Quote:
Originally Posted by cutting42
Two main types of batteries you will come across, Nickel Metal Hydride (NiMH) and Lithium Polymer (LiPO). Lipo are newer, offer much more ability to deliver lots of power quickly and have taken over all racing and most bashing.
NiMH are often packaged in ready to run kits and are fine but are an older technology. You can fully discharge a NiMH with no ill effects but you are recommended not to top up charge them, fully discharge and then fully charge - known as a cycle - from new and after storing.
LiPO must never be discharged lower than 3 volts per cell (many people don't discharge lower than 3.2 volts) or they will be ruined. However you can "top up" charge them so many people run a race, then top up the same battery ready for the next race. They must not be left full charged or discharged but in a state called "storage charge" around 3.6 volts per cell. Because a LiPO battery must not be discharged below 3 volts all modern Electronic Speed Controllers (ESC) have a built in LiPO cutoff so the car will slow dramatically when the voltage drops to 3 volts or so and will stop completely if you do not stop driving quickly. For this reason, only use LiPO batteries on an ESC that is designed to use them and has a Low Voltage Cutoff (LVC).
All batteries have a capacity measured in milliamperes per hour or mAh/hr. This is the number you have read on the batteries like 1700 mAh or 3000 mAh. These are typical values for a NiMH battery and a 1700 might just get you through a 5 min race.
LiPO's typically have much higher capacities from 5000mAh to 7000mAh which should keep you running for 20 - 30 minutes, great for bashing.
As my previous post the "S" refers to cells in (s)eries in the battery. More battery cells equals more voltage which means a faster motor speed. For racing all 10th off road is done on 2S (7.4v) and 3S is not needed or permitted AFAIK. For bashing you are free to do whatever and many use 3S to get faster motors speeds and therefore higher top speeds.
Most cars will be designed for a certain battery and can also be different shapes. Most common in NiMH are the 6 cell stick pack and rounded in shape. LiPO's are usually in a square hard case for most racing cars and are in "Stick", Shortie" or "Saddle Pack" format and your car will determine which one you should use.
You can get soft pack LiPO's but they are not allowed for racing and are more vulnerable to being punctured in a crash. This is a bad thing and can allow the pack to catch fire and the universe will end!
Hope this helps a little.
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wow - easy to confuse yourself if your a numpty like me lol - so when I get my car I will buy lipo batteries - my dad has the nimah batteries and they last for like 10mins before the car goes pretty slow which is naff, with lipo's I can get a proper play/practice with them, especially if I have 2/3 at the ready
Regarding the cut off when the get down to 3 volts - does the esc tell you on the display how much voltage is left on the lipo or is it just a case of making note of the time you start using it and stopping as soon as the power drops?
cheers