Guru
Joined: 13/10/2014
Location: AustraliaPosts: 1860
| Posted: 12:49am 22 Apr 2025 |
This may or may not be of interest: I was recently testing what effect High Inverter current with associated voltage fluctuations have on my LiFePO4 Battery bank. DSO and differential probe connected across the main DC bus between the Battery and Inverter at various locations. I'm looking at 100Hz ripple voltage from Inverter Current generating an SPWM waveform, not noise induced and coupling of HF fast transients and other 20Khz switching coupled wave-shapes.
Results:
3kW load 183mV RMS midway between the Inverter and Battery, and <20mV RMS across the Battery - very clean almost no 20kHz.
Switching out 3 battery banks at 3kW load made very little difference to Inverter current or the slight noise at the battery terminals.
6kW load 50mV RMS midway, <30mV RMS across the LFP Battery bank, and 68mV across the Inverter Input Terminals, the terminals are 1.7m from the battery bank and I could see more Transient switching noise at that point, I am not measuring fast transients.
HF noise and switching levels dropped dramatically on the DC Bus as the power level increased to 6kW, with very clean waveforms and low general Inverter noise consisting mainly of some fast rise-time switching transients, the battery was very clean, virtually DC.
I was a little surprised at how clean the DC Bus was at a constant 300A 100Hz peak DC Inverter current, but I've seen this in the past with higher power readings throughout this Inverter.
While testing at 6.4kW there was a 360A DC surge above the 6.4kW load (Wife starting workshop equipment), I was measuring the voltage 1/2 way along the DC cable and it suddenly increased, for a brief second the cleanest looking, "almost" perfect, 100Hz sinewave appeared on the DSO, what I would expect to see from the output of an Isolated Hall Current Sensor, as usual, not a peep from the Inverter.
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Edited 2025-04-23 09:30 by KeepIS