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Advice on adding 8' 4/0 cables from Battery Bank to Victron Power-In or Distributor

jim_in_socal

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Joined
Oct 22, 2024
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11
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California
For background, I have replaced my 4 x Group 24 SLA batteries with a single Epoch Essentials 300Ah LiFePO4 battery in the same exposed slide-out battery tray on the driver's side of my coach. I added a 300A MRBF to the positive terminal of the battery with 4/0 wiring to a disconnect switch which is connected to a 400A bus bar. I connected the negative side via a 4/0 wire to a Victron Smart Shunt which is then connected to its own 400A bus bar. All the existing OEM wiring for the 60A AC-DC Converter (which I've upgraded to a lithium version), a pair of 1000W inverters, the generator starter, the 12v house connections, and the house and chassis grounds were then reconnected to those bus bars and fuses/circuit breakers already in that battery compartment. The converter and inverters are in a compartment on the passenger's side so there are several 8-12' runs of 1/0 and 2AWG cable across the coach. Once I disconnected the BIRD/BIM to protect my alternator from overloading with the new lithium batteries, all is working as expected. I am now at the point now of adding a Renogy 50A DC-DC Charger with MPPT to allow my alternator to charge the house batteries and also connect 2 ground-deployed 400W solar panels. I am prewired for roof solar as well so I plan on adding panels with a Victron 100/50 MPPT in the future.

My question is this. I will need to run another set of 4AWG across the coach to the battery bank for the DC-DC Charger w/ MPPT and also prewire in a second set for the future MPPT. Would it by better and allow more future expandability (e.g., bigger inverters or a multi-plus) to run 7-' of new 4/0 wiring directly from the battery bank to the passenger's side basement compartment with something like a Victron Power-In (with mega fuse hack) which all my components would then connect to?I realize moving the battery bank itself would be ideal from a wiring perspective but unfortunately not realistic from a space perspective.

Any advice or experience with something like this? Any suggestions on additional fusing to protect that long 4/0 wiring run? I thought a 400A T-Class fuse between the battery and disconnect might be sufficient based on the 4/0 ampacity and expected load.
 
If you have the battery fused, you are safe from a dead short triggered fire.
That 4/0 run should be protected with at least a 250A fuse/breaker.
 
If you have the battery fused, you are safe from a dead short triggered fire.
That 4/0 run should be protected with at least a 250A fuse/breaker.
Thanks for the fast response but this raises a slightly different question. I may eventually add a second battery and if so, I'd protect each individual battery with an MRBF on the terminal but also with a 400A fuse before the battery disconnect. If I did that, would that be enough protection for that 4/0 wire from the bus bar across the coach to the Victron Power-In or do I need to fuse that wire separately? I understand that for smaller wires also attached to the bus bar to other devices, I'd need smaller more appropriate fuses. But wouldn't it be redundant to have essentially two 400A fuses protecting that 4/0 wire?
 
I would fuse the output of any device that has an output. Granted if both batteries are right next to one another I would just fuse the single output.

This means a charge controller, DC/DC charger, 120v charger, battery and inverter 120v side.
 
If it were me, what I would do is use a bus bar for your main connection points.

It is difficult to find DC breakers that for use above high continuous currents, so I would run dual ( 2 each ) 1/0 wires from the battery terminals - through 2 separate breakers for each battery instead of trying to run 4/0 cable.

When you add the second battery - do the same, so you end up with 4 each, 1/0 wires and 4 breakers from the dual batteries.

Perhaps use ~ 150 - 175 amp breakers like the bluesea 187 or MP 87 series.



Add your other large loads at the bus bar or smaller loads in via a fuse block.

You don't want to end up having small wires attached to a bus bar with batteries that can pump out 100s of amps without a breaker to isolate it off for maintenance and construction.
 

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Thanks for all of the replies. Based on what I've learned (hopefully correctly), here is my current plan to connect batteries to new Victron Distributor across the coach with a fused 7.5ft 4/0 wire so that most down/upstream connections can be made from there instead of multiple smaller wires running across the coach. Please let me know if you see anything wrong.
 

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Before you get too far along with this, make sure that one Epoch 300 amp battery can start your generator. The surge of the starter can be significant. If you have to crank the generator for more than a few seconds, the battery may get unhappy and the 150 amp fuse could blow. It should work, but I would want to know that for sure before wiring everything up.

I had dual 280 Ah LiFePO4 batteries in my prior camper. Each BMS was rated for 120 amps continuous. It should have been plenty to start the generator. Even so, I retained a separate lead acid battery to start the generator. This didn't stress the house batteries and it ensured that even if my house batteries were dead, I could still start the generator.
 
Before you get too far along with this, make sure that one Epoch 300 amp battery can start your generator. The surge of the starter can be significant. If you have to crank the generator for more than a few seconds, the battery may get unhappy and the 150 amp fuse could blow. It should work, but I would want to know that for sure before wiring everything up.

I had dual 280 Ah LiFePO4 batteries in my prior camper. Each BMS was rated for 120 amps continuous. It should have been plenty to start the generator. Even so, I retained a separate lead acid battery to start the generator. This didn't stress the house batteries and it ensured that even if my house batteries were dead, I could still start the generator.
Jim
Thanks for giving my plan a review. My single Epoch 300Ah is rated for 200A continuous. I have done a cold start of the generator with a Victron shunt installed and it pulls approx. 80 amps for a few seconds until its running. I imagine it could be a bit tougher in much colder weather though so I'll keep an eye on that. In a pinch, I guess I could use the "battery boost" button for the reverse of its intended purpose to provide a bit more amperage by temporarily connecting in the chassis starter battery via the isolation solenoid. Or like you, I could retain one of the SLA batteries just for the generator start since I still have room in the battery tray.

Also, I've traced Newmar's original wiring as best I can but as far as I can tell, they didn't install any fuse or breaker on that 1/0 wire to the generator from the original SLA battery bank. I was going to put a 150A or 200A fuse in place when I finish the install.
 
Thanks for all of the replies. Based on what I've learned (hopefully correctly), here is my current plan to connect batteries to new Victron Distributor across the coach with a fused 7.5ft 4/0 wire so that most down/upstream connections can be made from there instead of multiple smaller wires running across the coach. Please let me know if you see anything wrong.
Great Diagram, Did you creat that?
If so what did you use to create it?
 
Great Diagram, Did you creat that?
If so what did you use to create it?
Thanks. I did create it and spent way too much time doing so :) I used a free application called draw.io on a Mac. There is a web version as well so I can see my diagrams on my phone/tablet.
 
Jim - Interesting. I didn't even realize that the shunt might not be able to capture the surge. Is there a better way to do so?

There are clamp on ammeters that can catch the surge.

Note that I'm speculating that the shunt can't (or didn't) catch the surge. Here's a thread from a while back where a forum member measured the surge from his Onan genset. It was high, but not as high as I thought it could be.


Here's another thread.

 
I have the 300amp shunt, and my onan generator seems to start fine. Even when the battery was nearly dead. I think mine is a 4000 series though.
 

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