DIY Constant Current Load

78,320

312

124

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 !

Teacher Notes

Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.

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

20 People Made This Project!

Recommendations

  • Indoor Lighting Contest

    Indoor Lighting Contest
  • Make It Fly Challenge

    Make It Fly Challenge
  • Growing Beyond Earth Maker Contest

    Growing Beyond Earth Maker Contest

124 Discussions

0
None
SamikshaB1

Question 9 months 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

1 answer
0
None
JohnW669SamikshaB1

Answer 7 weeks ago

A mosfet is a voltage driven device with a slightly capacitive load. The opamp should have no issues at all driving it. Make sure you use the IRL version

1
None
_JoH_

2 years 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?

3 replies
0
None
albertoaav_JoH_

Reply 2 months ago

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

0
None
HarunB9_JoH_

Reply 1 year ago

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

0
None
GreatScottLab_JoH_

Reply 2 years 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.

0
None
FlingingB

4 months ago

Hi, can this be used to test a 1.5v AAA battery?

0
None
meysamimani

1 year 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
0
None
Calvin RohanRmeysamimani

Reply 8 months 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.

2
None
gleisonstorto

Tip 1 year 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
0
None
dipali9975gleisonstorto

Reply 9 months 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

0
None
khavocgleisonstorto

Reply 1 year ago

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

0
None
NiravP21

Question 1 year 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

0
None
khavoc

1 year 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 ?

0
None
KamilS55

Question 1 year 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

0
None
clonan

1 year 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?

0
None
HassaanG1

Question 1 year 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 ????

0
None
Keiichii FranciscoT

2 years ago

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...

2 replies
0
None

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.

0
None
Scuba_2Keiichii FranciscoT

Reply 2 years ago

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