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.
Technical Specifications
- 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.
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.
Step by Step Setting Up Procedure
- Initially keep the base/emitter of the BC547 shorted.
- Rotate the P2 preset wiper to ground level.
- Without any battery connected, switch ON the input power, and adjust the P1 preset until you get 14.2 V between the cathode of D1 and the ground line.
- Next, adjust the P2 preset, until the LED just illuminates.
- That's all, the setting up procedure is complete.
- Finally, remove the base/emitter short, your cordless battery charger circuit is now ready for the automatic charging and cut off..
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
Parts List
- Resistors
- All resistors are ¼ watt 5%
- 10K = 1no
- 1K = 1no
- 240 ohms = 1no
- 4k7 or 4.7K = 1no
- 10K preset = 1no at pin#3 of IC 741
- 10K pot = 1no connected with ADJ pin of IC LM338
- Capacitors
- 10uF/25V = 1no
- 0.1uF/50V = 2nos
- Semiconductors
- BC547 = 1no
- IC LM338= 1no
- IC7812 = 1no
- IC 741 or any similar opamp = 1no
- 1N4148 diode = 1no
- 1N5408 diode = 1no
- 6V and 3.3V Zener diodes = 1no each both can be ½ watt rated (can be replaced with 4.7V Zener for both)
hi swagatam.i like the 12 volt circuit for its cimplicity but i need a circuit to charge 5 cell li ion batteries in series thus mean 20 volt across them. can this circuit do the job?and if so how to adjust the 10k pot on pin3 of 741?my best regards.
Hi Nikos, yes that’s possible. For this you will have to adjust the 4k7 preset to get 20V at the output of LM338, and then adjust the 10k preset at a point where the LED just illuminates.
While setting up the 10k preset make sure to keep the BC547 collector disconnected from the ADJ pin of LM338, and also keep the 1N4148/1k link disconnected.
Connect them back once the setting up is complete.
hi.
i made a circuit like this, it works very well.
What exactly does feedback do?
When I removed this pin, the circuit worked fine.
thank you for everything
Hi, the 1N4148/1k feedback is introduced to latch the op amp output to high position and permanently switch off the IC LM338, until the input power is switched ON and OFF.
If you don’t put the feedback, when the battery is fully charged, the op amp output will switch ON, and disable the LM338 output cutting off power to the battery. Now, due to lack of charging voltage, within seconds the battery voltage will try to drop slightly below the full charge voltage level. This will prompt the IC output to switch OFF and the LM338 will again resume charging the battery. This rapid ON/OFf will go on at the full full charge threshold, if the feedback is not used
Good I am interested in this circuit because the charger of my drill burned and it is 18v, my query is in the diagram that you can see a 0.1uf capacitor between IN of the lm338 and connected to ground which cannot be seen in the PCB design also the other one that is 104 / 50v that is connected between ground and to the output of the lm338 which is the reason, finally I already placed all the components in their place but the preset connected one to pin 3 and the other to ground of the 741 it seems to me that it is a trimpot and the other terminal is on the air that says IN on the pcb what is the function of this terminal please thank you very much
The capacitors at the input and output of the IC LM338 are completely optional, since the input supply would be near to the IC. The capacitors are required only when the source input supply is some distance away from the IC.
The center pin of the P2 preset is connected to pin#3 of the IC, one of the other terminals is connected to ground and the 3rd terminal is connected to the body of the LM338 which is the output of the LM338. The LM338 body connection pads are shown as large round copper pads.
I have updated the diagram, and have removed the diode and resistor which were connected across pin#6 and pin#3, because these were not important.
hi.. im francis from the philippines, my question is this 18v charger is also good for 220v input?
Hi, You will need a 220V to 18 V DC adapter to feed the input of the circuit, and for charging the battery from mains
I have answered my own question. In looking up parts at jameco.com there is no listing for a 4k7 or 4,7k pot
In the schematic it shows a 4k7 pot connected to the ADJ on of the lm338. In the parts list it calls for a 10k pot to be connected to the ADJ pin of the lm338. Which is the correct pot to use?
Great design. I have several power tools with 18 volt nicad batters. The charger was lost during a recent move. Will be good to have use of then again.
Both will work! Higher values will cause higher portions of the pot’s dial calibration to become unresponsive and wasted. For 4k7 this may be 20% wasted and 80% working, for 10K this may be more than 50% wasted, and so on.
Glad you liked it, hope the design does the job for you.
Thank you.
John
Sir, are printed circuit boards available to purchase either from you or commercially if so how can I purchase one.
Throston,
Thank you
Sorry John, Ready PCBs are not available from me at this moment!
Hi Swagatam,
On your circuit diagram you use a 7812 voltage regulator, this is a 12 V regulator, is that correct for an 18V charger?
Can I / should I use something like ST L7818CV instead?
The battery I need to charge is only 1.5Ah, would charging it at 0.3A be ok and do-able with this circuit?
Great site by the way.
Cheers
Phill
Thanks Phill, the 7812 is for supplying 12V to the IC 741, it’s not for the battery. Because a 741 won’t tolerate over 18V. The input should be around 21/22V for charging a 18V battery. 0.3 A will be fine for a 1.5 Ah battery, just make sure the battery does not get warm during charging, otherwise you may have reduce the current.
Makes sense, silly me!
Thanks for prompt reply!
I’m bookmarking this place 🙂
My pleasure Phill, thanks for Bookmarking, appreciate it!
Sir Its working well. But LM338 too hot and burned. For a 14.4 battery, can I use 17volt DC instead of 24 volt? I don’t need to adjust the out put so can I remove the LM338 ?
Glad it’s working Ajit. An LM338 IC will require a heatsink for proper functioning, but under no circumstances it can burn because it has in-built over heat shut down.
Anyway if you don’t want to include the IC it’s fine, but you cannot connect 17V to a 12V battery directly, you will have to employ an auto cut off system such as this:
https://www.homemade-circuits.com/usb-automatic-li-ion-battery-charger/
Hi Mr Swagatam, God bles u for helping people. My observation is that some of the parts are not Labelled for identification. Pls,for we who ar not experts, kindly make sure to label them for identification. Am Yusuf
Thank you Yusuf, I’ll try to update the parts list soon for your convenience!
Dear Sir,
Sir can i use this circuit to charge 4S li-ion 18650 battery?
I have a 4S 18650 battery pack that my friend gave me for use with my cordless drill., or do i need to a balance charger for this?
Can you please give me some advise
Thank you very much sir..
Dear Paul, ideally you should use a balance charger, but on temporary basis you can use this charge\, it will do the job reasonably well just make…
Thank you for the reply sir..
Do you have a simple balance charger circuit sir for my 4S battery pack? Can you provide me a link for it..
Thanks a lot..
Paul
Paul, you can try this concept, but please try it only after understanding the concept thoroughly…
https://www.homemade-circuits.com/lipo-battery-balance-charger-circuit/
Hi
can we make led blinking/ flicker during charging and stable when fully charged?
that will require an additional circuit, cannot be done through easy methods
last three designs under this article
https://www.homemade-circuits.com/2015/03/battery-charging-fault-indicator-circuit.html
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.
Regards
Geoff
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.
….sorry, correction: the second LED should be connected across pin#6 and pin#7 of the opamp with a 1K series resistor.
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
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:
https://www.homemade-circuits.com/2016/05/how-to-set-ic741-battery-charger.html
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 .
Hello Amir,
please specify your exact requirement, because a 9V system cannot charge a 12V battery….it 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.
Hello sir .
I need AVR circuit (High frequency transformer stabilizer)
"Not low frequency such as UPS computer"
Hello Hawker, you can try the following concept:
https://www.homemade-circuits.com/2015/05/smps-mains-voltage-stabilizer-circuit.html
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