Critique my upcoming trailer build

WYOFamily

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Good morning, can you guys take a look at this very rough mspaint schematic of the system I’m intending to install on my cargo trailer? I have most of the parts already.

2 x 206ah SOK LiFepro4 batteries in series for 24v.
300a ANL on the positive. Battery disconnect switch on the negative (Or should I put this on the positive cable?)
2awg pure copper cables from bank.
Victron Smart Shunt after shutoff on Negative.
positive to bus bar
negative to bus bar
200a MEGA fuse on positive to 2000w 24v Giandel Inverter
Victron 150/70 MPPT Charge Controller 80a circuit breaker fuse on the 6awg to the batteries.
6 x Rich Solar 200w 12v panels 3S2P

calculated:

Max Voltage per panel at low temp: 28.6335v
Array Max Voltage: 85.9v
Amps into CC: 19.6
Amps Out CC: 58.46

63a breaker for panels. I may have gone way overboard on the breaker But each panel is internal fused right?

does this look okay? Do I need to consider anything else?
Thanks in advance. Again, sorry for the MS Paint!
 

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mikefitz

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Do I need to consider anything else?
Protective fuses/breakers directly after or incorporated with the positive buss bar. All cable feeds from the power source, the battery, need protection fitted at the power source.
For example the Victron 150/70 and its cable run is only protected by 300 ANL fuse, more suitable protection would be an additional 100A fuse/breaker directly after the buss bar.

Fuse distribution units are available , for example, from Victron,
Victron Fuse-buss bar.jpg
Mike
 

WYOFamily

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Protective fuses/breakers directly after or incorporated with the positive buss bar. All cable feeds from the power source, the battery, need protection fitted at the power source.
For example the Victron 150/70 and its cable run is only protected by 300 ANL fuse, more suitable protection would be an additional 100A fuse/breaker directly after the buss bar.

Fuse distribution units are available , for example, from Victron,
View attachment 71902
Mike
There is an 80amp breaker between the CC and the bus bar. Would I need an additional? Also, the pictures, is this the Lynx Distributor?

thanks!
 

mikefitz

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Was the breaker in the original diagram, if so my apologies I missed it.
The cable runs need protection , unless oversized so as to be protected by the 300A ANL.

Note the SOC battery is rated for 100 A so perhaps the protection fuse and breaker values are too high.
The max charge current is 50 amps.

The fuse holder in the pic is not the Lynx.
 

WYOFamily

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No it wasn’t actually. I thought I had caught the omission before anyone else did Lol.

I am still learning, when you say the SOK is rated for 100a. What do you mean? Is that max discharge amperage? And they will only charge at 50a max? Regardless of multiple batteries and the wiring config? Is this correct? If so, what fuse sizes will adequately protect this set up. It has been one of the hardest things for me to come up with calculations vs varying opinions so far. Originally I went with a 125a fuse on the inverter. 2000w/24v x 1.25. But i was told that didn’t adequately cover any surges even though I thought the X 1.25 accounted for it.

I really appreciate your time and knowledge. Thank you
 

mikefitz

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SOC data.jpg
The batteries are in series so the same current through both, maximum of 50 A recommended 40 amps.

Fuse values are set to between 1.2 and 1.5 the maximum allowed current in that leg of the circuit. The allowed current will depend on the current rating of the cable and what ever is on the end of that cable. The fuse is to prevent excess current from the battery causing damage and perhaps fire. With the SOC battery the current is limited by the BMS but in practice there is an slight chance the BMS protection could fail, unlikely with two in series but still possible.
Thus its good practice to add fuses/breakers to the system.
Midi/Mega fuses are usually slow blow type and will tolerate short term overload so your 1.25 value is OK.
For the inverter and its cable protection a fuse at buss bar of 150 amps will be OK as the inverter draw must not exceed 100 amps continuous due to battery limitation.

One thing you may need to consider is the inrush current to the inverter input capacitors the first time its connected. The fuse will tolerate the short term inrush but the BMS may not. Search the forum for advice and use a power resistor or filament bulb to control the charge current.

Mike
 

rmaddy

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You stated you are using 2AWG wire from the batteries. The max safe fuse size for 2AWG wire is 200A. Having a 300A ANL fuse is bad. The fuse will sit there all nice and happy while the wire melts and catches fire. The chosen fuse/breaker size must always be between the expected load size and the maximum safe fuse size for the chosen wire. 1.25 times the expected load is a typical choice as long as that is less than the maximum safe size for the wire.

You have a 2000W inverter on a 24V system. 2000W / 24V / 0.8 = 104A. That decides your wire size. 2AWG is a good choice. Now you need a fuse between 104A and 200A. I'd choose a 125A or 150A fuse instead of the 300A fuse. Also keep in mind that the SOK batteries are rated for 100A max continuous discharge. Another reason a 300A fuse is pointless.

The 200A fuse for the inverter should be made smaller as well. I would go with 125A or 150A. Technically 200A is at the limit for the 2AWG wire but why allow the wire to get to its limit? You could literally boil water at that limit assuming you have 105ºC rated wire.

The 63A PV disconnect breaker is not there to protect anything. It's only there to act as a disconnect. That's fine with your setup since your panels are in 3S2P.

You should have a fuse between the 24-12V converter and the bus bar.

The 150/70 SCC is much bigger than needed. You have 1200W of solar on a 24V system. That's a maximum of 50A charge current if you somehow get a full 1200W out of the panels why mounted flat on the vehicle roof. You could have used a 150/45. The 150/45 is technically a tiny bit low but if your batteries are over 25V (which they will be most of the time) then it would only be a limit if you actually somehow got 95% of your 1200W. Mounted flat on the roof of a vehicle it will be extremely rare you get anywhere near that. Then again, the 150/70 allows for more solar in the future.

If the Voc of your panels is under 30V in the cold, then at 3S you could have used a 100V SCC. The 100/50 would have met your needs. But again, the 150/70 gives you room to add more solar.

Since the SOK batteries have a recommended 40A charge current (50A max), the 70A SCC is too much. Another reason for the 150/45 or the 100/50.
 

WYOFamily

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You stated you are using 2AWG wire from the batteries. The max safe fuse size for 2AWG wire is 200A. Having a 300A ANL fuse is bad. The fuse will sit there all nice and happy while the wire melts and catches fire. The chosen fuse/breaker size must always be between the expected load size and the maximum safe fuse size for the chosen wire. 1.25 times the expected load is a typical choice as long as that is less than the maximum safe size for the wire.

You have a 2000W inverter on a 24V system. 2000W / 24V / 0.8 = 104A. That decides your wire size. 2AWG is a good choice. Now you need a fuse between 104A and 200A. I'd choose a 125A or 150A fuse instead of the 300A fuse. Also keep in mind that the SOK batteries are rated for 100A max continuous discharge. Another reason a 300A fuse is pointless.

The 200A fuse for the inverter should be made smaller as well. I would go with 125A or 150A. Technically 200A is at the limit for the 2AWG wire but why allow the wire to get to its limit? You could literally boil water at that limit assuming you have 105ºC rated wire.

The 63A PV disconnect breaker is not there to protect anything. It's only there to act as a disconnect. That's fine with your setup since your panels are in 3S2P.

You should have a fuse between the 24-12V converter and the bus bar.

The 150/70 SCC is much bigger than needed. You have 1200W of solar on a 24V system. That's a maximum of 50A charge current if you somehow get a full 1200W out of the panels why mounted flat on the vehicle roof. You could have used a 150/45. The 150/45 is technically a tiny bit low but if your batteries are over 25V (which they will be most of the time) then it would only be a limit if you actually somehow got 95% of your 1200W. Mounted flat on the roof of a vehicle it will be extremely rare you get anywhere near that. Then again, the 150/70 allows for more solar in the future.

If the Voc of your panels is under 30V in the cold, then at 3S you could have used a 100V SCC. The 100/50 would have met your needs. But again, the 150/70 gives you room to add more solar.
As alway, you’re a wealth of information. I will size my fuses accordingly. Back to Amazon I go lol.
 

rmaddy

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Glad to help. I was making an edit while you replied. Please look at the newly added last paragraph in my previous post. You really need to rethink your SCC choice.
 

WYOFamily

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I thought i would give it a bit of future expansion capacity but if you think I’m going to over cook things then by all means I will change it.

I haven’t opened any items yet so they are all returnable. Do you think 1200w is too much or could I be wiring this differently to be more efficient?

Here is what I calculated for this array In 3S2P

Max Voltage per panel at low temp: 28.6335v
Array Max Voltage: 85.9v
Amps into CC: 19.6
Amps Out CC: 58.46
 
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rmaddy

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Given the 40A recommended charge current for the batteries you want enough solar to actually give you 40A. Ideally that would be 1000W when the batteries are at 25V. If your panels are mounted flat on the roof then 1200W of panels will rarely if ever give you 1000W. So the 1200W of panels is fine. If your get the 150/45 or the 100/50 then even if you add a couple more panels appropriately, the SCC won't be able to push too much current to the battery. With the 150/70 and enough panels you could over push the batteries.

If you ever plan on adding two more batteries so you have 4 in 2S2P then your batteries can handle 80A (100A max) charge current. Then the 150/70 and more panels would be perfectly fine.
 

WYOFamily

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So if My calculations are accurate, the 150/45 will cap out the potential max amps out to 45a? The potential max amps out of my current SCC would be 58.46a. This wouldn’t overdrive the 150/45 SCC and the 100/50? I am starting to get the idea that Victrons SCC naming are max voltage In / max amps out. Not necessarily what the SCC can handle amps wise coming in. Is this accurate?
 

WYOFamily

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Will the victron allow me to set the max charging rate in the app? That would allow me to keep the current SCC and not have to return and rebuy.
 

rmaddy

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So if My calculations are accurate, the 150/45 will cap out the potential max amps out to 45a? The potential max amps out of my current SCC would be 58.46a. This wouldn’t overdrive the 150/45 SCC and the 100/50? I am starting to get the idea that Victrons SCC naming are max voltage In / max amps out. Not necessarily what the SCC can handle amps wise coming in. Is this accurate?
Yes. the naming is "max input voltage (the coldest Voc) / max output current to the battery".

A 150/45 (which happens to be what I have) will never output more than 45A. If you have enough solar wattage that could result in more than 45A, the extra above 45A is simply not produced.

The 150/70 can output up to 70A. But with 1200W you might get the 58.45A if your battery was down to 20.5V.

Remember, your flat mounted panels will rarely, if ever, reach the full 1200W. And your battery should never be down to 20.5V. If you manage to get 1000W while the battery is at 24.0V you would only get 42A.

Will the victron allow me to set the max charging rate in the app? That would allow me to keep the current SCC and not have to return and rebuy.
There is a setting in VictronConnect that lets you set the max charge current. So you could set it to 40A even with a SCC that can potentially output more than that. My 150/45 is setup for 40A this way. This should allow you to use the 150/70 that you have safely with the SOK batteries. And if you do add two more batteries and more panels, you could take full advantage of the 70A output.
 

WYOFamily

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I really appreciate it. So one last question (for now lol). The Breaker at the SCC, considering the SCC is a 150/70 and max charge will be set at 40a, should I keep the 80a breaker to protect the SCC or reduce it to 50a to protect the BMS?
 

rmaddy

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The breaker is to protect the wire. The 80A breaker is fine for the 6AWG wire.
 

WYOFamily

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Does this look better?
 

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rmaddy

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You still need a fuse between the 24V->12V DC converter and bus bar.
 
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