Frequently Asked Questions - Batteries
Electric Radio Controlled cars are powered by a battery pack made up of 6 cells connected together.
Any battery pack will provide the motive power, but for speed and endurance (to last the race) the cells need to be well matched, and in good condition.
Battery power depends on -
It is very important therefore, to buy the best cells and to maintain them well.
For more information, 'click' on the links in the list above.
Matched battery packs.
Battery cells are not identical. The amount of power which a cell will hold, and the rate at which the power will be released can vary considerably.
However, it is possible to record and compare these characteristics so that a 'matched' pack can be created in which the cells are similar. This increase the performance, and the useful 'life' of the cells.
The more expensive sets have cells which are very similar.
The efficiency of the connection between each cell
Ready-made 'stick' packs are assembled by the manufacturer and should have no connection problems.
'Saddle' packs are assembled by soldering connecting plates and/or wires to single cells so that the pack fits the space in the chassis.
The standard of soldering is crucial, with the most common fault caused by use of a relatively low powered soldering iron - 45 watts is the preferred minimum. Most 'domestic' soldering irons are rated at 25 watts or less!
The efficiency of the connection between the pack and the motor
Ready-made 'stick' cell packs are often fitted with a 'Tamiya' connector.
The connector is easy to use and is designed so that it is almost impossible to connect the wires the wrong way (e.g. red to black).
BUT the contact area for the electrical connections is quite small, and can become loose or distorted with use. This increases the resistance and reduces the flow of electric power.
The physical connection remains strong, so the problem is not obvious. Regular inspection is essential.
A popular alternative connector for 'stick' pack cells is the 'Deans' connector. This houses two spade terminals in a plastic case. Again, the connection cannot be 'cross-wired', but the contact are is larger and unlikely to be distorted through use.
The 'Corallie' system has a 'bullet' connector with a large contact area inside a matching tube. A very firm 'fit' is achieved - which aids the flow of electric power.These are often found on self assembly saddle packs.
How well the cells are charged/discharged
The method of charging/discharging depends on the type of cell.
Nickel Metal-Hydride (NMH) cells
- ....should not be fully discharged after use
- ....should be stored partially charged
- ....should be charged with a charger which includes a peak voltage detection device - to automatically stop charging when the cells reach their optimum voltage.
A suitable charger/discharger will discharge the cells to their optimum 'standby' level.
Nickel-Cadmium (Ni-Cad) cells
- ....should be fully discharged after every use
- ....should be stored fully discharged.
- ....should be charged with a charger which includes a peak detection device - to automatically stop charging when the cells are fully charged.
Ni-cad cells suffer from 'memory', and can lose performance if not fully discharged.
'Stick' type batteries can only be connected to a single source of discharge, either a lamp bulb or a special discharger.
Although the pack will be discharged, some cells may retain some charge, and the fresh charge will be restricted. Over time the pack will become 'unmatched'.
'Saddle packs' have their cell ends exposed and each cell can be discharged independently. This means that the pack is completely discharged and a fresh charge will be applied to an empty cell - memory is not a problem.
Both stick and saddle pack cells can be 'revived' by charging then discharging (fully) immediately afterwards. The process should be repeated 3 or 4 times.
Saddle pack cells revive better because they can be effectively 're-matched'
Battery Power
Two distinct types of battery are available and in regular use for RC racing.
Most commercially available battery packs are NMH (Nickel-Metal Hydride) with a power output of 3000mah or 3300mah (mah = milli-amp hours).
The older 'Ni-Cad' (Nickel-Cadmium) style of battery pack has a lower range of power outputs - mostly 2400mah - but tend to have more 'punch'. They are no longer readily available.
To put this battery power into perspective. If a 3,000mah cell pack is connected to a component that uses 1 amp, it will last for 3 hours (1000 milli-amp/hour = 1 amp/hour). If the component uses 3 amps, the cell pack will last for one hour.
Under race conditions, the same battery pack will last for between 7 and 10 minutes!
This discharge rate can only be achieved if the individual battery cells operate in exactly the same way, discharging at the same rate, and for approximately the same amount of time. The manufacturing process does not produce 'clones' however, so each cell is carefully tested and combined with others with the same operating pattern. The cells which are most closely matched tend to be more expensive.