External Logging
Logging of the current and voltage of an external source can be done by disabling the source and sink transistors (using switches S2 & S3) and connecting the positive of the external source to the F1 side of R1 using one of the test points of TP1. The negative side of the external source goes to system ground. The battery to be charged is connected as the load in the usual way with a current meter in circuit to check what is going on. In this way, both the current and the voltage of the external source can be monitored by the PC.
The program (charger) I wrote has facility for logging. With the standard measurement plug/dongle attached (see PC Battery Cell Measurement ), the external voltage will be divided between A0 to A3 for Bat1 circuit or A4 to A7 for the B2 circuit.
I had mixed success when trying this logging. Because the plug pack battery charger was unregulated, the charging current would surge 50 cycles per second. When logging at >1 second intervals, I'd only see half of the current pulses at various points on the sinusoidal curve. Reducing the sample interval means that data must be logged to memory first but will at least give you a truer picture of the charging current. Some external program would be needed to analyse the actual charging rate.
An alternative would be to provide a RC filter on the output of OA2 to the PC Interface, providing an average current value over the 20msec cycle. This could be switched in through one of the digital outputs provided on my PC interface. I don't think it should be a permanent filter (which could be equally achieved by raising the value of C1) as in the normal usage of this device for battery charging, rapid sampling of the peak current is useful.
Of interest for circuit modification, when you connect a battery with the PC Source unpowered, current appears to flow backwards through Q1 and effectively powering the device. Knowing this, when I tried to log the external current source, I removed fuse F1 to prevent this complication occuring. However, when I did this I recall a number of things (I forget which exactly) went strange. I will investigate this oddity one day but you can spend a lot of time trying to understand what should be a very simple circuit. If someone has a good electronics simulator, maybe they could explain it for me?