So just adding a low value resistor in the source of the MOSFET?
I also saw this design that uses a BJT transistor: https://youtu.be/9auu8hH4IPM?list=PLUMG8JNssPPzbr4LydbTcBrhoPlemu5Dt&t=457
Thanks a lot for the advice.
Scully has some great videos detailing the operation, but unfortunately some janky ways of reaching the same means
Best way to achive your desired result is to use a quad op amp, each controlling one mosfet which is connected to a separate source resistor. this way you can:
1) drop the power rating of both your fets and resistors -> cheaper parts
2) use way less parts -> more space on pcb + cost savings
I would strongly suggest you look into the illusive ADS1219, the bigger brother of ADS1115. also you can use X2Y capacitors for your adc input filter for less noise and higher accuracy. costs almost the same as the ADS1115 modules available on amazon but not as popular, so you should but it from mouser or digikey, but I can get about 100uV accuracy or better depending on the application. you can copy my ADC design from this picture:
In terms of mosfets, you can use logic level fets which should give you a better response ... not sure if the 1.4A limit on 1V is caused by the transconductance of the mosfet or not, but it's well worth trying an IRLZ44N. Others have mentioned some high linear SOA IXYS fets which are really expensive in my opinion. you can get better cooling and save cost if you go with 4 cheap fets rather than 1 or 2 expensive ones. also because of higher surface area of separated load, they will be a lot easier to cool (I could get about 20 watts using two passively cooled fets, if you have a fan (which you do) your load capacity will increase drastically) !
3D printed case is a nice idea but will soften and loose shape if your load gets hotter than about 60C which the chances are it will! even if you use ABS it's not much better. a good idea would be to make a silicon mold of your printed parts and creating resin castings from them which are a lot more durable!
one final note would be to use a proper dac instead of a PWM signal ... it depends on your budget to determine if it's worth it or not but a simple first order RC filter you used has some major flaws. you should preferably use a two stage second order filter if you want any decent settling of the voltage and level of accuracy. I strongly recommend a DAC if you can fit it in your budget.
here is a video of an dummy load I made, but it's fully analog as I will be monitoring currents and voltages externally but it was designed for the same purpose of testing battery capacities. you can add the digital parts as you like:
Sorry for the quick and lackluster answer, I'm out of time for now. if you want more details I can answer them later. hope you found this useful and good luck with the project!