Circuit Breaker Question

Wilis
Wilis Solar Expert Posts: 84 ✭✭✭✭
in General Solar Power Topics #1
A small question.

9 Kyocera KD210GX-LP
FM80 MPPT CC
Wire from CC to Battery is #4 (about 4’ in length)

I installed my 9th PV which allowed me to have my PV’s 3 in series with 3 strings. This has given me less loss because of increase voltage (I hope). The CC yesterday recorded 102Vp and 55.9Ap and the largest the CC recorded before now was 76Vp and 50.5Ap. I have #4 wire from the CC to batteries which is now feeling warm. Not hot but warmer then with 8 PV’s. I have seen more power input the last 2 days, after I made the PV change. I have purchased #2 wire and this should help the wire temp. I have not installed the #2 wire yet, but will soon.

The question is the OBB-80-125V DC breaker between the CC and the batteries also is running warmer. The stud on the circuit breaker is only 5/16”. I am using solder on AMP ring terminals at the circuit breaker and the other ends of the wire is fastened into the lugs in the E-panel. The 5/16” seems small for #4 wire and soon to be #2 wire. What are others using for the circuit breaker between their CC and batteries? I would like to have a circuit breaker that would let #2 wire slide in and tighten down with a screw. Is any 80 amp circuit breaker made that way? I called NAWS and they didn’t seem to know of anything in their stock. What are others using?

Thanks again for any information. Wilis
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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: Circuit Breaker Question

    I guess this is a 48 volt battery bank?

    Anyway, try replacing with the 2 awg wire first. Many times, circuit breakers are getting hot from the wire/termination. Make sure the crimps/binding screws are clean and tight.

    4 awg and 4' is only 0.1 volt drop at 60 amps--should not be a problem on a 48 volt bank.

    You can double check the voltage at the charge controller and at the battery bank and make sure that the voltage drop is on the order of 0.1 volts or less--If you have more drop--you have a cable/termination problem (and are generating excess heat too).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Wilis
    Wilis Solar Expert Posts: 84 ✭✭✭✭
    #3
    Re: Circuit Breaker Question

    Thanks Bill,

    I always forget something. I am running a 24v system. I will check the voltage tomorrow and see. Wilis
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Circuit Breaker Question

    Humour me and confirm my guess work, please!

    You have a 24 Volt system and roughly 1000 Amp/hrs of battery perhaps?

    4 gauge ought to handle 60 Amps, so how long are these wires?

    Warm is not necessarily a problem at peak Amps.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #5
    Re: Circuit Breaker Question
    Wilis wrote: »
    Wire from CC to Battery is #4 (about 4’ in length)

    55 amps * ~30 volts = 1,650 watts or so from the charge controller

    Guessing you are mixing array voltage and battery charging current...

    0.1 volt drop is not much of an issue for 24 volt bank either.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Wilis
    Wilis Solar Expert Posts: 84 ✭✭✭✭
    #6
    Re: Circuit Breaker Question

    Coot,

    Yes, I have 900AH of batteries and 24v. The wire is about 4" long. I just hate to see any power going to heat when I want it all to the batteries or used. It isn’t as important now with the summers sun but this will be my first full winter and I would like to be able to continue to run my Ref and freezer 24/7 and keep my batteries about 80% charge. Want to do what ever it take to be as efficient as possible.

    Thanks-Wilis
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: Circuit Breaker Question

    Just out of curiosity, what have you got the Absorb and Float Voltages set at?

    I'm thinking 900 Amp/hrs is a lot on a 24 Volt system: over 10 kilowatt hours!
    I have 1/3 of that, and will raise it just a bit next battery buy.
    But of course it depends on your loads.
    Some of us here figure 60 Amps is about peak efficiency for an FM 80, but it's a bit shy for a 900 Amp/hr bank.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #8
    Re: Circuit Breaker Question

    the wire itself may not be the problem as connection points can offer up far greater resistances when bad. keep in mind that there are 2 wires that are 4ft long, but even at that there should not be a problem with using the #4 unless there is a connection problem raising up the resistance to an unacceptable level. the fact that there is heat means without a doubt that there is power being unduly dissipated into the wire and most likely transferring to the breaker as well because copper is a good conductor of heat too. go with your plans of replacing that cable and recheck all of your other cables as well.
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  • Wilis
    Wilis Solar Expert Posts: 84 ✭✭✭✭
    #9
    Re: Circuit Breaker Question

    Hi,

    Thanks for all the answers. Now the sun is shining this morning I measured the voltage and Bill was right. I see 0.1 volt drop. It looks like most is across the Outback breaker. I will be able to shorten the wire and replace it with the #2. The highest KW input I have is 9.4KW recorded on the CC log. Now with the higher voltage on the PV’s I may go over 10KW. Many days I only have around 5KW. I only let my batteries go to 80% at night, as showen on the Tri Metric 2020 and start putting load back on the grid. When the sun is shining I can run ref, freezer, dehumidifier and we wash cloths. If 2 days of sun I can run everything all night. If the batteries are not down I go to float soon after noon. I feel the weakest point is the connection to the circuit breaker. The soldered AMP terminals are big for the lugs on the circuit breaker. That is why the original question about a circuit breaker with screw type connectors. Does anyone know of this type of breaker for 80 amps.

    My Absorb voltage is 29.6 and the Float is 26.4. I have set them there so the batteries are using a little water every month. In the last 7 months I have used about 1 gal of water. Now I have the 9 PV’s in bulk the fan on the CC is running about every 10 min for a min or 2. I might wait until one of the new CC come out and replace the Outback with 2 60 amp new ones. This system is mainly for water pumping if we have an extended grid outage. For day to day use I am trying to offset some of my KW that the AC is using. My electric bill was $57.00 for the month of June but July has been much hotter. We have a 1350 sq. ft house with good insulation. Heat in the winter is wood. Much of my electric goes for hot water, so that may be a good place to look for solar savings. Just trying to be as green as possible and having fun doing it. Wilis
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #10
    Re: Circuit Breaker Question

    The Outback Breaker is a bit of an "odd ball" in the sense it is rated 80 amps for continuous load.

    A replacement breaker rated by for NEC use would be:
    • 80 amp max continuous load * 1.25 safety/derating factor = 100 amp
    There are breakers that use thermal heaters for current measurement and those that use magnetic... And there are fast acting and time delayed.

    I wonder if you can get a 60+ VDC rated 100 amp magnetic breaker and if it would waste a bit less energy in heat?

    You can measure the "wasted" energy by measuring the voltage drop across the breaker at load and multiplying by the current. If the drop is 0.1 volt at 60 amps:
    • 0.1 volt * 60 amp = 6 watts of loss
    • 60 amp * 29 volt battery charging = 1,740 watts
    • 6 w / 1,740 w = 0.003 or 0.3% losses
    Probably not worth paying lots of money to recover a few tenth's of a percent in loss production and replacing with a magnetic breaker (assuming the Outback is thermal trip and you can get a magnetic trip).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Wilis
    Wilis Solar Expert Posts: 84 ✭✭✭✭
    #11
    Re: Circuit Breaker Question

    Update:

    Replaced wire from #4 to #2 last night. Was able to shorten about 8”, so not much change. Now only Outback circuit breaker feels warm. With my meter I am not reading the 0.1v drop from the CC to the epanel. Outback CC fan is still running at high speed alot. Think I better get a couple fans in stock because I am sure this will be a weak part of this CC. Has anyone had the fan on their Outback CC go out? Wilis
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #12
    Re: Circuit Breaker Question

    Yes (as I have read)--Fans will fail over time... There are instructions somewhere on fan replacement (at least for the MX 60 model).

    MX 60 fan problems (fan replacement link is broken in thread...)

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #13
    Re: Circuit Breaker Question

    "With my meter I am not reading the 0.1v drop from the CC to the epanel."

    ok, i'm in suspense here. what did you get for a voltage drop reading as there will be something there, even though smaller in value?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #14
    Re: Circuit Breaker Question

    If the fan is running it hasn't failed (so long as it does cycle off as well as on). They're thermostatically controlled, and the more Amps you push through it the warmer the unit gets and the more often the fan will run. How's the location for ambient temp and air flow?

    Just for comparative purposes, my batteries work better with Absorb set to 28.8 V and Float at 27.6. They stay charged well and use less water. Only yesterday I managed to get there for the first time since October; batteries were up, water level still well above plates. Added about 40 mL per cell.
    Your batteries may perform differently, of course. :D
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  • Wilis
    Wilis Solar Expert Posts: 84 ✭✭✭✭
    #15
    Re: Circuit Breaker Question

    Thanks again,
    Most likely I am not seeing any voltage drop because of the meter I have. It is from Home Depot and was purchased for electrical work. The smallest value is .1 that I can see. I will be looking at my absorb and float set values. I had only enough PV's to charge at about 4% before. My wire from PV's is 50 ft and I feel I was loosing some amps. Now with the increase voltage I seem to be receiving more amps. Just the second day of the new setup. Dont want to over charge but like wise this is my first set of batteries and dont want to do damage to my training batteries. Yes the fan is running, but now is more often. I know it is working right, but would like to have an extra in stock. Wilis
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