XW6048 with 2 MPPT60-150 charge controllers - one controller now gets F71 Battery Over Current

pcguy2u

All of a sudden after years of pretty normal operation, I get fault F71 on MPPT60 00, the circuit breaker trips and the 00 controller screen goes blank.  Flipping the breaker immediately brings it back to life and it happens again in a few days.  The other breaker, presumably for MPPT60 01, never trips during the time the 00 controller is off, or anytime.

I assume that this is a wiring issue and have checked/tightened all the lugs just a few moments ago (and read the related thread), so not sure if that has had any effect.  Also, the fault message says MPPT60 00 but as I think about it, this is after the event and I'm not sure if the 00 controller is actually the problem or not since the system views the controller as 00 when there is only 1; base zero and all.

Have also checked the voltages in and out of all the connection and there are no glaring differences.  Everything looks pristine, just like new...

Checked the lugs under the controller access cover and snugged them up a bit. Too soon to tell.

One thing that bothers me about the system is that from day one, MPPT60 00 has consistently read lower on the SCP than the 01  controller.  For example, right now at al most 11AM the 00 controller reads about 30A and the 01 reads about 41A and the watts readings vary likewise (00 gets a bit more sun early and 01 gets more late). The input voltages are also the same and read 107VDC+- with a DVM, but the SCP meters do not seem to coincide.  Just now read the SCP and 00 read 19A @ 106, while 01 read 23A @ 101.   Not sure if there  correlation to the problem here, but this is a bit

A couple of pics; the breaker that trips is always the one on the very left:

Any thoughts?

Many thanks, Nick

pcguy2u

Here's an update to the PV input numbers (SCP meter readings) provided above from just before 11AM.

00 19 106

01 23 101

And now at 11:45AM

00 22 106

01 25 102

But the input voltages on the back side of the breakers both read the same and were both 107+- much earlier this morning ???

pcguy2u

And I just checked the temperatures on the controllers and the wiring in the distribution box.  In particular, the battery connections going into the circuit breakers are different, even though they are both less than a foot long and are lugged on to the same bus.  00 was 86f and 01 was 76f on the input (upper) side.  On the output side (lower) they were the same.

The controllers were not the same; at a point just above the case where the cooling fins start at the center of the box:  00 was 116f and 01 was 111f.

Ambient was/is 51f and most everything else was not too far above ambient.

Dave Angelini

Probably a breaker is marginal. Swap the breakers to test this.

pcguy2u

Thanks Dave, thought about that but planned to see if it's less time consuming and cost effective to just buy a new one?  Need to find a source for the proper breaker first... 

Dave Angelini

The store here has them and it is a good thing to buy from them, in many ways. I use them alot of the time for certain clients.

pcguy2u

Overnight, while it was dark, started by removing/testing the two one foot cables from the positive battery buss to the breakers in question.  Both tested normally, even under twisting/torqued conditions.  So I reinstalled them and put them on the opposite breaker.  The issue of the two arrays/charge controllers producing significantly different outputs is now much less obvious and as the day progresses, the difference changes with the position of the sun, as it should.  Now at the end of the day, the controller getting the more direct sunlight produces the greater output.  I'm not totally sure, but it also seems that the "sell to grid" event occurs earlier???  The event log does not go back far enough to make a comparison... :0(

Also, the temp differences on the breaker/cable lugs have now largely disappeared.

More to follow,  Nick

pcguy2u

While this has not happened again, it is nonetheless troubling.  Primarily because of the differences between the input (charging voltage) on the lower side of the two breakers on the left, and the output side.  Also, the temp difference between the two cable connectors on the top of those same two breakers is confounding.  As reported above I removed the two and tested them but not under load; I should have use a battery load tester with each of the short connectors in series and I may do that.  Now the one with the higher temp reading has moved from the one on the left to the one on the right, although the difference is not glaring as it was previously.

Dave, what was the basis for your decision to replace the breakers you referred to above?  Do those breakers have an internal resistance originally?

TIA, Nick

Dave Angelini

It is a simple thing to do ! Basic troubleshooting.  Eliminate a problem source that is easy to do.
 Since I do not know the amp rating of the CB, it just was an easy call for me as you could be overthinking this.
Could also be a mosfet that is intermittent..

twistedtree

I periodically see the same error, but it clears quickly, and no breaker tripping.  The attached panels can't possibly drive it over current.

pcguy2u

I have been checking the charge controllers daily to date and have found no evidence of this recurring.

Dave Angelini

twistedtree said:

I periodically see the same error, but it clears quickly, and no breaker tripping.  The attached panels can't possibly drive it over current.

Firmware up to date?

twistedtree

Dave Angelini said:

twistedtree said:

I periodically see the same error, but it clears quickly, and no breaker tripping.  The attached panels can't possibly drive it over current.

Firmware up to date?

I believe so.   Unless there is something recent, I don’t think there have been any updates in years.   I checked probably a year ago. 

Dave Angelini

You are good then as there has not been much reason to update the old mppt-60.
Check your wiring !  Check your network wiring! Use the raceways designed for network cables.