DIY Constant Current Load

In this small project I will show you how to make a simple adjustable constant current load. Such a gadget is useful if you want to measure the capacity of chinese Li-Ion batteries. Or you can test how stable your power supply is with a certain load. Let's get started !

Step 1: Watch the Video!

The video gives you all the information you need to build a constant current load. But I will present you some extra help in the following steps

Step 2: Order Your Parts!

Here is the small list of parts that you will need (affiliate links):

Ebay:

1x Vero board: http://rover.ebay.com/rover/1/711-53200-19255-0/1?...

1x 1Ω / 5W resistor: http://rover.ebay.com/rover/1/711-53200-19255-0/1?...

1x LM358: http://rover.ebay.com/rover/1/711-53200-19255-0/1?...

2x PCB terminals: http://rover.ebay.com/rover/1/711-53200-19255-0/1?...

1x IRLZ44N N-channel MOSFET: http://rover.ebay.com/rover/1/711-53200-19255-0/1?...

1x 500k potentiometer: http://rover.ebay.com/rover/1/711-53200-19255-0/1?...

Aliexpress:

1x Vero board: https://s.click.aliexpress.com/e/_dVyKGn9

1x 1Ω / 5W resistor: https://s.click.aliexpress.com/e/_dYdV8ib

1x LM358: https://s.click.aliexpress.com/e/_dWVhDDz

2x PCB terminals: https://s.click.aliexpress.com/e/_dYbstfZ

1x IRLZ44N N-channel MOSFET: https://s.click.aliexpress.com/e/_dWhSrDl

1x 500k potentiometer: https://s.click.aliexpress.com/e/_dX83GAF

Amazon.de:

1x Vero board: http://amzn.to/1yZ4k1J

1x 1Ω / 5W resistor:http://amzn.to/1yZ4u9x

1x LM358: http://amzn.to/1GtRhNH

2x PCB terminals:http://amzn.to/1GtRU9R

1x IRLZ44N N-channel MOSFET: -

1x 500k potentiometer: http://amzn.to/1yZ4Vkb

Step 3: Build the Circuit!

Here you can find the schematic for the build and the board design that I created. Make sure to interrupt the copper traces underneath the LM358.

Step 4: Success!

Now you should be able to build your own constant current load.
Feel free to check out my Youtube channel for more awesome projects:

http://www.youtube.com/user/greatscottlab

You can also follow me on Facebook, Twitter and Google+ for news about upcoming projects and behind the scenes information:

https://twitter.com/GreatScottLab

https://www.facebook.com/greatscottlab

Comments

[vrooom]

Hi GreatScott, I have used this schematic, slightly changed and made PCB to test the 18650's. But i have a doubt, when you discharge the cell with 1ohm load and 5ohm load separately with same discharge current. Then for both the scenarios is the battery capacity calculation same or do we also have to take into load resistance value into consideration?
i have asked the same question here with circuit and PCB. https://electronics.stackexchange.com/questions/53...
Thank you

[HarshadB9]

Giving a PWM input to the non inverting input of the comparator is not a good idea.
This way you cannon control the discharge current.

You need to connect that to an analog signal value.

and no, as long as the current is same, it does not matter what the resistance value is

[3runo]

Can I power the circuit using 24V instead of 12V?

[HarshadB9]

Yes

[LikeTheSandwich]

Is the trimmer pot just a voltage divider? Can I use a 10k, since I have those handy? Or does it need the high 500k value?

[HarshadB9]

Yes, you can use 10k

[HarshadB9]

Yes, you can use 10k

[Jbulli]

Hi, I’m trying to build this circuit with a LM339n but the output of the op amp is only giving 0.3V. After a bit of research it seems it may need a pull up resistor to pull the output high. Why isn’t this the case with the LM358?

[mahio4u]

LM339 has open collector output, and it needs a pull up resistor to drive the output high.

[Jbulli]

Hi, I’m trying to build this circuit with a LM339n but the output of the op amp is only giving 0.3V. After a bit of research it seems it may need a pull up resistor to pull the output high. Why isn’t this the case with the LM358?

[AnvitV]

Hi,

I have tried to recreate this exact circuit, but have always failed. What do we attach at "load", like a resistor or what?

[SašoD1]

The "load" is the battery that you want to discharge.

[Samnonyellow]

So the 5V on the op amp and pot can be a 9v battery?
I've seen a schematic where someone uses a 7805.

P.s
I know I'm incredibly late !

[SašoD1]

Had to reset my password so I could even reply to you 😅. Yes the LM358 can take up to 32V supply voltage. With higher voltages the current setting will be a bit more "jumpy" because the voltage on the potentiometer will change faster. You can add a resistor that has roughly the same value as the potentiometer between it and the + rail, this will bring the pot voltage down.

[Samnonyellow]

Wow thanks alot man I appreciate it. I will apply those chsnges

[MirekF]

Hello ,

What programs are doing in electrical circuits for universal board

[3runo]

Lochmaster

[ThomasVDD]

Great project! What is the difference between an IRLZ44N and an IRFZ44N? I don't know why it works with the IRL, but not with the IRF.

[3runo]

IRLZ44 is a logic level mosfet instead IRFZ44 is regular one. IRFZ44
needs a higher Vgate to turn on (Vg~10V). At 5V and 3,3V (Logic levels)
the IRLZ is the rigth one. If you use 12V OTOH the IRFZ44N will work

[satannatas]

Could I use an IRFP250 MOSFET ?
It has a G-S threshold of min-2v max-4v
Thanks