12V Battery Charger Circuits using LM317, LM338, L200, Transistors. 12v battery diy

How to Wire 12V Batteries in Series Parallel (w/ Photos!)

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In this tutorial, I’ll show you step-by-step how to wire batteries in series and parallel, as well as how to combine the two to create series-parallel combinations. I’ll also cover when to use series or parallel wiring.

Click on a wiring method to jump to its instructions:

How to Wire Batteries in Series

Wiring batteries in series sums their voltages and keeps their amp hours the same. It’s particularly useful for wiring two 6V lead acid batteries, or four 3.2V lithium cells, to make a 12V battery.

Series connections can also be used to wire multiple 12V lead acid or lithium batteries together to make a 24V, 36V, or 48V battery bank, which is useful in DIY and off-grid solar applications.

Parts Tools

  • 2 identical batteries — I’ll be using Chins 12V 100Ah LiFePO4 Batteries
  • 1 battery cables — the number of cables you need is the 1 less than the number of batteries you’re wiring in series
  • Screwdriver or ratchet — for tightening bolts
  • Optional: Multimeter — for checking battery bank voltage
battery, charger, circuits, using, lm317, lm338

Step 1: Connect the Negative Terminal of One Battery to the Positive Terminal of Another

Connect the battery cable to the negative terminal of one battery. To do so, use a ratchet or screwdriver to unscrew the terminal’s bolt. Thread the cable’s ring terminal through the bolt, then screw the bolt back on the terminal.

Note: Some people prefer to use black cables for series connections, others prefer red. I prefer black, but there’s no right or wrong choice. Just use the color of cable you prefer or have on hand.

Connect the other end of the battery cable to the positive terminal of another battery.

That’s it! Your batteries are now wired in series. You’ll often hear connected batteries referred to as a “string” of batteries. So now you have a series string of 2 batteries.

If you want, check your battery bank’s voltage with a multimeter. Because I wired two 12V batteries in series, I expect to measure a voltage of around 24 volts. (In reality, a 12V LiFePO4 battery’s resting voltage will usually be closer to 13-13.5 volts, so I’d expect a voltage of around 26-27 volts.) I got 26.4 volts, which is exactly in line with expectations.

Check! My two 12V 100Ah batteries are now wired in series, resulting in a 24V 100Ah battery bank.

Note: If you don’t want to bother with wiring batteries yourself, many brands offer pre-made 24V batteries and 48V batteries.

Step 2: Repeat as Needed

If your battery allows it, you can repeat the above steps to connect more batteries in series.

You can wire three 12V batteries in series to create a 36V battery bank. Once again, just connect the negative terminal of your 2-battery series string to the positive terminal of the third battery.

And, once again, you can use a multimeter to check that the voltage is around 36 volts. I got 39.7 volts, so I know my 3 batteries are correctly connected in series.

You can wire a fourth battery in series following the same steps. My batteries can handle up to 4 wired in series, so let’s do one last one for good measure.

And we’ll check the battery bank’s voltage with a multimeter, expecting a voltage of around 48 volts. I got 52.9 volts, so we’re good to go.

Done! Like I said, you can wire as many in series as your batteries allow for. LiFePO4 batteries are often limited to 4 batteries in series to protect the BMS. However, there are some that can’t be wired in series, such as the Renogy 12V 100Ah Smart Lithium Iron Phosphate Battery. Be sure to check!

How to Wire Batteries in Parallel

Wiring batteries in parallel sums their amp hour capacities and current limits and keeps their voltage the same.

Parallel wiring is useful when you want to keep your battery voltage the same — such as when you’re powering 12V devices directly off a 12V battery — while increasing runtime and current limits.

Parts Tools

  • 2 identical batteries
  • 2 battery cables — for 2 batteries you need 2, for 3 batteries you need 4, for 4 batteries you need 6. Formula: 2 (x – 1), where x is the number of batteries.
  • Screwdriver or ratchet — for tightening bolts

Step 1: Connect the Positive Terminal of One Battery to the Positive Terminal of Another

Use a battery cable to connect the two batteries’ positive terminals together. I recommend using a red battery cable for this connection.

Step 2: Connect the Negative Terminal of the First Battery to the Negative Terminal of the Other

Use a second battery cable to connect the two batteries’ negative terminals together. I recommend using a black battery cable for this connection.

Your 2 batteries are now wired in parallel. This is what people mean when they say you wire batteries in parallel by connecting positive to positive and negative to negative.

In this example, I wired two 12V 100Ah batteries in parallel to get a 12V 200Ah battery bank. Because parallel connections don’t affect voltage, there’s no way to use a multimeter to check the connection.

If you want, you can do a capacity test. That requires some extra equipment, though, so I won’t cover that here.

Note: If you don’t want to wire batteries in parallel yourself, many battery brands also sell 12V batteries in 200Ah, 300Ah, and 400Ah sizes.

Step 3: Repeat as Needed

If your batteries allow it, you can repeat the above steps to connect even more batteries in parallel.

To connect a third, again wire positive to positive and negative to negative. This results for me in a 12V 300Ah battery bank.

To connect a fourth, repeat the connections. Now I have a 12V 400Ah battery bank.

How to Wire Batteries in Series-Parallel

You can use a combination of series and parallel connections to make a battery bank with your desired voltage and capacity. There are many different series-parallel wiring configurations you can choose from. I’ll cover the simplest in this tutorial.

Series-parallel wiring can get confusing. It pays to research and ask around for help on online forums if you’re unsure how your specific setup should be wired.

Parts Tools

  • 4 identical batteries
  • 4 battery cables — the exact number you need will depend on your wiring configuration
  • Screwdriver or ratchet — for tightening bolts
  • Optional: Multimeter — for checking battery bank voltage

Step 1: Wire Your Batteries in Series Strings of Equal Length

Decide what voltage you want your battery bank to have. For this example, I’ll go with 24 volts. I’m using 12V batteries, so that means each of my series strings needs to be 2 batteries in length.

Wire your batteries in series strings of equal length. I have 4 batteries, so I wired them in 2 strings, each of which has 2 batteries wired in series.

If you want, check the voltage of each string with a multimeter. In this case, I’d expect mine to read something close to 24 volts.

Now I have two 24V 100Ah battery banks, and I can connect them in parallel to expand their amp hour capacity.

Step 2: Wire Your Series Strings in Parallel

Wire the 2 series strings in parallel by connecting positive to positive and negative to negative.

If you want, check the voltage of your finished battery bank with a multimeter. I wired two 24V 100Ah battery banks in parallel to get a 24V 200Ah battery bank, so I expect a voltage of around 24 volts. I got 26.4 volts, which is exactly as expected.

Done! You can use these principles to wire even more batteries into different series-parallel combinations.

Note: A shorthand that people use to describe a battery bank’s wiring configuration is to list the number of batteries wired in series followed by the letter “s” and then the number of batteries wired in parallel followed by the letter “p”. For instance, I just created a 2s2p battery bank. Some LiFePO4 batteries can be wired into as big as 4s4p configurations.

How Wiring in Batteries in Series Parallel Affects Voltage Capacity

Wiring batteries in series sums their voltages while keeping their amp hour capacity the same. Wiring two 12V 100Ah batteries in series gives you a 24V 100Ah battery bank.

Wiring batteries in parallel sums their amp hour capacities while keeping their voltage the same. Wiring two 12V 100Ah batteries in parallel gives you a 12V 200Ah battery bank.

Amp Hours vs Watt Hours

Amp hours (Ah) and milliamp hours (mAh) are commonly used to describe battery capacity. However, the total amount of energy a battery can deliver is best expressed in watt hours (Wh), which is equal to a battery’s amp hours times its voltage.

Formula: watt hours = amp hours × voltage

What this means is that, regardless of how you wire your batteries together, you’re increasing the total watt hours of your battery bank. A 24V 100Ah battery bank and a 12V 200Ah battery bank both have 2400 watt hours.

24V × 100Ah = 2400Wh 12V × 200Ah = 2400Wh

You can use our battery capacity calculator to calculate the amp hour or watt hour capacity of your battery given how many batteries you have wired in series and parallel.

When to Wire Batteries in Series vs Parallel


  • You want to save money on wiring and equipment such as solar charge controllers. Series wiring increases voltage which helps keep current (amperage) low. Wire and other electrical equipment get more expensive the higher their current ratings get. That being said, electrical equipment also has voltage ratings, so be careful not to exceed these, either. Voltage ratings tend to be higher, though, and you don’t as often need to worry about them in DC electrical systems.
  • You can raise voltage while still powering your devices. Often, you’ll want to power a device directly off the battery. For instance, you may want to connect 12V LED lights or a 12V inverter to your 12V battery. Devices have acceptable voltage ranges — 12V LED lights might be able to accept 11-15V, for instance — so wiring in series is best when you can raise battery voltage without exceeding the acceptable input voltages of your devices. If you’re connecting your batteries to a solar charge controller, also check that the charge controller is rated for the higher battery voltage.


  • You want to increase runtime while keeping your battery bank voltage the same. Parallel wiring increases amp hour capacity while keeping voltage the same, meaning your battery bank will last longer while still being able to power the same devices.
  • You want to increase your battery’s max charge and discharge rates. Batteries have recommended charge and discharge rates, which are based on their amp hour capacity. For instance, most 100Ah LiFePO4 batteries have a recommended max continuous charge rate of 50 amps, and most 100Ah lead acid batteries have a recommended max continuous charge rate of 30 amps. Because these rates are based on battery amp hours, you can increase them by adding more batteries in parallel. You can estimate charge time using our battery charge time calculator.
  • You want to lower your battery’s C-rate. How fast a battery charges and discharges can be expressed as something called a C-rate. Different types of batteries have different recommended C-rates for charging and discharging, and exceeding these can shorten your battery’s lifespan or affect how many amp hours the battery actually outputs. You can lower your battery’s C-rate by expanding your battery bank’s amp hour capacity while keeping charing and discharging currents the same.

V Battery Charger Circuits [using LM317, LM338, L200, Transistors]

In this article we will be discussing a list of simple 12V battery charger circuits which are very easy and cheap by its design yet extremely accurate with its output voltage and current specs.

All the designs presented here are current controlled meaning their outputs will never go beyond a predetermined fixed current level.

UPDATE: Looking for a high current battery charger? These powerful Lead Acid battery charger designs might help you to fulfill your requirement.

Simplest 12 V Battery Charger

As I have reiterated in many articles, the main criteria to charge a battery safely is to keep the maximum input voltage slightly below the full charge spec of the battery, and keep the current at a level that does not cause warming of the battery.

If these two conditions are maintained you can charge any battery using a minimal circuit as simple as the following one:

In the above simplest layout the 12 V is the RMS output of the transformer. That means, the peak voltage after rectification will be 12 x 1.41 = 16.92 V. Although this looks higher than the 14 V full-charge level of the 12 V battery, the battery is not actually harmed due to the low current specification of the transformer.

That said, it is advisable to remove the battery as soon as the ammeter reads near zero volts.

Auto Shut-OFF: If you want to make the above design to auto shut off when the full charge level is reached, you can easily accomplish this by adding a BJT stage with the output as shown below:

In this design, we have used a common emitter BJT stage which has its base clamped at 15 V, which means that the emitter voltage can never go beyond 14 V.

And when the battery terminals tend to reach above the 14 V level, the BJT gets reversed biased and simply goes into an auto shut down mode. You can tweak the 15V zener value until you have around 14.3 V at the output for the battery.

This transforms the first design into a fully automatic 12 V charger system, which is simple to build yet entirely safe.

Also, since there’s no filter capacitor the 16 V is not applied as a continuous DC, rather as 100 Hz ON/OFF switching. This causes less stress on the battery, and also prevents sulfation of the battery plates.

For High Current Battery Charging, the above Schematic can be Modified as Shown Below:

Why Current Control is Important (Constant Current Setup)

Charging any form of chargeable battery can be critical and involves some attention to be paid. When the input current at which the battery is being charged is significantly high, adding a current control becomes an important factor.

We all know how Smart the IC LM317 is and it’s no surprise why this device finds so many applications requiring precise power control.

The Current Controlled 12V Battery Charger Circuit Using IC LM317 presented here shows how the IC LM317 can be configured using just a couple resistors and an ordinary transformer bridge power supply for charging a 12 volt battery with utmost accuracy.

How it Works

The IC is basically wired in its usual mode where R1 and R2 are included for the required voltage adjustment purpose.

The input power to the IC is fed from an ordinary transformer/diode bridge network; the voltage is around 14 volts after the filtration via C1.

The filtered 14 V DC is applied to the input pin of the IC.

The ADJ pin of the IC is fixed to the junction of the resistor R1 and the variable resistor R2. R2 can be fine set for aligning the final output voltage with the battery.

Without the inclusion of Rc, the circuit would behave like a simple LM 317 power supply where the current wouldn’t be sensed and controlled.

However with Rc along with BC547 transistor placed in the circuit at the shown position makes it capable of sensing the current that’s being delivered to the battery.

As long as this current is within the desired safe range, the voltage remains at the specified level, however if the current tends to rise, the voltage is withdrawn by the IC and dropped, restricting the current rise any further and ensuring appropriate safety for the battery.

The formula for calculating Rc is:

R = 0.6/I, where I is the maximum desired output current limit.

The IC will require a heatsink for operating optimally.

The connected ammeter is used for monitoring the charge condition of the battery. Once the ammeter shows zero voltage, the battery may be detached from the charger for the intended use.

battery, charger, circuits, using, lm317, lm338

Parts List

The following parts will be required for making the above explained circuit

  • R1 = 240 Ohms,
  • R2 = 10k preset.
  • C1 = 1000uF/25V,
  • Diodes = 1N4007,
  • TR1 = 0-14V, 1Amp

How to Connect pot with LM317 or LM338 Circuit

The following image shows how the 3 pins of a pot needs to be correctly configured or wired with any LM317 voltage regulator circuit or a LM338 voltage regulator circuit:

As can be seen the center pin and any one of the outer pins is selected for connecting the potentiometer or the pot with the circuit, the third unconnected pin is kept unused.

Practical Results

The above LM317 battery charger circuit was suitably modified using fixed resistors, by one of the dedicated members of this blog Mr. V. The modified circuit was then utilized to charge a battery optimally and safely.

The following circuit diagrams exhibit how this was implemented, and the next prototype image shows the test results.

Adjustable High Current LM317 Battery Charger Circuit #3

For upgrading the above circuit into a variable high current LM317 battery charger circuit, the following modifications can be implemented:

) Compact 12 volt Battery Charger Circuit Using IC LM 338

The IC LM338 is an outstanding device which can be used for unlimited number of potential electronic circuit applications. Here we use it to make an automatic 12V battery charger circuit.

battery, charger, circuits, using, lm317, lm338

Why LM338 IC

Basically the main function of this IC is voltage control and can also be wired for controlling currents through some simple modifications.

Battery charger circuit applications are ideally suited with this IC and we are going to study one example circuits for making a 12 volt automatic battery charger circuit using the IC LM338.

Referring to the circuit diagram we see that the entire circuit is wired around the IC LM301, which forms the control circuit for executing the trip off actions.

The IC LM338 is configured as the current controller and as the circuit breaker module.

Using LM338 as a Regulator and Opamp as the Comparator

The whole operation can be analyzed trough the following points:The IC LM 301 is wired as a comparator with its non inverting input clamped to a fixed reference point derived from a potential divider network made from R2 and R3.

The potential acquired from the junction of R3 and R4 is used for setting the output voltage of the IC LM338 to a level that’s a shade higher than the required charging voltage, to about 14 volts.

This voltage is fed to the battery under charger via the resistor R6 which is included here in the form of a current sensor.

The 500 Ohm resistor connected across the input and the output pins of the IC LM338 makes sure that even after the circuit is automatically switched OFF, the battery is trickle charged as long as it remains connected to the circuit output.

The start button is used to initiate the charging process after a partially discharged battery is connected to the output of the circuit.

R6 may be selected appropriately for acquiring different charging rates depending upon the battery AH.

Circuit Functioning Details (As Explained By ElectronLover)

As soon as the connected battery is charged fully, the potential at the inverting input of the opamp becomes higher than the set voltage at non-inverting input of the IC. This instantly switches the output of the opamp to logic low.

According to my assumption:

When The battery charges fully Icharging reduces. V- become greater than V, output of the Opamp goes low, Turning on the PNP and LED.

R4 gets a ground connection through the diode. R4 becomes parallel to R1 reducing the effective resistance seen from the pin ADJ of LM338 to GND.

Vout(LM338) = 1.21.2 x Reff/(R2R3), Reff is the Resistance of pin ADJ to GND.

When the Reff reduces the output of LM338 reduces and inhibit charging.

) 12V Charger Using IC L200

Are you looking for a constant current charger circuit to facilitate a safe charging battery? The 5th simple circuit presented here using the IC L200 will simply show you how to build a constant current battery charger unit.

Importance of Constant Current

A constant current charger is highly recommended as far as maintaining safety and long battery life is concerned. Using the IC L200, a simple yet a very useful and powerful automobile battery charger providing constant current output can be built.

I have already discussed many useful battery charger circuits through my previous articles, some being too accurate and some much simpler in design.

Although the main criteria involved with charging batteries largely depends on the type of the battery, but basically it’s the voltage and the current which particularly needs appropriate dimensioning to ensure an effective and safe charging of any battery.

In this article we discuss a battery charger circuit suitable for charging automobile batteries equipped with visual reverse polarity and full-charge indicators.

The circuit incorporates the versatile but not so popular voltage regulator IC L200 along with a few external complementing passive components to form a full fledged battery charger circuit.

Let’s learn more about this constant current charger circuit.

Circuit Operation

The IC L200 produces a good voltage regulation and therefore ensures a safe and a constant current charging, a must for any kind of chargeable battery.

Referring to the figure, the input supply is acquired from a standard transformer/bridge configuration, C1 forms the main filter capacitor and C2 being responsible for grounding any left residual AC.

The charging voltage is set by adjusting the variable resistor VR1, with no load connected at the output.

The circuit includes a reverse polarity indicator using LED LD1.

Once the connected battery becomes fully charged i.e. when its voltage becomes to the set voltage, the IC restricts the charging current and stops the battery from over charging.

The above situation also reduces the positive biasing of T1 and creates a potential difference of above.0.6 volts, so that it starts conducting and switches LD2 ON, indicating that the battery has reached its full charge and may be removed from the charger.

The resistors Rx and Ry are the current limiting resistors required to fix or determine the maximum charging current or the rate at which the battery needs to be charged. It is calculated using the formula:

I = 0.45 (Rx Ry) / Rx.Ry.

The IC L200 may be mounted on a suitable heatsink to facilitate consistent charging of the battery; however the built-in protection circuitry of the IC virtually never allows the IC to get damaged. It typically includes built-in thermal run away, output short circuit and over load protections.

Diode D5 ensures that the IC doesn’t get damaged in case the battery accidentally gets wrongly connected with reverse polarities at the output.

Diode D7 is included to restrict the connected battery from getting discharged through the IC in case the system is switched OFF without disconnecting the battery.

You may quite easily modify this constant current charger circuit to make it compatible with the charging of a 6 Volt battery by doing the simple changes in the value of a few resistors. Please refer the parts list to get the required info.

Parts list

  • R1 = 1K
  • R2 =100E,
  • R3 = 47E,
  • R4 = 1K
  • R5 = 2K2,
  • VR1 = 1K,
  • D1—D4 AND D7 = 1N5408,
  • D5, D6 = 1N4148,
  • LEDS = RED 5mm,
  • C1 = 2200uF/ 25V,
  • C2 = 1uF/25V,
  • T1 = 8550,
  • IC1 = L200 (TO-3 Package)
  • A = Ammeter, 0-5amp,
  • FSDV =Voltmeter, 0-12Volt FSD
  • TR1 = 0. 24V, current = 1/10 of the battery AH

How to Set up the CC Charger Circuit

The circuit is set up in the following manner:

Connect a variable power supply to the circuit.

Set the voltage close to the upper threshold volt level.

Adjust the preset so that the relay remains activated at this voltage.

Now raise the voltage slightly more to upper threshold volt level and again adjust the preset such that the relay just trips off.

The circuit is set, and can be used normally using a fixed 48 volts input for charging the desired battery.

A request from one of my followers:

I got your email from a website www.brighthub.com where you shared your expertise with regards to construction of a battery charger.

Please i have a little problem that i hope you could help me out:

I am just a layman with no much knowledge of electronics.

I have been using a 3000w inverter and recently i discovered it doesnt charge the battery (but inverts). We have no much experts around here and for fear of further damaging it, i decided to get a separate charger to charge the battery.

My question is: the charger i got has an output of 12volts 6Amps will that charge my dry-cell battery with 200ahs capacity? If yes, how long will it take to full and if no, what charger capacity do i get to serve that purpose? I have had experience in the past where a charger damaged my battery and i dont want to risk that this time.

My Answer to Mr. Habu

The charging current of a charger should be ideally rated at 1/10 of the battery AH. That means for your 200 Ah battery the charger must be rated at around 20 Amps. At this rate the battery will take around 10 to 12 hours for getting fully charged. With a 6 amp charger it may take ages for your battery to get charged, or simply the charging process might fail to initiate.

7) Simple 12V Battery Charger Circuit with 4 LED Indicator

A current controlled automatic 12V battery charger circuit with 4 LED indicators can be learned in the following post. The design also includes a 4 level charging status indicator using LEDs. The circuit was requested by Mr. Dendy.

Battery Charger with 4 LED Status Indicator

I would like to ask and look forward to you to be made Automatic cellphone charger circuit 5 Volt and Battery Charger Circuit 12 V (in the schematic circuit and the first transformer CT) automatic / cut off by using a battery indicator and

LED lights red as an indicator were charging (Charging On Indicator) using IC LM 324, and

LM 317 and a full battery using a green LED and breaking electrical current when the battery is full.

For cellphone charger circuit 5 Volt I want to have levels of the following indicators:

0-25% battery is in the charger using a red LED.25-50% using a blue LED (red LED goes out)55-75% using a yellow LED (LED red, blue outages)75-100% using a green LED (LED red, blue, yellow outages) next to Battery Charger Circuit 12 V I want to use the 5 LED lights as follows:0-25% using a red LED25-50% using orange LED (red LED goes out)50-75% using a yellow LED (LED red, orange outages)75-100% using a blue LED (Led red, orange, yellow outages)more than 100% using the green LED (LED red, orange, yellow, blue outages).

I hope you, the components are common and accessible and made a circuit schematic above as soon as possible because I really need schematics details.

I hope you will help me to find a better solution.

The Design

The requested design make use of 4 level status indicator and can be witnessed below.The TIP122 controls over-discharge of the battery while the TIP127 ensures an instant supply cut-of for the battery, whenever an overcharge limit is reached for the battery.

The SPDT switch can be used to select the battery charging either from a mains adapter or from a renewable energy source such as a solar panel.

Circuit Diagram

The following tested 12V charger circuit schematic was sent to be by Ali Solar with a request to share it in this post:

Smart 12V Battery Charger Circuits

The following automatic 12V Smart battery charger circuit was exclusively designed by me in response to requests from two keen readers of this blog, Mr. Vinod and Mr.Sandy.

Let’s hear what Mr.Vinod discussed with me through emails regarding the making of a Smart battery charger circuit:

8) Discussing a Personal 12V Battery Charger The Design

Hi Swagatam, My name is vinod chandran. Professionally i am a dubbing artist in malayalam film industry but i am an electronic enthusiast too. I am a regular visitor of your blog. Now i need your help.

I just built an automatic SLA battery charger but there is some problems with that. I am attaching the circuit with this mail.

The red LED in circuit is supposed to glow when battery is full but it glows all the time.(my battery shows only 12.6v).

Another problem is with 10k pot. there is no difference when i turn the pot left and right So i request you to either correct these problems or help me to find an automatic charger circuit which gives me a visual or audio alert when battery is full and low.

As a hobbyist i used to make things from old electronic appliances. For the battery charger i have some components. 1. Transformer from an old vcd player. out put of 22v, 12v,3.3v.

And i don’t know how to measure ampere. My DMM has only the ability to check 200mA. It has a 10A port but i can’t measure any ampere with that.(meter shows 1) So i assumed that the transformer is above 1A and below 2A with the size and requirements of the vcd player. 2. Another transformer.12-0-12 5A 3.

Another transformer. 12v 1A 4. Transformer from my old ups(Numeric 600exv). Is this transformer’s input is regulated AC ? 5. couple of LM 317’s 6. SLA battery from old ups- 12v 7Ah. (Now it has a 12.8v charge) 7. SLA battery from old 40w inverter. 12v 7Ah. ( the charge is 3.1v) One thing i forgot to tell you. After the first charger circuit, i made another one (i’ll attach this too). This is not an automatic one but it is working. And i need to measure the ampere of this charger.

For that purpose i googled for an animated circuit simulation software but didn’t get one yet. But i can’t draw my circuit in that tool. there is no parts like LM317 and LM431(variable shunt regulator). not even a potetiometer or led.

So i request you to help me to find a visual circuit simulation tool. I hope you will help me. regards

Hi Vinod, The red LED should not glow all the time and turning the pot should change the output voltage, without the battery connected.

You can do the following things: Remove the 1K resistor in series with the 10K pot and connect the pot’s relevant terminal directly to ground.

Connect a 1K pot across the base of the transistor and ground (use center and any one of the other terminals of the pot).

Remove everything that’s presented at the right side of the battery in the diagram, I mean the relay and all. Hopefully with the above changes, you should be able to adjust the voltage and also adjust the base transistor pot for making the LED glow only after the battery is fully charged, at around 14V.

I don’t trust and use simulators, I believe in practical tests, which is the best method of verifying. For 12v 7.5 ah battery, use a 0-24V 2amp transformer, adjust the output voltage of the above circuit to 14.2 vollts.

Adjust the base transistor pot such that the LED just starts to glow at 14V. Do these adjustents without the battery connected at the output. The second circuit is also good but is not automatic. is current controlled, though. Let me know your thoughts. Thanks, Swagatam

Hi Swagatam, First of all let me say thank you for your fast replying. I will try your suggestions. before that i need to confirm the changes you mentioned. I will attach an image consisting your suggestions. So please confirm the changes in the circuitvinod chandran

Adjust the transistor base preset until the LED just starts glowing dimly at around 14 volts, with no battery connected.

Hi Swagatam Your Idea is great. The charger is working and now one LED is glowing to indicate the charging is in progress. but how can i configure the charge full indicator LED. When i turn the pot to ground side (means lower resistance) LED starts glowing.

when resistance goes high LED will be off. After 4 hours of charging my battery shows 13.00v. But that charge full LED is off now. Plz help me.

I am sorry disturb you again. The last email was a mistake. i didn’t see your suggestion correctly. So please ignore that mail.

Now i adust the 10k pot to 14.3v(it’s quite difficult to adjust the pot, because a slight variation will result a bigger voltage output. ). And i adjust the 1k pot to glow a little. Is this charger supposed to indicate a 14v battery? After all let me know the danger level full charge of the battery.

As you suggested, everything was alright when i test the circuit from breadboard. But after solder into PCB thing are happening strangely.

The red LED is not working. charging voltage is ok. Anyway i am attaching the image that shows the present condition of the circuit. plz help me. After all let me ask you one thing. Could you please give me an automatic charger circuit with a battery full indicator. ?

Hi swagatam, Actually i am in the middle of your automatic charger with hysteresis feature. I just added a few modifications. i will attach the circuit with this mail. plz check this out. If this circuit is not ok then i can wait for you to tomorrow.

Simple Circuit Diagram #8

I forgot to ask one thing. My transformer is about 1. 2 A. I don’t know what is the correct. how can i test with my multimeter? Besides if it is a 1A or 2A transformer, how can i reduce the current to 700mA. regards

Hi Vinod, The circuit is OK, but won’t be accurate, will give you a lot of trouble while adjusting.

A 1 amp transformer would provide 1amp when short circuited (check by connecting the meter prods to the supply wires at 10amp range and set to either DC or AC depending upon the output).

Meaning the maximum power of is 1 amp at zero volts. You may use it freely with a 7.5 Ah battery, it won’t do any harm, as the voltage would drop to the battery voltage level at 700 ma current and the battery would get safely charged. But remember to disconnect the battery when the voltage reaches 14 volts.

Anyway, a current control facility would be added in the circuit that I would be providing you, so there’s nothing to worry

I’ll provide you with a perfect and easy automatic circuit, please wait until tomorrow.

Hi swagatam, I hope you will help me to find a better solution. Thank you. regards vinod chandran

In the meantime, another keen follower of this blog Mr.Sandy also requested a similar 12V Smart battery charger circuit through Комментарии и мнения владельцев.

So finally I designed the circuit which will hopefully satisfy the needs of Mr.Vinod and Mr.Sandy for the intended purpose.

The following 9th figure shows an automatic 3 to 18 volts, voltage controlled, current controlled, double stage battery charger circuit with standby charging feature.

You’ll also like:

  • 1. nbspCamper, Motorhome Battery Charger Circuit
  • 2. nbsp4 Simple Battery Desulfator Circuits Explored
  • 3. nbsp6 Useful DC Cell phone Charger Circuits Explained
  • 4. nbspGel Cell Battery Charger Circuit [Constant Current, Constant Voltage]
  • 5. nbspNi-Cd Low Battery Monitor Circuit using Lambda Diode
  • 6. nbsp12V LED Backpack Power Supply Circuit

Resources and News for Sound Mixers Recordists for the TV/Film Industry

Batteries: Part 2 – DIY Modding The Talentcell 12v Lithium Battery

In Part 1 I walked about how to charge and gather 18650 Li-Ion Cells from cell phone USB batteries. In part 2 I will show you how to mod the very popular 12v Talentcell Lithium battery for use in your audio bag.

Right now if you were to go to the Zoom F8F4 group on you would be presented by hundreds of people asking how to power their Zoom recorders. A lot of the Комментарии и мнения владельцев suggest using the Talentcell 6000mAh battery. I just have 1 massive problem with this suggestion, the Talentcell battery features a nonlocking toggle switch. The last thing you want is to lose power during a recording because something like a cheap toggle switch got flipped. Some people have modded their battery to have a plastic guard over the button. That’s fine but you than have to still deal with the fact that the 2.1mm DC jack doesn’t lock. Here is how you can fix both problems!

Items Needed:

2.5mm Locking DC Plug to Hirose Cable – http://amzn.to/2k7Nnqj

12v 6000mAh TalentCell Battery (You want the NON-USB edition) – http://amzn.to/2ngHyYT

Step 1:

Unscrew the screws holding the clamshell plastic case together.

Step 2:

Use remove the small piece of plastic that is filling the gap in the case where the USB port would be on the upgraded model. File this opening to be bigger till you can slide your 2.5mm Jack into the slot. You will also want to bend the tabs of the DC JACK outwards so they are flat with the back of the jack. This will help it fit without touching the LED Meter PCB. You may want to still put some electric tap on the PCB.

Step 3:

Solder 6-7″ of 18Awg Red/Black wire to the circuit board that is mounted on the 6x 18650 cells. You will solder Red to P and Black to P-. Or you could use common sense and match it to the 2 wires already soldered to the BMS circuit. Leave the stock cables in place, you will still be using them along with the original secondary PCB with the big toggle button.


Sparks will fly! And if you cross the pads long enough you could do serious damage to your BMS circuit board.

Step 4:

Solder the Red Wire to the center pin of your Locking 2.5MM Jack and the Black wire to the “chassis” pin. In a lot of DC jacks the negative and the ground are connected. You want to select the pin on your connector that is making contact with the side “spring” that touches the outside jacket of the 2.5×5.5mm DC plug. That is a long sentence! Here is a generic DC jack diagram that hopefully makes more sense than I do.

Step 5:

Close it all up. Put your fender washer over your DC Jack and lock it into place using the nut. It will look like this when you’re done. Yes I realize the photo below looks like it is a 1/4″ TS port, but it is not. I’m a sound mixer, not a phone photographer.

So, what have we really done:

The new port we’ve added to the Talent Cell bypasses the toggle switch. We are taking a clean feed directly from the 3S Battery Management System PCB. The 3S BMS handles all the cutoff voltages to protect the 18650 cells from over discharge. It also protects the cells from over charging past 4.2v a cell. So a 3S battery really is 12.6V (3 cells in series) and our 6000mAh is a 2P (2 cells in parallel per series.) This means each cell is 3000mAh each. And while that number is hard to believe, I have seen others run test online and confirm that they hover pretty close to that number. Talentcell produces their own 18650 cells and don’t publish a proper datasheet.

The original 2.1mm non-locking DC jack will still be used for changing just like always. This way when you go to charge the battery you don’t have to buy a new 2.5mm 12.6v Li-Ion charger. If you own a Talentcell you probably never noticed that the charger that came with it is really 12.6 and not 12v. This way it charges the cells all the way up to 4.2v each and not just 4v. By using the original DC jack you still can use the LED battery meter when your charging to know when your battery is full.

The other big advantage to using a modded Talentcell is you no longer have to use battery cups like you do with the Inspire Energy Battery or NP1 style batteries. A right-angle locking 2.5mm DC jack acts like your battery “cup.” No more accidentally having the NP1 battery jump out of the cup or the cup coming loose off the battery. It’s now locked on!

For the cost of doing one mod you are still coming in less than just one of the 98Wh Inspire Energy Batteries. The Talentcell is not 98Wh though, it’s only 74Wh. But that is more than enough to get the average person who would be doing this DIY project to lunch to swap batteries. I haven’t tried yet to mod the 3000mAh Talentcell yet because the original LED PCB goes from wall to wall internally. But Talentcell does make a 132Wh battery if you really need something that big. I found the 6000mAh pack to be a good size vs weight in my bag. Also the 6000mAh unit is roughly the same size as a Lectrosonics UCR211/411.

What do you about batteries do you want to know more about? Leave a comment below!

Also if you found this article helpful, and maybe I just saved you a few hundred dollars on batteries, help me out. Donate so I can continue to provide articles like this one.

We offer this content free to everyone. It takes us days to months to research some of these topics. Help us out if you felt this info was helpful to you.

Don’t Dispose, Reuse: 5 DIY Projects Using Old or Dead Batteries

Don’t ditch those old batteries. reuse them with these amazing DIY projects.

Readers like you help support MUO. When you make a purchase using links on our site, we may earn an affiliate commission. Read

Old batteries pose a significant threat to our surroundings when disposed incorrectly – but you don’t have to dispose or recycle old or dead batteries!

If you’ve been keeping old batteries and you don’t want to trash them, you will be happy to know you can turn them into the next exciting and useful DIY project. Here are five cool DIY projects using old or dead batteries. These projects are fun, easy to execute, affordable, and most importantly, they let you turn your old and dead batteries into something useful.

Safety Tips for Using Dead or Old Batteries

Some of the cool DIY projects using old or dead batteries below will have you not just handling but also opening up batteries. Ensure you do the following while going about it:

  • Wear gloves and a mask: Chemicals found in batteries are toxic, and when you’re working with old and dead batteries, there’s always a chance these chemicals might spill out if you cut wrongly. Wear safety gloves to prevent chemical burns and a mask, so you don’t inhale these toxic substances in case of a spill.
  • Dispose of decayed or leaking batteries: If the battery you were planning to use is leaking or decaying, dispose of immediately since it’s a safety hazard. Ensure you clean up any spot it might have spilled on right away.

In addition to reusing your old or dead batteries, you can make Earth a better living place by trying out DIY electronic recycling projects.

DIY Solar Powered Generator

With global warming threatening the extinction of entire species, the least you could do for Mother Nature is switch to sustainable energy. An easy and affordable way to do this is by making your solar power generator using:

  • A solar panel: mono-crystalline 400Wp, 17.2v
  • Charge controller
  • Deep cycle 12V/7.2ah batteries
  • Inverter
  • Wires and wire connectors

Start by connecting the inverter to the battery. To do this, take a negative wire, connect it to the negative terminal and then do the same with the positive. Connect the charging controller to the battery and then to the solar panel.

Leave the solar panel outside and position it, so it’s exposed to maximum sunlight for charging. Once it’s above 50%, feel free to connect your smartphone and enjoy free sustainable solar energy. You can include a case to make it portable. When fully charged, this DIY solar generator can keep your Xbox one running for over three hours and your energy-saving light bulb on for up to 25 hours.

A Portable Rechargeable Lighting System

A DIY portable lighting system won’t just put your old batteries to good use – it’ll also come in handy during power blackouts and overnight outdoor activities like camping. You’ll need:

  • A 4-volt old battery
  • LED plate
  • On/off switch
  • Diode IN4007
  • 1000 Ohms Resistor
  • Red LED light
  • Charging socket
  • Superglue
  • Soldering tool

Using superglue, stick the on/off switch and the charging socket on top of the battery. Superglue the LED plate on one of the battery’s sides, and solder its negative wire to the on/off switch. Next, solder the LEDs positive wire and the diode’s positive point to the battery’s positive terminal.

Solder the diode’s positive point and one end of the resistor to the positive end of your charging socket. Bring in the red LED light, and solder its negative end to the battery’s charging socket, and the on/off switch negative points.

Connect and solder the red LED light’s positive point to the remaining end of the resistor. You’ll have created a powerful portable lighting system you can use during power emergencies or even enhance photography.

A Portable Mini Fan

A portable mini fan doesn’t just look cool, it also keeps you cool, and it’s a surprisingly easy DIY project using old or dead batteries. Here’s a list of what you’ll require:

  • 9V old or recently dead 9V battery
  • Battery clips
  • DC Motor
  • Red and black wire
  • Cutting pliers
  • Soldering iron

Pry open your battery and use a pair of pliers to disconnect batteries from the battery clip. To create a battery clip for the fan, solder a red and black wire to the battery clip you got after the first step. Solder the two wires to the motor’s negative and positive terminals. Glue the motor to the bottom side of the battery, and finally, install the mini hand fan blade.

Cool DIY Flashlight with 9V Batteries

Looking for a cool and fun way to spend an afternoon with your tech-curious nephew or niece? If yes, you’ll love this cool DIY project using old or dead batteries. It’s so simple; you won’t even need a soldering iron. Check out what you’ll need:

  • 9V battery
  • Mini LED light (you can use any color)
  • Resistor
  • On/off switch
  • Pliers

Cut the LED’s transistors using pliers, and then glue it on the top left of the battery such that the battery’s negative terminal is on the right and the positive side on the left. Hot glue the switch on the top right side of the battery, so it has the same arrangement as the LED. Next, glue your resistor in the middle so it touches one side of the switch and the battery’s negative terminal. Press the on/off switch to light it on, and watch your niece or nephew jump in glee at your little invention.

A DIY Magnet Holder

Like the DIY flashlight project above, this too is a cool DIY project using old or dead batteries to do with your little one.

battery, charger, circuits, using, lm317, lm338

Because aging and dead batteries already feature magnetic ends, get all your magnets and stick them to these ends. You can add as many magnets as you want to create a décor item or a unique-looking toy for your little ones. Alternatively, you could use it as a magnet holder to keep all your magnets organized.

Have Fun Reusing Old or Dead Batteries

DIY projects are a fun way to put your creativity to work and turn things that would have ended up in the trash into something useful and practical.

Our cool DIY projects using old or dead batteries above are perfect proof it is possible. So keep the two safety tips we highlighted in mind, and have fun reusing your old and dead batteries.

How To Make A 12V Battery Bank At Home

In layman’s terms, A battery bank is a group of batteries that are connected together in such a configuration that either allows you to boost output voltage or increase storage capacity, or both. Battery banks are a common application in both the electrical electronic industries, with their uses in many different places. They are safe relatively cheap to make at home. So, in this article, we are going to build a 12V Battery bank using three 4V Lead Acid Batteries.

In order to Make a 12V Battery using solely 4V Batteries, we have to arrange them in a series configuration. Connecting batteries in series adds the voltage of the two batteries, but it keeps the same amperage rating (also known as Amp Hours).

Hardware Components

The following components are required to make a 12V Battery Bank Circuit

1) Lead Acid Batteries 4V/1A 3
2) Soldering Iron 45W – 60W 1
3) Soldering Wire with Flux 1
4) AVO Meter w/ probes 1
5) Alligator Clips 2
6) Electrical Tape 1
7) Jumper Wires As per need

Useful Steps

Following are the step-by-step instructions on ‘How to make a 12V Battery Bank’.

1) Stack the 3 Lead Acid Batteries together cover them with electrical insulating tape.

2) Solder each.ve terminal of each battery in the stack with the ve terminal of the other battery, leaving the first ve the last.ve terminal disconnected.

3) Insulate the exposed terminals using electrical tape.

4) Test the Battery bank using an AVO Meter

Working Explanation

The Working of this battery bank circuit is pretty simple. A jumper wire is used to connect the negative terminal of the first battery to the positive terminal of the second battery while another set of wires is used to connect the open positive and negative terminals to any external DC device.

When connecting batteries never cross the remaining open positive and open negative terminals with each other, as this will short circuit the batteries can be dangerous to both the battery and the user.


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