Lead-Acid Charger Signals End of Charge

Chester Simpson
National Semiconductor, Santa Clara, CA

The battery charger lead acid in Figure, works with any gel or wet cell, lead, 12V battery. The charger includes adequate temperature compensation for output voltage of the charger, and a detector which indicates when the battery is fully charged.

The best battery chargers for lead-acid battery is a voltage source current limited power sources on the battery until it reaches the point of tension. The shipper must provide enough current to keep the battery voltage to this value. To 12V, the lead-acid batteries, a voltage magnitude of approximately 13.8 V  at 25 ° C is typical. However, the optimal set point voltage call depends on the temperature. Battery manufacturers recommend a CT scan of 22 mV /°C, so the charger voltage setting of the TC tracks the battery.

You can determine the state of charge of a lead-acid battery voltage and load current. When charging the battery with a voltage source set to 13.8 V, the charge current gradually decreases to a very low value when the battery is fully charged. The design in Figure includes a detection circuit that turns on full charge LED when the current falls below this threshold.

This design features a 12V charger, 0.5A wall transformer and a voltage regulator LM2941CT, IC2. The wall transformer provides regulated DC voltage of IC2, the circuit used to charge the battery and keep tension on 13.8V. R3, R4, and D3 through D12 set the output voltage regulator. R4 should be adjusted for an output voltage of 13.8 V with the battery disconnected. An important feature of any wall transformer load regulation is poor. For example, the transformer of Figure  set to 12V when charged to 0.5V,but approximately 17 to 18 V without load. The design takes advantage of this feature, because it means that IC2 not require heat sink.

D12 D3 through negative-TC set out required to match the voltage of the battery terminal. Measurements of some 1N4148 diodes at 1 mA show a TC of 2.2 mV / °C, so 10V of these diodes in series to provide the necessary 22 mV / °C. R5 and D13 indicate the presence of power or when the battery is connected to the output and provide the minimum load required for IC2. Stabilizes C1 for IC2.

A battery has a voltage of about 10 to 12V. If you connect a battery charger output, IC2 fully active (saturated fatty acids) the pass transistor. Under this condition, all power leads IC2 possible to try to force the battery voltage to the reference point 13.8. Thus, while the battery is below 13.8 V acts, IC2 as a power source. The maxim that the wall transformer may be provided in the voltage determines the maximum load current.

As the battery is charged and its voltage increases, the amount of current that the transformer wall can provide decreases. In this case, a battery voltage of 11.5 V and a corresponding output voltage 12V, maximum load current of approximately 0.5 mA is available. At the time of the battery reaches 13.8 V,a maximum of only about 250 mA. IC2 remains fully until the battery voltage reaches 13.8V. So IC2 reduces the charge current as necessary to maintain this battery voltage. At this point, IC2 is operating in a constant voltage mode. While IC2 is in the current mode of code, the voltage drop across IC is 250 mV, which means that the power dissipation is less than 0.2 W. Because of this low power dissipation, IC2 requires no heatsink.

While a lead-acid battery is charged at a constant voltage, load current continuously decreases until it reaches its final value, usually about 1% of nominal ampere-hour battery. By adjusting R2, this charger can be calibrated to correctly detect a fully charged battery with a capacity of up to about 10 Ahr. You can measure the load current and the voltage drop across R1. D1 turns on and shunts current around R1 when the voltage exceeds 0.2 V, which minimizes power dissipation in R1. Because D1, the voltage measured across R1 is correct only when the load current is less than 0.2 V. However, since the end of his tenure the detection occurs in the currents below 0.1 A, this range of measurement is more than enough.

IC1A, a differential amplifier with unity gain, shifts the voltage drop across R1 to produce a ground signal is concerned. IC1B compares this signal, which is proportional to the load current to a reference voltage set R2. When the load current drops low enough that the voltage at pin 6 of IC1B falls below at pin 5, the oscillations of high-performance and D2 turns on to indicate that the battery is fully charged. The best way to calibrate the end-of-charge detection circuit to let the battery is fully charged and then adjusted R2 D2 only to light up.

Car Battery Charger

This charger quickly and easily charge most any lead acid battery. The charger delivers full current until the battery power falls to 150 mA. At this time, a lower voltage is applied to finish and avoid overload. When the battery is fully charged, the circuit is turned off and lights a LED, which indicates that the cycle has finished.

Schematic:

 

Parts:
R1 .................................. 500 Ohm 1/4W
R2 .................................. 3K,  1/4 W
R3 .................................. 1K 1/4 W
R4 .................................. 15 Ohm 1/4 W
R5 .................................. 230 Ohm, 1/4 W
R6 .................................. 15K, 1/4 W
R7 .................................. 0.2 Ohm, 10 W
C1 .................................. 0.1uF / 25V (ceramic capacitor)
C2 .................................. 1uF / 25V (electrolytic capacitor)
C3 .................................. 1nF / 25V (Ceramic Capacitor)
D1 .................................. 1N457
Q1 .................................. 2N2905 (PNP transistor)
U1 .................................. LM350 (regulator IC)
U2 .................................. LM301A (operational amplifier)
S1 .................................. Normally Open switch button (NO)
MISC ............................ Cable of the Board, the heat sink for U1, Case, Poles or crocodile clips for output

Notes:

1. The circuit was designed to be powered by a power source, so no transformer, rectifier, filter capacitors or the schematic. There is no reason why you can not add them.
2. A heat sink is required for U1.
3. To use the circuit, connected to a power supply / plug it in. Then connect the battery to charge to the output terminals. All you have to do now is push S1 (the "start" switch), and wait until the final circuit.
4. To use the charger without having to provide an external power source, use the following circuit.
   
   
    
   Parts:
   C1 .......................... 6800uF / 25V electrolytic Capacitor
   T1 ..........................  transformer 15V, 3A
   BR1 ........................ 50V 10A (rectifier bridge)
   S1 ........................... 5A SPST Switch
   F1 ........................... 250V, 4A 
5. The first time you use the circuit, you should check up on it from time to time to ensure it works properly and the battery is being over charged.Related Circuits

Warning Broken Connection Charger

Detects whether the device is not connected properly to your offer
Suitable for battery chargers, portable supplies, etc.

Circuit diagram:

Parts:
R1______________10K, 1/4W
R2_______________1K, 1/4W
R3_______________1K, 1/4W Resistor (Optional Notes, see)

D1, D2________1N4007 1000V 1A Diodes
Red D3______________LED (optional Notes, see)

Q1, Q2_________BC557 45V 100mA PNP Transistors

BZ1___________Piezo probe (oscillator incorporating 3KHz)

Device Purpose:
The above circuit can be used to detect if the load of the battery charger or plug-in supply adapter is not connected properly. The load can be a set of batteries to charge, or any other type of battery or DC low voltage operation of the device.
The safety circuit can operate in a range of 3 to 15V and a maximum of 1A. current provided the voltage is about one volt higher than the voltage required by the load.

Circuit Operation:
The circuit is inserted between the supply and load, therefore, until a leak of the load current of at least 100μA is flowing toward the load, D1 and D2 performed. The voltage drop (about 1 V) available through the diode, Q2 units in the conduct and, consequently, Q1 is cut.
If there is no sensible load is connected to the output of the circuit will cut Q2, Q1 will conduct and the piezo-siren will beep.

Notes:
An optional LED and its series resistance limit can be connected in parallel to BZ1, as shown in dotted lines in the circuit diagram.
In this case you can omit the piezo tube to get a visual warning only.

Cut Out Battery Charger

Here is the outline for the autoloader I've been using for the car battery of my children. The charger is a small molded unit that probably provides no more than an amp and this circuit has much more problems. No current limit is provided by this circuit - is based on the charger for that. The circuit can be modified to provide more current by lowering the 470 and 330 ohm resistors in the base circuit of 5195 and 10k in the collector 4401. A relay could also be used in place of the pass transistor.

That's how it works: When the battery voltage is low, the voltage at the base of the first 2N4401 (right) is not enough to turn and the second 2N4401 is biased by the 10k resistor. The power transistor is on and LED lights. When the battery is fully charged, the voltage exceeds a somewhat arbitrary "over-voltage" value slightly below 14 volts and the regulator is disconnected. The 470k feedback resistor gives the circuit some hysteresis so it will not turn back on until the battery voltage drops below 13.5 volts. When the battery is nearing full charge, the light starts to blink and after a few hours the only light that comes on from time to time. This occasional overvoltage jolt that seems to keep the batteries in great shape

Small Battery Capacity Tester

I have a client who makes use of lots of batteries. His sells a tool which is powered by a 3v lithium coin cell & they sells thousands of them. It seems that plenty of of the batteries they has been importing from China have a milliamp-hour capacity which is much lower than quality batteries from US or Japan manufacturers. In plenty of cases the capacity was less than half of what it was suppose to be.
His measurement method was crude. They would insert of the batteries in to his product & time how long it powered it before dying. Plenty of fresh Chinese batteries lasted only half as long as batteries from Energizer or Panasonic. But, his check can take a long time. In of his products it takes a full month to complete a check. They wanted a more correct measuring method & they also wanted that would tell him the capacity of the battery in a much shorter time period. I proposed an automatic tester which could give him some check results overnight. With the tool I proposed, they could check a few sample batteries against some standard quality batteries. In the event that they tested OK, they could then approve them for his product.
The only truly correct way to measure the current capacity of a battery is by connecting the battery to a constant current load & measure how long the battery can maintain that current before its voltage drops below a recommended âcutoffâ point. The circuit below is designed to do this type of check.

designed by David A. Johnson, P.E.

The circuit is powered by a +5v source. A low power 5v regulator powers the circuit from a 9v battery. The left side of the circuit forms a constant current sinking circuit. A 1v reference voltage is produced with a voltage divider. The FET transistor is fed the exact amount of voltage to maintain this one volt drop across the 200 ohm resistor. Thus, battery current is drawn at five milliamps for the part values chosen. By changing the 200 ohm resistor to some other value, other check currents can be produced. The check current is: 1/R.
  
The middle section of the circuit is configured as a voltage comparator. With the part values chosen, the comparator will change state when the battery voltage drops below two volts.
A flip/flop is used to start & automatically cease the check. When the pushbutton switch is pressed the flip/flop starts the check. When the battery voltage drops below the cutoff voltage, the flip/flop changes state & stops the check.
To measure the elapsed check time, I use a modified wrist watch. The battery has been removed & wires have been connected to the watchâs battery holder. The watch starts operating when the check is jogging & stops after the check. You set the watch at 12:00 midnight to start a check. At the finish of the check, the watch retains the elapsed time. If a wrist watch containing a day & date display is used, the check can last as long as 31 days.
The tester can check  any little battery, from little hearing aid cells to larger coin cells. However, the maximum load check current ought to be kept below 100ma with parts indicated. With some modifications & part changes, the same method could be scaled up to check much larger batteries.
Keep in mind that due to the internal resistance of plenty of batteries, the elapsed check time for a shot overnight check may be much shorter than expected. As an example, a quality lithium coin cell might have a specified capacity of 220ma-hours but will reach the 2v cutoff voltage in only about twenty hours. This would lead to think that the capacity would only be twenty x five = 100 milliamp-hours. However, when the check is done at 100 microamps, the battery may last months. The idea is to compare the check result times between quality batteries to those of unknown origins.

Two 12v Battery Isolator Circuit with a LTC4412

designed by David A. Johnson, P.E.
Linear Expertise has announced a tidy small chip (LTC4412). It's been designed to be used together with an outside P-channel power FET, to form an ideal diode function with a low 0.05v voltage drop. The chip monitors the voltage on either side of the FET.
As long as the voltage on the drain side is greater than the source side, the FET is turned on. The tool controls the voltage at the gate of the FET to maintain a voltage drop of about 0.05 volts across the FET. When the current direction tries to reverse, the hobby circuit senses the voltage polarity change and turns off the transistor, blocking the current. This action mimics how an ideal diode would function. The circuit below shows how this tool can be used with a FET from International Rectifier, to form an ideal diode with a rating of twenty amps and a voltage up to 28v.
How are these devices used? Letâs suppose you owned a recreational vehicle (RV). When the RVs engine is running, you would like the engineâs alternator to charge both the engineâs battery and the battery used in the RV. But, when the engine is off you donât require the 12v RV lots to pull current from the engine battery. Likewise, you donât require to pull current from the RV battery when the engine is running. way to solve this issue is with the use of diodes. The alternator output of the engine is fed to the anode side of power diodes. diode routes current to the engineâs battery while the second diode routes current to the RV battery.
The diodes block any current path between the batteries. In a traditional circuit, high current diodes would be used. But, since there could be a sizeable current passing through the diodes, they must be mounted onto a immense heat sink, to be able to handle the power dissipated in the diodes. The circuit shown below is much more efficient. It shows this battery isolator using ideal diodes. With the parts shown, the electronic circuit ought to be able to handle 60 amps of current to each battery.
source: www.discovercircuits.com

Lithium Ion Battery Charger Powered by Circuit Solar

The circuit below feeds a control current and voltage of a lithium ion battery 3.6v. The current is limited to 300 mA and the voltage is limited to 4.2 volts. The circuit uses a LTC1734 IC from Linear Technology. No diode is needed between the circuit and a 6-volt solar panel.
The circuit below feeds a control current and voltage of a lithium ion battery 3.6v. The current is limited to 300 mA and the voltage is limited to 4.2 volts. The circuit uses a LTC1734 IC from Linear Technology. No diode is needed between the circuit and a 6-volt solar panel. Some very nice 6-volt solar panels are available in http://www.plastecs.com Su-SP6 200-12 rods about 1 watt, while the Service Pack 6-300-12 can produce about 2 watts. Assuming that a sunny day, 6 hours, 2-watt panel will pump about 1.8 amp-hour battery.