Tuesday, March 10, 2020

Constant current load

In my electronic toolbox i did not yet have a nice constant current load.
(Almost) finished constant current load in my enclosure.
This simple device that can be used to check power supplies was a long time missing for my electronic experiments and projects. When i needed a (dummy) power load for testing or development i used a 12V car lamp or some high current resistors. I did also buy a simple very cheap USB discharge device with two resistors on Aliexpress. A constant current load was for a long time on my wish list. When i did see the video https://www.youtube.com/watch?v=D5SsvbCBD6o on the YouTube channel of learnelectonics i was impressed by the small relative cheap constant current load module with a color display. According to the video description the manufacturer is TKXEC and the model is WEL3005.
I did order one and even in this period with Chinese new year and other things that could cause delays did receive it relative fast. The price without enclosure is below 20 euro's. As i already had an enclosure that i could use i did not order it. 

Items needed

Items is used for this project:

  • Constant current load module (see below)
  • Enclosure
  • Power supply for the module (
    • I used an 9 volt battery,
    •  with a switch and a battery holder clip snap on connector to connect the 9 volt battery 
    • and a tie-wrap to fixate the battery in the enclosure )
  • Binding posts / Banana clips female
  • Some wires
You can find a photo of the (almost) finished constant current load in my enclosure in the beginning of this blog post.

I tested the device with another 9 volt battery. (So i needed 2 x 9 volt batteries with battery holder clip snap on connectors). See result at end of this post.

Also some simple tools are needed to make this project. (Screwdriver, something to make fitting holes in the enclose [dremel] and a soldering iron if you want or need to solder the connections)

The module description

(Text and photos from AliExpress)

1, can display voltage, current, power, ampere-hour, watt-hour, discharge time, internal resistance, temperature
2, can set the discharge current, constant current discharge
3, discharge safety, discharge time automatic statistics
4, can be suspended, can accumulate discharge data
5, fan intelligent temperature control, more than 45 degrees fan start
6, a variety of protection mechanisms, anti-reverse protection, over-current protection, under-voltage protection, over-power protection, over-heat protection

Product parameters:

Supply voltage: 6V-30V
Measuring voltage: 0-30V
Discharge current: 0A-5A continuously adjustable
Discharge power: up to 30W (Note: Do not use super power!!)
Working temperature: -10~+75 degrees
Resolution: voltage 0.01V, current 0.001A
Accuracy: voltage 1% ± 1 word, current 1% ± 1 word
Undervoltage protection: Yes (1.5-30V)
Over power protection: Yes (1-30W)
Overheat protection: Yes (more than 45 degrees fan start, overheat protection is 75 degrees)
Input anti-reverse: Yes
Wiring method: small screen printing B+B- for measuring voltage, large screen printing B+B- for measuring current
Fan: 4010 double roller fan, speed 8000
Module size: length 79mm width 43mm height 70mm
Opening size: length 76mm width 39mm
Weight: 95g

LOCK: Under non-discharge, press the LOCK button to measure the internal resistance of the battery and automatically disconnect for three seconds. Measuring internal resistance (please use four-terminal wiring method)

Setting instructions:
P1: Press the P1 key to switch to the interface shown below: (Note: long press the P1 key to clear the test data, short press the code switch to pause)

P2: Press the P2 button to switch to the interface shown below:
SET: Press the SET button to switch to the interface shown below: After entering the SET menu interface, rotate the "Encoding Switch" to adjust the data, and then "Code Switch" to switch the coarse adjustment and fine adjustment data, and then connect the SET button again. Menu items can be switched.


As mentioned in the "learnelectronics" video and some comments about the product a strange thing is that you need to remove the fan (and also pull out the top pcb) to connect the wires using a screwdriver.
I did fit the module in a small (metal) enclosure. On the front panel i added two female banana plugs for the load and an on of switch for switching the power to the module on or off. The power supply needed is 6-30V. I powered it using a 9 volt battery and it seems to work oke. 
Unfortunate the required current for powering the device is not mentioned. I also did not measured the power consumption myself (with and without the fan running and with different voltage inputs. 
When power connectors i ordered in China come i want to add these power connectors on the backside of the box. This way i can use another power supply than the 9 volt battery that i placed temporary in the box.  
I tested it using a second 9 volt battery and after some experimenting it worked well when setting the current below 0.900 A and the voltage limit at 1.5 Volt. I higher current will try to drain the battery fast and turns the load off after a few seconds as the voltage will drop rapidly. After the module has switched off the load you can see the battery voltage rise again.
When i revered the polarity of the 9 volt battery  that i was testing the display the display showed an input voltage above 30 volts.  This is as the module has an anti-reverse protection to protected against this connection of the load with switched polarity.

1 comment:

dbdb said...

Why does this have 4 wires for testing, 2 for voltage and 2 for amps? The diagram just shows them joining at the test battery, surely might as well just have two wires?