FYI: Using Voltage Setpoint Offsets to balance multiple Schneider MPPT Chargers

[JBertok]

When running more than one Schneider MPPT in Voltage Battery Control Mode, I've found through trial their internal DC bus voltage calibrations can be up to a few tenths off from each other. It seems all the Schneider gear has vague calibration practices for DC voltage except for the two inverters between each other. I've gotten into a habit of using a specific voltage offset for the MPPTs to ensure balanced functionality. With the chargers especially, it's most critical when the chargers are in float and the loads on the XWs are very near the PV capacity at that moment. At that particular point you could lose some PV because the MPPT thinks the bus voltage is higher than it actually is. Additionally, when running in Enhanced Grid Support you don't get the option of making small adjustments to Grid Support Voltage, so calibrating Float Voltages on the MPPTs is necessary to prevent them individually from throttling down to a point the XWs undesirably lean on the grid. Without a voltage offset there will always be an imbalance; MPPT #1 and #2 in my setup end up doing most of the work, and #3 of #4 would end up throttling off allowing the DC bus to fall below power flow threshold from them. MPPTs respond to 100ths resolution, so this is important.
(There is no way to obtain a voltage in 100ths accuracy for the XW Pro, whether directly though the GUI, InsightMobile, or InsightCloud. 10ths only. In fact, most DC voltage settings within the XW are tenths only.)

Here's what I get from all devices at rest - no DC loads or charging:
Measured at batteries with Kaiweets HT208D: 50.88V
XW Pro - 1 (Master): 51.3V
XW Pro - 2 (Secondary): 51.3V
Battery Monitor: 51.07V
MPPT 60 150 - 1 (Primary): 50.74V
MPPT 60 150 - 2 (Secondary): 50.82V
MPPT 60 150 - 3 (Secondary): 51.06V
MPPT 60 150 - 4 (Secondary): 51.03V


What works for me is taking the lowest one, MPPT-1 in my case, and then adding offset to the others to artificially make them all respond simultaneously to the same voltage points on the DC bus. Unless we eventually get a backdoor into the the factory calibrations on these things, this is the best option available currently in my opinion.
MPPT 60 150 - 1 (Primary): 50.74V No Offset
MPPT 60 150 - 2 (Secondary): 50.82V Offset +0.10V
MPPT 60 150 - 3 (Secondary): 51.06V Offset +0.32V
MPPT 60 150 - 4 (Secondary): 51.03V Offset +0.29V

Hope this helps.

 

[Philip53]

Thanks for the info, but....how do you allow for the offset? Adjust each of the charging parameters, or by some other method I don't see?

 

[JBertok]

You basically put in a falsified value for each parameter modified by the positive or negative value of observed offset.

Imagine "This thing thinks it's seeing 55 Volts but it's really GETTING 54 because it's 1 volt high. So, if I want something happening at exactly 51 Volts I need to tell it 52 to get the 51 I need."

 

[seneysolar]

This same practice can be used on Midnite Classics. Seems like no 2 units read the same.

 

[cotter]

I just stumbled upon this today with differences in DC volt readings between my Master XWPro and the slave. The MPPT is reading the same as the slave but will check tomorrow without no load as JBertok advises. I guess this might be one of the factors not letting Grid Support to work in my case.

Thanks for posting your experience!

 

[GoldenGateCanyon]

I just stumbled upon this today with differences in DC volt readings between my Master XWPro and the slave. The MPPT is reading the same as the slave but will check tomorrow without no load as JBertok advises. I guess this might be one of the factors not letting Grid Support to work in my case.

Thanks for posting your experience!

You are right. My primary XW Pro reads .5V higher than the secondary. So, if I want to balance the inverter outputs selling to the grid, I'll have the primary set .5V higher than the secondary. For instance, I set the GSV for the primary at 54.4, and the secondary at 53.9. The MPPT CC reported voltage is about halfway between the two inverters. And, of course the batteries themselves report what I consider to be accurate voltage, it agrees closest to the secondary inverter and my fluke meter. So, yes, play around with the GSV and the charging voltages to get what you desire.