NiCd and NiMh Batteries

NiCd's and NiMh's are the most commonly used source of power for radio transmitters and receivers.

If a NiCd or NiMh battery is repeatedly fully charged and then used an amount that is less than full capacity (let's say you charge and regularly have three or four flights in a session), after a period of time, it may not be able to deliver any more than the capacity frequently used. This is called memory effect. Quite often this apparent memory condition may simply be voltage depression where the voltage of a cell is slightly less than rated. This can happen for several reasons such as operating at higher temperatures, extended overcharging, operation below 0°C, etc. The cell may actually be operating at or close to full capacity but the voltage appears slightly less. If you wish to avoid this condition, you can "cycle" the batteries, that is, fully discharge the pack and then fully charge it. To do this you will need to purchase a battery "conditioner" or "cycler", there are quite a few to choose from and really it is down to how much you want (can afford) to spend.

Delta Peak and other transistor/computer controlled chargers  are becoming  the norm now. Many people no longer trickle charge their batteries overnight, they are charged by a controller charger and quite often this is done at the field. It makes perfect sense really, you KNOW they are charged. There is nothing worse than wondering if the "glow" is charged or not and is that the cause of the engine not starting!

For a standard receiver pack we would recommend a 4.8V NiCd or MiMh pack with at least a 1700mAh capacity. For a helicopter using faster and more powerful servos along with a digital gyro and engine governor a 2400mAh or even 3300mAh pack would be a necessity and should only be used for a maximum of four flights before it is charged.
 

These batteries are becoming more and more common for powering electric helicopters. The pro points for this type of battery is its much lower weight and ability to produce a more consistent power delivery. It is important to never totally deplete a Li-Po battery below its threshold level of around 3 volts per cell as the battery cells will be permanently damaged. The symptoms of damaged Li-Po cells are that the cell skin will puff up like a balloon, or the battery can no longer accept a charge. When the cell is damaged, the peak charger will shut down quickly every time you connect the charger to the battery and if you keep trying to charge a defective Li-Po pack, then it might explode violently. You must never charge the battery unattended and never short out a pack, as they can be very volatile, if the cells are shorted, or the charger is put on a wrong setting, too high a charge current is used, or if the cells are damaged and you repeatedly attempt to charge them, then the battery can explode.

Unlike NiCd or MiMh battery packs Li-Po's do not suffer from memory effects but the life of the battery is limited to a particular number of cycles and each time you 'top it up' you are effectively loosing a cycle life.

It is necessary to buy a charger that is designed specifically for charging Li-Po cells. These can vary in price, but have come down quite a lot in the last few months. A simple Li-Po charger that can charge up to three cells in series and at up to one amp current can be had for as little as £20 to £30. Sophisticated Orbit and Schultz Li-Po chargers can charge up to 11 Li-Po cells in series and at up to 8 amps, and can be bought for £120 to £300 pounds.
 

Li-Po Batteries: for radio receiver power
 

It is possible to use a Li-Po battery for your radio receiver supply though this is not common practice for your average club flier and most opt for a NiCd or NiMh pack of suitably high capacity. If you do wish to use a Li-Po then there are an increasing number of options available on the market. Duralite produce an excellent range of receiver batteries rated at 7.4V and up to 4000mAH. These packs are arranged with four cells (2S2P) wired for two cell redundancy with two cells in series and two cells in parallel. Li-Ion and Li-Po batteries rated at 7.4V require the use of a voltage regulator. Regulators vary between 5.1V, 5.6V and 6.0V if your radio gear can handle the extra voltage. A 6V regulator would also need a step down to 5.1V for your gyro/tail servo in a helicopter. Duralite regulators have an 'electronic switch'. The current does not pass directly through the switch, the switch merely turns the regulator on and off. Should the switch fail in flight the regulator remains on until the battery is unplugged.