Electronic load for battery cell testing

[m.k]

New project, i want do build a battery discharge tester for single cell testing.

Specs:
-voltage range: 0-4,5V (full current sink should be available down to 2V, maybe 25-30A down to 1V if possible)
-current range: 50mA-75A (would be cool to have an universal setup that can either test an AAA NiMH battery for capacity and really push smaller Li-Ion -cells like 18650, 21700 and 26650 to their limits.) Should be able to switch off the current flow so the battery in test doesn't get overdischarged.
-data logging via a arduino and a computer (because i can't do proper uCs yet)
-temperature measurement and cutout
-input should be floating so you can test an 3,3V earthed powersupply with an earthed data logging/showing computer.

I never layed out an PCB before and have small electronic design experience (hey, i built a lab power supply with 2 LM317 ) so i may ask some rather dumb questions down the road when I'm at the board layout stage. But eventually I end up with a nice battery cell tester and share my design which may is helpful to anyone

For now i did search for components and started with the schematic, next up is ordering the parts and doing some breadbording as well as figuring SPI out. Then think a litte about decoupling and component values and finally layout.

[nctnico]

I'm missing a fuse in case the MOSFETs short due to a failure.

[m.k]

I had a look at some automotive style fuses and already found some nice ones with low enough voltage drop to keep the internal impedance of the thing down. Going to definitely use a fuse

I thought about reverse Polarity protection, because i guess the MOSFETs would act like a short if one does reverse the polarity, but keeping the internal resistance down makes this not fully trivial. Goes in the "nice to have" category.

[VoltJesus]

I started researching info on building one of these as well. Got a bunch of cells I need to test.
I'll be watching this thread to see how your project goes.

[MarkF]

I'm building an Electronic Load (no microcontroller) based on designs put forth by Peter Oakes



and Dave Jones

.

Mine is low power but you should see Peter's design and how he blew it up because your load section is very similar.