Posts Tagged ‘battery capacity tester’

Internal Resistance Tester For Batteries

This circuit is designed to check the condition of lead-acid and gel cell batteries with capacities greater than 20Ah. It switches a load of about 18A at a rate close to 50Hz so that the internal resistance of the battery can be measured using a digital multimeter across the battery terminals. The measured AC voltage in millivolts divided by 10 (ie, a shift of the decimal point) is approximately equal to the battery’s internal resistance in milliohms. As shown, the circuit is quite straightforward and is based on two 555 timer ICs (IC1 & IC2) and power Mosfet Q1. IC1 operates as a monostable timer with a period of 10s.

When switch S1 (Test) is pressed, IC1′s pin 3 output goes high for 10s and this enables IC2 which operates as a 50Hz astable oscillator. IC2 in turn drives power Mosfet Q1 which is connected across the load in series with three 0.22W 50W resistors. IC2 then turns off again after 10s – ie, at the end of the monostable timing period. LED1 provides power indication when the circuit is connected to a battery, while LED2 (green) comes on during the test period. The thermostat is not necessary unless the unit is to be used repeatedly (the Jaycar ST-3823 70°C unit is suitable) and you want to protect the output circuit against overheating.
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Author: Victor Erdstein – Copyright: Silicon Chip Electronics
Read more: http://www.extremecircuits.net/2010/06/internal-resistance-tester-for_14.html

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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.
Author: J. Van der Sterre
Copyright: Elektor Electronics
Read more : http://www.extremecircuits.net/2010/06/hyper-simple-battery-capacity-tester_07.html

Simple but reliable car battery tester

author: Jonathan Filippi

This circuit uses the popular and easy to find LM3914 IC. This IC is very simple to drive, needs no voltage regulators (it has a built in voltage regulator) and can be powered from almost every source.

This circuit is very easy to explain:

When the test button is pressed, the Car battery voltage is feed into a high impedance voltage divider. His purpose is to divide 12V to 1,25V (or lower values to lower values). This solution is better than letting the internal voltage regulator set the 12V sample voltage to be feed into the internal voltage divider simply because it cannot regulate 12V when the voltage drops lower (linear regulators only step down). Simply wiring with no adjust, the regulator provides stable 1,25V which is fed into the precision internal resistor cascade to generate sample voltages for the internal comparators. Anyway the default setting let you to measure voltages between 8 and 12V but you can measure even from 0V to 12V setting the offset trimmer to 0 (but i think that under 9 volt your car would not start). There is a smoothing capacitor (4700uF 16V) it is used to adsorb EMF noise produced from the ignition coil if you are measuring the battery during the engine working. Diesel engines would not need it, but i’m not sure. If you like more a point graph rather than a bar graph simply disconnect pin 9 on the IC (MODE) from power. The calculations are simple (default)

For the first comparator the voltage is : 0,833 V corresponding to 8 V
* * * * * voltage is : 0,875 V corresponding to 8,4 V
…
..
for the last comparator the voltage is : 1,25 V corresponding to 12 V

Have fun, learn and don’t let you car battery discharge…
From: http://www.electronics-lab.com/

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