Radio Technique
George M. Myers
70 Froehlich Farm Rd., Hicksville, NY 11801
Abstract
CaRa Trickler: maintaining electric-power Ni-Cd batteries with trickle charging.
Types of Ni-Cd Chargers
There are four types of battery chargers for nickel-cadmium (Ni-Cd) batteries:
- Fast — recharges in one hour or less
- Quick — recharges in three to six hours
- Overnight — recharges in 10 to 15 hours
- Trickle — continuous, long-term maintenance
Trickle Chargers — Purpose and Principles
Trickle chargers are designed to keep a charged battery ready for immediate use. They supply a small steady current (about C/50, where C = rated cell capacity) to make up for self-discharge. Using a trickle charger will not cause "memory" in Ni-Cd batteries.
Key points:
- Self-discharge at room temperature (≈75°F) is typically C/50 to C/100, meaning a fully charged battery will self-discharge completely in about 50 to 100 days.
- A trickle charger sized at approximately C/50 milliamps compensates for this self-discharge but cannot restore a lost charge; it supports other charging methods.
- The same charger current will act differently depending on pack capacity. For example, a 40 mA charger:
- is a trickle charger for a 1,200 mAh pack
- is an overnight charger for a 500 mAh pack
- is a quick charger for a 250 mAh pack
- is a fast charger for a 50 mAh pack
CaRa Trickler — Setup and Field Experience
My experience with the CaRa Trickler:
- Before an Alaska trip, I prepared adapter plugs, organized a trickle-charge setup, and charged and tested all Ni-Cd packs (old and new) I would leave at home. I then connected all of them to the Trickler.
- Six months later (a period similar to typical winter storage), discharge tests showed the Trickler had maintained those packs at approximately 95% of their charge level when connected. Excellent long-term maintenance.
Capacity recovery example:
- A 550 mAh pack tested at 537 mAh on 4/28/89.
- Left unattended on a workbench for six months, it tested at 275 mAh after the first recharge.
- After three charge/discharge cycles it recovered to 400 mAh, and after six cycles it recovered to 540 mAh.
CaRa RC System Automatic Cycler/Charger
Features:
- Can be powered by 110 VAC or 12 VDC (both cables provided).
- Discharges a pack and captures capacity (milliamp-hours) on a digital display.
- Automatically switches charging modes as full charge is attained (it will move from fast/quick charging to trickle charging).
- Two outlets on the back provide additional trickle charging for up to four transmitters or four flight-pack batteries.
- The Cycler can simultaneously trickle-charge multiple packs (examples given: three transmitters and five receiver packs).
The original purpose of the Trickler was to free the Automatic Cycler/Charger for field use; many owners of the Cycler will buy a Trickler to simplify life.
Cables, Connectors, and Capacity Options
- The CaRa Trickler is delivered with four RCA-type sockets; charge cords are ordered separately.
- Standard charge cords (start with an RCA plug, about five feet long) are:
- Lo — 100 mAh
- Normal — 500 mAh
- Hi — 1,200 mAh
- Optional cords are available for batteries up to 4,000 mAh.
- Each charge cord contains two pairs of wires (to maintain two batteries), terminating at cut ends so you add your own matching plugs.
- Each wire pair has a limiting resistor sized for a particular pack capacity and a green LED that glows when charging current flows.
- Maximum recommended pack size for standard Tricklers is 1,800 mAh; up to 4,000 mAh has been accommodated on special order.
- One Trickler can maintain up to 32 packs; you can double the number of charging cable assemblies using RCA phone Y-connectors.
Organizing many wires:
- I color-coded the wiring to avoid mistakes:
- Red tape — transmitter-charging wires
- Yellow tape — flight-battery-charging wires
- Blue tape — low-capacity packs (150–250 mAh)
- White tape — high-capacity packs (1,200 mAh)
- Care is required to avoid over- or undercharging.
Practical tip:
- To get special plugs, I cut them from the charger that came with my RC system and spliced them to Deans plugs so I can still use the RC system's charger in the usual way.
Alternatives and Accessories
- Compendium: Trickler — $34.95 (cables $5 each) from CaRa Products, Canton, SD 57013 (tel. 1-605-987-5924).
- Ace R/C, Inc. offers an Add-A-Trickle device that attaches to the charger supplied with many RC systems; it's inexpensive and doesn't add much to the wire clutter. Useful to try if you want to test trickle-charging benefits without reorganizing everything.
Battery Testing — Lessons from Electric Model Work
Background:
- I learned that battery capacity depends on discharge rate, but had not done extensive testing of electric-powered airplane batteries until a friend's project prompted real-world tests.
Case study (Bob's small electric plane):
- Bob used battery packs rated at 450 mAh when discharged at 225 mA. Those packs showed 450 mAh when discharged at 900 mA and even at 3.6 A on a Charge-A-Matic tester (which can program discharge currents up to 3.6 A).
- However, the airplane motor draws roughly 10 A at 3.6 V. To obtain required voltage, two 3-cell packs were put in series and then paralleled to supply current. Under that load the indicated capacity was cut in half and current dropped instantly and continuously. The packs were inadequate for the motor despite appearing to have full capacity in lighter tests. Don Srull was correct in his assessment.
Follow-up testing:
- Sanyo N-800AR cells tested with that motor/resistor pack held 10 A for five minutes and showed over 900 mAh usable capacity. This demonstrated the importance of testing under realistic conditions.
Receiver power problem:
- Bob used a 4-cell, 50 mAh pack for the receiver to save weight. The idle current was about 20 mA and surged to hundreds of mA when servos moved; the 50 mAh pack exhausted quickly.
- A 3-cell, 175 mAh pack of similar weight improved RC performance but flight was still poor.
- Oscilloscope investigation showed the Benson SC-1 speed controller was not driving the motor at 100% duty cycle; motor current showed pulses with about 80% duty cycle.
- The SC-1 needs a full-voltage pulse from a four-cell pack to reach 100% duty cycle. The 3-cell pack satisfied servos but not the speed controller.
- Using a four-cell, 100 mAh battery for the radio and a three-cell N-800AR for the Imp 30 motor produced good flight performance.
Conclusion:
- Drawing significantly more than the rated current from Ni-Cd batteries reduces terminal voltage and may prevent recovery of the rated capacity.
- To know what you really have, test batteries under the realistic load and conditions they will experience in use.
Transcribed from original scans by AI. Minor OCR errors may remain.
