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Almost There, Need Help with Breaker Sizing

Cabinfever

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Joined
Jun 22, 2020
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Hi all and thanks for your help so far. It wont be long now and I will be ready to hook up my off grid system.

*MPP LV 2424 Hybrid All in One Unit
*Qcell 425 W Panel
*4 six volt 220 amp hour golf cart FLA batteries

I want the ability to completely shut down the system when I leave the cabin. So, first off from what I read in the MPP LV 2424 manual, a 125 Amp breaker/fuse will be what is needed from batteries to LV 2424, is the info correct? Should I go with an ANL fuse and cut off switch or just a DC breaker which will serve both purposes.

For the PV wires, can I also use a DC breaker for protection and shut off of the system? Based on the photo I have included which show the panel specs as well as the LV 2424 specs , what are your thoughts. Batteries will be within 5 feet of LV 2424 and panel will be around 25 feet from LV 2424 using 2 AWG wire from batteries to LV 2424. What size breaker is required for panel please. Once I get these items I can go ahead and set it up. Your help is always appriciated.

Also the LV 2424 manual says to use 6 AWG wire to panel, is this right, my panel has 12 AWG and most people I see are using 10 AWG....thoughts ?

MPP LV 2424 includes:

  • 2400W 24V​

  • 80A 24V Solar Charge Controller​

  • 60A Ac Charger​

  • Supports up to 2000W of Solar​




Qcell.jpg
 
The DC breaker is sized at 125% of the maximum load (100Amps @ 24V) that the inverter can draw from the battery so it is sized correctly.

Output of the LV2424 is 20A @ 120V. So the breaker for your AC panel should be 25A. 10Ga wire would be recommended. 12ga is limited to a 20A breaker.
 
I want the ability to completely shut down the system when I leave the cabin. So, first off from what I read in the MPP LV 2424 manual, a 125 Amp breaker/fuse will be what is needed from batteries to LV 2424, is the info correct? Should I go with an ANL fuse and cut off switch or just a DC breaker which will serve both purposes.
A 2400W inverter with batteries down to 20V can pull up to 2400W / 20V / 85% efficiency = 141A from the batteries. Wire for 141A between the battery and inverter - 1AWG minimum, 1/0AWG would be better. 141A x 125% = 176A fuse size. I would go with a 175A or 200A ANL fuse near the battery. Either sized fuse can be used with 1AWG or 1/0AWG.

Add a master battery switch between the ANL fuse and inverter if desired. I wouldn't use a breaker between the battery and inverter.

For the PV wires, can I also use a DC breaker for protection and shut off of the system? Based on the photo I have included which show the panel specs as well as the LV 2424 specs , what are your thoughts. Batteries will be within 5 feet of LV 2424 and panel will be around 25 feet from LV 2424 using 2 AWG wire from batteries to LV 2424. What size breaker is required for panel please. Once I get these items I can go ahead and set it up. Your help is always appriciated.
How many panels do you have and what arrangement will they be in?

Panels should fused if you have 3 or more strings in parallel.

Independent of that you should have a PV disconnect switch near the charge controller. A 2-pole DC breaker is a common choice. Make sure it is DC rated for more than the max voltage supported by the charge controller. And its amperage rating should be higher than the panel array's current. The disconnect breaker is not there to protect anything. It's there only to act as a disconnect.

Also the LV 2424 manual says to use 6 AWG wire to panel, is this right, my panel has 12 AWG and most people I see are using 10 AWG....thoughts ?
10AWG and 12AWG wires would be used for lower amperage branch circuits. The main wires from the inverter's AC-out to the breaker panel's main breaker should be 6AWG if that is what they recommend. But that does seem oversized for an inverter that only outputs 20A.
 
A 2400W inverter with batteries down to 20V can pull up to 2400W / 20V / 85% efficiency = 141A from the batteries. Wire for 141A between the battery and inverter - 1AWG minimum, 1/0AWG would be better. 141A x 125% = 176A fuse size. I would go with a 175A or 200A ANL fuse near the battery. Either sized fuse can be used with 1AWG or 1/0AWG.

Add a master battery switch between the ANL fuse and inverter if desired. I wouldn't use a breaker between the battery and inverter.


How many panels do you have and what arrangement will they be in?

Panels should fused if you have 3 or more strings in parallel.

Independent of that you should have a PV disconnect switch near the charge controller. A 2-pole DC breaker is a common choice. Make sure it is DC rated for more than the max voltage supported by the charge controller. And its amperage rating should be higher than the panel array's current. The disconnect breaker is not there to protect anything. It's there only to act as a disconnect.


10AWG and 12AWG wires would be used for lower amperage branch circuits. The main wires from the inverter's AC-out to the breaker panel's main breaker should be 6AWG if that is what they recommend. But that does seem oversized for an inverter that only outputs 20A.
Thanks for the reply, I only have the one panel right now and I just found the specs on the internet which state maximum fuse size for the panel is 20 amp so I assume I should go with that size in a 2 pole DC breaker ?
 
Since the disconnect breaker is not there to protect the wires I would choose breaker with a higher current rating.

With one panel you don't need a fuse for the panel.
 
Hello CF
With that size battery, I'd suggest that your solar input is a bit on the low side. A flooded lead-acid battery is typically most happy being charged at 1/10th to 1/8th of C, so for a 220Ah battery that would be (220Ah/8) X 25Vcharging X 1.175 fudgefactor = 808W. The fudgefactor is a correction assuming that your panel never produces more than 85% of it's rated output in the real-world (see NOCT rating).

I would get a second identical panel and wire them in series to feed your MPPT. It has a Voc limit of 145V, so two in series would be significantly less than that even during your winter lows. With a second panel, your daily production would likely be high enough that you won't have to bother with shutting it down to conserve power.
 
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