What size battery stud fuse block for this set-up?
- Thread starter marcfest
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I think you are asking about the needed amp rating for a bus bar. You should have both a positive bus bar and a negative bus bar to make all of the connections much simpler.
Given that the largest thing shown here is the 250A inverter fuse, a 300A or larger bus bar would be fine.
You should have a 250A Class T fuse between the battery and the positive bus bar. This would also make the inverter fuse redundant.
Unrelated but note that your charge controller may be undersized. You have 4 350W panels for a total of 1400W. On a 24V system that can be up to 58A of charge current. You show a 40A controller. You should have at least a 50A controller.
You will need smaller wire for the charge controller. A 40A or 50A controller will likely not accept 2/0AWG wire. 6AWG would be a much better choice.
And you certainly do not need 2/0AWG to the DC-DC converter and fuse block.
Given that the largest thing shown here is the 250A inverter fuse, a 300A or larger bus bar would be fine.
You should have a 250A Class T fuse between the battery and the positive bus bar. This would also make the inverter fuse redundant.
Unrelated but note that your charge controller may be undersized. You have 4 350W panels for a total of 1400W. On a 24V system that can be up to 58A of charge current. You show a 40A controller. You should have at least a 50A controller.
You will need smaller wire for the charge controller. A 40A or 50A controller will likely not accept 2/0AWG wire. 6AWG would be a much better choice.
And you certainly do not need 2/0AWG to the DC-DC converter and fuse block.
marcfest
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Also, I suppose if I upgrade to a 60A charge controller, I should upgrade its circuit breaker from 50AM to 70A, right? Or 80A?
Hedges
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SCC output amperage is not affected by PV panel configuration, input voltage, or input current. SCC takes in PV watts (volts x amps) at any voltage higher than battery, and switches an inductor to produce battery voltage at higher current. Similar to what a transformer does, but for DC.
PV_volts x PV_amps / battery_volts = battery_amps, which are delivered by SCC.
If you wire PV panels 2s2p and orient one "2s" South East and the other "2s" South West, about a 90 degree angle between them, area presented to sun will be about 0.7 as much, so peak current will be about 0.7x as much, and power harvested will be more flat and last longer through the day. Could be a better fit to your loads.
When using fuses or thermal-magnetic breakers (or thermal breakers), it is recommended to size them 1.25x larger than continuous current.
Some magnetic-hydraulic breakers say 1.0x is sufficient.
The headroom is to prevent nuisance trips, which can happen due to hot day and heat from wire and connection affecting the element.
Consider lowest battery voltage when calculating battery current.
(For inverters, besides those factors, I also suggest an additional 1.12x factor because 60 Hz ripple causes additional heating.)
4000W / 24V / 85% efficient x 1.12 x 1.25 = 275A minimum fuse
So I would rather have larger than 250A fuse (and wire ampacity) unless you won't actually draw 4000W for more than a few minutes.
2/0 is OK for 300A if individual wires in free air (not bundle) and rated 90 degree C.
In this case I used 24V not 20V because that's around lowest voltage for LiFePO4. For lead-acid I would have used 20V.
8000W surge not considered because it is brief.
As stated, the arrangement doesn't change anything. It is still 1400W. 1400W / 24V = 58A. A 50A charge controller will likely be plenty since your battery voltage is going to be closer to 26V and you will rarely get 1400W out of the panels.
The rule of thumb is 125% of load size to get the fuse size but confirming the chosen size isn't too large for the wire. Remember, the fuse is there to protect the wire. So a 60A controller should have a 75A fuse. But you may not find a 75A so 80A should work and 80A is safe for 6AWG wire. If you go with a 50A controller then a 60A or 70A fuse is needed as well as 6AWG wire.
marcfest
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Thank you
The 2/0 awg marine grade cable is good to 330 amperes. Fuse the battery positive terminal with 300A Class-T fuse. Use a larger Busbar such as Blue Sea ; https://www.bluesea.com/products/2104/PowerBar_600A_BusBar_-_Four_3_8in-16_Studs
Less money on Amazon; https://www.amazon.com/Blue-Sea-Systems-PowerBar-BusBar/dp/B000XBB758/
I use MRBF fuses on the BusBar for the other devices. https://www.bluesea.com/products/5191/MRBF_Terminal_Fuse_Block_-_30_to_300A
Fuse each device's sub-circuit at the BusBar. A 250A would be fine for the inverter.
Less money on Amazon; https://www.amazon.com/Blue-Sea-Systems-PowerBar-BusBar/dp/B000XBB758/
I use MRBF fuses on the BusBar for the other devices. https://www.bluesea.com/products/5191/MRBF_Terminal_Fuse_Block_-_30_to_300A
Fuse each device's sub-circuit at the BusBar. A 250A would be fine for the inverter.
