For single cell charging I have tried many things...
In the end
If you want to succeed as a hobbyist in anything remotely related to Electrical - you will - require a variable power supply.
AKA - Lab Supply
At a minimum this device has a power switch and 2 dials
One dial sets the max voltage limit
One dial sets the max current limit
At any given time
The supply will attempt to "rail"
First the voltage...
So with the current dial set at an arbitrary value (greater than 0) one will see the voltage rise to the set point.
Upon applying load the current will increase until it hits the current limit
At the current limit and beyond the voltage will begin to sag as a function of Power:
Power = Voltage x Current
Example: Voltage set to 10V, Current set to 10A
Maximum available power = 100W
Should a load of 1 ohm be applied...
Theoretical max is 10V/1ohm = 10A
Should the load be doubled to 1/2 ohm (two 1 ohm resistors in series)
the math works out to 10V / 0.5ohms = 20A
Since the current limit is set to 10A, we use a different formula for power:
Power = current squared * resistance
10A * 10A * 0.5ohms = 50W (which is indeed below the 100W setpoint)
Should the current limit dial be increased to 20A we will see
Where our limit was at 10V * 20A = 200W
The resulting "sag voltage" for a 0.5 ohm load on a 20A current limit with a 10V voltage limit works out to:
Volts = current * resistance (ohms law)
20A * 0.5ohms = 10V
Ah - balance again
Lab supplies can be had in many flavors
$50 - $250 is a reasonable range to look at.
You will NOT get anything you love for $50
$250 is where you START (with risk) to look at something awesome.
Your voltage must go as high as your pack (or whatever you want to test to... say 60V)
Your current... well... more is better eh? 20A is a nice spot to charge at yea?
I promote Sorensen DCS Power supplies, the DCS series
https://store.programmablepower.com/pro ... -dc-supply
You can see that they are a couple of kilo-bucks
Look to Ebay (and BE CAREFUL...)
They can be had for under $350 regularly
Most common failure mode is the fan
Second most is overheated internals
I have purchased over 20 used
I regularly charge with a power supply as described above.
One can set the supply to 4.2V and 20A
You can average out a pack QUICK like that... just mind your C rates
I calculate as follows:
AH of cell?
# cells in parallel?
Quality of cell (Good or Bad)
I start by assuming 1C
I multiply the AH rating of the cell by the number of cells in parallel
I multiply that by 1 for bad cells and 2 for good cells (super general)
So for 3Ah cells
With 3 in parallel
Assuming good "vaporizor" quality cells...
3*3*2 = 18A
So ... for a 3P pack of good 18650's I crank the supply up to 18A and let it rip to 4.2V
These supplies come with many modes of remote control
There are simple switch inputs
Active low inputs...
These are inputs which can be activated by simple "BMS" circuits
I have in the past
Released designs of the SIMPLEST form possibly imaginable
Involving (per series cell) only TWO PARTS
A sensors... and an opto coupler (to gang the outputs and avoid the ladder of potential)
A circuit like this can be very easily verified with a $5 "test circuit" to exercise LVC and HVC
Using a circuit like this one can do aggressive stuff more confidently...
Dont forget cell temperature
Monitoring and dealing with this is beyond the scope of this -
Just do your charging in a spot that can tolerate a good size lithium fire
And you are set
Grab a $10 Arduino
Hook to it a $1 temperature probe or 10
And... gang its output to the inhibit line of the charger
Increasing battery voltage and controller current limit will result in a non linear experience