[RE-wrenches] Outback FNDC calibration

Tom Ruscitti truscitti at taitem.com
Fri Nov 18 08:40:48 PST 2016


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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