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LiPo Batteries

Recently a friend of mine nearly had his house burn down. The cause of the fire was a LiPo battery. The battery was new and had only been charged twice previously. It had also not been in a crash or damaged in any way. Lucky my mate is the owner  of his own company dealing in special effects/stunts and pyrotechnics for the movie industry. Needless to say there are a lot of fire extinguishes in his house and garage which is what saved his house from burning down, although he lost some of his planes and a great turbine jet. He is some guide lines to LiPo batteries…

LiPo Do’s and Don’ts

There is a lot of confusion about LiPo batteries out there especially after problems where they have caught fire. This is mainly because of people that do not have a clear understanding of how to work with Lipo batteries and the do’s and don’ts. Hopefully some of these tips will help people in the right direction.

Lipo batteries are big in the world of rc planes, rc jets  and radio controlled models in general, where the advantages of both lower weight and greatly increased run times can be sufficient justification for the price for the rc hobby. However, lithium polymer-specific chargers are required to avoid fire and explosion. Fire can also occur if the battery is short-circuited, as tremendous current passes through the cell in an instant. Radio-control enthusiasts must take special precautions to ensure their battery leads are properly connected and insulated. Furthermore fires can occur if the cell or pack is punctured.

Using Lipo’s properly and charging them correctly is no trivial task. There are many things to consider before using lithium cells for e-flight. But none is more important than safety!

Safety is IMPORTANT!

Until you are willing to follow all safety precautions, DO NOT use lithium batteries. If prefer just to just plug in a battery and not worry about it, run it flat, charge it hot then Lipo technology is not for you!

Lithium cells must be charged very differently than NiCD or NiMH cells. Firstly they require a special charger specifically designed to charge lithium cells, NEVER use NICD or NIMH only chargers on Lipo batteries! You must use a Lithium Ion or Lithium Polymer charger that is designed to handle the number of cells you are trying to charge. Charging Lithium cells is the most hazardous part of using lithium batteries. EXTREME care must be taken when charging them to avoid damaging the cells or worse causing them to catch fire. It is important to set your charger to the correct voltage or cell count. There have been fires directly caused by lithium batteries so PLEASE BE RESPONSIBLE when charging lithium batteries.

Here are some IMPORTANT guidelines when using LiPo batteries:

1. Only use a charger approved for lithium batteries!  You should clearly see Li-Po, Li-Ion marked on the charger or specified in the operations manual of the charger. Both batteries are charged in exactly the same manner.

2. Make sure you set the correct cell count on your charger. This is important as it depicts the total voltage for the pack. Ensure that charger displays the correct cell count when you start charging. If you don’t know how to do that, consult your chargers manual or get a charger that displays this information. Each cell must never be charged to more than 4.2 volts. Overcharging a cell will cause the chemical composition of the Lithium to become unstable which could lead to flames coming from the cell.

3. Balance charge your Lipos. Having an unbalanced pack can cause damage to the cells if cells are not within 0.1 volts of each other. Most proper Lipo chargers come with a balance option, if yours does not have it we strong suggest you get one. Depending on how much current you drawing from you Lipo each flight you may want to balance your packs every 3-5 flights to ensure each cell is individually charged to 4.2 volts so that they are all equal. If after every flight the cell of the pack is unbalanced you may have faulty cell. Balance the cells more frequently to see if you can correct the problem. If the problem persists consider replacing the pack.

4. NEVER leave your batteries charging unattended. This is the number one reason for house fires. If something goes wrong you want to attend to it quickly!

5. Charge your batteries on a surface that will not be damaged by fire. Should a lipo catch fire you want to avoid the problem spreading to other surfaces. Vented fire safes, pyrex dishes with sand in the bottom, fireplaces, plant pots, are all good options to consider. The most practical solution today is to purchase Lipo safe bags for charging.

6. NEVER CHARGE AT MORE THAN 1C unless the battery pack vendor has explicitly proven it is safe to do so. Keep it at less than or equal to 1C of the battery’s capacity rating if you are unsure. Many Lipo related fires are due to people charging at a greater current than what the Lipo is rated to be able to handle. The concept of fast charge should never be applied to Lipos!

7. Never discharge your Lipo cells to less than 3.3volts per cell, not the total pack voltage. Most ESC’s today will do a soft cut-off at 3.3volts per cell and a hard cut-off at 3.0volts per cell. However some will not give you and warning. Best advice is to fly with a timer and monitor the voltage and adjust your flying time if needs be.

8. NEVER puncture the cell, ever! If a cell balloons rapidly place it in a fire safe place immediately. If this happens and smoke and heat is coming from the lipo get it clear of all other items and be prepared for flame to come out! If after many hours have passed (days) and the pack is still ballooned but have not combusted, discharge the pack slowly and dispose of it in a proper way.

9. If you have a crash with your lithium cells they may be damaged internally! The pack may look fine but may only balloon in time. If you have crashed, carefully remove the battery pack from the model and watch it carefully for at least the next 30 minutes. Ensure the pack is cool to touch before transporting it.

10. Charge your batteries in an open well ventilated area. If a battery does become unstable you want the hazardous fumes and material to be vented from the room.

11. Keep a bucket of sand nearby when you are flying or charging batteries. This is a cost effective way to extinguish fires.

12. Do not think it won’t happen to you! Safety is no accident!

Some useful tips for keeping your Lipos healthy:

1. Let your packs cool down before recharging. It is very important to the internal chemical composition of the cells not to run hot or worse be hot when charging as only more energy and heat is being put back into the cells. So wait 30min to 1hour before charging your packs again.

2. Stick to the 80% rule! This basically means never push more than 80% of its discharge rate and drain more than 80% of the capacity of your Lipo battery pack. When one drains more than 80% the capacity it starts to cause allot internal heating in the cell and basically start eating away at itself. So basically if you have a 2200mah pack, you want to only put back 1760mah when charging. Most chargers display the number of mah on a charge so you can adjust your flight time, gearing, etc based on this figure to make your Lipos last longer.

3. Discharge your packs to storage levels if you not going to use them within a week or two of the last charge. This will help make packs last longer especially if you don’t fly every week. If you leave Lipos fully charge for long periods it start causing deterioration internally to the cell. Most new chargers have storage discharge options these days for this reason. If yours does not have this option simply discharge to between 3.8 to 3.9volts per cell. Then you can store them in a safe place. Some people also refrigerate their packs when in storage.

4. Break-In (Cycle-In) your Lipo! Lipos don’t really need a break in period as such like a Nitro motor but they do require a few cycles to reach their full power potential. After a few charge/discharge cycles you get the chemical reaction established in the pack and they do start performing a little better after this. So ideally a pack should by cycled 3-4 charges before you make use of the battery’s full potential. There are several ways to cycle your pack, simply charge/ discharge them on your Lipo charger. If you use them in your helicopter you can do short 2-3min hover flights and recharge.

How puffed is puffed?

When you get you lipo packs the covering looks like it have been vacuum sealed together. If after a number to cycles they might develop a slight bit of air between cells it probably not a total wreck. I mean we are talking a millimetre or so then you can most likely continue using them. Just monitor that it does not get worse. If the battery is puffed up like a bicycles inner tube then dispose of it.

How to dispose of a Lipo?

There is a couple of suggested ways of disposing of Lipos. The most common one is to take a bucket and fill it with salt water mixture. The put the Lipo in the salt water with the idea that the salt water creates a low conductive current to drain the Lipo battery.  Secondly the salt water will seep into the cells and neutralize the chemical reaction.

Fire risk?

The most common reason for Lipo batteries to catch fire is because of improper charging. Whether it is using the incorrect charging, wrong cell count setting on the charger or charging the cells to over 4.2volts each. What happens at this point is the chemicals stay going into a thermal overload failure and start heating up, causing hydrogen gas to be emitted which cause it to puff to the point of fracture where then it vents fire. Best solution here is to buy some Lipo-safe charging bags to do your charging in or store potentially fragile packs.

Secondly you never want to short the cells or puncture the casing as will also cause the chemical reaction explained above and can cause a fire risk. Lipos won’t just combust in storage unless there is some damage to the pack externally or internally. Therefore if you take care charging and using your packs you should have no problems.

Hope this helps people understanding how to work with Lipos. If you follow these guides you should have good success with Lipos.