Just a heads up about a recurring issue we've had with FNDC calibration.
The issue is not about the software voltage calibration of inverters and
charge controllers, or the correct point to measure. It's about FNDC
calibration. We check FNDC reported voltage vs. actual during
commissioning. When we measure voltage at the bus where the FNDC twisted
pairs are landed, the FNDC disagrees. We've had this with 4 or 5 units
now, including the warranty replacement just received for a previous
project. The new one also reads about 0.5V high. Over time we've checked
against 3 different voltmeters, so while we don't have a calibration
standard I don't think our measurements are the issue. I'm hoping not to
be humbled by an obvious measurement error.
We calibrate the CC and inverter voltages to actual, so this ends up in
a disagreement with the FNDC, which can't be field calibrated. It's
confusing for monitoring and for training off-grid customers on how to
monitor their state of charge using voltages as well as calculated SOC.
Functionally, I believe the AGS uses FNDC voltage rather than inverter;
if so it also affects voltage based auto gen starts as well unless the
settings are tweaked to compensate for the error.
Are others seeing this as well?
- Tom
--
Tom Ruscitti
Senior Engineer
Taitem Engineering, PC
110 S. Albany Street, Ithaca, NY 14850
Mobile: (607) 220-7022
www.taitem.com
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