Can Lipo batteries explode?

 

Lipo (Lithium-polymer) batteries are huge in the RC industry. They have taken over from the old technology of Nimh (Nickel-metal hydride) and Nicad (Nickel-cadmium) batteries. They are superior in longevity and constant current but they do have there downsides.

The quick answer is yes, they can explode and catch fire. If you take the time to understand how they work you can pick up on what makes them safe. Safety is very important when it comes to any type of battery. Prevent the batteries from having punctures and keep a look out for any swelling.

The Internet has a whole host of Lipo battery explosions. Over the years Lipo batteries have been improved and developed to be safer. Back in 2017 it was reported that Mike Zimmerman (Professor & Engineer at Tufts University) was working on a new type of Lipo battery that holds more energy and will not explode.

Source: PBS – Nova

Lipo batteries are not just used in electric remote control cars. They come in all shapes and sizes, and fit into other aspects of the radio control industry. To name a few nitro cars (receiver battery), starter boxes, RC boats, RC aircraft and transmitters.

How does a Lipo battery explode?

A Lipo battery is capable of containing a huge amount of electrical energy in a tiny space. Lipo batteries can explode through the following means. You will notice that these causes are often through misuse or without due care and attention.

  • Shortage – if the positive and negative side of a Lipo battery touch this will short out the battery. This could happen through human error. Connecting the negative and positive terminal the wrong way round into your ESC (electronic speed controller). Wear and tear as you connect and disconnect your battery. The connectors can become loose and touch each other. If you get a small nick in the battery cable this could also cause the battery to short out.
  • Puncture – when a Lipo battery becomes punctured all the energy inside is released in an instant. When this happens the battery rapidly expands and white smoke pours out which can turn into fire. A puncture tends to happen during high impact crashes. Hard case Lipo batteries are safer for remote control cars. The hard plastic outer shell offers more protection.
  • Over charging – You can’t charge Lipo batteries the same way as Nimh and Nicad batteries. You need to use a specific lipo battery charger. Make sure it’s a good reputable brand name the market is full of fakes. Each cell within a Lipo battery needs the voltage to be constantly monitored as it’s charging. Your Lipo charger should under no circumstances charge your battery at more than 4.2v per cell. When a Lipo battery is overcharged it will expand and continue to until it can no longer hold the energy and poof!
  • Over discharging – Lipo batteries have a current rating labeled as “C”. When you have a high current application you can be asking for more energy than your battery can provide. You often get warning signs of over discharging before too much damage is done. The battery will start to swell or feel hot. Make sure you don’t let a Lipo battery go below 3.0v per cell, it’s very unlikely to have a battery explode from going below 3.0v per cell. However it will cause damage to the battery. It’s important that the device you connect your battery to is compatible with Lipo batteries. When a device is compatible it will automatically ensure the voltage does not go below 3.0v per cell.

What to do if your Lipo battery expands.

When a Lipo battery expands it’s a red flag telling you something is wrong. There are a whole host of techniques available on-line with different ideas, on how to save a swollen battery. Don’t do it it’s simply not worth the risk the more your battery becomes swollen the more unstable it is.

Lipo batteries do expand during operation. If your Lipo battery stays swollen after use and no longer fits in the battery housing. Unfortunately it needs to be correctly disposed of. You local hobby shop will be able to help you dispose of unwanted batteries.

How to correctly charge a Lipo battery.

Lipo safe bags are a fantastic aid in preventing damage to your home. I say “home” because while they will not prevent a battery from exploding, they will however contain a battery failure.

Using a genuine brand name charger will ensure your battery is correctly monitored during charging. There are 2 main ways to charge a Lipo battery. The first is a standard charge on this setting you connect your battery to the charger using the negative and positive wires (black and red). The charger will automatically detect the number of cells in your battery and start to charge. You can also fast charge lipo batteries on some chargers. In the instruction manual which came with your battery the manufacturer will state the maximum C rating for charging.

If you have a 6,000 mah Lipo battery and you charge it at 1 C you will be charging at 6 amps. If you charge at 2 C you will be charging at 12 amps. Some manufactures have very high maximum charge ratings, personally I don’t like to charge my Lipo batteries at more than 1 C.

The second method is balance charging. When you balance a Lipo battery it can take longer to charge. The difference is you connect the balance lead (usually a white plug) as well as the negative and positive terminals. As the battery is charging the charger will be monitoring each cell. Adding more or taking away current as the battery is being charged. It’s wise and widely recommended in the RC community the balance charge your Lipo batteries every so often.

How long does it take to charge a lipo battery?

This depends on the capacity of your Lipo battery and the rate at which you charge. Below is a table with 3 examples, you will notice you can charge different capacity batteries in the same amount of time. This is as long as your charger can cover the charging current needed.

Battery capacity0.5c charge rate1c charge rate2c charge rateTime
6,000 mah3,000 mah (3 amps)6,000 mah (6 amps)12,000 mah (12 amps)0.5c = 2 hours | 1c = 1 hour | 2c = 30 minutes
5,000 mah2,500 mah (2.5 amps)5,000 mah (5 amps)10,000 mah (10 amps)0.5c = 2 hours | 1c = 1 hour | 2c = 30 minutes
2,000 mah1,000 mah (1 amp)2,000 mah (2 amps)4,000 mah (4 amps)0.5c = 2 hours | 1c = 1 hour | 2c = 30 minutes

Manufacturers will state the maximum charge rate of the charger in amps. For example the Turnigy Reaktor 250w charger is rated at 10 amps, and can charge 1 to 6 cell Lipo batteries. This means you can charge at a maximum of 10 amps.

These times are only achievable if the battery cells are not severely imbalanced. When cells are not correctly balanced the charger works harder. Charge is added to the battery and the cell that is higher is drained down a little to match the lower cell (as best as possible). This process continues until the charger reaches the best result.

A healthy battery can have the cells out by a few points of a volt example 4.20v – 4.17v. If the cells are out by more than 0.15v or 1 cell has significantly gone above 4.2v (example 4.35) then your battery is very unlikely to become balanced again.

Storing Lipo batteries safely.

Store Lipo batteries in Lipo safe bags. Batteries discharge very slowly over time, the longer you leave a lipo battery unused the more it will discharge. This brings me on to Lipo storage voltage. RC chargers have a storage charge setting. This will charge your Lipo battery to a rating of 3.8v per cell. Whilst I don’t believe you need to do this every time you come home from the race track. I like to leave my batteries with at least some charge in them and always more than 3.0v per cell.

The folks at Propwashed conducted a test on 3 different states of storing a Lipo battery. Full charge, storage charge & no charge. Granted they do use batteries designed for quad copters. Hard case Lipo batteries could have different results, perhaps I should do a similar test, let me know in the comments below. The results in their test show that at the 3 different states the batteries performed similar to one another. The battery stored at full charge performed the worst.

What are all the numbers on Lipo batteries?

There are several numbers on Lipo batteries it can get a little confusing trying to understand what they all mean.

Example A: 8,000 mah, 2S, Lipo battery.

Example B: 6,000 mah, 2S, Lipo battery.

  • C rating – this tells you the maximum amount of current the battery can supply. My 8,000 mah battery has a 100 c discharge rating. This means the battery can supply 800 amps (8 x 100 = 800) enough current to start a full size car. My 6,000 mah battery has a discharge rating of 90c this battery can provide 540 amps.
  • Mah rating – the mah is the capacity of the battery 1,000 mah = 1 amp. So my 8,000 mah battery is 8 amps and the 6,000 is 6 amps. The larger the capacity the longer run time you will get on your RC car.
  • Cell count – this tells you the amount of cells inside the battery. You will find this on batteries as an “s” rating example 2s is a 2 cell battery. Don’t worry if your battery does not have this rating you can easily work it out with the voltage. Lipo cells are rated at 3.7 v per cell. (even though fully charged they will go up to 4.2v). So my 8,000 mah battery has 7.4v on the sticker, if we take 3.7 and multiply it by 2 we get 7.4 so this is a 2s battery. A 14.8v battery will be 4s 3.7 multiplied by 4 equals 14.8.
  • Watt hours – this reading tells you how many watts per hour the battery can provide. To work this out we take the volts and multiply that by the amps. We can see that my 8,000 mah battery is 8 amps and we also know its a 7.4v battery. 7.4 multiplied by 8 gives us 59.2. This means the battery can provide 59.2 watts per hour.
  • Voltage – very important to know the voltage of the battery1/8th scale racing has a restriction of 4s. You can be disqualified for using anything above this limit. We know that voltage can be used to work out cell count. So a 4s limit will be a 14.8v battery, In my case I will need 2 of the 8,000 mah batteries in series to reach 14.8v. It’s also important to know voltage for limits on your devices.

Other types of batteries used in rc cars.

Nicad – Nickel-Cadmium batteries operate in very low temperatures are 1.2v per cell and release energy at a constant rate till they die.

The main downside to Nicad batteries is the “memory issue”.  As an extreme example if your let a Nicad drop to 50%. Then charged it up to 100%, then let it drain down again. When it gets to 50% of its capacity it will forget it has 50% more capacity. To get the most out of a Nicad it’s best to fully discharge the battery before charging it up.

Nimh – Nickel-Metal Hydride batteries have been around for a long time in the RC car industry. If you had an RC car as a kid then it likely had a Nimh battery. Not as common today as Lipo batteries however these are still used by enthusiasts and sold in RC shops around the world.

These are 1.2v per cell the energy release slows down towards the end. You know when a Nimh battery is about to die. Your car will slow down and run slower as the battery depletes. A common size for RC cars is a 6 cell nimh battery which makes 7.2v.

Li-Fe – Lithium Iron Phosphate batteries are a similar technology to Lipo batteries. These are rated at 3.6v per cell sometimes 3.7v. They require a special charger like Lipo batteries and shouldn’t be discharged below 3.0v per cell. Lipo chargers have a setting to charge LiFEPO4 batteries as well (this could be labeled as Li-fe). The most common use in RC cars is RX (receiver) packs in nitro cars.

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