Hyper-Simple Battery Capacity Tester

The circuit described
here is eminently suitable to indicate the capacity of a battery. We use
a cheap electric clock for this. By connecting a resistor across the
battery terminals, the battery is discharged somewhat faster than with
the clock alone. If we pick a resistor with a value of 5.6R, the
discharge current amounts to 1.2 V / 5.6 R = 214 mA. If we multiply this
with the number of hours that the clock ran after the battery was
connected up then we know (approximately) the capacity of the battery.
When discharging a NiCd battery we need to make sure we remove the
battery the moment the clock stops running. NiCd batteries do not
tolerate too deep a discharge very well. We therefore recommend keeping
an eye on the voltage in one way or another, for example by connecting a
multimeter in parallel with the resistor.

Hyper Simple Battery Capacity Tester Circuit

Hyper-Simple Battery Capacity Tester Circuit Diagram

Author: J. Van der Sterre
Copyright: Elektor Electronics

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Battery Charger Display Using LT1639

The Over-the-Top type of
operational amplifier is ideal for use as a current sense for battery
charger applications. The design described here can be used with
chargers for rechargeable batteries (Lead/acid or NiCd etc). The 5 V
operating supply for the circuit is derived from the battery on charge.
The circuit uses a sense resistor R8 to determine the value of current
flowing in or out of the battery. An LED output
shows whether the battery is charging or discharging and an analogue
output displays the battery charge or discharge current. The circuit can
also be altered to shown different ranges of charging current to cater
for higher capacity cells. IC1a and IC1b together with T1 and T2 form
two current sources, which produce a voltage across R5. The voltage
across R5 is proportional to the current through resistors R8 and R1
(for IC1a) or R8-R3 (for IC1b).

Circuit

Circuit diagram

The current source formed by IC1a and T1 is active when the
batteries are discharging and IC1b and T2 is active when the batteries
are being charged. In each case the inactive opamp will have 0V at its
output and the corresponding transistor will be switched off. IC1d
amplifies the voltage across R5, which is proportional to the sense
current. The component values given in the diagram produce an
amplification factor or 10. A sense current of 0.1 A will produce an
output voltage of +1 V. The supply voltage to the circuit is +5 V so
this will be the maximum value that the output can achieve. This
corresponds to a maximum charge/discharge current of 0.5 A To display
currents from 0 to 5.0 A, resistor R7 can be omitted to give IC1d a
voltage gain of 1.

Higher currents can be displayed by using a lower value of sense resistor R8. A DVM
or analogue meter can be used at Vout to give a display of the
charge/discharge current. The constant current sources can only function
correctly when the supply to the voltage regulator circuit (UBatt. e.g.
6V or 12V) is greater than the operating voltage of the opamps (+5 V).
The supply voltage to the LT1639 can be in the range of +3 V and +44V
and voltages up to 40V over the supply voltage are acceptable at the
inputs to the opamp. IC1c controls the charging/discharging LED
output. The inputs to this opamp are connected to the outputs of the
current source opamps and its output goes high when the battery is being
charged and low when it is discharging.

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Low Battery Indicator II

This circuit indicates
the remaining battery life bAy varying the duty cycle and flash rate of
an LED as the battery voltage decreases. In
fact, the circuit actually indicates five battery conditions: (1) a
steady glow assures indicates that the battery is healthy; (2) a 2Hz
flicker (briefly off) indicates that the battery is starting to show
age; (3) a 5Hz 50% duty-cycle flash is a warning that you should have a
spare battery on hand; (4) a brief flicker on at a 2Hz rate indicates
the battery’s last gasp; and (5) when the LED
is continuously off, it’s time to replace the battery. IC1 is wired as
an oscillator/comparator, with a nominal fixed voltage reference of
about 1.5V on its pin 2 (inverting) input (actually, it varies between
about 1.7V and 1.4V depending on the hysteresis provided via R6).

Circuit diagram:

Low battery indicator Circuit

Low battery indicator Circuit Diagram

This reference voltage is derived from a voltage divider consisting
of resistors R4 & R5, which are connected across the 5V rail derived
from regulator REG1, and feedback resistor R6. Similarly, IC1’s pin 3
input (non-inverting) is connected to a voltage divider consisting of R1
& R2 which are across the 9V battery. Using the component values
shown, the circuit will switch LED1 from being continuously on to flash
mode when the 9V battery drops to about 6.5V. Subsequently, LED1 is
continuously off for battery voltages below 5.5V.

Naturally, you can tweak the resistor values in the divider network
for different voltage thresholds as desired. In operation, the circuit
oscillates only when the sampled battery voltage (ie, the voltage on pin
3) is between the upper and lower voltage thresholds set on pin 2.
Capacitor C3 provides the timing. Above and below these limits, IC1
simply functions as a comparator and holds LED1 continuously on or off.
Finally, to precisely set the “dead-battery” threshold, make R4
adjustable to offset the variations in regulator tolerance.

Author: Ashish Nand – Copyright: fgf

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Flat Battery Indicator

This small circuit was
developed to monitor the battery in a model hovercraft. The lift in the
model is produced by an electric motor driving a fan. To avoid the
possibility of discharging the rechargeable battery pack too deeply, the
design lights a conspicuous LED mounted on
the model when a preset threshold voltage is reached. The circuit only
uses a few components, which helps keep the total weight of the model
down. The circuit connects to the model only across the two points where
the voltage to be monitored can be measured. These also supply power to
the circuit.

The best place to connect the circuit is not at the battery
terminals, but rather at the motor connections. The circuit is suitable
for use with nominal battery voltages of 4.8 V to 9.6 V (four to eight
1.2 V cells). For example, if there are six cells in the battery, its
nominal terminal voltage will be 7.2 V. A discharge threshold voltage of
around 1 V per cell is appropriate, which means that for six cells the
threshold is 6 V. We now need to set the voltage UZ across the
adjustable Zener diode D1 (an LM431) to about 0.5 V less than the
threshold voltage at which we want LED D2 to light.

Circuit

Circuit diagram

This voltage is controlled by the choice of the value of resistor
R1. As indicated in the circuit diagram, this is done with the help of a
trimmer potentiometer (R1.A) with a fixed resistor (R1.B) in series.
Using the suggested values (10 kΩ for both the potentiometer and the
fixed resistor) allows the discharge threshold voltage to be set between
about 5.5 V and 8 V. For lower or higher voltages R1.B should be made
correspondingly smaller or larger. Once the desired value of UZ has been
set the total resistance (R1.A plus R1.B) can be measured and a single
fixed-value resistor of this value substituted at R1.

In the example mentioned of a six-cell battery, a voltage of 7.2 V
will appear at the emitter of T1 when the battery is charged. At its
base is UZ, which should be 5.5 V (6 V – 0.5 V) in the case of a
discharge threshold voltage of 6 V. As long as the battery voltage
remains at least 0.5 V higher than UZ, T1 will conduct and T2 will
block, with the result that LED D2 will not light. If the battery voltage should fall below about 6 V (UZ + 0.5 V), T1 will block, T2 will conduct and LED
D2 will light. To ensure stable operation of the circuit R6 provides a
small amount of switching hysteresis. By adjusting the resistor value
between 100 kΩ and 220 kΩ the amount of hysteresis can be varied.

The current drawn by the circuit itself is less than 5 mA (as measured with a battery voltage of 7.2 V). When the LED lights an additional 10 mA (the LED
current) is drawn, for a total of around 15 mA. The adjustable Zener
diode can be replaced by a fixed Zener with a voltage 0.5 V less than the
desired threshold. Resistors R1 and R2 can then be dispensed with. A
flashing LED can be used for D2 (without series
resistor R7). An acoustic alarm can be provided by replacing D2 and R7
by a DC buzzer with a suitable operating voltage.

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Battery Desulphation Progress Monitor

A number of readers have
asked how to tell when the Lead-Acid Battery Zapper has done its job
and battery desulphation is complete. In the author’s experience,
batteries that are going to respond to this treatment will generally
show quite a high peak voltage across the terminals at the beginning of
the treatment. If this steadily decreases and practically disappears,
then the treatment is near to complete. This may take anything from a
week to many months, depending on the size and condition of the battery.
In the absence of an oscilloscope to monitor the voltage peaks, a
simple peak detector can be constructed from a fast diode and 100nF
capacitor. Any high-impedance multimeter (eg, most digital types) can
then be used to measure the average DC voltage across the capacitor.

Battery Desulphation Progress Monitor Circuit

Battery Desulphation Progress Monitor Circuit Diagram

Author: Graham Lill – Copyright: Silicon Chip Electronics

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Battery Tester For Deaf and Blind Persons

Many blind and
deaf-blind persons use portable electronic devices to assist their
everyday lives but it is difficult for them to test the batteries used
in this equipment. Talking voltmeters are available but there is no
equivalent usable by deaf-blind persons. This battery tester uses
vibration and a user-settable control to enable blind and deaf-blind
persons to test both ordinary and rechargeable AAA, AA, C, and D cells and 9V batteries. For ease of use and maintenance the device is powered by the battery under test.

The design is dominated by the fact that the pager motor will
operate down to only 0.7V. With a 0.3V drop from the switching
transistor, a weak cell, at 1.0V, will only just operate the motor. This
means that the 1.5V cell sensing circuitry cannot be isolated from the
9V test terminals using steering diodes – they would introduce too great
a voltage drop. The solution was to duplicate the level sensing
circuitry for each set of test terminals. On the 1.5V side of the
circuit, a resistance network consisting of two 10kO multi-turn trimpots
(VR2 & VR3) and user control VR1a produces an adjustable proportion
of the voltage of the cell under test.

VR1a selects a division ratio between the low and high limits set by
the trimpots. The resistance of VR1a is 10 times larger than the
resistance of these trimpots to minimise the interaction between their
settings. The voltage from the resistance network is applied to a
combined threshold detector and current amplifier formed by Q1 to Q4 and
associated components. When the threshold (about 0.6V) is exceeded the
pager motor is energised, causing the battery tester to vibrate. In use,
VR1 is first set to its fully counter-clockwise position, then a cell
is connected.

If the cell’s voltage exceeds the 1V low threshold set by the 1.5V LOW
trimpot (VR2), the battery tester will vibrate. Rotating VR1 clockwise
applies a progressively lower voltage to the threshold detector until a
point is reached when the threshold is no longer exceeded and the pager
motor switches off. The angle of rotation of VR1 then indicates the
voltage on the battery. VR1 is fitted with a pointer knob to make the
angle of rotation easy to feel. Having the pager motor switch off rather
than switch on ensures that the voltage of the battery is sampled while
it is supplying the load of the pager motor.

This gives a more accurate indication of the state of the battery
than its open-circuit voltage. To ensure that the user turns VR1
clockwise during the test, the circuit is designed so that once
vibration has ceased, it cannot be made to start again by rotating VR1
counter-clockwise. This also eliminates any possibility of user
confusion arising from any hysteresis in the circuit. This feature is
implemented by Q5, which forces the base of Q2 high if Q4 ceases to
conduct strongly. A 1µF capacitor between the base and emitter of Q5
forces it off when power is first applied, to give Q4 a chance to
conduct.

Battery Tester Circuit For Deaf and Blind Persons

Battery Tester Circuit Diagram For Deaf and Blind Persons

The parallel 1MO resistor discharges the 1µF capacitor when power is
removed, to reset the circuit. To prevent the pager motor being driven
through the base-emitter junction of Q5, the base of Q5 is connected to
the collector of Q4 via 10kO resistor. Another 10kO resistor is
connected in parallel with the pager motor to ensure that Q5 switches on
when Q4 switches off. The 9V test circuit is similar to the 1.5V
circuit. A 68O 1W resistor limits the current through the motor to
prevent it from being over-driven by the higher voltage.

In addition, there is a series diode to protect the 9V circuitry
against reverse polarity. A diode is not possible for the 1.5V side of
the circuit because it would introduce too great a voltage drop;
fortunately, it is also unnecessary since 1.5V is below the reverse
breakdown voltage of the transistors used. The 1µF capacitor across the
pager motor smoothes the load provided by the motor so that measurements
made by the circuit are consistent from one trial to another. The
1N4001 diode across the pager motor clips any back-EMF generated by the motor.

A D-cell holder and an AA-cell holder connected in parallel were
used for the 1.5V test terminals. The 9V test terminals are the studs
from a standard 9V snap screwed to the box. To calibrate the battery
tester, start with VR1 fully counter-clockwise. First adjust the 1.5V LOW
trimpot by turning it fully counter-clockwise, then apply 1.0V to the
1.5V test terminals and turn the trimpot slowly clockwise until
vibration just ceases. Now turn VR1 fully clockwise and adjust the 1.5V HIGH trimpot similarly with 1.6V applied to the 1.5V test terminals.

There is a small amount of interaction between the low and high settings, so repeat the adjustment of the 1.5V LOW
trimpot. Similarly, calibrate the 9V side of the circuit for a range of
6.0V to 9.6V. To test a battery, rotate VR1 fully counterclockwise
before connecting the battery to the appropriate set of test terminals
(1.5V or 9V). If the device does not vibrate, the battery is completely
dead. Otherwise, rotate VR1 slowly clockwise until the device just
ceases to vibrate. The position of VR1 then shows the condition of the
battery under test.

Author: Andrew Partridge – Copyright: Silicon Chip Electronics

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Car Battery Failure Detector

A car battery
deteriorates in use and its life seldom exceeds four years. When new,
its voltage may drop to only 2V while cranking the engine. As the
battery ages, its internal impedance increases and so the voltage drop
while cranking also increases, until ultimately the drop is high enough
to prevent the engine from starting. This gradual increase in voltage
drop while cranking can be used as an early warning of looming battery
failure and so this circuit triggers an alarm when the battery voltage
drops to 8V during cranking. IC1 is a precision 2.5V device used as the
reference for two comparators based on IC2, an LM358 dual op amp.

Car Battery Failure Detector Circuit

Car Battery Failure Detector Circuit Diagram

IC2a monitors the voltage from trimpot VR1 and normally its output
at pin 1 will be low while the output of IC2b will be high and LED1 will
be green. When pin 2 of IC2a falls below pin 3, its output at pin 1
will go high to drive the red section of LED1 to indicate a fault. At
the same time, IC2b inverts the signal from pin 1 and its output at pin 7
goes low and turns off the green section of LED1 to indicate a fault.
Since the battery voltage drop occurs momentarily while cranking, a more
permanent indication of the fault is provided by flashing LED2. When
IC2a’s output goes high momentarily, the SCR is latched and LED2 flashes and can only be deactivated by pressing pushbutton S1.

Author: Victor Erdstein – Copyright: Silicon Chip Electronics

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High-Current Battery Discharger

If you have a motley
collection of 12V batteries in varying states of health, this simple
circuit will allow you to easily check their capacity. It’s basically a
high-current discharge load which is controlled by the NiCd Discharger.
This involved increasing the existing 10µF capacitor across LED1 to
100µF, to enable it to supply the brief current pulses required by the
clock mechanism. The discharger’s “clock connection” now controls a
BC457/BD139 Darlington transistor pair (Q1 & Q2) via a 1kO resistor.
These in turn activate a car headlamp relay to switch in a preselected
lamp load (one of three).

High Current Battery Discharger Circuit

High-Current Battery Discharger Circuit Diagram

With 12V selected, the prototype unit stops the discharge at 11.4V
which corresponds to a cell voltage of 1.9V (this is a pretty good
indication of a discharged 12V battery). The loads consist of three
automotive lamps, selected to provide discharge rates to suit the
battery being tested. These lamps should be fitted to sockets, so that
they can be easily swapped for other lamps with different wattages, if
required. That way, the discharge current can be varied simply by
changing the lamp wattage. By the way, this circuit will also work with
6V batteries, provided the relay holds in. This gives an “end-point”
voltage of about 5.7-5.8V.

Author: Reg Carter – Copyright: Silicon Chip Electronics

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Improved Vibrating Battery Tester

Many blind and
deaf-blind people use portable electronic devices to assist their
everyday lives but it is difficult for them to test the batteries used
in that equipment. Talking voltmeters are available for the blind but
there is no commercially available equivalent usable by deaf-blind
persons. This device enables blind, deaf-blind and sighted people to
test batteries. It will test AAA, AA, C and D
cells, as well as 9V “transistor” batteries. All rechargeable and
non-rechargeable cell types are supported. The circuit needs no
calibration. To use the tester, turn potentio-meter VR1 fully
counter-clockwise and then connect the battery to be tested to the
appropriate set of test terminals. If the battery has any usable charge,
the pager motor in the tester will immediately vibrate.

VR1 is then slowly rotated in a clockwise direction just far enough
to stop the vibration. The position of VR1 then indicates the loaded
voltage of the battery on a scale of 1-1.5V (if the battery is connected
to the 1.5V test terminals) or 6-9V (if the battery is connected to the
9V test terminals). A regulated +5.1V rail is generated from the
battery under test with the aid of zener diode ZD1. For 9V tests, a 150O
resistor limits the zener current, while diode D2 protects the circuit
from reverse polarity battery connection. For 1.5V tests, a blocking
oscillator formed by Q1, Q2 and L1 steps up the battery voltage before
it is applied to the regulator. This configuration works reliably with
inputs down to below 0.9V. The output of the oscillator is rectified by
D1 and smoothed by the 33µF capacitor.

The circuit has to survive reverse connection of the battery under
test. This creates a problem, because the LM393 cannot withstand a
voltage more negative than -0.3V at its inputs. Diodes D1 and D2
indirectly protect the non-inverting inputs from negative voltages but
series diodes cannot be used to protect the inverting inputs because of
the unpredictable voltage drop they introduce. The solution used is to
shunt negative voltages at the 1.5V test terminals with diode D3 in
conjunction a 1kO resistor (R1). D3 limits the voltage at its cathode to
about -0.7V, while resistors R2-R4 divide this by three to give no less
than -0.23V at the inverting input (pin 2) of IC1a. When the battery is
connected the right way around, D3 is reverse-biased and R1-R4 form a
voltage divider that applies a quarter of the battery voltage to IC1a’s
inverting input.

Improved Vibrating Battery Tester Circuit

Improved Vibrating Battery Tester Circuit Diagram

Similarly, D4 and R5-R10 protect the inverting input (pin 6) of IC1b
from reverse-connected batteries at the 9V test terminals. However, in
this case only 1/24th of the battery voltage appears at IC1b’s inverting
input. Battery voltages in the range 1-1.5V at the 1.5V test terminals
will therefore produce 0.25-0.375V at the inverting input of IC1a, while
battery voltages in the range 6-9V at the 9V test terminals will
produce 0.25-0.375V at the inverting input of IC1b. Potentiometer VR1
forms part of a voltage divider used to generate a comparison voltage
that is variable over the same 0.25-0.375V range. This is applied to the
non-inverting inputs of both IC1a and IC1b. When the sampled battery
voltage exceeds this comparison voltage, the respective comparator
output swings low, switching on Q3/Q4 to energise the pager motor.

The 68O resistor in the collector circuit of Q4 ensures that higher
battery voltages do not overdrive the motor. When testing an earlier
version of this circuit with batteries that have high internal
impedance, it was found that when VR1 was advanced to the indicating
point, the pager motor slowed down rather than switched off. This
occurred due to a rebound in battery voltage at motor switch-off, which
in turn caused the circuit to immediately switch the motor back on
again. To counteract this effect, a small amount of positive feedback is
applied around the comparators when the motor switches off. The
feedback is disabled while the motor is running so that the indicating
point of VR1 is not affected. This works as follows: when the motor is
running, Q5 is conducting and D5 is reverse biased, so the comparison
voltage at the non-inverting inputs of the comparators is not affected.

If the motor stops running, Q5 switches off and the 2.7MO resistor
pulls the comparison voltage higher via D5 to ensure that the resulting
battery voltage rebound does not restart the motor. Finally, diode D7
prevents reverse breakdown of Q4 in case of reverse battery connection
at the 9V terminals. There is no need for a similar diode in the 1.5V
part of the circuit because 1.5V is well below the reverse breakdown
voltage of Q3. The prototype used “Magtrix” magnetic connectors on short
flexible leads as the 1.5V test terminals. These allow the connection
of AAA, AA, C and D cells but are arranged so
that they cannot be brought closely together enough to connect 9V types.
Unfortunately, magnetic connectors cannot be used for the 9V test
terminals because some brands of 9V batteries have non-magnetic
terminals. A conventional 9V battery snap can be used instead. For blind
people, the knob on VR1 should be pointer-shaped (eg, DSE P-7102) so that the degree of rotation can be easily assessed by touch.

Author: Andrew Partridge
Copyright: Silicon Chip Electronics

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In-Situ Battery Test Probe

This item describes a simple probe that allows in-situ AA and AAA
battery voltage and current drain measurements without removing the
cells from the holder. In use, the probe is simply pushed between the
positive end of one cell and either the negative end of the adjacent
cell or the battery holder terminal. The probe leads are then plugged
into a multimeter set to a voltage range and the device switched on so
that the no-load voltage can be read. Switching the multimeter to a
current range allows the device to power up so that the current drain
can be read. Warning: be sure your meter has a fuse in its current
metering circuit, in case the device being tested has an internal short.
The prototype probe was made by gluing strips of brass shim (using
plastic adhesive) to both sides of a strip of tough, flexible plastic.

Author: Robin Stokes
Copyright: Silicon Chip Electronics

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