Automatically disconnect the battery charger after a full charge
It is recommended that car battery chargers be equipped with an automatic switch that turns it on when the battery voltage drops to a minimum value and turns it off when the charge is complete. This is especially necessary when using the battery as a back-up power source or when storing the battery for a long period of time without use to prevent the battery from discharging itself.
Description of the automatic battery charger switch-off
The described automatic battery charger cutout switches the battery on when the battery voltage drops to a defined level and switches it off when the maximum voltage is reached. The limiting voltage for acid car batteries is 14.2 – 14.5 volt and the minimum voltage allowed for discharging is 10.8 volt. It is recommended to limit the minimum voltage to 11.5…12 volts for better safety.
This circuit contains a comparator on transistors VT1, VT2 and a switch on VT3, VT4. The circuit functions as follows. After the battery is connected and the mains voltage is applied, the SB1 “Start” button must be pressed. Transistors VT1 and VT2 lock, opening the key VT3, VT4, which activates the electric relay K1.
Relay its normally closed leads K1.2 turns off the relay K2, normally closed leads of which (K2.1), connect the charger (CU) to the network. Such a complex electrical connection scheme is used for two reasons:
- Firstly, a galvanic isolation of the high-voltage electrical circuit from the low-voltage circuit is created;
- secondly, for electric relay K2 to be activated at maximum battery voltage and deactivated at minimum voltage, because the used electric relay RES22 (Russian Federation passport 4500163) has operating voltage of 12…12.5 V.
Contacts K1.1 of the electric relay K1 are switched to the lower position according to the diagram. During charging the battery potential on resistors R1 and R2 increases, and when reaching the opening voltage on the base of VT1, transistors VT1 and VT2 open, closing the key VT3, VT4.
Relay K1 turns off, including K2. Normally closed leads K2.1 open and disconnect the charger. The outputs of K1.1 are switched to the upper position according to the diagram. Now the potential on the base of the compound transistor VT1, VT2 is caused by the voltage drop on the resistors R1 and R2. During the discharge of the AB the potential at the base of VT1 decreases, and at a certain point VT1, VT2 close, opening the key VT3, VT4. Again the charge cycle takes place. The capacitance C1 is designed to eliminate the noise from the bouncing of the contacts K1.1 during switching.
Setting of the automatic unit for switching off the charger
The adjustment of the device is done without battery and charger. You need an adjustable power supply with adjustment range of 10…20V. It is connected to the terminals of the circuit instead of GB1. Slide resistor R1 to the upper position and slide resistor R5 to the lower position. The source voltage is equal to the battery min voltage (11.5…12 V).
By moving the slider R5 the electric relay K1 and the LED VD7 are switched on. Then, by increasing the power supply voltage to 14,2 … 14,5 volt, by moving the potentiometer slider R1, K1 and LED are turned off. By changing the supply voltage in both directions, it is made sure, that the connection of automatic unit is made at voltage. 11,5 … 12 V, and switching off at 14,2 … 14,5 V. At this point the setting is finished. It is recommended to use multi-turn variable resistors SP5-3 or similar as R1 and R5.
Automatically disconnect the battery charger after a full charge
Recently there was a topic on 4pda
Interested in the topic and a little bit of discussion, I found a comment of the person that this already exists for android This person showed me on ebay such an accessory and I found for ios (search for “rock auto disconnect cable iphone”)
This feature is that the charge reaches 100% and turns off to argue about the feasibility would not want to … of course, many are aware of how the battery and the controller at full charge, but just for information, I can clarify a couple of issues Most frequent repairs of devices – battery, controller (also modem, but another story) … One of the causes of mortality acum and controller – economy (marketing) in manufacturing . . if you often leave the device on charge all night, the controller fails. It certainly works fine in the beginning and well “beats off” the current at 100%, but then the controller fails (it could happen anytime, and may not happen – depends on many factors), the device heats up hell on a charge and this is the beginning of the end … the device ceases to normally hold the charge
In general, it is better and desirable – avoid long charging And this chip should help
Ordered myself and tested on several devices … apparently, the wire disconnects at the first actuation of the controller device that kicks the charge when it reaches 100% On 5s, which is over three years (or even more) and can imagine how many charging cycles, this wire glitches … charges to 90% and stops, while not turning off (light at the connector is lit), but also not charging further . . in this case, we can assume that the real acum capacity is much smaller and the controller is triggered unpredictably On another 5s, iphone 6, ipads 4-6 this wire works perfectly – brought to 100% and the lamp on it goes out – shut down, charging no longer goes You can pull / plug back into the device and the wire will turn off, because the controller again triggered 100% …
To a large extent, I am a staunch oem-shchik and use only native chargers, but I think that this wire is not the worst option from third parties, and even wire this company certified by apple under the program MFi You can try and order … no stores do not allocate – where you want, there you buy (now the price in China from 600r for ios)
I ordered not with auto off, but with indication, although I contacted the support team, they say that there is also auto off, the indicator goes out and auto off, as will be the wire in hand so I will write it down. http://www.woodforddes…aw-led-lightning-cable
The message was edited by Denpech – 06.12.15, 13:06
On my wire: – indicator lights up when connected to the network, – indicator blinks slowly and smoothly when charging the device, – indicator turns off and not lit when you reach 100% of the charge in the device
The second point is a little annoying and distracting if you use the device while charging The indicator color is always green
Simple automatic battery charger
For those who have no time to “bother” with all the nuances of charging the car battery, keep track of the charging current, turn off in time not to overcharge, etc., we can recommend a simple car battery charging circuit with automatic shutdown when the battery is fully charged. This circuit uses one low-power transistor to sense the battery voltage.
Schematic of a simple automatic car battery charger
List of necessary parts:
- R1 = 4.7 kohms;
- P1 = 10K trim;
- T1 = BC547B, KT815, KT817;
- Relay = 12V, 400 ohms, (can be automotive, for example: 90.3747);
- TR1 = secondary voltage 13,5-14,5 V, current 1/10 of the capacity of the battery (for example: battery 60A/h – current 6A);
- Diode bridge D1-D4 = with current equal to the nominal transformer current = at least 6A (e.g. D242, KD213, KD2997, KD2999 …), mounted on a radiator
- Diodes D1 (in parallel with the relay), D5,6 = 1N4007, KD105, KD522 ..;
- C1 = 100uF/25V.
- R2, R3 – 3 kOhm
- HL1 – AL307G
- HL2 – AL307B
The circuit has no charging indicator, current monitor (ammeter) and charging current limiter. If you want, you can put an ammeter on the output in the gap of any of the wires. LEDs (HL1 and HL2) with limiting resistors (R2 and R3 – 1 kOhm) or bulbs parallel to C1 “network” and to the free contact RL1 “end of charge”.
Modified circuit.
The current equal to 1/10 of the capacity of the battery is selected by the number of turns of the secondary of the transformer. When winding the secondary of the transformer it is necessary to make several taps to select the best version of the charging current.
Charging of the automotive (12 volt) battery is considered completed when the voltage on its terminals reaches 14.4 volts.
The cut-off threshold (14,4 volt) is set with the trimmer resistor P1 when the battery is connected and fully charged.
When charging a discharged battery, the battery voltage will be about 13V, while charging, the current will decrease and the voltage will increase. When the battery voltage reaches 14.4 volts, transistor T1 will disable relay RL1 the charge circuit will be broken and the battery will be disconnected from the charging voltage from diodes D1-4.
When the voltage drops to 11.4 volts, charging resumes, this hysteresis is provided by diodes D5-6 in the emitter of the transistor. The circuit threshold becomes 10 + 1.4 = 11.4 volts, which can be considered to automatically restart the charging process.
Such self-made simple automatic car charger will help you to control the process of charging, not to trace the end of charging and not to overcharge your battery!
Materials from the site: homemade-circuits.com
Another version of a circuit for a 12 volt car battery charger with automatic shutdown at the end of charging
The circuit is a little more complicated than the previous one, but with a clearer triggering.
Handmade crafts for car enthusiasts
Automatic battery disconnection or attachment to the charger
The circuit is a system of automatic shutdown of the battery when fully charged, that is, it is not quite a battery charger, of course if you complement it with a transformer and rectifier, we will get a full-fledged battery charger.
The original circuit was subjected to some changes the board finalized in the course of testing the final version of the board can be downloaded at the end of the article.
Let’s look at the circuit.
As you can see it is painfully simple and contains only one transistor, an electromagnetic relay and some small stuff. I also have a diode bridge at the input and a primitive protection against polarity reversal (these nodes are not shown in the schematic).
The circuit input is a constant voltage charger or any other power source, here it is important to note that the charging current must not exceed the allowable current through the relay contacts and the current triggered by the fuse. In my case the circuit is 8 amps.
How it works – when power is applied to the input of the circuit the battery is being charged, the circuit has a voltage divider (R2, R3, R4) which monitors the voltage directly on the battery.
As the battery charges, the voltage on the battery will rise, as soon as it becomes equal to the circuit’s trigger voltage, which can be set by turning a trim resistor, the stabilizer will trip, signaling the base of the low-power transistor and it will trip.
Since the electromagnetic relay coil is connected to the collector circuit of the transistor, the latter will also be triggered and these contacts will open, and further power supply to the battery will stop.
At the same time the second light-emitting diode will go off, notifying you that the charging is over.
There is another LED in the circuit, it is permanently lit, it is essentially an indicator of voltage on the board.
As I said before, the divider monitors the voltage of the battery directly, so if the battery connected to the charger is discharged to a certain value, the circuit will automatically go off and the charging process will resume.
Since the divider is connected directly to the battery it will discharge it, but the discharge current is so small that it can be ignored.
To tune the circuit, a high capacity capacitor is connected to its output, we have it in the role of a fast charging battery. I took ionistors connected in series and connected them instead of the capacitor.
If you take a capacitor, its voltage must be 25-35 volts, first connect the ionic cells (in my case) or the capacitor to the output of the circuit, observing the polarity,
At the end of the charge first disconnect the charger from the network, then the battery, otherwise the relay will be false. In this case nothing bad happens, but the sound is unpleasant.
Next, we take any regulated power supply, such as the lab unit and set on it the voltage to which it will charge our battery and connect the unit to the input of the circuit.
Slowly turn the trimmer resistor until,
until the red LED goes off, then make one full turn of the trimmer in the opposite direction, since the circuit has some hysteresis.
Now let’s check the operation
The voltage on the ionistors or capacitor, will show the multimeter when it reaches the threshold value, the system will turn the power off.
If the voltage drops on the battery, the circuit will work again and charge the battery again to a predetermined value.
Battery charger with automatic shutdown
The device is designed for charging the 6 volt sealed lead battery of a child’s electric motorcycle, but with minimal modifications it can be used to charge other types of rechargeable batteries (batteries), with any voltage, for which the end of the charge is a certain voltage level. In this device the charging of the battery stops when the terminal voltage reaches 7.3V. Charging is carried out with an unstabilized current, limited at 0,1C by resistor R6. The voltage level at which the device will stop charging is set by VD1 with an accuracy of a tenth of a volt.
The “heart” of the circuit is an operational amplifier (Op-Amp), turned on as a comparator, and connected with the inverting input to the reference voltage source (R1-VD1 chain), and not inverting to the battery. As soon as the battery voltage exceeds the reference voltage, the comparator will switch to a single state, transistor T1 will open and relay REL1 will disconnect the battery from the voltage source, simultaneously supplying a positive voltage to the base of transistor T1. Thus T1 will be open and its state will no longer depend on the voltage level at the output of the comparator. The comparator itself is covered by positive feedback (R7), which creates hysteresis and leads to abrupt, jumpy switching of the output and opening of the transistor. This gets rid of the disadvantage of similar devices with mechanical relays, in which the relay makes an unpleasant rattling sound because the contacts balance on the switching edge, but the switching does not happen yet. In the case of a mains power outage, the device will resume operation as soon as it is available and will not allow the battery to be overcharged.
The device is assembled from available parts, starts working immediately, and does not need to be adjusted. Cut off voltage depends only on the parameters of the regulator. DT specified in the schematic, can work in the range of supply voltages from 3 to 30 volts, and when you connect the battery with a different voltage, for example 12V, you must pick up a regulator for the voltage of a charged battery (14.4V).
The device is assembled according to the diagram and the figure of the circuit board, tested in operation.
Automatic disconnection of any car charger when charging is complete, circuit
Hello all, today consider a few universal circuits that will disable the charger when the battery is fully charged, in other words, the implementation of these circuits can build an automatic battery charger or retrofit the function of automatic shutdown of industrial charging.
I want to clarify one thing, if the charger operates on the principle of stable current – stable voltage, then there is no point in using the auto-disconnect function because naturally as the battery is being charged the current in the circuit will drop and at the end of the charge it is zero. The circuits we are going to look at today are designed to work with automotive lead-acid batteries, although they can work with any charger without any modification of the latter.
Let’s start with simple circuits…
The first version is built with just one transistor, the switching element in the circuit is a relay with a coil voltage of 12 volts.
The contacts used are those that are closed without power to the relay
A resistor divider or a variable resistor sets the desired voltage, the bias at the transistor base, the transistor turns on and supplies power to the relay winding, so that the relay turns on by opening a contact which was closed at rest and through which the charging current was flowing. Using a trim resistor we can set the voltage at which the transistor is triggered.
To adjust the circuit it is convenient to use a regulated power supply, where you need to set the voltage to about 13.5-13.7 volts, which is equal to the voltage of a fully charged car battery.
Then slowly turning the trimmer resistor to get the transistor and therefore the relay to operate at the set voltage. Now check the circuit again, let’s say at the beginning of charging voltage on the battery 12 volts, as the charge it increases and upon reaching the threshold of 13.5 volts relay will work by disconnecting the charger from the network.
By the way, you can connect the relay in the following way, in this case the charger is not disconnected from the mains, but simply the output voltage disappears and the charging process will stop, in this case the relay contacts should be designed for currents one and a half times the maximum output current of the charger.
Transistor literally any reverse conductivity, I advise to take medium power transistors like BD139, diodes in the emitter circuit of the transistor are not critical too, circuit current consumption is only 10-20 milliamps, but the circuit has some disadvantages.
For example, low noise immunity, which can cause false triggering of relays and low accuracy due to the lack of a reference voltage source and other stabilizing nodes.
By adding a stabilitron in the key base circuit, we can solve these problems and it will be possible to set the desired pickup voltage quite accurately.
I suggest using a multi-turn trimmer resistor for tuning. The diode VD1 protects the transistor from self-induction in case the relay opens.
We set the circuit exactly as in the first variant, the lamp simulates the charging process and is connected instead of the battery, when a certain threshold is exceeded, the relay goes off and the lamp goes out.
The second circuit is built on the basis of any timer NE555, this version is similar to the previous, circuit NE555 in his design contains two comparators, low reference voltage forms a bridge, the threshold is set trimmer resistor, as soon as the battery voltage will be equal to the threshold, on the output of the timer will get a high level, as a result of which triggered the transistor.
In this variant use those relay contacts which are in open state without power supply. During the setting the point “A” is opened from the output contact and connected to the plus of the charger. A lamp is connected to the output contact of the relay, the second lead of the lamp is connected to the power supply mass.
In both circuits, the threshold can be set in the range from 13.5 to 14 volts, voltage fully charged car battery is from 12.6 to 12.8 volts but when the engine comes on voltage reaches 14.5 volts, so that a small overcharge the battery does not hurt.
A similar circuit can be built on the basis of a comparator or an operational amplifier in comparator connection, the principle of operation is the same as in the case of implementation of the NE555 timer. In the same article, the simplest and most accessible options are given.
All printouts in .lay format can be downloaded for repetition.
