Help me not burn my truck down

[bonuscup]

Hi all, would appreciate a review of my wiring diagram for safety and correctness. This is my first attempt at building out a solar setup. It's going in my Overlnd camper on a 3g Tacoma. Designed for self-sufficient remote camping for 2-4 days at a time.

System includes:

2x Epoch 105ah Essential series LifePO4 batteries
3x 100W BougeRV flex panels
Victron 100 | 50 MPPT
Victron Phoenix 12 | 500 inverter
Various 12v loads included in the diagram

Many thanks.

 

[carterd]

Class T fuses are generally recommended for lithium ion batteries. MRBF is probably acceptable for smaller 12V banks like yours, but they still have disadvantges to Class T. Epoch may have specific recommendations for their batteries.

You should have equal cable lengths for each battery's positive and negative connections to the busbars.

This will be a nice setup.

 

[slomatt]

Looks like a fun project. Based on the BlueSea 12v current chart it looks like your 2/0 and 6 awg wires are protected by reasonable sized fuses that are located near the power source or where wire size is reduced.

A couple of suggestions:

- I'd recommend adding add another switch between the solar charge controller and the positive bus bar. That would allow you to shut off +12v from solar when you are working on the panels, and you could shut off all power by turning off that switch and the switch for the batteries. Also, since the charge controller is a current source you might want to put a fuse close to the controller to protect the wire going to the terminal block. Blue Sea likely has recommendations for how to fuse this device.

- The 2/0 wire for the chassis ground is probably overkill and you could save some money and weight by going with a smaller gauge wire. With the current design the only power using the chassis as a return path would be through the 60A feed to the fuse block.

- What is the max draw of the inverter, is a 60A fuse large enough?

- The fuse size chart in the upper right includes ~5 different fuse sizes. Generally the idea is the run wire that is large enough to handle the current draw of the load and then to size the fuse to protect the wire. To simply things you might want to select 2 wire sizes (one large, one small) and 2 sizes of associated fuses. That way you could buy them in bulk, and you would reduce the number of spare fuses you need to carry. For example, 14 or 12 AWG wire protected by 10 or 15A fuses for most of the circuits, and something larger for the dual USB plug (can it really draw 25A?).

 

[Verkstad]

charge controller is a current source you might want to put a fuse close to the controller to protect the wire going to the terminal block.

While it wont hurt anything to fit a fuse there. How to decide its ampacity ?
Plus its fairly redundant.
The 12" 6AWG (assuming quality copper...) shown is protected on the battery side by 60A fuse. 6AWG will easily handle the 25-ish amp max current the 300W solar array is capable of. If by magic the array could increase its output, The charge controller output is current limited also.

should have equal cable lengths for each battery's positive and negative connections to the busbars.

As shown, the battery cables are equal between them, connection to the bussbar & main fuses is irrelevant.
Is there an electrical reason for that suggestion ?

 

[carterd]

In a parallel battery setup, using cables of equal length for each battery helps ensure that the current is distributed equally among the batteries. This minimizes imbalances during charging and discharging, optimizing performance and lifespan. Here is a link to some Victron guidance on this topic. https://share.google/Xu96puiUVQwqMwcYW

 

[bonuscup]

In a parallel battery setup, using cables of equal length for each battery helps ensure that the current is distributed equally among the batteries. This minimizes imbalances during charging and discharging, optimizing performance and lifespan. Here is a link to some Victron guidance on this topic. https://share.google/Xu96puiUVQwqMwcYW

Really helpful, thanks for sharing this. Is this in reference to the wire length for connection between batteries only? Or also the wire length from the positive terminal to the switch and negative wire to bus?

 

[bonuscup]

Class T fuses are generally recommended for lithium ion batteries. MRBF is probably acceptable for smaller 12V banks like yours, but they still have disadvantges to Class T. Epoch may have specific recommendations for their batteries.

You should have equal cable lengths for each battery's positive and negative connections to the busbars.

This will be a nice setup.

I have a 120A Blue Sea class-t fuse that I was considering using after the two terminal MRBF fuses before the switch, which is ABYC code. In my case I'm not sure it's needed, but all for extra insurance. Not sure though to your point if needed with this smaller bank size. If I eventually add more power, I would consider it then.

 

[bonuscup]

- I'd recommend adding add another switch between the solar charge controller and the positive bus bar. That would allow you to shut off +12v from solar when you are working on the panels, and you could shut off all power by turning off that switch and the switch for the batteries. Also, since the charge controller is a current source you might want to put a fuse close to the controller to protect the wire going to the terminal block. Blue Sea likely has recommendations for how to fuse this device.

I had originally planned to do this but someone else said it wasn't necessary for only 300w of solar. I'm going to add a 60A breaker.

- The 2/0 wire for the chassis ground is probably overkill and you could save some money and weight by going with a smaller gauge wire. With the current design the only power using the chassis as a return path would be through the 60A feed to the fuse block.

That's what I figured too. I already have a 10ft run of 2/0 so I'll probably just use it anyways.

- What is the max draw of the inverter, is a 60A fuse large enough?

900w and 92% efficiency, so actually it should probably be 100A fuse? With an inverter should I be fusing for continuous power or max?

900w/12v = 75a, then factor for 92% efficiency = 69a, then add 1.25x = 86, so 100a fuse is appropriate for 6 awg wire? It's about a 2ft run.

- The fuse size chart in the upper right includes ~5 different fuse sizes. Generally the idea is the run wire that is large enough to handle the current draw of the load and then to size the fuse to protect the wire. To simply things you might want to select 2 wire sizes (one large, one small) and 2 sizes of associated fuses. That way you could buy them in bulk, and you would reduce the number of spare fuses you need to carry. For example, 14 or 12 AWG wire protected by 10 or 15A fuses for most of the circuits, and something larger for the dual USB plug (can it really draw 25A?).

Great call. I am using 10/2 and 16/2 duplex for everything. I need to double check the draw on that socket, but I think it was 30A, which seems high.

 

[Verkstad]

Really helpful, thanks for sharing this. Is this in reference to the wire length for connection between batteries only? Or also the wire length from the positive terminal to the switch and negative wire to bus?

As shown on your picture is the correct method to parallel connect your two batteries.
If your 2 batteries are adjacent to each other or separated by some distance, those "jumper" conductors should be made the same length but they dont have to be since the pos & neg charge/load conductors attach to "opposite corners" of the battery array.
From that point on, distance to busbars, fuses, etc. is irrelevant to the method of parallel connecting batteries.

 

[Verkstad]

Btw,
The output of your plug-in battery charger should be fused connected also.
Commonly that's done with a separate fuseholder directly at the battery, or you could connect on that multicircuit fuseholder.
Just be aware, if connected at that fuseholder, turning off the big red switch will disconnect battery charging too.
Further,
To maintain optimum balance when charging, Negative of the battery charger should be connected to neg. on the other battery or the 'grounded side' of the battery monitor device.

 

[bonuscup]

Btw,
The output of your plug-in battery charger should be fused connected also.
Commonly that's done with a separate fuseholder directly at the battery, or you could connect on that multicircuit fuseholder.
Just be aware, if connected at that fuseholder, turning off the big red switch will disconnect battery charging too.
Further,
To maintain optimum balance when charging, Negative of the battery charger should be connected to neg. on the other battery or the 'grounded side' of the battery monitor device.

This is such a great catch, I should have thought of this. Thank you.

 

[bonuscup]

Btw,
The output of your plug-in battery charger should be fused connected also.
Commonly that's done with a separate fuseholder directly at the battery, or you could connect on that multicircuit fuseholder.
Just be aware, if connected at that fuseholder, turning off the big red switch will disconnect battery charging too.
Further,
To maintain optimum balance when charging, Negative of the battery charger should be connected to neg. on the other battery or the 'grounded side' of the battery monitor device.

Do you have a link to an example of what type of fuse is used for this? Because the busbar will have MRBF fuses integrated and terminal fuses on each battery, I'm not sure where to put one unless it was inline on the positive cable of the charger somewhere close to the battery.

 

[Verkstad]

Do you have a link to an example of what type of fuse is used for this?

If the battery charger is less than 30A,
I would use a FHA series fuseholder spliced into the pos. lead of the battery charger.
They are inexpensive and keeps all smaller fuses the same ATO style.

 

[slomatt]

While it wont hurt anything to fit a fuse there. How to decide its ampacity ?
Plus its fairly redundant.
The 12" 6AWG (assuming quality copper...) shown is protected on the battery side by 60A fuse. 6AWG will easily handle the 25-ish amp max current the 300W solar array is capable of. If by magic the array could increase its output, The charge controller output is current limited also.

As shown, the battery cables are equal between them, connection to the bussbar & main fuses is irrelevant.
Is there an electrical reason for that suggestion ?

Because the charge controller is a voltage source (like a battery) some people like to put a fuse on both ends of the positive output to protect the wire. The fuse on the battery end protects from shorting the battery +12v to ground, and the fuse on the charge controller end protects from shorting the controller +12v to ground. Both could be sized based on the current capacity of the wire.

That said, I checked the instructions from Victron and they only show a fuse (55-70A) on the battery side of the wire, so the controller hopefully is internally protected against shorts. Interestingly the diagram also includes a fuse on the positive wire coming from the solar array.

 

[slomatt]

900w and 92% efficiency, so actually it should probably be 100A fuse? With an inverter should I be fusing for continuous power or max?

900w/12v = 75a, then factor for 92% efficiency = 69a, then add 1.25x = 86, so 100a fuse is appropriate for 6 awg wire? It's about a 2ft run.

I would defer to the installation docs for that inverter which state...

"The inverter is fitted with an internal DC fuse. If the battery cable length is more than 1.5m, an additional fuse or DC circuit breaker must be added to the battery cable, located close to the battery."

Also, it looks like the inverter only fits a max of 8awg wire, so the 6awg you have in the diagram might not fit in the positive terminal.