DIY Constant Current Load

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About: Awesome Electronics Tutorials, Projects and How To´s

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:

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?...

Amazon.com:

1x Vero board: http://amzn.to/1OeN41p

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

1x LM358: http://amzn.to/1OeMz7o

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

1x IRLZ44N N-channel MOSFET: http://amzn.to/1H8jr1l

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

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

15 People Made This Project!

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122 Discussions

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meysamimani

3 months ago

hi dear GreatScottLab

i made this project two times and i used 3 ohm that are 3.3 ohm and connected them in parallel to get 1.1 ohm and i used IRZF44N instead of IRLZ44N and powered it with 12 v using power supply but in both circuit the current is not constant.

i connected the battery in series to the circute because if i connect it in parallel to the constant current circuit it doesn't work.

the current on my multimeter start from 2 amp and will decrease to 0.5 amp .

can some one help me what's wrong with it.

1 reply
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Calvin RohanRmeysamimani

Reply 14 days ago

I have a feeling that the resistance is a bit high. It should be 1.57 ohm if they are in parallel. Try to reduce the resistance. Or, you could set current to 0.5A at start and see if the current is 0.5A for the entire duration.

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SamikshaB1

Question 19 days ago

Can the Opamp supply sufficient current to turn on mosfet?
Can we use another MOSFET like IRF640N or so and another OPAMP IC like LM341

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gleisonstorto

Tip 10 months ago on Step 4

Hello GreatScott, I have added a current cut-off feature on the constant current discharge circuit. The schematic is attached.

schematic_constant_current_load.png
2 replies
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dipali9975gleisonstorto

Reply 19 days ago

I made it and works awesome. one more tip want to give is put 10nf capacitor( ceramic) pin no 6 of ic and ground and it will give constant current without fluctuation. thanks @gleisonstorto for tip

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khavocgleisonstorto

Reply 5 months ago

Amazing work my man. I will have to integrate this into mine

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_JoH_

1 year ago

I've been reading the comments and some people are asking about the different between the IRLZ44N and the IRFZ44N.

I was only able to find the IRFZ44N at my local electronics store, some said it works, others said it doesn't.

But there was no definitive answer about the difference of those 2.

Can anyone please help?

2 replies
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HarunB9_JoH_

Reply 4 months ago

İ made it using IRFZ44N powered it with 12v and it worked perfect. I can adjust the constent current with pot.

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GreatScottLab_JoH_

Reply 1 year ago

IRFZ needs a higher gate voltage to turn on. If you want to power the circuit with 12V it does not make a big difference. But If you want to use 5V and below I would recommend the IRLZ because it requires a lower gate voltage.

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NiravP21

Question 4 months ago

Hello, GreatScott, So I have made this circuit, is it bad that I connect the my load opposite polarity to what is on the diagram, because, if I have the positive of the load connected to the drain of the MOSFET and the load connected to ground. A uncontrollable 1 AMP passes through. But it i change the polarity I can control the current

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khavoc

5 months ago

So, I have made this, it works awesome, and I am about to use it with an arduino to make a battery capacity tester, but, there is one thing I would like to know. Is there a reason why the IRLZ44N is hooked up on the positive side of the resistor instead of the negative side? I mean, I know it works this way, so obviously it can get the Vgs that it needs, but, would it be better to switch the two ?

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KamilS55

Question 5 months ago

Hi i used a irl540n and cdz44n but i have only about 1V on my 10W1R resistor and i cannot get more event with 5V at pin 3

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clonan

6 months ago

What else can you use as a load? For instance, could I run it through a boost converter to use the power for something else?

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HassaanG1

Question 7 months ago

i made the circuit but the current that flows from the battery is very low !!!

with 1 ohm resistor and 1 V Vref

i connected a 4 ohm resistor parallel eith the 1 ohm

and the current increases to 1 amp

what is the problem ????

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hi sir great scott...may i have a question? since the op amp LM358 have 2 comparator...can i use them both??

2pcs. IRFZ44N, 2pcs. 500k potencio meter, 2pcs 1ohm resistor but 1pcs LM358....

thanks for your time to reply...

3 replies
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PedroB114Keiichii FranciscoT

Reply 8 months ago

Hello! I did exactly what you said, but as i need to have the same current in the second battery, I've use the same feedback of potentiometer on pin 5 (pin 3 and 5 shorted) in that way you can use only one potentiometer for the same load on both

But if you want to do 2 different loads, so you can use 2 potentiometers instead.

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Scuba_2Keiichii FranciscoT

Reply 1 year ago

I had to power with 10v to get the IRFZ44 to work 5v would not turn it on enough.

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khavocScuba_2

Reply 12 months ago

The IRFZ44N is not a logic level, so yeah, you would need more voltage, the IRLZ is the logic level version, but as long as you can supply the turn on voltage I don't see why either would not work. There are also other mosfets that are logic level that should work.

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FabRec'Up

Question 9 months ago on Introduction

Hi, i've made a mistake on my order and i bought a bunch of 100k potentiometers can i use them instead of the 500k ?

1 more answer
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jctjepkemaFabRec'Up

Answer 8 months ago

Yeah should not be a problem, as you can see the inputs on the potentiometer are the 5V and GND, this means that twisting the potentiometer changes the voltage, on the output of the potentiometer. This is called a resistor bridge, voltage divider etc. The higher ohm of the potentiometer is chosen to save energy.