Electrical wire sizing

[kromboy]

Sorry to post a question that's been beaten to death, but I just want to double check and make sure I don't burn my bus down.

I have a mock up of my first phase of power system for the bus, I figure by skipping the solar and all the roof work involved with it, I can save a bit of money and lots of time and use the bus as a weekend warrior for now, so this is what my initial setup will look like.

Having said that, I just want to make sure my wiring diagram is correct and want some help with sizing the wires, I bought some 2/0 wires based on some previous posts I've been poring through but man are these things expensive and hard to work with, so I want to make sure I'm not doing anything that's overkill and also to ensure I'm not risking the bus burning down.

What would you guys recommend as far as wire sizing goes here? and what about fuses? ANL? or blade? Is there anything I'm overlooking or a way to simplify the system more? 12v distribution panel will be mostly for lights (~8 10W lights so about 1A each, and will eventually have a fan, diesel heater and water pump)

Thanks for all the help as always,

Edit: Oh and as far as wire runs, I'm keeping them as short as possible, everything will be less than 5' in length, I'm going to drill a hole through the battery compartment which is by the rear wheel wells and my power system will be built either under the bed or on top of the wheel well in a shelf, longest run will probably be from the starter batteries to the DC to DC charger and rest will be less than 2' each. Fixtures connecting to the distribution panel will run longer, likely 40' for one of the light, and ~30' for a diesel heater (5kW), assuming the heater to be the highest draw connection to the panel.

 

[turf]

i've been working through similar project so....

i'd say....
from the battery to inverter to bus bar
2000w/12v= 166A.... so 2/0

for the chargers...

80A...so 4awg

for simplicity, i'd use the same wire size for the 60a charger.


https://blazeoffroad.com/blogs/electrical-systems-reference-data/determining-the-correct-wire-size-for-a-circuit

 

[desrtdog]

http://faroutride.com was my go to for electrical system design and specs. They have a calculator that you can purchase that will do calls on wire sizes, etc … probably some other free resources out there, but when I built my system a few years ago, this was the first thing to pop up…

 

[kromboy]

Thank you both! I guess I will need to keep my 2/0 wires, what about the connection between the batteries? How much amperage would flow between the two being connected in parallel?

 

[AlphaHare]

I've always liked this chart for ampacity and wire length.

IMO - use the 3% voltage drop length, and always go bigger when on the fence. Some value in having common sizes, even if technically too big, just to keep all the hardware and crimps the same. I.E. I'd prefer to over-do everything with 0/2 than have 2awg, 1awg, and 2/0 mixed in together.

https://www.bluesea.com/support/art...oosing_the_Correct_Wire_Size_for_a_DC_Circuit

 

[turf]

hey Krom,

i just noticed that you're also in Colorado. I'm up in the northeast corner of the state by sterling, so if you eve want to chat, feel free to hit me up.

the way you have it drawn, between the 2 batteries, i'd keep it the same cable 2/0.

if you changed your wiring diagram and parallel setup to meet at the bus bar, then you could use the 4awg for each single battery to the bus bar. you would only have a big wire from the bus bar to the inverter then.

battery
80A
I
bus bar ==160A=== inverter
I
80A
battery


vs

battery80A==battery160A==inverter==busbar





if that makes sense.

 

[Iceni John]

i've been working through similar project so....

i'd say....
from the battery to inverter to bus bar
2000w/12v= 166A.... so 2/0

for the chargers...

80A...so 4awg

for simplicity, i'd use the same wire size for the 60a charger.


https://blazeoffroad.com/blogs/electrical-systems-reference-data/determining-the-correct-wire-size-for-a-circuit

My Magnum 2000W inverter requires a 250A fuse, so I used 4/0 for its cables. (I use ANL fuses and VTE fuse holders for all high-current needs such as for the inverters, and 300A Class T fuses for the battery banks' catastrophe fuses.)

There's not much difference in cost between 4/0 and 2/0, so why not just use 4/0 for all high-current cables? If you buy 4/0 welding cable in 50-foot rolls it's cheaper (OK, less expensive) per foot. I REALLY REALLY don't want voltage sag under load, so I'm happy to use heavier cables wherever possible. Besides, in the overall context of a multi-thousands dollars conversion, a few more bucks on heavier cables is peanuts.

Just as important as the gauge of cables is how they are terminated. It's pointless using a heavy cable if you use some crappy little hammer-type "crimper" for the lugs. Truly reliable connections require the use of a proper circumferential crimper with size-specific dies, the only way to achieve a true "gas-tight" metal-to-metal fusing (essentially a cold-welding) of the lug and wire strands; anything else will eventually cause problems. The FTZ 94284 is a decent inexpensive crimper that can handle lugs up to 250MCM, and Harbor Fright's little hydraulic crimper does a pretty good job on the smaller connections.

John

 

[nikitis]

You'll need to add some fuses between the batteries and the bus bars. Also a battery disconnect on the ground would be good too.

 

[kromboy]

Thanks Turf! That makes total sense, I didn't even think to add the two batteries to the bus bar to create a parallel connection that way.

I'll have to consider how much wire I'll need and if my current spool is long enough (it was only 5ft of each color and cost me like $60)

I may take you up on the offer, I like the Northeast corner of the state, it's really nice and peaceful up there and great for stargazing, I'm in Aurora myself so not much for sights around here, once the bus is ready to hit the road I'll be exploring around the eastern plains for sure, seen enough of the mountains already!

hey Krom,

i just noticed that you're also in Colorado. I'm up in the northeast corner of the state by sterling, so if you eve want to chat, feel free to hit me up.

the way you have it drawn, between the 2 batteries, i'd keep it the same cable 2/0.

if you changed your wiring diagram and parallel setup to meet at the bus bar, then you could use the 4awg for each single battery to the bus bar. you would only have a big wire from the bus bar to the inverter then.

battery
80A
I
bus bar ==160A=== inverter
I
80A
battery


vs

battery80A==battery160A==inverter==busbar





if that makes sense.

 

[Albatross]

I used a propane torch to soldier my battery connectors, and then added some shrink-wrap on top of it all.



Also, you will probably want to get some hard plastic covers for your bus-bars if they didn't come with them. Mine are out of the way, but I still managed to drop a screwdriver just right to make a huge spark and scare the crap out of myself once. And once was enough to correct that problem.


And I second Iceni John's point about using the same high-gauge wire for the battery connections. Your batteries will likely always be the highest-current wires, so you should pretty much always have the fattest cables possible coming from the batteries--even if you've got a bunch of them in parallel.

 

[turf]

don't trust my wire size on the second setup. like the other say, bigger is better.

the different wiring setup would change the amperage calculation to the battery. i was hasty in making a recommendation yesterday.

like the others say, bigger is better.

i screwed up yesterday because i made the assumption that your max amperage was the inverter. your max amperage would be the combined inverters and chargers, any dc loads, and potentially any future solar as well.

if you tried to run the AC off of the inverter, then plugged into shore, you could send your chargers into bulk mode and your inverter to its max pretty easy. that be 165a +80A = 245A.. right? call it 250 then divide by 2 batteries.... so 125A each?

so 1/0
:biggrin:

 

[nikitis]

To gauge wiring properly, the way to think about it is, if it's on the same network use the same gauge wiring across it all.

If you hit a node on the network that downsteps you can use thinner wiring past that node.

Your system is a 12V system all the way through, so you'll be pushing more amps which means you need thicker wiring. One of the advantages of going higher voltage is you don't need as thick of wiring. AWG wire thickness is about amps not volts. Higher amps thicker wiring needed. So even post bus bar I'd use the same AWG Wiring that you used from the batteries, So say you went from batteries to bus bar, then bus bar to 12v bus bar for smaller wiring, you'd use the same AWG as from batteries to main bus bar, but from Main bus bar to the 12v bus bar meant for smaller gauge wiring. The 12v bus bar goes from that to all the devices like lights etc but can use a smaller AWG like 12-14.

Not to confuse you as technically you wouldn't "NEED" a 2nd 12v bus bar because you are making your own and you could just tie all of the devices to the main bus bar, but I would add a 2nd 12v bus bar like pre-made from amazon. Reason being is you can add a fuse between the main bus bar and the 12v bus bar for devices, and the amazon bus bar will have fuses in-between. The reason this is important is because with your parallel setup, amperage could be higher if there were a surge requirement, and all devices being on the same 12v circuit could potentially blow fuses during that initial surge. So if you have a 2nd 12v bus bar with a fuse between the main bus bar and the 12v one it's less likely to have issues down the road with blowing circuits.

So in your graphic, I'd use the same AWG across it all personally, but once you get to the 12v bus bar or in your graphic, the 12v distribution panel then you can shrink down to 12-14 awg because the distribution panel will have fuses built in, plus add a main fuse between main bus bar and the 12v distribution panel.

 

[LargeMarge-TC]

... want to double check and make sure I don't burn my bus down...

Having said that...to ensure I'm not risking the bus burning down...

.
Fuses and circuit-breakers.
.
PS:
I 'triple-check'.
Then I verify.

 

[Rucker]

Curious what the house batteries are, and whether you have or plan on a BMS and shunt.

With a shunt, every negative lead goes to that first, then to the battery.

My setup has literally every component fed to or from the bus bars.

Negative pole of battery->shunt->BMS->bus bar

Positive pole of battery-big fuse-bus bar

 

[fishe160]

I think others have given advice for specific sizes. I wanted to add the tools I had found for selecting wire sizes:

Explains how: https://www.omnicalculator.com/physics/wire-size
Does it for you, to find the wire size: Advanced Wire Size Calculator
Does it for you, to tell you what a wire can carry: Advanced Wire Ampacity Calculator
Simple formula with lookup table: https://ressupply.com/learning-center/wire-sizing-chart-and-formula
Pretty useful website, get links directly to amazon: https://explorist.life/wire-sizing-calculator/

I also used the photo referenced by turf and AlphaHare. And farout ride (built more for vans).
I found the hard part trying to justify the starting voltage and the acceptable drop LOL. 14V? for charged, 12V? for in use, 10.5V for worst case amperage as the battery dies?

Hopefully you considered wiring the house batteries in series to get a 24V system? Wires get smaller... not to throw a wrench in your plans.

Cheers!