MNDC Mini DC panel 63 amp breaker tripping

[ClassicCrazy]

I have a Classic 150 hooked up to MNDC panel and have the battery charge circuit 6 gauge using 63amp Midnite breaker.  This breaker has been tripping when coming up on 60 amps so I used the classic amp limit to lower Classic output to 50 amps where it seems to hold . I hadn't had a problem with over amping this breaker until I started running some big loads on the Outback inverter and it cooled off outside so the panels started cranking out closer to their capacity.

I guess from the data below I need to install a 100 amp breaker on the battery circuit and use 4 gauge wire.  Am I correct in this ? From what I read 4 gauge is the largest size wire that the Classic will handle. The Midnite 100 amp breaker is a different type that doesn't use the rail to snap on. So will I have to also replace the PV input breaker with the same type breaker to get them all to fit and mount in the MNDC box ? Seems like I remember seeing a different breaker mounting plate that also came with the box when I got it that I assume is for this other type breaker.
Thank you for any advice .
And planning on ordering the upgrade breakers and a Whizbang Jr at the same time !
Number Of Modules In Series 5
Number Of Parallel Strings 3
Total Modules 15
Rated PV Array Power 2025 Watts
Anticipated Array Power @ 37 C 1916 Watts
Rated PV Array Current 22.89 Amps
Battery Charging Current @ 28.8V 70.3 Amps
VMP (Maximum Power Point Voltage 88.5 Volts
VOC (Open Circuit Voltage) 110.5 Volts
VMP @ -30 C 110.5 Volts
VOC @ -30 C 132.5 Volts

[Vic]

Hi CC,

It appears that the 80 & 100 Amp Mnedc breakers are still DIN-Rail mounted.  These breakers take up two positions (as they are two paralleled breakers).  They DO have different terminals on the top and bottom:
http://www.solar-electric.com/misomn150vdc.html

You might want to check the torque on each terminal of your 63 A breaker on the output of the Classic,  to make certain that these are both well torqued.  If not torqued to spec,  this can cause local heating in the breaker,  and CAN cause nuisance tripping at currents close to,  but below the rated current.  IIRC,  these MN breakers are rated for continuous DC current AT the rating of the breaker,  with reasonable ambient temperatures.

You might want to try setting the output current limit of the Classic to about 60 A to see if the breaker will hold that.

My opinions,   Good Luck,   Vic

[ClassicCrazy]

Vic,
Vic - After the first trip I changed the wire on these breakers and installed some new crimped lugs where needed ( thanks to a Harbor Freight hydraulic crimper which works great )
I don't have a small torque wrench but tightening the screws on those breakers much harder than i did with a screwdriver would seem to break the breaker or strip the screw so I think they are tight enough.
I will double check this though.
I had scaled the amps down from 60 to 58 and lower and it was still tripping so I went to 50 just to be sure it wouldn't trip again.
Hmmm - just dug out the MN DC instructions and it doesn't show using anything other than installing the Din rail type breakers. I was thinking of the Midnite combiner that had two different breaker mounting plates.

Hi CC,

It appears that the 80 & 100 Amp Mnedc breakers are still DIN-Rail mounted.  These breakers take up two positions (as they are two paralleled breakers).  They DO have different terminals on the top and bottom:
http://www.solar-electric.com/misomn150vdc.html

You might want to check the torque on each terminal of your 63 A breaker on the output of the Classic,  to make certain that these are both well torqued.  If not torqued to spec,  this can cause local heating in the breaker,  and CAN cause nuisance tripping at currents close to,  but below the rated current.  IIRC,  these MN breakers are rated for continuous DC current AT the rating of the breaker,  with reasonable ambient temperatures.

You might want to try setting the output current limit of the Classic to about 60 A to see if the breaker will hold that.

My opinions,   Good Luck,   Vic

[Vic]

CC,

Re-read your first post,  and am not certain just what box you have,  BUT,  the only MN 63 A breaker that I know of is the DIN Rail mount.

There is a "MNDC" box that will take 15 ea Panel Mount beakers,  but the Panel Mount breakers screw mount from the front of the box.  These PM  breakers do have studs on the rear that accommodate Lugs.

But,  believe either the PM breakers or the MNEPV (the DIN Rail type)  breakers should be able to carry rated current  continuously.

Have you checked the breaker that is tripping (assume that it is on the output of the Classic) to make sure that it really IS 63A?

Some confusing points:  63 A DC MN breaker is DIN Rail,  So do not see how crimping lugs would apply,  as these have shoes that are screwed down onto a bared end of wire.

MNDC and MN DC QUAD boxes seem to only use PM breakers.

There are the MN Baby and Big Baby Boxes that are DIN Rail only type Boxes.

Perhaps you have an e-Panel that this tripping breaker is installed in?

And,  yes  #4 AWG THHN or similar 19-strand,  Building Wire is the largest that can be used in the Classic's terminal block,  that is to say,  the #4 AWG wire should NOT be finely stranded wire,  which will be too fat to fit  into the Classic terminals.   BUT,  this wire is generally considered to have an Ampacity of 95 A if used in conduit.  In free air,  the Ampacity is about 140 A.

Depending on exactly how you are using the wire and its rating you could be OK,  or off a bit.   If the system is going to be inspected,  it COULD possibly fail.   As you know,  circuit breakers are installed to protect wire/cables from being overheated due to excessive current.  Enough for now,   VIc

[ClassicCrazy]

The crimped on lug I was talking about goes  from bottom of 63 amp breaker to bottom of inverter breaker stud which is the positive connection for B+ charging. I used the Midnite schematic that is pasted on the door of this box ( which really made the wiring much easier )
The link below shows that the bigger breakers with the 1/4 inch connecting studs can fit in there but I either didn't get the mounting plate or misplaced it - will have to look around for it.
http://www.midnitesolar.com/productPhoto.php?product_ID=76&productCatName=Mini%20%20DC%20Disconnect&productCat_ID=8&sortOrder=5&act=p
No I don't have to worry about inspectors. But I try to do it right anyway.
Thanks again for your comments Vic.
 

[Vic]

Hi CC,

Thanks for the link to the box that you are using.

YES,  I do see the note  that two different breaker mounting plates are supplied -- one for PM breakers and the other for DINs.  The PM breaker is very good,  and is about half the price of the 80 and 100 A DINs.   But,  of course,  if you need additional DIN breakers the double-wide 100 A DIN would be the way to go ...   guess.  FWIW.

Sure do not know why the 63 A breaker is tripping,  though.     Vic

[ClassicCrazy]

CC,


And,  yes  #4 AWG THHN or similar 19-strand,  Building Wire is the largest that can be used in the Classic's terminal block,  that is to say,  the #4 AWG wire should NOT be finely stranded wire,  which will be too fat to fit  into the Classic terminals.   BUT,  this wire is generally considered to have an Ampacity of 95 A if used in conduit.  In free air,  the Ampacity is about 140 A.

Depending on exactly how you are using the wire and its rating you could be OK,  or off a bit.   If the system is going to be inspected,  it COULD possibly fail.   As you know,  circuit breakers are installed to protect wire/cables from being overheated due to excessive current.  Enough for now,   VIc

I rewired with the 4 gauge and new 100 amp breaker. You were right about nothing bigger than 4 gauge slipping in those Classic terminals.   The Harbor Freight hydraulic crimper works great for the various lugs that need to be installed.

When I went to turn the current limiting back up in the Classic I noticed that the output current only goes up to 93 or 94 amps - forget which. So there is no way to go above the 95 amp rating of the wire. Now I can put the max capacity of panels on my classic which is 2700 watts into 24 volt battery. The Classic really out performs the competition in array size, mainly due to being able to handle  the extreme cold temp open circuit voltages.