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Battery Discharger/Capacity Meter (1)

design and control module

Battery Discharger/Capacity Meter (1)
This circuit can measure the capacity of individual cells as well as battery packs with an open circuit voltage of up to 35 V. The only requirement is that the discharged cell voltage has to be between 0.5 V and 2.5 V. During the discharge period, the instantaneous voltage is measured at one minute intervals and stored in memory. This allows the voltage curve to be drawn once the discharge process is completed.As can be seen from the title photograph, the appearance of the battery discharger is simple and clearly arranged. There is a small keyboard with 12 keys for the input of data. All information is displayed on a 16-character LCD. The battery is connected to the two instrument terminals, a black one and a red one. In addition there are two slide switches, one is for on/off, the other one we will describe later. On the back is a sizeable heatsink onto which the discharge transistor is mounted. There are also eight large holes in the front panel, because the enclosure contains a cooling fan that blows air over the heatsink during the discharge period. This allows the power dissipation capacity to be nearly doubled.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor Members can exclusively download these files for free as part of their Membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service. Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

Control board
R1 = 2O2
R2 = fuse, 1AT (time lag) Picofuse (e.g., Farnell 446-944)
R3-R12 = 1kOhm
R13,R18 = 27kOhm
R14 = 100kOhm *
R15 = 120kOhm
R16 = 1kOhm 5
R17 = 220kOhm
R19,R20 = 4kOhm 7
R21,R22 = 10kOhm
P1 = 5kOhm preset
C1,C2 = 100µF 25V radial
C3,C10-C13 = 100nF ceramic
C4,C5 = 27pF
C6 = 1µF 63V radial*
C7 = 4nF7, lead pitch 5mm
C8 = 4µF7 63V radial
C9 = 470pF
D1*,D3-D7 = BAT85
D2 = 1N4148
IC1 = 4001
IC2 = ST62T65, programmed, order code 010201-41
IC3 = 4066
IC4 = ST24C16
IC5 = 4094
K1-K4 = 12 x 3-way pinheader
K5 = 2-way pinheader
K6 = 9-way sub-D socket female), angled pins, PCB mount
K7 =14-way SIL-header
JP1 = 3-way pinheader with jumper
S1 = pushbutton type D6 (ITT/Schadow)
X1 = 8MHz quartz crystal
Bz1 = AC buzzer
LCD dot matrix module, 1×16 characters, 80×36×10 mm (e.g., Farnell # 142-542)
14 way female PCB connector for LCD
PCB, order code 010201-1 (see Readers Services page), supplied with discharger board 010201-2)
*) not fitted when using ST62T65 type C
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