Looking for feedback on my system diagram. General feedback and also feedback on where to put circuit breakers.

loac

New Member
I've been loving learning about off-grid PV system design, haven't been this interested in a hobby in a long time!

The goal of this system is to learn about electrical systems and to hopefully have a functioning source of power to run a refrigerator/freezer in the case of an extended grid power outage.

I welcome any general comments on the attached system diagram. The areas that still have me scratching my head are:

  1. Sizing of conductors: Watching WIll's videos, it seems I need 2 gauge wire from the battery to the inverter and MPPT. However, when I put it in a wire sizing calculator I get 6 gauge for 4 feet at 1.5% loss. Am I missing something or is will just being conservative since he is talking to a large audience?
  2. Circuit breakers: I think that circuit breakers in a system like mine a largely used just for isolating parts of the system for convenience/safety, is that accurate?
  3. Circuit breakers/fuses: are circuit breakers and fuses interchangable from a safety standpoint in system like mine?
  4. Current in the circuit: This question is kind of challenging to word, but do the positive and negative conductors in between the charge controller, battery, and inverter all have the same current and voltage at all times since they are all tied to the same bus bars? There is 30A max coming from the MPPT, however there is 250A max going to the inverter. Does that 250A just basically go past the leg going to the MPPT?
Thank you in advance for any comments you have! Have a great weekend!
 

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HRTKD

Boondocker
A circuit breaker before and after the Victron 150/35 is appropriate. Many of us are using a double pole breaker mounted on a DIN rail for before the solar charge controller. It's mainly there to shut off PV input to the solar charge controller for when you have to work on the system. That should be a 20 amp breaker. 45 amp breaker after the solar charge controller.

A 300 amp fuse may be overkill for that battery since the BMS is rated for 100 amps continuous. I recommend a Class T fuse.

There should be a circuit breaker between the positive common bus bar and the inverter. The 3000 watt inverter would need a breaker of around 175 amps (3000 watts / 24v / .9 inverter efficency * 1.25 fudge factor). Could the inverter pull 175 amps? Probably not. At least, not for very long. Your battery bank isn't big enough to support that.

On your drawing, you should provide the wire gauge and length, not the amp rating. Sometimes you have the distance, sometimes not. Be consistent.

The inverter manual will often provide recommendations on fuse/breaker as well as wire size. All my wire/cable implementations were based on the calculator below that uses voltage, amperage and distance. A lot of people look at ampacity charts which only tell part of the story. The distance is very important. A short distance can mean a smaller gauge wire.

 

rmaddy

Solar Addict
Sizing of conductors:

3000W / 24V = 125A. 6AWG is much too small. It's fine for the voltage drop but too small for the amps. 2AWG would be the smallest wire you would want. And that's only for the 3000W. If you want to be able to handle the full 6000W surge capability then you need 3/0 or 4/0 to handle the 250A. Don't forget to enter 8', not 4' for the calculations since you need to enter the full round trip wiring length.

What does the inverter manual recommend?
 

loac

New Member
A circuit breaker before and after the Victron 150/35 is appropriate. Many of us are using a double pole breaker mounted on a DIN rail for before the solar charge controller. It's mainly there to shut off PV input to the solar charge controller for when you have to work on the system. That should be a 20 amp breaker. 45 amp breaker after the solar charge controller.

A 300 amp fuse may be overkill for that battery since the BMS is rated for 100 amps continuous. I recommend a Class T fuse.

There should be a circuit breaker between the positive common bus bar and the inverter. The 3000 watt inverter would need a breaker of around 175 amps (3000 watts / 24v / .9 inverter efficency * 1.25 fudge factor). Could the inverter pull 175 amps? Probably not. At least, not for very long. Your battery bank isn't big enough to support that.

On your drawing, you should provide the wire gauge and length, not the amp rating. Sometimes you have the distance, sometimes not. Be consistent.

The inverter manual will often provide recommendations on fuse/breaker as well as wire size. All my wire/cable implementations were based on the calculator below that uses voltage, amperage and distance. A lot of people look at ampacity charts which only tell part of the story. The distance is very important. A short distance can mean a smaller gauge wire.

Thank you! You have provided a lot of good feedback. I’ll look more into breaker sizing and pick up a couple of those.
interestingly enough, I fired up my system (with only one pv panel connected just to test it out) for a few minutes and used a clamp meter to see the amperage going through different conductors. It was very enlightening! It answered my question about whether there is the same amount of current going through all the conductors connected to the bus bar. There is less current in the conductors coming from the charge controller.
 

loac

New Member
Sizing of conductors:

3000W / 24V = 125A. 6AWG is much too small. It's fine for the voltage drop but too small for the amps. 2AWG would be the smallest wire you would want. And that's only for the 3000W. If you want to be able to handle the full 6000W surge capability then you need 3/0 or 4/0 to handle the 250A. Don't forget to enter 8', not 4' for the calculations since you need to enter the full round trip wiring length.

What does the inverter manual recommend?
Yes, you’re right of course. The wire sizing calculator I used specifically said it was for sizing just one wire but I should have put in double the length.
The inverter manual doesn’t recommend a wire size strangely enough.
 

DIDDLYV

Solar Enthusiast
A circuit breaker before and after the Victron 150/35 is appropriate. Many of us are using a double pole breaker mounted on a DIN rail for before the solar charge controller. It's mainly there to shut off PV input to the solar charge controller for when you have to work on the system. That should be a 20 amp breaker. 45 amp breaker after the solar charge controller.

A 300 amp fuse may be overkill for that battery since the BMS is rated for 100 amps continuous. I recommend a Class T fuse.

There should be a circuit breaker between the positive common bus bar and the inverter. The 3000 watt inverter would need a breaker of around 175 amps (3000 watts / 24v / .9 inverter efficency * 1.25 fudge factor). Could the inverter pull 175 amps? Probably not. At least, not for very long. Your battery bank isn't big enough to support that.

On your drawing, you should provide the wire gauge and length, not the amp rating. Sometimes you have the distance, sometimes not. Be consistent.

The inverter manual will often provide recommendations on fuse/breaker as well as wire size. All my wire/cable implementations were based on the calculator below that uses voltage, amperage and distance. A lot of people look at ampacity charts which only tell part of the story. The distance is very important. A short distance can mean a smaller gauge wire.

I had really planned on putting my shut offs before the common positive bus bar just so I shut batteries off from all loads, should I rethink? Do agree with shutoffs and breaker between panels and SCC and SCC and batteries
 
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HRTKD

Boondocker
I had really planned on putting my shut offs before the common positive bus bar just so I shut batteries off from all loads, should I rethink?

A more thorough description/diagram of your system in a separate thread would be in order.
 
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