Why not design your own charger?

I want a computer controlled charger, here is my first tests:

PCB’s are cheap, so I made one for my test.

Not bad for a LiIon charge curve. Charge voltage can be selected from 0 to 4.5V and termination current from 10mA and up.

The NiMH is also good, except I dropped something on my setup during the test. I use both -dv/dt and 0dv/dt termination here, it is not enough to handle low current charge, but I have not decided if I will support it.

Link to finished project: https://lygte-info.dk/project/Charger%20UK.html

Yes, we want a HKJ BLF CHARGER!!

i\m in, sign me up, thanks!!

It is not a product, but something I want for my testing. It will not have any display or buttons on it, everything is controlled from USB or serial.

On the Arduino console I write “start LiIon 1” to charge a LiIon cell with 1A and 50mA termination or “start cccv 1 3.6 10m” to charge a LiFePO4 cell with 1A to 3.6V with 10mA termination (The LiIon is just a shortcut that sets the voltage to 4.2V).
This is not really a practical design for most people.

I can also ask it to list charging:
Index Time Voltage Current Capacity Energy
12 12 1.587 0.999 0.0031 0.0049
13 13 1.587 1.001 0.0034 0.0054
14 14 1.588 0.998 0.0037 0.0058
15 15 1.589 0.997 0.0040 0.0063
16 16 1.589 1.002 0.0042 0.0067
17 17 1.590 0.999 0.0045 0.0071
18 18 1.590 0.999 0.0048 0.0076
19 19 1.591 0.997 0.0051 0.0080
20 20 1.591 1.001 0.0053 0.0085

Being a computing type with not enough hobbies to suck his calendar and wallet dry, I’m interested in what you’re doing. :beer:

This may not be something that is practical for “most people”, but you are on BLF… I too find this project interesting.

If there is interest in it, I may put it on my project page when I am finished in a few months. It is not very expensive, the most expensive parts are Arduino Nano and a ADS1115 module (This 15 bit ADC secures good voltage and current precision). The other stuff is fairly cheap, except you usually have to buy multiple items and there may be some shipping.

That sounds fantastic!

I like the plan.
Does / can it scale past a single cell holder on a controller?

It may be cheap to build, but I use one very small IC (I could not find a larger version of it). It is near the battery connector and not much larger than the small SMD resistors.

No, the Arduino is rather busy controlling the current, it directly controls the switcher, there is no switcher chip.

I got calibration of current, voltage and time working now.

VERY interesting!

Nice project Henrik! :-)

As many people use a Raspberry Pi for DYI things I wonder if it could be suitable, too.

Not as replacement for the Arduino, but for controlling the Arduino it would be fine.

To charge and log you can just send this “start nimh 1;list” over the USB port and then you will receive the table from above while it is charging.
My charging modes at the current time are: CCCV, DVDT, LiIon, NiMH, the last two uses the first two, but with some predefined parameters.
I have 3 different list format, one with tabs, one with US CSV and one with EU CSV.

Looks like a great project.

I think you will see a lot of interest in your progress :slight_smile:

Oh wow, interested….

Got around to add a timed charge, i.e. charge with specific current for a specific time. The normal charge modes will not have a time limit.
I added to code to handle a temperature sensor (LM35) and stop on over temperature. One of the 3 pin connectors on the PCB is for the sensor.
The other 3 pin connector is for an external status led. I use a WS2812 for that, this means I use color to show actual status (I can also be read from the serial/USB port). The colors are: green:idle, blue:working, weak read:current on, bright red:error. They are combined.

That would be awesome, i would like something as that, seems not too difficult to build !

Then all it needs is a 3D-printed casing and a label that says: “HKJ-2020”.

Maybe HKJ can offer it as a kit ? :wink:

I need a 3D printer and space for it.

No way.

I have put the specifications and implemented commands : in a document
It is not listed on my website.

Trying to provoke the charger. I used my oldest cell with very high internal resistance (AW18350-IMR) and low capacity. Start current was 1A (That is begging for problems on this cell) and termination current 10mA.

It looks nice enough, but is there something at the start?

Zooming in on the start shows that the charger hits 4.3V for 1 second, not really a problem.

The charger is a constant current charger, it cannot do constant voltage, that is done in software. Usually regulation is within a mV, but if the voltage raises fast it need some time to adjust the current and may go a bit to high.
Current regulation is fast, but voltage regulation is slow. I will try to improve the speed slightly of the voltage regulation.