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18V Cordless Drill Battery Charger Circuit

In this post we learn how to build and use a 18V battery charger circuit for a cordless drill machine. The idea was requested by Mr. Chibuzo.

The Request

Sir, am very very sorry to bother you.

I can see your are a very busy person and my concern may be pretty trivial. Kindly accommodate me.

Here is the issue. I don't have any cordless drill battery charger at all. But I have variable voltage car battery charger.

I did try to use it by sticking metal plates on the terminal of the battery pack but I found out that the battery pack became warm /hot after a while, so I quickly disconnected it.

The battery is 18V nicd and I fear if it is not already dead/roasted I might destroy it by pushing in too much current at once using the car battery charger.

I know you are a very good subject matter expert in this regard, am looking forward to you suggestion. Like I said earlier, am a hobbyist with interest in many areas and I use these tools but getting them charged is an issue for me so am looking for a permanent solution.

Finally am going to try my hands on as many of your projects I can possibly find parts to handle. Can I personally get across to you if I have problem as I make effort to improve my knowledge of electronics using your platform. Am willing to be your student.

Thanks for such a large heart as to be willing to share what you know with total strangers. Again, am very sorry to trouble you.

Bye now Chibuzo

The Design

Whether it's a lead acid battery, a Ni-Cd or a Li-ion, this multipurpose battery charger shown below can be applied for any of these for charging them efficiently and without worries:

The salient features of this universal automatic battery charger are:

1) Constant voltage charging

2) Automatic cut-off when battery is fully charged.

3) Max current 5 amps, which means batteries up to 50AH can be charged with this charger normally.

4) Fully customizable as per the battery specs.

5) Low cost

6) No special parts required, all are standard  and easily available.

7) LED indicators for cut-off and charging status monitoring.

8) Suitable for garages and home use.

How to set up this simple cordless drill battery charger circuit:

The entire procedure has been comprehensively discussed in this post which explains how to set or adjust an opamp 741 IC based battery charger circuit for implementing an automatic cut-off

The above universal charger circuit is a constant voltage charger and a constant charger when it's implemented as a 5 amp charger, however for lower current charging this circuit might require an additional charging LM338 constant current circuit between the input supply and the above circuit.

How to Charge a 18V cordless drill battery with the shown universal charger circuit

Cordless drill battery can be mostly a Ni-Cd battery which is not as critical as the lead battery counterparts as far as the charging parameters are concerned.

Quite like the Li-ion batts these too will allow you to charge then through a current which may be 1/10th of their AH rating or as high as their specified AH rating.

For example if the drill battery is rated at 3AH, it could be charged at 3/10 = 0.3 amp or 300mA current rate, or any current within 3 amp but not exceeding this limit.

However at the full 1C charging rate the battery could get significantly warm, which must be taken care by an automatic temperature controller circuit or through fan cooling.

PCB Design for the above explained Cordless drill battery charger circuit 

Track side view

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    1. Hello sir .
      I need AVR circuit (High frequency transformer stabilizer)
      "Not low frequency such as UPS computer"

      1. Hello Hawker, you can try the following concept:

    2. Hello and good day sir...I need to design a microgrid system consists of one wind turbine(9v) and four solar panels(9v each) connected in parallel. The wind turbine and solar panels are connected to different charge controller(pmw) but with the same battery (12v)...can you please do the schematic diagram for the system .

      1. Hello Amir,

        please specify your exact requirement, because a 9V system cannot charge a 12V will depend on the specifications of the charge controllers, their rating and operational modes, so please the details which will help me to understand the actual situation.

    3. Thanks a lot. I did not see this earlier, I had sent a reminder. Thank once again i will get busy with this and give you feed back.
      Just before then, pls the batery capacity is 1300mAh. I guess this translates to 1.3amps. If right, at 20v what would be the best charging current?

      Again thanks. You are a great man

      1. You are welcome Chibuzo,

        for a 1.3ah Ni-Cd cell, a 1amp current would be good and will charge the it fairly quickly...

        for more info regarding the above charger circuit you can refer to the following post also:

    4. Hi Swagatam,

      One hopes all is well on your end, Iam building this circuit to replace the charger of garden tool the original charger had a meltdown. I know battery voltage is 18V but don't know the amperage the charger spec plate says 3.6-18VDC 1.5A. Could you please confirm the follow is correct, in feed voltage 24 the setting voltage 20.3, also the Led is it on whilst charging then off when charged or vise versa.


      1. Hi Geoff,

        you have understood it correctly except the red LED, which is supposed to illuminate when the battery is fully charged. you can connect another LED from opamp pin#6 to ground with a series 1K resistor....this LED would stay illuminated while the battery is charging.

      2. ....sorry, correction: the second LED should be connected across pin#6 and pin#7 of the opamp with a 1K series resistor.

    5. Hi
      can we make led blinking/ flicker during charging and stable when fully charged?

      1. that will require an additional circuit, cannot be done through easy methods

      2. Hi, can you provide me link for that circuit

      3. last three designs under this article


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