I completely agree with everything in that post. The power stage of the charger is great. The control board though is pure crap. I had originally planned on replacing the entire control board until I opened up the charger and saw what was in volved in having to completely dissassemble the charger, cut out and desolder the old control board, resolder in the new one, and hope that everything would go back together without having those extra pieces left over that always seem to show up. I decided on the easier route of just replacing the socketed chip. I figured it would be much easier for others as well to just replace a chip on their own.
Yes, you can use the temperature probe input to control the board anyway you want. The probe input circuitry is shown on page 6 of the original schematics. It's signal just shows up as an analog signal at one of the a/d pins of the PIC. So, in other words, once you sample the voltage you can do anything you want with it. For our own setup, we are not currently using the temp probe so we don't yet have temperature compensation built into our code.
In documenting my code, I'm trying to make it as simple as possible for everyone with different versions of the charger to work with. I understand how my 144Vdc out version works; however, I don't yet have a good feel for all of the different versions (voltage and chemistry types) of chargers out there. For example, my NG3 was originally configured as a 144Vdc 15A lead acid charger. When they modified it to LiFePo all they did was change the chip, add a jumper, and maybe tweak the pots. However, I'm currious if there are any real changes they make for other chemistries. Here is why I'm asking, in Zivan's user manual they discuss the cell tension, which for lead acid is 2.0V. This 2.0V tension is what my 144V charger is based off of, which I will try to explain later. But they state the tension for other chemistries is different. I'm curious if they actually used different hardware settings for the cell tension for example if you originally bought say a NiCd charger.
Here is why I consider my 144Vdc charger to be based off of a 2.0V cell tension. This is all based on the circuitry that is on the right half of page 1 of the control board schematics. U7A generates a buffered reference voltage (Vref) 1.954V. U6D buffers the voltage divided battery input. If my battery pack is at 144V and the voltage pot is set to 0 ohms (left schematically) then the buffered voltage (Vbatt_divided) out is 1.999V. If the battery pack voltage is 144V and the voltage pot is set to 2k ohms (right schematically) then the output is 2.588V. This tells me that there is a 481k ohm voltage divider resistor on the power board. Likewise for a 144V system, they assume 12 batteries with 6 cells each or 72 total cells. Again the voltage divider math works out 6.8k + 2k + 481k =~ 490k, or another way to look at is 6.8k ohms/cell * 72 cells = 490k.
So, the voltage that the A/D (Va/d) of the PIC sees is:
Va/d = ( Vbatt_divided - Vref ) * (100k/15k)
From this, and assuming the pot is at 0 ohms, I can set my CV point anywhere from 140.7V to 195.1V before I clip the A/D input. If the pot is at 2k then it is reduced to between 110V and 150.1V.
The big question is, given the range of possible CV setpoints, do all different versions of the chargers have slightly different hardware or does it skip every 48V or so? Obviously I would expect some differnces beween say a 72V system and a 144V but what about systems that are closer in output? For example I might expect that a 156V system with an additional 6 cells would have a voltage divider resistor on the power board that is 521.8k. Any thoughts or measurements that can be made would be appreciated.