24v Question

[LeoLopez]

So my system is a 24v system. My question is that Will in his site about the 2000w 24v blueprint, he states that one needs a circuit breaker between the solar charge controller and the main fuse bar. I have two solar charge controllers, do I need a bigger circuit and/or two different circuit breakers?

TIA

 

[FilterGuy]

So my system is a 24v system. My question is that Will in his site about the 2000w 24v blueprint, he states that one needs a circuit breaker between the solar charge controller and the main fuse bar. I have two solar charge controllers, do I need a bigger circuit and/or two different circuit breakers?

TIA

Use 2 different breakers

 

[rmaddy]

FYI - your question and its answer are not affected by having a 24V system. You would use two breakers for two SCC on a 12V, 24V, 48V, or any other voltage system.

You don't mention which charge controllers you have. The size of each circuit breaker (and wire) depends on the output battery current of each controller.

 

[LeoLopez]

FYI - your question and its answer are not affected by having a 24V system. You would use two breakers for two SCC on a 12V, 24V, 48V, or any other voltage system.

You don't mention which charge controllers you have. The size of each circuit breaker (and wire) depends on the output battery current of each controller.

Oh okay! I have two 50 amp SCCs. What size breaker would I need then?

 

[time2roll]

Oh okay! I have two 50 amp SCCs. What size breaker would I need then?

60a each and #6 wire minimum.

 

[LeoLopez]

60a each and #6 wire minimum.

One more question, in his diagram he has a main fuse but how do I know what size to use? He mentions 100 amp to 300 amp and I don't know which one I am supposed to get.

 

[time2roll]

24v into 2000 watt inverter probably 150 amp is fine with #2 wire.

 

[LeoLopez]

24v into 2000 watt inverter probably 150 amp is fine with #2 wire.

I am wanting to have a 3000 watt inverter charger. Would that go up to 200 or 250? If you don't mind can you explain how to calculate this?

 

[John Frum]

I am wanting to have a 3000 watt inverter charger. Would that go up to 200 or 250? If you don't mind can you explain how to calculate this?

3000 ac watts / .85 conversion factor / 24 volts low cutoff = 147.058823529 service amps
147.058823529 service amps / .8 fuse headroom = 183.823529412 fault amps

That means a minimum fuse size of 183ish amps.
The fuse is meant to protect the wire so you need wire rated for at least 183 amps.
For pure copper wire with insulation rated for 105 Celsius the smallest size that can handle 183 amps is 2 awg.
Since 2 awg can handle ~210 amps I suggest a 200 amp fuse.
The next readily available size is 0 awg which can accommodate a 250 amp fuse.

We have not talked about voltage drop which should also be considered.
For that we need to know the round trip circuit length.
Then we can use this calculator https://www.calculator.net/voltage-drop-calculator.html to make sure the voltage drop is less than 3%.

We calculate fist for ampacity because we don't want the insulation on the wires melting or catching fire, its imperative for safety.
We calculate second for voltage drop to make sure the system runs optimally.
Most of the experienced folks here tend to oversize the wires because we don't want them getting hot.

 

[LeoLopez]

3000 ac watts / .85 conversion factor / 24 volts low cutoff = 147.058823529 service amps
147.058823529 service amps / .8 fuse headroom = 183.823529412 fault amps

That means a minimum fuse size of 183ish amps.
The fuse is meant to protect the wire so you need wire rated for at least 183 amps.
For pure copper wire with insulation rated for 105 Celsius the smallest size that can handle 183 amps is 2 awg.
Since 2 awg can handle ~210 amps I suggest a 200 amp fuse.
The next readily available size is 0 awg which can accommodate a 250 amp fuse.

We have not talked about voltage drop which should also be considered.
For that we need to know the round trip circuit length.
Then we can use this calculator https://www.calculator.net/voltage-drop-calculator.html to make sure the voltage drop is less than 3%.

Thanks so much! I am definitely under the 3% drop. I am at slightly over 2%. This is awesome information! Thanks again!

 

[John Frum]

See my updated post.

 

[Dzl]

I am wanting to have a 3000 watt inverter charger. Would that go up to 200 or 250? If you don't mind can you explain how to calculate this?

Since it seems you want to learn the how and why (that's the spirit) behind the direct answers, here are a couple good resources on fuses/breakers/circuit protection. Both have beginner and intermediate DIY'ers as the target audience:

Fuses and Circuit Breakers (Video by Pacific Yacht Systems)
DC Fuse and Breaker Sizing and Placement (PDF from forum member FilterGuy)

 

[LeoLopez]

Since it seems you want to learn the how and why (that's the spirit) behind the direct answers, here are a couple good resources on fuses/breakers/circuit protection. Both have beginner and intermediate DIY'ers as the target audience:

Fuses and Circuit Breakers (Video by Pacific Yacht Systems)
DC Fuse and Breaker Sizing and Placement (PDF from forum member FilterGuy)

Thank you very much! I do want to learn more, I want to be able to locate an issue that may be in my system and how to fix it as well. I appreciate all of the help!!

 

[Dzl]

Thank you very much! I do want to learn more, I want to be able to locate an issue that may be in my system and how to fix it as well. I appreciate all of the help!!

Pacific Yacht Systems (the first link above) has a lot of good beginner oriented youtube videos on Marine Electrical which is very applicable to other areas of off-grid electrical as well. They have a good video on overall system design, and a few good playlists on their youtube channel.

 

[eXodus]

That means a minimum fuse size of 183ish amps.
The fuse is meant to protect the wire so you need wire rated for at least 183 amps.
For pure copper wire with insulation rated for 105 Celsius the smallest size that can handle 183 amps is 2 awg.
Since 2 awg can handle ~210 amps I suggest a 200 amp fuse.

go with the 200A fuse.

I got a 3000W inverter - that thing surges up 4000W for a second or so - a 150A fuse tends to get trip. Rather annoying

Thanks so much! I am definitely under the 3% drop. I am at slightly over 2%.

You need to size the fuse/wiring for the surge rating of your inverter. (or at least above the maximum running watts) otherwise you get phantom tripping at high loads.

 

[FilterGuy]

You need to size the fuse/wiring for the surge rating of your inverter. (or at least above the maximum running watts) otherwise you get phantom tripping at high loads.

This is primarily a problem with Fast blow fuses like the Class-T. However, for the Large LifePO4 banks we use, class-T fuses with the high AIC ratings are definitely recommended.

 

[John Frum]

This is primarily a problem with Fast blow fuses like the Class-T. However, for the Large LifePO4 banks we use, class-T fuses with the high AIC ratings are definitely recommended.

It depends on the inverter and the fuse.
Devil is in the details as usual.

Fuse A3T / Class T 200 Amp - Blue Sea Systems

Use with Class T Fuse Blocks for circuit protection of devices including inverters. high interrupt capacity for large battery banks including Lithium-ion and TPPL batteries.

www.bluesea.com

The trip curve on this class t fuse is not likely to be problem with even the beefiest low frequency inverter charger that you can find.
High frequency inverter chargers has a 2x surge rating of ~20ms and therefore are not a factor in fuse selection.