger and put in 3000 mah lets say. You still get that 3000 mah back out of it, you just leave what it came with. It's not like you put in 3000, only get 80% back out then put in another 3000 and only get 80% out of that again, that would be a legitimate problem to complain about.
Click to expand...


Ok, this makes perfect sense, thanks for the 'simpletons' explanation, something which I can understand :)
I thought you put in, to use your example, 3000, then you were only able to use 20% of that 3000, but now it's much clearer :)
 

mmurfitt

mmurfitt

Member
plingboot said:
…on the subject of safety, it' worth getting a few used ammunition cases to store your lipos in, there's loads of sellers on ebay with them - i picked up 3 x .50cal cases for about £30.

they lock tight and are a better option than just leaving lipos sitting around on shelves, in drawers or other combustable locations.
Click to expand...

Just ordered myself one, thanks.

I see you're from my neck of the woods, where are you based? I'm near Kingston Upon Thames..
 

J

jrlederer

Member
There is a lot of wisdom being shared regarding liposuction here, so I thought I'd add a bit of info that is good to know, if you don't already. One is to heed a previous poster's advice about watching a couple vids on YouTube on Lipo fires. Listen to the sound they make right before they burst into flames. Being able to recognize the sound has definitely saved my butt from much larger problems when, on rare yet memorable occasions, I've had a good pack go bad whilst charging.

Secondly, NEVER charge Lipos unattended. I used to do this all if the time until I finally had a firsthand experience with a battery catching fire. Never again will I be that careless. I'm just very fortunate that I did not learn the very hard way, but my safety practices we're reconfirmed just weeks ago when a former owner (for nearly 20 years) of a legendary local hobby store made this cardinal mistake and decided to leave his batteries for that day's event (pylon race I think) charging while he went to breakfast around the corner, only to come back to his entire garage leveled by fire -- in it also completely destroyed were his two favorite classic cars that he'd poured his heart and soul into restoring over the years. Fortunately fire department contained the fire before it engulfed his entire home. That is a lesson learned the hard way, IMO.

Lastly, I feel that it should be mentioned that Lipo-Safe Bags should really be termed Lipo-SafER Bags. I won't get into details here, as it's kinda a long story, but two 2600mAh 6S Lipos were in a Lipo-SafeR bag when they combusted. I would definitely say better to have them than not -- that's for certain -- but in this case, by the end of the fireworks display the bags were nothing but mesh sacks holding the ashes together. The flame throwing nature of these batteries was contained for the most part, with the exception of the opening, as after the first couple seconds the Velcro was incinerated and the pouch's openings spewed long flames.

Sorry for the long post, but I hope it saves somebody's property and well-being.

Jonathan
 

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