Over the summer I have been working not only on refinements to this integrated engine controller and alternator regulator firmware, but have also been working on the stand-along alternator regulator project (arduinoalternatorregulator.blogspot.com/). One of the goals of the standalone regulator was to self-adjust for 12v up to 48v batteries. After I finish the stand-alone regulator I will be taking all the learning’s and rolling them back into the integrated controller, but there is one learning that I think would be appropriate to share today…
The INA-220 is a great chip, and core to these designs. It also is limited to 28v max. As such, to use it for any system greater then 24v divider resisters are needed to pre-scale VBat (and even 24v batteries can exceed this limit during equalization). What I found out over the summer is the input impedance of the INA-220 is not that stable from part to part, and is also rather low. As such the resister divider network tends to introduce a wider range of error that I would like – errors that delta from part to part.
Fortunately, TI now offers an upgraded part called the INA-226. This is pin compatible to the INA-220 and has much better input impedance characteristics – both higher and better controlled. And more interesting, it is tolerant up to 36v natively! So, this means that NO pre-scaling will be needed for 12v or 24v systems, even during equalization on 24v batteries.
So if anyone is looking to do a 24v or 48v system you might want to look to upgrade the INA-220s to INA-226s. It will give you much more accurate results as well as reduce the need to ‘fine tune’ adjustment factors. (and 24v systems will need no resistor divider at all) There is a firmware change needed as the new parts have a slightly different register layout; I have some parts on order and will be updating the firmware over the next couple of months.