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Facts regarding Lipo batteries

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Facts regarding Lipo batteries

Post  ototw on Wed Nov 30, 2011 8:17 am

I have recently experienced the loss of a lipo,and I keep on asking myself,what did I do wrong,seeing that a lipo battery is expensive. I foung interesting reading material regarding Lipo batteries:

What is a LiPo?
LiPo or Lithium Polymer is a type of battery chemistry. These batteries are excellent for use in an application such as remote control aircraft due to their high energy to weight ratio. However, they do require a little special care to make sure that they always work as expected and to minimise risk of battery failure.

LiPos can be dangerous if overcharged, or over-discharged. Lithium burns very quickly when exposed to air, so fast that it looks like the lithium is exploding.

Nominal or resting voltage - 3.7v/cell (volts per cell)
Charged or peak voltage - 4.2v/cell

Charged or peak voltage is the maximum voltage the battery pack will store.

Naming convention
A battery is a collection of cells. All batteries have a naming convention which is designed to help the user identify how many cells the battery is made of and in what configuration they are. every cell has a capacity (stored energy), measured in mAh (milliamp hours) and a voltage, measured in volts. Cells within a battery can be connected in series or parallel. Please note that all the cells must be exactly alike.

Series connection - add the voltages of each cell together while the capacity of the whole battery remains the same as for 1 cell.
Parallel connection - add the capacities of each cell together while the voltage of the whole battery remains the same as for 1 cell.

For example, lets say we have a bunch of 1000mAh 3.7v cells.

If we connect 3 cells in series, the battery would be a 11.1v (3.7v + 3.7v + 3.7v) 1000mAh battery.
If we connect 3 cells in parallel, the battery would be a 3.7v 3000mAh (1000mAh + 1000mAh + 1000mAh) battery.

Now, with regard to the naming convention, the battery is named according to the following: the voltage of the whole battery, the capacity in mAh, the number of cells in series and then number of cell series in the battery.

The above 2 examples would be named as follows:

3s1p 11.1v 1000mAh - a battery made up of 3x 1000mAh cells connected in series.
1s3p 3.7v 3000mAh - a battery made up of 3x 1000mAh cells connected in parallel.

A 14.8v 2200mAh 4s1p LiPo battery would mean that the battery is made up of 4x 2200mAh 3.7v LiPo cells connected in series.

C rating - what is it and what does it mean?
The C rating, or discharge rating of the pack is a very important concept to understand if you're going to be doing anything with LiPo batteries. A LiPo pack should have a C rating on the label, anywhere from 10C to 40C typically. The C rating is the maximum safe discharge current, measured in Amps, that the battery is capable of delivering. The C is simply the capacity of the pack, and the rating is given with a precursor number, ie 20C.

Lets take the battery pack above, the 14.8v 2200mAh 4s1p LiPo. If it was a 20C pack, then the maximum discharge in amps would be calculated as follows: 20x2200 = 44000mAh. To get the value in amps you divide the answer by 1000 as 1Amp = 1000milliAmps. 44000/1000 = 44Amps. This pack's maximum discharge current is 44A. Any setup which draws more than that current will risk damaging the battery.

As a general rule, at ChargedRC we always recommend that you set up your power system to pull no more than 80% of the max charge rate at full power. This leaves you with a bit of headroom just in case. If your pack's max discharge rate was 50A, aim for your setup to pull 40A at full power on the ground. If you need more amps (and we all do Wink ), consider a higher C rated battery pack, or a pack of larger capacity.

Please charge your LiPo battery only on a charger specifically designed for LiPo batteries. Those chargers will have a special LiPo charging mode. There may also be just a normal charge mode, as well as a balance charge mode. Please check your LiPo before you charge it. Look for signs of swelling of the individual cells, any discolouration or if any part of the pack is warm. If your pack has any of those characteristics, please DO NOT charge or discharge it.

Now that the naming convention has been described, please make sure of the following when charging:

  • When you plug your battery in to charge and begin charging, wait and make sure that the voltage on the display screen of the charger does not exceed whatever the pack voltage is. Ie if you have a 4cell (4s) pack, the voltage should not exceed 16.8v (4.2v x 4).

  • If the charger is capable of doing a balance charge (charging all the cells in the pack individually and at the same time), make sure that all the cells are around the same voltage
  • Never leave a charging battery unattended
  • Always charge your battery on a non-flammable surface or in a container specially designed for charging LiPo batteries

Charge Rate
A lot of people ask us what charge rate to use for their LiPo. Charging your LiPo at the correct rate is essential to ensuring the life and quality of the pack, as well as charging it as fast as possible, but within its limits. The answer though is very simple. Unless otherwise stated, a battery's charge rate is simply 1C.

If you had a 2200mAh battery, the charge rate would be 2.2A (2200/1000).
If you had a 5000mAh battery, the charge rate would be 5A.

We hope that this guide gives you a better understanding of LiPo batteries. If you have any questions, please jump on our forum, or contact us for more information.

I crashed Sad Is my battery still OK?
Everyone crashes, we've all done it and it's a part of the hobby. If you happen to crash an aircraft which is powered with a LiPo, please approach the crash site carefully. Disconnect the battery from the ESC very carefully, and try not to touch the pack too much. If you can, move the pack somewhere out of the way and keep an eye on it for at least 30 minutes. Watch for swelling or softness on the battery surface and if any part of it heats up. As explained above, Lithium reacts very violently with air. The pack may have somehow been punctured in the crash. If the puncture is very small, it can take quite a while for air to work its way into the pack. If the pack is swelled or puffed DO NOT touch the pack directly. The battery is definitely damaged and you should follow the disposal instructions. Also, if the pack is deformed or damaged in any way PLEASE do not use it again and dispose of it carefully as per the instructions below.

LiPo battery disposal

  • In order to properly dispose of a LiPo battery, you must first discharge it as low as possible. Please, if the battery has been damaged DO NOT discharge it, just proceed with the next step
  • Fill a bucket or some plastic container (NO METAL) with water, and add salt. Add approximately 1/4 cup of salt for every litre of water. The container may have a lid but must not be air tight

  • Immerse the battery in the salt water fully. Make sure that even the power connectors are submerged. Leave the battery for at least 2 weeks.
  • After 2 weeks, remove the battery, wrap in newspaper and dispose of in rubbish bin like normal rubbish.

taxi driver

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Re: Facts regarding Lipo batteries

Post  the DJ on Wed Nov 30, 2011 11:34 am

Nice find!! Interesting way of disposing of the batt.
the DJ
taxi driver

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Re: Facts regarding Lipo batteries

Post  2quick on Wed Nov 30, 2011 11:54 am

The possibility of a Lipo blowing up is non existent. LiPo batteries do not blow up.
If over charged, or shorted they can rupture and shoot flames. If punctured they can shoot flames.
If undamaged and stored at about 50% charge in a cool place the possibility of any of this happening is very low.
Always storage discharge if more than 50% charge or storage charge if less then 50% charge or no charge.
Lipo's bubble or swell if you continuous storage charge it if it holds more then 50% charge.

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