Batteries
There are 3 main chemistry compositions of batteries used in RC cars, Lipo, NIMH and NICD. NICD batteries are not really used anymore, and wont be discussed any further, if you have some the chances are they are too old to be useful anyway!
A quick review of the positives and negatives of the remaining two is below:
So it is simple, LIPOs are better but more expensive. LIPOs popularity has really taken off in recent years, as such it is hard to get hold of proper racing standard NiMH packs, primarily as NIMH need maintenance as the voltage drops with time, if the voltage drops below a certain level then they degrade quickly. As such, model shops and distributers don’t want to stock many of them and so they are harder to get hold of. However you can buy cheaper, lower performance NIMH packs which are fine for beginners but you will normally want to change to LIPo at some point.
If you want to go LIPO then expect to pay between £40-£90 per pack, but you can get away with only one pack if you keep organised. For touring cars, you need a 2S pack which means 2 cells wired in series. Each cell has a nominal voltage of 3.7V thus a pack has a nominal voltage of 7.4V. This brings us to the first very important safety point with LIPO batteries. Under no circumstances should an individual cell drop below 3V or go above 4.2V. This means a 2S pack should always be between 6V and 8.4V. Lipos come in 2 different forms, saddle packs or stick packs. Saddle packs are normally used in offroad cars – these basically are where each cell is in its own case and the two cells are then wired together in series externally. Touring cars normally use stick packs, whatever you use, it should be hard cased. Softcase lipos are not allowed as they do not offer adequate protection to the cells in case of impact. Although you do not need to use lipos from the BRCA approved list, most people do. This list is normally easily found by searching for BRCA lipo approved in your favourite search engine.
There are 2 numbers which to concern yourself with, the pack capacity and the “C” rating. The higher the capacity, the longer the pack will last but for touring car racing with 5 minute heats, overall capacity is not too critical, although the higher the capacity then the higher the voltage will remain throughout the race. If you are starting out then a 3000mah pack is sufficient but the top drivers normally use 6000mah+. The “C” rating is the max charge / discharge rate for the pack. 1 “C” is the capacity in mah divided by 1000. For example, on a 5000mah pack then 1C is 5amps. The pack will normally say something between 20C and 90C, this relates to the maximum continuous (not peak) discharge current, i.e. a 50C 5000mah pack can discharge at 250amps when full. For safety reasons, never get a pack that is less than 20C as you will be drawing too much current from it when running at high speeds and loads. It is not advisable to charge at more than 1C, i.e. 5amps for a 5000mah pack. I don’t believe anyone has to charge at higher than 1C to ensure they have a full pack for the next race, sticking to 1C is the best way to look after your lipo and ensure it will last 2-3 seasons racing. If your pack states it can be charged at 2C then fine but remember it won’t last as long if you do! If you charge at 1C, then a battery takes roughly 1 hour to charge from minimum voltage (3v per cell). Rough guidance on how much capacity you will use in different classes of racing is below (all 5 minute races) – but various things can change this including temperature, grip levels, driving style, motor type etc. I have assumed that this is typical of a good club driver put use as guidance only – I also have put a typical battery specification for each application (you can always go higher!)
* See speed controller section for boosted / unboosted description
You can see from above that if you use 5000mah packs, you can expect to need to charge for 30-40mins between races at 1C – this is typically about as much time as you will have between rounds so isnt a major issue but it is a little bit hectic so although it is possible with 1 battery, 2 makes life easier if you can afford.
Next point is how to charge your lipo, charge it in a LIPO sack – this is a protective bag in case the lipo fails during charging and will protect you and your surroundings. Ensure you use a charger in LIPO mode – this is critical, charging a lipo battery with a NiMH charger will be extremely dangerous. See the charger section for more details
