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Hi Bob,
There is one issue that seems to have slipped or ignored and that is the strict 2-wire communication & power transfer vs. alternatives using more than 2 wires.
Using two extra wires that can take multiple roles should be considered. From the discussions so far, it seems that a four wire solution would solve much more issues than it creates:
1. There is an issue with supplying power over only two leads: Many devices with capacitors on the input connections creates a heavy load or sometimes sparks when connected. For discharged batteries, the load can be so severe that the UPAMD electronics in the device does not get sufficient voltage for communicating if using two wires only. With two separate wires it is easy to supply a few mA to the device UPAMD interface electronics and start communication to turn on the UPAMD primary power at voltage as communicated.
2. It would be beneficial if the UPAMD adapter could be used for price sensitive low cost devices where every part counts and where no digital domain exists. This could easily be implemented using separate wires.
3. For low power consumption we should avoid methods and technology that cause unnecessary power loss. Modulating communication on power lines will indeed increase power consumption and running cost.
4. To guarantee communication between all adapters and consumers using arbitrary length of cord, the communication scheme should be robust and free of pitfalls for the manufacturers. It should also be easy to test and qualify. Having communication on separate wires would make communication more robust and less prone of problems caused by various power loads, cable lengths, connector impedance etc.
5. For good voltage regulation it should be based on measurement done on the consumer. Sending the measurement signal on the same wires supplying power is complex and could create issues within the control loop. Avoiding measurement on the consumer would reduce quality of regulation and increase cost of cord. Using two independent wires measuring the voltage directly would allow a robust analog regulation loop that also monitors losses in cord and connectors.
6. For long life, the connector is important. With a two pole connector, it is not possible to sense removal of plug before current is cut. With two extra poles, those can be made to close last when plugging in, and open first when unplugging.
Kind regards,
Per