Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length.

[evo679]

Are the cheap lipo batts any good if not y?

[barriew]

Maybe this will answer your question! Taken from an email from Hobbyking.

Barrie


B-Grade lipo, at dirt-cheap prices.

For those not-so-serious applications!
B-Grade Lithium Polymer packs are great for those not-so-important models or testing. They have a high internal resistance (thats bad), normally wont last past 60 full high-discharge cycles and may become puffy over time.

B-Grade packs are structurally sound, but lack the performance of our A-Grade packs such as Flightmax, Rhino and TURNIGY.

hexTronik usually sells B-grade batteries to smaller vendors who in turn sell online at a discount. However we are now offering them direct to you at discounted prices, for those not-so-serious applications.

[Timo2]

Hi All

    Battery cost do not add up ? ?

 me thinks 


                                      
   B Grade  LiPo   ???                                       Cost per Charge      
                                 
                                 
    B-Grade 5000mAh 2S 40C Lipoly Battery      14.81      0.247      60 Charge per Pack
                                 
   Turnigy 5000mAh 2S 40C Lipo Pack         22.39      0.224      100 Charge per Pack
                              
   Turnigy 5000mAh 2S 20C Lipo Pack         14.51      0.145      100 Charge per Pack


   Timo2

[Roadrunner]

sure i said this in the first post you asked about fast electric's you want a good battery you gonna have to cough up the price, cheap = 'rubbish'

Well i did warn you....
 

[grasshopper]

I think that the 'B' grade would be more of an issue with flying models. For marine use you might find they would be an OK alternative.
Obviously if you were racing you need the reliable higher output (more expensive) cells - for fun use I'd consider them

Is the cost per charge idea relevant? ,  they are only recommended for 60 charges, they might do a lot more, especially if not used at maximum discharge rates, they might last a lot longer.

[evo679]

What does the 20 30 c mean
Cheers Greg

[Timo2]

Hi
   
  Info   @        http://en.wikipedia.org/wiki/Lithium-ion_polymer_battery

   More to come   


   Timo2   

[essex2visuvesi]

when it comes to Li Pos buy the best you can afford, the effects of a bad cell can be devastating.

[Timo2]

Hi All

   Sorry it,s so long but details on LiPo from an orther Forum explained.
The Bacis  principles.


Hopefully this explains LiPo’s to some of you looking to change over from NiMH’s.

To start off we’ll use the old analogy. Think of electricity like water. Amps = flow
Volts = pressure.

Amps are like water flow, like liters per hour. There can be flow at low pressure and
you can have flow at high pressure.
Volts are like pounds per square inch, psi. This says nothing about quantity or how much is flowing, just how hard it is being pushed. You can have 100 psi
with zero water flow.

Amp hours is how much flow can be sustained for how long. It is used as a
way of measuring how much electricity is in the battery. Like how many
gallons of petrol in your tank. It is a capacity number. It means nothing about
flow or pressure, it is about capacity.

1 amp = 1000 miliamps (mili means 1/1000 amps)

For example.

A 3 cell lipo provides 11.1V (pressure).

The motor will draw electricity from the pack at a certain flow rate, or
amps.

If you have a have a 1000 mili amp hour pack (mAh), it can deliver a flow of 1
amp (1000 miliamps) for one hour. If you draw it out faster, it
doesn't last as long. So your motor might pull 10 amps for 1/10 of an
hour, or about 6 minutes. (10C= 6 minutes)

A 2000 mah pack has twice the capacity of the 1000 mah pack, so it should
last twice as long.


What is C rating?

C ratings are simply a way of talking about charge and discharge rates for
batteries.

1C, = 1 times the rated mah capacity of the battery. So if you charge or discharge your
650 mah pack at 1C, you charge it a 650 miliamps, or 0.65 amps.

1C on a 1300 pack is 1.3 amps. Duration = 1 Hour (60/1)

2C on a 1300 pack is 2.6 amps. Duration = 30 minutes (60/2)


If you have a 1500 mah rated at 8C it knocks out
can deliver 12 amps. Duration = 7.5 minutes

If you have a 2000 mah pack rated at 20 C that means
it can deliver 40 amps. Lasting only 3 minutes.

If you have a 2000 mah pack rated at 30 C that means
it can deliver 60 amps! Lasts 2 minutes!

So, if you need 60 amps you can use a pack with a higher C rating (2000mAh 30C) or a pack
with a higher mAh (4000mAh 15C) rating to get to needed amp delivery level.

Burst Rating

Back to the 2000mah 11.1v 3S battery. Let’s say the rating of this battery is 20C constant and 30C max. This would be a high performance battery

So as we know the maximum constant discharge rate would be 20 x battery capacity (2000mah or 2amps),so 20 x 2amps = 40 amps constant. Using a 2000mah battery at 40amps will make it flat pretty quick – about 3 mins flight time only. You will see batteries marked as 20C constant 30C burst.
The battery cannot discharge at this rate for very long – maybe just a few seconds, but during this time its knocking out max power. So in this instance

2000mah (2amps) x 30 = 60amps!

This means a 30C 2000mah Battery is actually capable of delivering a whopping 60amps @ 11.1volts. This translates to 11.1 x 60 = 666watts power. (Watts = Volts x Amps).

However - It is best to size your battery packs so they run below their
max C rating. You will stress them less and they will last longer. Eg if your motor needs a battery that can deliver 10 amps, getting a 1000
mah pack that is rated for 10C ( 10 amps ) will meet the spec, but it is
running at its limit. A 15 C rated 1000 mah pack would be better, or
perhaps a 1300 mah 10 C pack. In either of these cases, the pack will be
less stressed and should handle the load much better over the long term giving you a long lasting, better performing lipo.
I’m often asked what effect does voltage have on the duration of a lipo.
Duration = number of minutes / C rating. There’s nothing about volts in there.
Voltage doesn’t enter into it. However, if you have a 1200rpm/v (kv) motor running on 11.1V (3 cells). 11.1v x 1200 = 13320 rpm.

Imagine you put a 4 cell on there. That’s 14.8v. Look what happens to the rpm and the power (VxI). Things should be falling into place now...

Why Are The "C" Ratings Important?

If you over-discharge the Lipo, it will get VERY hot and probably catch fire. If you want to give your plane a good sending off, put a battery rated for 20 amps burst into a plane that will demand 40 amps - November 5th would be good choice for this sort of stunt.
Check your motor’s manufacturers specs out for how many amps it needs. Every motor has them so it shouldn’t be too challenging. As a safety net if a motor needs 20 amps get a lipo that can give it 40amps. The battery can’t force feed it amps unless you over prop it. If that happens and you’ve factored in the extra amps you’ll lose your motor, but you won’t lose your lipo, esc and probably your plane and motor to the Balrog.


In Series and Parallel

When you put cells in series, their voltage is added together. For example:
-----> [- 3.7V +] [- 3.7V +] [- 3.7V +] ----->

This battery has 3 cells in series, so this is called a "3S" battery or “3S1P”. The total voltage of this battery is 3*3.7V = 11.1V.

When you put cells in parallel, their capacity is added together. For example:
.--> [- 1.2Ah +] --.
---|--> [- 1.2Ah +] --|--->
'--> [- 1.2Ah +] --'

This battery has 3 cells in parallel, so this is called a "3P" battery or “1S3P”. The total capacitance of this battery is 3*1.2Ah = 3.6Ah.

You can use combinations of cells in series and in parallel to achieve different levels of Voltage and Capacitance. For example:
.--> [- 1.2Ah, 3.7V +] [- 1.2Ah, 3.7V +] [- 1.2Ah, 3.7V +] [- 1.2Ah, 3.7V +]--.
---|--> [- 1.2Ah, 3.7V +] [- 1.2Ah, 3.7V +] [- 1.2Ah, 3.7V +] [- 1.2Ah, 3.7V +]--|--->
'--> [- 1.2Ah, 3.7V +] [- 1.2Ah, 3.7V +] [- 1.2Ah, 3.7V +] [- 1.2Ah, 3.7V +]--'

This battery has 3 parallel groups of 4 cells in series, so this would be called a "4S3P" battery.
The total voltage of this battery is 4*3.7V = 14.8V, and the capacitance of the battery is 3*1.2Ah = 3.6Ah

Timo2

Hope it helps you

 

[Subculture]

One thing I'd like to add regarding the 'C' rating. Unless it specifically mentions it, the 'C' rating does not refer to the rate you can charge these batteries, only discharge.

Unless stated otherwise, you should always charge lipo packs at no more than 1C, e.g. a 1000mAH pack should be charged at no more than 1000mAH.

Some packs are able to be charged at up to 5C, but this will be stated by the manufacturer (it's good marketing).