*Title Updated*: Surely a bad design!
I just finished to test a second BK8500 unti I have here at work. SAME RESULT, the problem is reproducible
!
This tells me the following two golden rules:
1) In CR mode the eDC load can adjust ONLY the current and not the voltage to achieve the desired V/I ratio.If the unit is attached to a constant current Is and the CR<VeDC/Is (where VeDC is the voltage sensed by the eDC load) then
1) constant current limit of the PSU kicks in
2) the eDC load reacts by decreasing the current in order to get the set CR value
3) the current limit of the PSU switch off
4) the eDC load reacts by increase the current in order to get the set CR value
5) back to 1)
This make sense if I imagine an immense MosFET in the eDC load which can only change the Ids betweent the terminals. The eDC load can not generate a voltage in order to get the desired CR with a constant current set.
2) In CR mode the eDC load can ONLY work in situation where an increasing current will cause MORE power to dissipateNow back to the case with a eDC load in series with a R and a constant voltage PSU Vs. As long CR>R the eDC load will dissipate more energy by increasing the current in the eDC load.
If CR<R the eDC load should dissipate less energy by increasing the current at the terminals. For some stupid design reasons this can not apparently happen.
Why in a over $1000 device BK did not implement a big RED LED (or event a buzzer) in the front to signalize a error condition like this? It could also be used in the CP mode where the outside network can not deliver the required CP to the eDC load....
Moreover it is surely worth ot mention that there is a reverse pn junction between + terminal and - terminal of the eDC load (I read this in this forum somewhere, I can find it anymore where sorry). So even with a power off unit if you inver the voltage on the terminals you will get a diode conducting current from the - to the +.
And of course not a word in the manual
, on the other side I did not have to repair the unit
.
So thank you guys to guide me here, I hope it was useful for somebody out there.