Cable length(s) between battery and inverter
All Hoymiles inputs should be connected to the battery
Does this mean:
- "All DC+ cables" should have the same length? or
- "All DC- cables" should have the same length? or
- "All DC+ & DC- cables" should have the same length?
SW-Niko and spcqike were kind enough to write some explanations:
First of all, different length of cables = different losses.
It makes sense therefore, that all DC- cables have the same length and all DC+ cables have the same length.
However, there is a much more important reason:
If the DCminus inputs of the Hoymiles are connected internally, then the return current to the battery flows preferentially via the connection with the lower-impedance .
In other words, more current flows in one return line than in the other return line.
This could lead to an overload of the internal conductors or the external cables.
In the event of a fault (lower line high resistance or interrupted), the entire return current could flow via one line.
The external line can cope with this, but whether the internal connection can do the same, is questionable.
This is not the first time that Ground (DC-) is so important: This is the reason why galvanic isolation for the earth of the VE.Direkt cable is so important level shifter - optocoupler
A quick check on a HMS-2000 showed that all DC- lines are connected internally. No problem with galvanically isolated power sources (= solar panels), but if all inputs are connected to one source (= battery).... Yes!!!!
In Summary: Have same length DC- cables 👍
A more detailed explanation is here: https://github.com/helgeerbe/OpenDTU-OnBattery/wiki/HOYMILES
Most probably, differences in length of the DC+ cables is less of concern as the electronic limiter of the Hoymiles should offer enough protection