driving via canbus Eltek 2kW Flatpack2 supplies


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poida

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Joined: 02/02/2017
Location: Australia
Posts: 1117
Posted: 12:40am 05 Dec 2020      

The PCBs arrived from Wiseguy.
This means it's time to parallel 2 Eltek Flatpack 2kW 48V supplies.

The first test is CV, that is, I set the output voltage and let the current go where it pleases.
The load is a modified mppt dc-dc converter that presents zero current load at
45V and max load at 56.7V input. This makes for about 2500W total load on the converter's output, rapidly bringing the water cooled resistor to a boil.

pics or it didn't happen, right?




This shows the 2 Elteks and their output voltages and currents.
The setpoint is in volts and is used to program both Elteks to output that
voltage.
The display shows
Eltek PS #1 reports 53.9V and 12.1A on the output
Eltek PS #2 reports 54.0V and 12.3A

The canbus wiring has both Elteks parallel their can-high, can-low and can-ground
pins, which are then fed into the MCP2515 module.
Talking to one or the other PS is done with different canbus ID.
No need for two (or more!) MCP2515 modules. The canbus standard permits
multiple devices on the single bus.




This is the display from the dc-dc converter. It shows input voltage and current
as well as output information.
It shows 24Amps in at 53.7V

The two PSs are sharing the output.

How does it go dynamically?




Blue is setpoint voltage.
Read and Yellow are output voltages as reported by the PSs
Green and Purple are output currents as reported by the PSs

There are clearly differences in the closed loop control performance
when tracking a voltage setpoint. This will not be able to be remedied
since it's a function of Eltek firmware.
But to me it looks fine. What is a couple of Amps difference in output
going to matter?

There are good reasons why they do not track in lockstep perfection.
1 - different DC output lead lengths
2 - different calibration from PS to PS, factory set calibration too.
3 - possibly a difference in firmware revision yielding altered PID performance.