Inspired by Piloddogs tincan charger and with some useful infos found in this forum I managed to mod the mc1 for adjustable current.
The MC1 is just glued around the seam; I used a knife and started at the microusb port and slowly worked my way around. After half the way the case cracked a bit open which made it easier to cut around. I slipped one or two times so better wear some gloves and maybe you can tape the charger to prevent scratching it.
Opened MC1.
The circuit consist of two parallel 4057 charging circuits, the one on the bottom is connected to the LEDs. The resistor marked R1 and with the label “59B” is the current selecting resistor. This site said it is a 4kohm resistor. R2 and R3 are currentlimiting resistors for the Leds.
Mc1 PCB bottom
The top has the same charging chip which has also the same value current selector resistor marked R4.
Mc1 PCB top
After a short search I found a datasheet with lots of Chinese in it, after using google translator a bit I just went with the self explaining pictures:
Here is a schematic of a standard circuit, which is also kind of used in the Mc1
Here is a table which shows which Rprog results in which current
So let’s check that info…in the charger there is a 4kohm resistor for each circuit and the table says this gives you 250mA so two times 250mA should give us 500mA….and that is exactly what the mc1 delivers in normal operation. I am unsure why they used two circuits in parallel because the datasheet says that one chip can deliver 500mA, maybe they feared thermal throttling or so.
After knowing what goes on I removed one of the resistors and got 250mA charge current. The resistors are really small, but there is plenty of room and with a small soldertip it was easy.
You could do this as a mod to half the stock current resulting in 250mA I recommend removing the top resistor because the bottom one is connected to the LEDs. I am unsure if this disable the chip because I can’t read the datasheet I just know it worked in my test. To be 100% sure you should check the datasheet ,unsolder the whole chip or cut the chips GND line…
Then I soldered in a small 10k pot and was able to adjust current, I tried to use one pot for both chips but that didn’t work.
I soldered on the resistor spots some cables, it’s only neccesary to use three cables because the pots are between GND and the Prog Pin. GND is everywhere the same so no need for an additional cable.
Mc1 cables for pot
Here is a short demo, the Pot I used is a stereo 10kohm pot. Of course it is to big(physical size) but it was the only one I have. 10K gives 100mA for every circuit so 200mA is the smallest possible With this setup
If I turn the resistance down I can get up to 1.5A(USB voltage needs to be high)or so, I nowhere found information of minimum Rprog….maybe someone else can find that info. I recommend using a minimum resistor in series with the pot to set maximum current to 1A. As I will try to find a smaller pot this is just a prototype for me and I always use a USB voltage detector anyway.
It runs on 1A for half an hour or so and from my feel the case gets warmer than with stock current. There are modules for sale which are basicly the same design and are using a 1.6kohm resistor for 1A resulting current so I guess it should work fine…I made this for using smaller currents because I want to charge my smaller batteries with it, which I usually do around 0.3A(0.5C).
I just measured the voltage with my DMM on the 9V battery setting(it pulls some mA while measuring) and the voltage differs when I turn the pot. On 500mA setting the voltage is a bit(0.03V) lower. I don’t trust my multimeter in this range for absolute measurements but I guess that is why they have used two parallel chips. So watch out the termination voltage might be a bit higher than stock or lower…
Edit:
I just assembled it together after I sprayed the metal piece some days ago with matt black paint. I changed wiring to come out of the small side and soldered a 1.5kohm resistor to reduce maximum current inseries with each pot. I now have 0.96A max and 0.15A minimum current. I also put a bit of 2k epoxy on the micro USB socket to enforce it a bit, it looked super strong but Warhawk mentioned it somewhere that his broke…
I simply used a permanent Marker for marking the different currents, maybe a logarithmic pot would have been better because if you watch the distances between the lines it’s not linear.
or some more of the mc1 modded and labeled to different currents…but I have no fear using the wrong current because I usually double check everything and there are even people who charge everything even the 14500 with 1A without any direct problem. Also a poti seems to be a really intuitive selector.