hot breaker

[mofawayesu]

I have an Outback e-panel and am using MNEDC-100 breakers on the input and output connected to a Classic 150.  Input voltage is around 40-55 volts and output is at 12v nominal.  Normal input amps runs around 20 or so, and output up to 85.   Since commissioning the system a year ago, the output breaker has run hot - hot enough to burn skin if the terminal is touched for anymore than a brief moment.  (The input breaker has always run at room temps, but that is expected because it rarely handles more than 20 amps.)

I assumed it was because I was using slightly undersized wire, 6AWG on both sides of the breaker.  Recently I replaced the wire with 2awg between the input bus of the epanel to the breaker and 4awg from the breaker to the Classic.  No improvement. 

I then thought that perhaps the high heat had damaged the breaker over time, so I swapped breakers with the input breaker, again with no result. 

Assuming the heat doesn't damage the breaker assembly at some point, there is also a .3v drop across the breaker when it is hot which means the Classic never 'sees' the correct voltage of the battery - unless the breaker is cooled down.  I could adjust the Classic to compensate, but the voltage loss in the breaker is obviously amperage dependent, so a fixed adjustment on the Classic isn't optimal at lower amperages.

I'm out of ideas.  Any thoughts from all the wise ones on this forum?  Shouldn't a 100A breaker be able to handle close to 100A without significant heat issues?

Thanks in advance!

Mike

[TomW]

You might have a faulty breaker.

You might have a loose wire connection to the breaker.

I would torque down the terminal(s) on the breaker. It is a normal post install recommendation that you re-torque all wire connections to compensate for cold flow in copper wire.

If you can borrow an IR non contact thermometer you can easily see if it is internal heat or terminal heat.

Just a couple thoughts on tracking down the cause.

Tom

[mofawayesu]

Thanks Tom.  I could imagine one faulty breaker, but it would be a stretch to think that I got TWO bad ones, though I suppose not impossible. That's what I was thinking when I swapped it with the input breaker, but it didn't seem to make much difference.  I've torqued and re-torqued them as well - they're on nice and tight.  These breakers take lugs (which are soldered onto the wire), so there isn't much copper flow to happen there.

The sequence on the breaker post, from breaker outwards is nut, washer, lug, washer, nut.  I couldn't find any other instructions online as how to connect the lugs to the post, so this was my best guess for greatest surface area from lug to post.  Do I perhaps have them mounted incorrectly?

Unfortunately, I don't have access to an IR thermometer.

Mike

[Mtn Don]

What metal are the washers and nuts?  Stainless steel has higher resistance; maybe that is part of the problem?  Just guessing.

[mofawayesu]

Good thought.  Unfortunately, they're whatever came with the breaker, so I would assume that it's suited for this purpose.

Mike

[zoneblue]

I use the exact same breaker. Will check the temp today. Not something ever looked at it.

[dgd]

The sequence on the breaker post, from breaker outwards is nut, washer, lug, washer, nut.  I couldn't find any other instructions online as how to connect the lugs to the post, so this was my best guess for greatest surface area from lug to post.  Do I perhaps have them mounted

Should that not be breaker post, lug, washer, lock washer then nut ?
Why is there an extra nut and washer between post and lug?

Dgd

[Vic]

If the input breaker is also running hot,  with "around 20 amps or so"  then there is something terribly wrong ...

What is the wire gauge on the input and output of each of these breakers?

Generally,  in my opinion,  soldering lugs is a bad idea.   IMO,  lugs should really be crimped only,  with a good crimper.   Some people crimp and solder,  but,  if a crimp is good,  no solder should be needed.

Use MNEDC breakers with currents in the 70 - 80 amp range,  and there is very little heat on the breaker studs,  lugs or wires.

My opinions,   FWIW,   Vic

[Westbranch]

did you use the lug type shown on the right side of this page?
https://www.google.ca/search?q=copper+lug&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a&channel=sb&gfe_rd=cr&ei=7yJ-VJarFcyV8Qe3lYHIDg

Following up on Vics' question, did you solder them without crimping?

[mofawayesu]

dgd, that's what I wondered too.  The breaker comes with no lockwasher, which I would have expected - it's just two standard washers and two standard nuts.  I thought about trying the order of what you suggested, but the amount of metal surface at the base of the post itself is quite small - maybe less than half that of the included washer, so it looked unlikely to me that that was what was intended - especially if it was to carry 100A.  I assumed then that one nut was supposed to be locked tight to the post providing the base for the lug above it, but I couldn't find any documentation to say one way or another.

Vic, the input breaker runs cold, no problems there.  Input breaker: 6awg both in and out.  Output breaker: 2awg out (from breaker to epanel), 4awg in (from Classic to breaker). 

Good to hear that yours run 'cold'!  Good thought on crimping them - it's because I don't have access to a crimper (I'm in west Africa and good tools are hard to come by!) that I'm soldering them, but maybe I should reconsider and go looking for one.  Fwiw, the original cables I had on the output breaker were crimped-lug 6awg that I had been given as salvage.  These also had a heat problem.  I presumed at the time that the problem was wire gauge, but the temp was definitely hottest at the breaker stud and was not evenly distributed along the length of cable, so I'm suspecting that the wire wasn't really the culprit. 

Btw, what order do attach your lugs, nuts, washers? 

[mofawayesu]

Westbranch,

Yes, I'm using copper lugs as shown.  The ones I have access to are oversized for these lugs (3/8" rather than 1/4), but they're washered down so there's lots of surface area to make the connection.  All connections on the output breaker are soldered at this point because I don't have access to a crimper.  However, the former 6awg cables that used to be on this breaker DID have crimped 1/4" lugs on them, but it was with these cables that I first found the breaker running so hot. 

[Westbranch]

I'm in west Africa and good tools are hard to come by!

Do you have a good battery service depot/retailer reasonably close? 

They should have good crimper if they make up battery cables and such. How reliable is the mail/parcel delivery?  A lot of us over here get our specialty tool delivered that way as we are more remote than some think...  even Ebay....

[Vic]

Thanks,  mofawayesu for the added info.

We all cam emphasize with you being (perhaps) in a remote area Continents away from North America where many of these items are made.

For these higher current levels,  run a physically larger breaker,  usually.  This E-Frame breaker is sometimes used on e-Panels,  but usually as a 125 A battery breaker.  They have 3/8" studs,  and accommodate large cables,  well.

Your output cable sizes seem quite adequate to me,  for copper conductors.   But,  to nit-pick a bit,  a 100 Amp breaker is a bit too large for #6 AWG,  even if the wiring is in "free air".   If these cables are inside the e-Panel ONLY,  then it is probably OK,  and might even have been provided by MidNite.  If these input cables are in conduit,  then #6 is a bit too small -- actually,  the breaker is a bit too large for that cable.   Breakers (and fuses)  are to protect cables and wiring from risk of fire.   Breakers are handy switching devices,  as well.   Nit-pick over ...

I have run the MNEDC 80,  and 100 A  breakers on occasion,  and do not recall any over heating.   But,  your ambient temperatures may well be higher that those usually seen here,  and  normal breaker heating,  and heating normally seen from the breaker itself and from the small voltage drop  at the lug  is a temperature rise,  above ambient temperature.   Still,  approaching burning the skin temps  really seem excessive to me.

The nut/washer sequence should be the same as supplied on the breaker -- nut on the bottom,  one washer,  lug,  washer and the nut on top.   Believe that this is as you described.   This spec sheet shows the stud with nuts and washers:
http://www.midnitesolar.com/pdfs/CA1-X0-17-767-321-L.pdf

Believe that the MNEDC breakers have been changed a bit from the following drawing (now recall that they have a formed metal "platform" for the stud mounts.  This design (if recollection is correct for the EDC)  should allow more torque to be applied to the nuts,  without the concern of over-torqueing the nuts and perhaps cracking the plastic breaker case ...  just guessing.

The MidNite breakers are really top-notch,  are well rated for our uses,  and are very inexpensive,  and quite compact.

All just my opinions.     Good Luck,   Vic

[TomW]

That first nut to go on is to hold the stud to the  breaker. If it is not holding that snug I think it will get hot as it is not a good connection. They can break, too so it cannot hold it properly.

Just thoughts from experience

Tom

[zoneblue]

Well, i can somewhat confirm the heat issue. I turned off our array until noon, and its just now run at 60A for about 30min. The classic panel mount breaker before i started was at 20C ambient. It now reads 45C in the top corner nearest the post, and 30C in the other three corners. The top post is around 40C, so it appears that the breaker is generating heat in that top outer corner. I can fully believe that running this at 80A would get quite hot.

None of the other breakers are more than tepid, and they are all carrying amps at the moment.

I also have the nut, washer, lug, washer, nut config, but based on the IR readings fairly sure that the heat is internal.