Guide to Using a LiPo Battery
I’m going to try really hard not to bore you with science here but it is important for your safety that you know how to use your battery properly. Although they can be found in millions of electronic devices, Lithium Polymer batteries are unlike other types of rechargeable battery you’ve used before and require care to keep them from failing.
You’ve probably heard horror stories about how Lithium batteries explode without warning. The truth is that the chemistry can be quite volatile and if they do catch fire, it can be difficult to extinguish. Fortunately they are inherently very safe as long as you don’t abuse them. After all, you probably have one in your pocket right now, quietly powering your mobile phone.
First off, let’s talk about the various numbers on the packs and what they mean.
All batteries consist of cells. For LiPo batteries, a single cell has a nominal voltage of around 3.7 volts. When manufacturers produce a battery with a higher voltage, they simply combine the cells in series. Two cells (abbreviated as ‘2S’) would be 7.4V, 3 cells (3S) would be 11.1 volts and so on. When fully charged, each cell should be around 4.1v making the ‘peak’ voltage of a 2S LiPo around 8.2V.
It is important to consider that unlike many other battery chemistries, Lithium cells have a minimum charge voltage also. This is typically 3-3.2V. If a battery cell voltage drops below this voltage it may cause irreparable damage to the battery. Once a LiPo cell drops below this threshold it is likely you’re your charger will refuse to charge it and thus, the battery is rendered useless. For this reason it is important to store your battery correctly and to monitor the voltage when using it. Please see the ‘Voltage Alarms and Meters’ section below to find out how.
This figure is commonly misunderstood. The capacity of the battery is the amount of power the battery can provide. This figure is given in milliamp hours (mAh) and essentially states the amount of current that can be drawn for 1 hour before the battery is empty. For example, the battery pictured above is 2200mAh. This means the battery could supply 2200 miliamps (or 2.2 amps) for one hour. A draw of 1.1A would last 2 hours and so on. The science of battery discharge is actually pretty convoluted because it varies depending on a lot of factors, but this is a general rule of thumb.
Also known as the ‘C’ rating, the discharge rating essentially states how quickly the battery can be safely depleted. Using the pack in the picture as an example, we know it has a capacity of 2200mAh. We can see that the ‘C’ rating is 40C. This means that we can safely discharge the pack at 40 times the normal rate by drawing a maximum of 88 amps. It’s not a good idea to do this however, high discharge currents cause the batteries to heat up and reduces their lifespan but it is important to understand the ‘C’ rating in order to select the correct battery for your needs.
Depending on which charger you have, the charging process will differ so it is important that you read the instructions that come with your charger before you begin.
The battery itself may get warm during the charge cycle so it’s always a good idea to ensure your battery and charger is away from any flammable material, on a heat-proof mat or ceramic plate. Ideally the battery should be placed in a LiPo safe bag when charging. Never leave your pack charging unattended.
A balance charger (also known as a smart charger) will constantly monitor the voltages of the various cells during the charging cycle. This is known as ‘balance charging’ since the process will make sure that all cells are charged by the same amount. There are two different types of balance charger, the ’plug and play’ type or the more complex multipurpose charger.
A plug and play chargers such as the Overlander RC3S is the simplest type of balance charger. Plug it in, switch it on and it will do all of the complicated stuff itself. The drawback of this type is that you can’t monitor the battery levels as it charges so you cannot check the condition of the battery. This isn’t a big issue if you only have one battery but if you have many different types it’s worth upgrading.
A multipurpose charger such as the IMAX B6 (pictured) comes with all the bells and whistles. These chargers can often be programmed with lots of different modes and can charge just about any type of battery there is. Great if you have lots of different batteries and want to monitor their condition, but they can be very complicated to use properly.
If you have this type of charger which allows you to manually change the variables, make sure your charger is set to charge the type of pack that you have. It is recommended that you charge select ‘Balance Charge’ when charging a LiPo for the reasons mentioned above. When setting the charge current, it is always best to set it to same value as your battery’s capacity. For a 2200mAh battery this would mean the charging current should be set at 2.2A. Although most batteries can be charged at a much higher current (and therefore reach full capacity much more quickly), doing so can reduce the life of the pack.
Voltage Alarms and Meters
As you use your blaster, the voltage in the battery will decrease so it is important to monitor it during use. As mentioned above, depleting your battery below a certain voltage will damage it.
There are various ways of doing this. If you have a voltmeter installed in your blaster this is easy. Assuming that you have a 2S pack, you would need to ensure the voltage didn’t drop below an absolute minimum of 6.4V. Make sure you check the voltage regularly.
If you don’t have a voltmeter installed in your blaster, the next best option is a LiPo alarm (pictured below). These little devices plug directly into the battery’s balance lead (small wires, white plug) and report on the voltage of the cells via LEDs and a loud buzzer. When you plug them in (making sure it’s the correct way round), the LEDs will flash green and the buzzer will ‘bleep’ to signal that the battery is charged. You can then leave it attached and insert the battery into your blaster. When the battery begins to run out of juice, the alarm will beep constantly signalling that it’s time to recharge your battery.
When using a blaster fitted with a LiPo alarm, you may notice that the buzzer will sound occasionally when you rev the flywheels. This is a normal reaction to the power drain caused when the flywheels start up and can even happen when the battery is freshly charged.
If you use your blaster regularly it is a good idea to adopt a routine for charging your battery. Ideally it should be charged before and after use to ensure that it has the optimal charge. There’s nothing worse than turning up to an event with a flat battery.
Like all batteries, lithium cells gradually loose charge over time. In order to ensure that the voltage doesn’t drop below the critical 3.2V per cell, it is important to make sure LiPo packs are in good condition before placing them in storage for a period of time. Make sure they are either fully charged or placed in ‘storage mode’ (if you have a multipurpose charger, see your manual). It is also important to ensure that the pack is disconnected from the blaster and any voltage alarms and stored somewhere safe. LiPo safe bags are a good idea when storing your blaster and pack for long periods.
Disposing of a dead/damaged battery
As I’m sure you’re aware, you can’t really throw batteries in normal rubbish (icky chemicals, environment, fires and whatnot). This is more important when it comes to LiPo batteries because too much moisture or physical damage could make them go thermal.
The best option is to take them to your local recycling depot. Most RC model shops offer a battery disposal service and in the UK, most council recycling centres will take lithium batteries but it’s always best to check.
This document is a guide only. UKNERFWAR.COM does not accept any liability whatsoever with regards to any injury or damage caused by advice included or omitted within this guide. Always refer to instruction manuals provided with your own equipment.
Do’s and Dont’s
Only ever use a charger specifically designed to charge Lithium Polymer cells. Failure to do so may a cause fire, which may result in personal injury and/or property damage.
Check and double check that you have set the correct voltage/number of cells and the maximum current does not exceed the stated charge rate (normally 1C). If using an automatic charger, check that it has detected the correct number of cells. Check it again through every stage of charging. Do these checks for EVERY charge.
Keep all batteries out of the reach of children.
Ideally you should check the voltage of your LiPo pack before charging with a digital multimeter. Only charge if it is 3.30V or greater per cell (e.g. 9.90V for a 3S pack).
Only charge in an isolated area away from other flammable materials and on a non conductive and non flammable surface. Use a LiPo safe bag or use a non-conductive container like a casserole dish with a lid as it will help contain any fire. LiPo battery fires can not be extinguished with water. If a fire occurs, either cover it with sand or better still salt. On no account use water to extinguish a fire. Water acts like petrol on a LiPo battery fire.
Store LiPo batteries at room temperature between 5ºC and 27ºC (40ºF and 80ºF) for best results.
If you plan to store your LiPo cells for an extended period (over 1 month) then discharge them as you would normally. Then charge them to only 3.80-3.85V per cell.
Physically disconnect batteries to prevent slow over-discharge.
Always check that batteries are physically and electrically undamaged before charge or discharge.
Do not use a charger that is not specifically designed to charge Lithium Polymer cells.
Do not leave cells un-attended when charging. You should always remain close to the charging cells to monitor the charging process and react to potential problems should they occur.
Do not charge LiPo batteries in the blaster.
Do not carry LiPo batteries in your pocket. They have been known to short against coins and keys and cause fires.
Do not puncture the cells.
Do not place LiPo batteries in a fire.
Do not short the wires of your LiPo cells/battery. This is very dangerous and can cause a fire. If you accidentally short the wires of your LiPo cells/battery, isolate it immediately and place it somewhere safe. Usually you’ll be alright but it’s best to leave it for a few minutes to ensure it’s safe.
In the event that you drop your blaster, check the battery immediately for damage and isolate it if there are any signs of physical damage or bloating.
Do not charge cells if they are cold. Storing them in a garage or shed is fine but make sure they are at room temperature before you charge them. Similarly, you shouldn’t charge your battery if it is still warm from use. Always allow it to settle to room temperature.
Do not store your LiPo somewhere that is likely to get hot (i.e. in a car on a sunny day).
Do not eat your battery. Should go without saying but you never know.
Do not allow charging to continue above 4.25V per cell. This is VERY important as a fire could result. If you have a smart charger this shouldn’t be an issue.
Do not discharge you LiPo cells below 3.2V per cell (e.g. 9.6V for a 3S pack) as this will damage the cells and dramatically reduce the life of your cells. If you do accidentally discharge them below 3.2V per cell, leave them for 30 minutes and if the voltage recovers to over 3.4 per cell then they should be OK to use them again. If they do not recover to at least 3.2V per cell then I’m afraid you have damaged them and they should be disposed of (Please see below as the correct method of disposal).