Setting up 2 Classic 150's in follow me, strange results

[dougbarnard67]

New to the forum, thanks for the add.  I have recently added another array to my Schneider 6848 xw.  I only had 1 midnite Classic 150, so added another one and set up follow me.  First array is right at 3200 watts and the second array is right at 3000 watts.  They are feeding 800ah battery bank at 48v.  Everything was good with the first array but needed more solar.  Well after having everything set up and wired in my 2 classic almost take turn charging the bank.  The original will run along and have about 3200 watts coming in while the second classic, or the new one, is at 0 watts and resting.  Then after maybe 15 minutes they switch and the second, newer, classic will go up to about 2800 watts and show bulk mppt while the original classic will go down to 0 and resting.  Then after 10 to 15 minutes they switch again.  Is this normal??  Have I set something up wrong, I thought they would both throw their array totals into the bank.  Thanks for any help or guidance.

[Vic]

Hi Doug, Welcome to the Forum.

There are three Follow Me Topics on the Classic Knowledge Base,  the following is the Link to the last of the three:

https://www.midniteftp.com/support/kb/faq.php?id=77

The other two cover setup,  and testing,  here is the link to the KB,  scroll down:
http://www.midniteftp.com/support/kb/faq.php?cid=1

Vic

[dougbarnard67]

Thanks Vic, those are what I have followed.  However, they should charge independently, only one of the 150's will show that it is charging at a time.  The original shows say 3200 watts while the new one is at 0 watts and resting.  Then after a little of time they literally switch roles and the new classic will show bulk mppt and say 2900 watts while the original 150 is at 0 and resting.  The batteries are only at say 52.0 so plenty to go before fully topped off.  Panel arrays are within 20 feet of each other so sun is on them fully during this whole time. 

[Vic]

OK, Doug,  it has been too many years since I've set up FM.

And,  you have seen the following KB page (?):
https://www.midniteftp.com/support/kb/faq.php?id=91

Do both Classics have identical Firmware  versions?

Thanks,  Vic

[ClassicCrazy]

It seems like your two Classics are not reading the battery voltage exactly the same.
Have you used the Battery Voltage offsets to make sure they both read the same voltage ?
You would want to use a meter and take voltage reading of battery at a peak ( charge voltage , current ?) and then see what the Classic is showing . There is a menu to adjust the offset. What it sounds like is happening is that when one Classic takes the lead the voltage rises and the other Classic goes to resting because the voltage is higher .
Larry

[boB]

+2 on What Classic Crazy said...

I would use a volt meter to get an idea of how far off the voltage readings are on the Classics before modifying the Offset...  Just yet anyway.   IF the Classics are within just a few tenths of a volt as seen at the Classic battery terminals (on the Classic itself or VERY close to it) then you might move one Classic up 0.1V and the other Classic down 0.1V in that offset adjustment for the battery voltage reading.

It is important to know that two or more Classics are NOT necessarily going to share when they are not in MPPT mode.  i.e. when they are in Absorb or Float.    This is because the currents are usually pretty low in order to hold those voltages at that set-point because the batteries are almost full.

When the power requirements are higher and sun is available, the both Classics should be pretty much well below the Absorb or Float set point and THEN both Classics should be working hard.

When voltages are very near set point voltage, they just don't want to share on and off very much because target charging voltage moves around a little bit and the resolutions are only  0.1V

Make sure the battery terminals on both Classics are tight and not heating up.  Just for safety's sake as well as a good reason for battery voltage to be reading off some.