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Electric RC Car batteries

Posted by RC Masters on 14th Jan 2013

We know how important batteries are in the RC industry. Whether you’ve just quickly developed a passion for the hobby or you’re already a regular racer you would simply understand that electric RC cars rely on batteries or battery packs. With electric RCs the runtime is dependent both on how long the battery lasts and how long it takes to recharge the battery pack, which means if your battery is running low you will be coming in dead last, and that just cuts the fun of driving outright.

There are various types of battery for electric RC. The rechargeable ones are nickel-cadmium (NiCd), nickel-metal-hydride (NiMH), lithium-ion (Li-ion) and lithium-polymer (LiPO). Alkaline type of batteries is also ok since they last longer, but the downside would be the very low power output which can make the car move and respond slow. NiCd and NiMh are commonly used because they’re practical and economical. You just need a charger and won’t have to buy new set of alkaline batteries when they wear out.

A standard 7.2v RC electric car battery pack measures at 130mm x 45mm. The MaH indicates the capacity of the battery. The greater the MaH, the longer it will last and the greater the capacity, the more it costs. You need to determine what you like most. Battery runtime can be affected by factors like how it is driven and the surface it is driven on and pretty much the power the engine uses.

Most electric RC cars are designed to last for at least 5 minutes, as much as the international standard for electric car racing goes. Majority of RC cars come with a battery that has 7.2 volts and a capacity of 1800 MaH or greater.

When it comes to charging the battery, this may vary greatly depending on a lot of factors. Just make sure you don’t cause damage to your batteries by overcharging them. When the battery is dead flat you can use this equation to determine how long you would need your batteries plugged in otherwise, just charge them until they start getting warm (not hot).

Battery capacity (battery’s mAh rating) / charger output x 1.3 (for losses in charging around 30%) = Number of hours

In essence, if you have a 1000mah battery and a charger which outputs at 100mA you would need to charge it for 13 hours. (1000 / 100 =10 x 1.3)

If you’re looking to use a higher voltage, make sure you check with the manufacturer to see if the ESC and motor can handle a higher voltage.

Let’s take a closer look into the four different types of rechargeable batteries. Voltage and cell counts differ amongst the Lithium batteries and NiCd and NiMh. Unlike conventional NiCad or NiMH battery cells that have a voltage of 1.2 volts per cell, Lithium battery cells are rated at 3.7 volts per cell. When charging and discharging, each type exhibits a different action. Lithium batteries are fully charged when each cell has a voltage of 4.2 volts. They are discharged completely at 3.0 volts on each cell. It is vital that you do not exceed both the high and low voltage limits as this may damage the battery.

LiPo is the latest upgrade to battery technology; they give a very linear power output. When the voltage drops, there is a sudden drop in power and you will need to stop using the engine. Lithium batteries have taken the electric RC world by storm. They are mainly lightweight, have large capacities, and have high discharge rates to power the most demanding electric motors. But these benefits also have some drawbacks, especially with charging and discharging. Lithium cells must be charged differently from NiCd and Ni Mh. Charging cells is the most risky part of using Lithium batteries. Because of the volatile electrolyte used in LiPo’s, they can catch fire or explode. It is important to set your charger to the correct voltage or cell count to avoid danger. You have to exercise extreme caution and should follow safety measure. RC LiPo batteries require unique and proper care if you want them to last for long. Charging, discharging, and storage all affect the lifespan – get it wrong and it becomes garbage.

Never charge the batteries unattended. Use a safe surface to charge your batteries on that in the event of explosion, no damage will happen. You can use plant pots with soil in them, vented fire safes, LiPo Sacks, etc. If a cell swells, especially when you’re charging it, place it in a fire safe place and do not try to deflate or puncture it.

Discharge rate is simply how fast the battery can be discharged safely. In the RC LiPo battery world it is called the “C” rating. A battery with a discharge rating of 1 C would mean you could safely discharge it in 1 hour and 2 C would discharge it in half an hour. All batteries holding capacities are rated in milli Amp hours (mAh) so it is quite useful if you understand the concept of Watts, Volts and Amps.

Taking a temperature reading of your packs after running them is another good way to gauge if you're using a high enough c rating, in this case a handheld Infrared Temperature Gauge might come in handy. For optimum battery life, try to keep your cells from reaching 70 degrees Celsius after use and keep it away from cold, especially during winter. For battery connectors, the white plug (Tamiya plug) and the red (Deans) plug are used more often. Now, here’s a simple advice you may want to try, cut the Tamiya plug off and solder the Deans plug on and that should set it.

RC battery chargers are one of the single most important items you need to purchase when getting into the electric-powered RC world. There are tons of chargers available in the market, however to simplify everything here’s the 3 most popular type there is:

  • Slow Charger – cheaper and normally outputs around 150 mAh and takes longer hours to charge. It doesn’t auto turn off even when the battery’s fully charged.
  • Fast Charger – outputs up to 5 amps and takes lesser time to charge. Example, a 2000 mAh battery will take about 30 minutes to charge. It also automatically shuts off when the cells are fully charged.
  • Field Charger – are more convenient since you can charge anytime wherever you are. You simply have to clip the alligator clamps to any 12 volt battery to charge.

For Lithium batteries, you may need a totally different kind of charger. There may be new chargers that already support Lithium cells, but you still have to emphasize and indicate that you’re using Lithium batteries. So keep an eye out for which battery would work best for you. Weigh and consider their benefits and disadvantages to help you with your choice.