RADIO CONTROL HELICOPTERS IN THE LAST ISSUE presented some safety checks helicopter after winters rest However area didnt discuss detail proper care feeding Ni-Cd batteries continue weak link radio systems Battery technology virtually unchanged past several years continue different points view battery technology among experts Since am certainly battery expert asked two people help article can learn Mike Mahoney Double M Electronics nice enough respond several pages information talked length Larry Sribnick SR Batteries get opinions ideas article could have written help basic Ni-Cd battery referred cell has nominal working voltage under loadsuch running servos transmitterof 12 volts Most radio systems have four such Ni-Cds series airborne power supply 48 volts eight Ni-Cds transmitter 96 volts Although nominal voltages fully charged battery will read higher figures voltage obviously dropping over time battery delivers power decline working voltage versus time depicted Figure 1 normal discharge curve 48-volt airborne pack An interesting point about Figure 1 aware until researching articleis exact shape discharge curve fully charged pack will read about 52 volts will drop 48 volts after pack has depleted about 25% its capacity curve remains 48 volts until about 15% capacity remains begins drop off rapidly always under mistaken 52 48 BtUy V&bg 007550250 PtgIThtt,y R ,inigaaFnctio d sr cne fr48i-d pk Figure 1 Normal discharge curve 48-volt Ni-Cd pack assumption bad word once reached 48 volts battery approaching caution area should recharged Larry feels battery safe flying until voltage drops below 48-volt level shown far right curve indicates pack ready make sharp drop voltage digital voltmeter would handy accurate measurements reading 48 volts dont know exactly discharge curve Another good way test batteries cycle periodically Most battery cyclers available cycle batteries down 11 volts per cell gives us good idea condition battery pack Mike has different idea believes what really interested amount capacity battery has full charge down 12 volts per cell since nominal voltage radios designed around provide adequate safety factor flying designingand will soon manufacturethe FatCat II PeakCharging Cycler/Analyzer will tell user condition battery pack both down 12 volts per cell well 11 volts per cell Another factor considered memory Although definitions battery memory good would premature drop voltage means could flying along thinking everything fine sudden batteries start drop voltage causing crash next obvious question What memory what can about Ni-Cd battery memory result irregular chemical distribution within battery cell caused charging partially discharged batteries what called shallow cycling memory development accelerated shallow-charge high rates such fly few times fast charge fly few times fast charge etc battery will actually get used discharge-charge pattern will enter premature discharge mode after few flights good news memory reversible cycling battery pack two three times SR Batteries May1994 87 Double M Electronics Fat Cat SRs Smart Charger/Cycler Hitec RCD Inc has ESV Multi Charge-A-Matic cycle keep Ni-Cds top shape warn potential problems charge monitor almost battery needs ElectroDynamics EDR-2 NiCd Testera digital multimeter testerchecks Ni Cds under actual load conditions manufacturer know guarantees batteries will develop memory Another phenomenon associated Ni Cds dendrites thin whisker-like tentacles grow inside cell point short out positive negative plates no real way determine long battery pack will last until dendrites begin appear Ni-Cds have finite life 300 500 cycles better packs lasting up 1000 cycles check pack dendrites give full charge cycle determine its capacity Assuming have good pack start charge again let sit four five days before cycling good battery pack will lose 1% 2% its capacity per day loses substantially have dendrites shorting out cells can either find replace cells exact duplicates buy new battery pack choice has always buy new pack because has charged enough times cause cell fail others may far behind Dendrite formation has caused difference opinion regarding proper care batteries stored long period Mike opinion batteries should topped off month Larry believes batteries should fully charged before storage left alone room temperature idea leaving alone reduces number charge cycles therefore lengthening life battery Since experts dont agree point choice charging left up last point consider wiring connector Both have tendency heavily used abused during flying season pull connector out receiver wire correct way hold connector removing everyone gets hurry pulls wire instead like use magnifying glass check wires going connector make sure new secure condition hope has added understanding Ni-Cd batteries take care little better know has Double M ElectronicsPO Box 159 Glen Dale Maryland 20769-0159 manufacturers FatCat Charger/Cycler FatCat uses l2VDC automatically discharge pack fast-charges about 95% automatically reverts slow charge Transmitter receiver batteries can independently cycled charged progress monitored several LEDs SR BatteriesBox 287 Bellport NY 11713manufacturers SR Smart Charger/Cycler also operates 12VDC peak slow charge cycle battery packs Its features too numerous list fully adjustable modes has LCD monitors temperature batteries charging well providing audible alert system Hitec RCD Jnc10729 Wheatlands Ave Suite C Santee CA 9207 1 distributes Multi Charge-A-Matic Powermate ESV Charge-A-Matic operates 12 volt power source selectable voltage current unit will peak charge Ni-Cd pack 270 mA up 1800 MA automatically revert trickle charge cycler portion displays battery efficiency LED ElectroDynamics Inc9557 Crosley Redford MI 48239manufactures EDR-2 NiCd Tester uses constant-current voltage- polarityindependent short-circuit-proof load check both Tx Rx Ni-Cds under load display results digital multimeter can also used cycle batteries spot weak bad cells pack using EDR-2 watch could make discharge curve packs spot weak before causes crash 488 Model Aviation
