Blowing Controller Output Breaker on Midnite Solar XW-E Panel

[Emerald Power]

Hi All,

New here, and have a question about my new system. Xantrex XW 4548-grid tied with 14 Canadian Solar, 250w panels, output around 60 volts at 56 amps. Using Midnite Solar XW E-Panel with all MS breakers and GFI. Solar charge controller is a Xantrex MPPT 60-150 with a 60 amp max output.
The problem is that about mid day when things really get hopping, The output on the charge controller  shows to be about 51 volts and 30 amps, and the 63 amp MS breaker gets hot to the touch and trips. The input breaker to the controller from the PV is the same 63 amp unit and stays cool and never trips. Driving me nuts.
Any thoughts?

[Vic]

Hi Emerald .,

The first thing to check is that the screws on the popping breaker are TIGHT.  A poor connection will cause heating at these connection points.  In time,  this heating will make the breaker more prone to pop as the current through it increases.

The second thought is that if the cable that connects the CC to the breaker and/or the cable on the output of this breaker,  connecting to the battery is too small gauge,  its heating  'might'  cause the breaker to pop.

Just a couple of things to check.     Vic

[Halfcrazy]

QUESTION
You do have the negatives isolated right? So the PV negative goes straight to the XW? I ask because they use the negatives to measure current.

Keep in mind that 14 panels at 250 watts is 3500 watts and at say 48v that is 73 amps. The XW does not current limit real well so it will over shoot the breaker size. I would wire it for an 80 amp breaker. But I would also make sure the PV- is direct to the XW controller so it can measure current properly

[Emerald Power]

Hey Vic,
The connections have been re-torqued and are tight. The manual called for #6 wire, but I used #4 instead. The infrared thermometer says the outside of the breaker is at about 135 degs f when it trips. I also swapped the MNEPV63 used for the input to the output position and had the same results. Both breakers are new.

[Emerald Power]

Hey Halfcrazy,

The negatives run from the panels to a MS Disco combiner then directly to the PV negative bussbar in the MS E-Panel. From there it goes directly to the XW controller. The only other connection to the PV negative bussbar is the negative from a MS DC Lightning Protector.

[Halfcrazy]

Do you have a clamp on amp meter? I suspect the XW is not telling the truth on Amperage and it is actually more like 65 amps

[Halfcrazy]

Wait you say you are using a midnite solar GFI?? This is not on the PV side of the XW is it?

[Emerald Power]

Hey Half crazy,

I don't have a DC ammeter at the moment, just an AC. I ordered a DC clamp on meter a couple of days ago and will have it Monday. I suspect the same thing, that the XW controller is lying to me. But why?

About the Midnite Solar GFI. Yes, it is on the input side of the PV. The MS instructions said it did not matter which side it was installed on. Is this incorrect? I did a test by taking the GFI out of circuit completely and jumping the input breaker directly to the XW controller. Had the same results with the breaker heating.
Why should the GFI be on the controller side of the breaker?

[Halfcrazy]

I am not sure what to say other than the amount of PV you have is capable of more than 63 amps. You swapped the breakers did the problem stay with the breaker or with the location (IE battery Side)?

[vtmaps]

I did a test by taking the GFI out of circuit completely and jumping the input breaker directly to the XW controller. Had the same results with the breaker heating.

When you disconnected the GFI, did you disconnect the small breaker that is ganged to the 63 amp breaker?  Where am I going with this... I'm wondering if the small breaker (1 amp or less) part of the GFI is bonding your PV negative to ground.   

--vtMaps

[Vic]

Hi Emerald Power,

Thanks for the added info.

Ryan,  thanks for reminding me about the XW SCC's required PV negative wiring.  AND,  I had not considered that tying the bat and PV neg  together away from the CC could cause the SCC to output excessive current.

Vic

[Emerald Power]

Hey Halfcrazy,

It is a puzzler. This unit is grid tied and the output on the inverter display is reading only about 2.7kw when the breaker pops. The local load in only another 300 watts or so. So I am far below overloading the unit with input. After swapping the breakers, the problem remained with the battery side, input from the XW controller.
I know there is something amiss, because there is 800 watts difference in the readings between the watt displays on the controller and the inverter. The inverter being the higher of the two. You can't get something for nothing.

[Emerald Power]

Hey vtMaps,

I did completely isolate the MS GFI, disconnecting all of it's wires. The XW controller has it's own GFI which uses a jumper and pins to disable or enable. This XW GFI uses a standard 1amp fuse that is not resettable, hence the reason I went for the MS units.

[Halfcrazy]

Hey Halfcrazy,

It is a puzzler. This unit is grid tied and the output on the inverter display is reading only about 2.7kw when the breaker pops. The local load in only another 300 watts or so. So I am far below overloading the unit with input. After swapping the breakers, the problem remained with the battery side, input from the XW controller.
I know there is something amiss, because there is 800 watts difference in the readings between the watt displays on the controller and the inverter. The inverter being the higher of the two. You can't get something for nothing.

Yes thats about what I would expect is 3000 to 3200 watts and that coupled with the fact the XW does not current limit well would explain it to me. I would swap to an 80 amp breaker if ti where me.

Ryan

[Emerald Power]

Hey Ryan,

Could you explain to me more about current limiting. The XW has a manual setting for limiting the current, and I can set it at 60% and it will put out about 2400 watts (as reported on the inverter display) ,  all day long and not trip the breaker. If I adjust it up to 65% it will eventually heat up the breaker to about 120 degs and it will trip. Isn't a MS MNEPV63 supposed to be rated at 63amps continously? I don't think I am anywhere near that, but won't know for sure until I get my new meter on Monday.