Battery Charger
A simple dual-cell charger designed for Ni-MH and Ni-Cd batteries (accumulators).
- Trickle charging method
- Galvanic isolation from the mains power supply
- Handles two battery cells simultaneously and independently
Electronic circuit
The charger uses a trickle charging method. The simplest of the safe charging methods is with a fixed low current equal 0.1*C (where C is the current equivalent to the capacity of the battery divided by one hour). The total charging time is limited to 16 hours.
Icharging = (Vref / R1) + Iadj = 1.25V / R1
| # | Designator | Quantity | Part Number | Package | Description |
|---|---|---|---|---|---|
| 1 | A1 | 1 | STC‑A22O50I700USBA‑A | 40x25x10mm | AC-DC Power Supply; Input: 100-240V AC~50/60Hz 200mA; Output: 5V DC 700mA |
| 2 | IC1, IC2 | 2 | LM317T | TO-220 | Adjustable voltage regulator in current stabilization mode; Vref = 1.25V |
| 3 | R1, R2 | 2 | CF-1/4W-16RJ | 0.25W | Resistor 16 Ohm ±5% (limits charging current to 75 mA for 750 mAh battery |
| 4 | D1, D2 | 2 | 1N4001 | DO-41 | Protection diode, any of 1N4001-1N4007, etc. |
| 5 | LED1 | 1 | L-132XHD | D=3mm | Any red LED for charging indication |
| 6 | R3 | 1 | CF-1/4W-1KJ | 0.25W | Resistor 1K Ohm ±5% |
| 7 | P1 | 1 | CEE 7/16 Europlug | Type C | Two-pole round-pin domestic AC power plug |
| 8 | B1 | 1 | BH-321-2A | 59x33x15mm | Battery holder for 2xAA cells (with modified terminals) |
Device design
