Fuses and breakers when connecting multiple charge controllers

Vovanenok

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Jun 28, 2021
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Hi all, I'm happy to find this super useful forum. I'm upgrading my current solar setup which has 1 array of 4 x 235W panels ( Voc 37v, Isc 8.6a), Outback 150v/60A charge controller, 24v battery bank and Magnum 4000w 24v inverter

Because the parts I ordered will come at different times, I'm planning 2 upgrades:

Upgrade #1
  • Keep the current 4 x 235W panels ( 2 panels in series parallel another 2 panels in series ) + Outback 150/60A charge controller
  • Keep the existing 24v battery bank and Magnum 4000w 24v inverter
  • Add 8 panels: 2 solar arrays (connected in series), each 4 x 330W ( Voc 46.8v, Isc 10a )
  • Add 2 x Victron SmartSolar MPPT 250/60 charge controllers
  • Add Victron lynx distributor
1624933486185.png

Upgrade #2 (once my new batteries and Victron 48v inverter arrive)
  • Keep the current 4 x 235W panels ( 2 panels in series parallel another 2 panels in series ) + Outback 150/60A charge controller
  • Replace 24v battery bank with the new 48v lithium battery bank
  • Replace Magnum 4000w 24v inverter with Victron energy Quattro 48/5000/70
  • Re-wire the current 8 panels (2 arrays x 4 in series) as 1 array (parallel 4 in series + 4 in series)
  • Add another 8 panels and make the same array: parallel 4 in series + 4 in series
1624933524015.png

As I understand, each Victron SmartSolar MPPT 250/60 charge controller will be receiving up to 330w x 8 = 2640w ( a little more on colder days), then output will be 2640w / 48v = 55a

My questions are:
  1. Do my diagrams and upgrade plans look ok?
  2. Can I use 6 AWG copper stranded wire and 60A MEGA fuse for each positive wire between a charge controller and lynx power distributor? Or should I go with larger wire and fuses?
  3. I'm also planning to install a disconnect breaker in a PV combiner box. If I want to connect 2 string in parallel, (each string is 4 panels connected in series, so the current remains Isc=10a), can I use a double 15a breaker to connects 2 strings (in upgrade #2)? Or should I go with a higher amp one?
Many thanks in advance!
Vlad
 

snoobler

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Welcome to the forum.

1. yes
2. 6awg is good for 55-75A depending on insulation rating. 20' run one-way will have a 2% voltage drop. Your fuse size should be 1.25X max continuous current.
3. Your panels should have a maximum fuse rating on the sticker. That's the size you should use on each series string.
 

Vovanenok

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Jun 28, 2021
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1. yes
2. 6awg is good for 55-75A depending on insulation rating. 20' run one-way will have a 2% voltage drop. Your fuse size should be 1.25X max continuous current.
3. Your panels should have a maximum fuse rating on the sticker. That's the size you should use on each series string.
Thank you very much Snoobler, this is very helpful.

2. 6awg is good for 55-75A depending on insulation rating. 20' run one-way will have a 2% voltage drop. Your fuse size should be 1.25X max continuous current.
Since this is going to be between each charge controller and a bus bar, the length will be under 2'.
Excuse me in advance for a dummy question, but I have to ask it as it does bother me. A bus bar makes a parallel connection, so if all 3 charge controller output 60a, will the amperage before bus bar will be 60a and after bus bar 180a? Does it also mean the following?
  • I can use a 6AWG wire and 75A fuse between my charge controller and bus bar?
  • I should size a wire from the bus bar to the battery bank and inverter to handle 180A+? 3/0 or 4/0?
3. Your panels should have a maximum fuse rating on the sticker. That's the size you should use on each series string.
Yes it is there: 15A, so this is what I'm going to use (see in violet below). Thanks

I've seen people often use 60A breaker before a charge controller as PV disconnect. Is my understanding correct, if I have 20A coming from my PV array, I can use even 30A breakers?
1624983222381.png

Many thanks in advance!!!
Vlad
 

snoobler

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75A fuse/breaker between each charge controller and bus bar.

Bus bars still need to have sources/loads connected with best practice in mind.

From "Wiring" in link #2 in my sig:

1624992819630.png

Yes to 75A and 6awg connecting each MPPT to bus bar. It will be 60A from each charge controller and 180A to the battery bank.

180A between bus bar and battery. You'll want to size the wire for the maximum continuous power you expect to see, and you'll want a fuse between the battery and bus bar.

Using a breaker as a single switch to cut all input into the SCC is not uncommon. Just make sure it's 1.25X the wire rating.
 

Vovanenok

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Thanks a lot snoobler, your help is so much appreciated
I'm checking all the links in your signature, it is a whole library :)

Yes to 75A and 6awg connecting each MPPT to bus bar. It will be 60A from each charge controller and 180A to the battery bank.
I could not find a quality 75A fuse, so I will consider going with 80A fuse and 4 AWG wire. Does it sound right?

180A between bus bar and battery. You'll want to size the wire for the maximum continuous power you expect to see, and you'll want a fuse between the battery and bus bar.

Thanks! Using the awg chart link from your signature, it recommends 0000 (4/0) wire and I think 250A fuse before the battery bank. Does it sound right?

Using a breaker as a single switch to cut all input into the SCC is not uncommon. Just make sure it's 1.25X the wire rating.

I will have a 15A breaker (as clarified with your help above) for each of the parallel connected string (before a bus bar in the combiner box), so the wires from PV panels to SCC will be already protected. Since I will get 20A ( 2 x 10A parallel) from the combiner box to the SCC running 10 AWG, from what I see I can install either 30A or 60A double breaker directly before the SCC. Does it sound right?

Thank you a ton again! I think this will be super helpful for many people looking to connect multiple SCCs
Vlad
 

snoobler

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80A fuse is fine. Skip the 4awg wire unless you want to. It's unlikely that an event would fall perfectly between 75 and 80A.

4/0 and 250A fuse from bus bar to battery.

If you've listed it, I've missed it, but the breaker should be sized for the wire between the combiner box and the MPPT. Yes, it's not that important since you already have overcurrent protection on each string, but you don't want this breaker to create any problems, so size it for the wire.

FWIW, on your setup with only two strings in parallel on any MPPT, no overcurrent protection is required between your panels and MPPT to meet NEC code:


The panels themselves are the "fuses" in a 2P array.

Very common to configure as you are simply for convenience. You can isolate a single string or the whole array two different ways.
 

Vovanenok

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You are so great snoobler, I appreciate you taking time to answer all my questions in details! Thanks for the links as well!
And thanks for this forum, it is a wonderful place for solar DIYers.
 

snoobler

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You are so great snoobler, I appreciate you taking time to answer all my questions in details! Thanks for the links as well!
And thanks for this forum, it is a wonderful place for solar DIYers.

Thanks be to Will. I'm just the top post whore here. :)
 
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