Help, with 12v set-up inline fuses size/location

[fixedweasel]

Hello, how are you guys and gals? Hope you're well. I am just finishing up a Honda Odyssey conversion and awaiting my 12v electrical from Renogy. Here's what I ordered............

100ah Lithium Battery
12v DC to DC On-Board Battery Charger (Battery Isolator)
1000w 12v Pure Sine Wave Inverter (2000w surge)
Monitoring Screen

So, I'm pretty comfortable wiring it up but would just like to hear folks recommendations for in-line fuses as far as amps and location. Can you guys check my math here? Basically I'm going to run 4g from the van battery to the Battery Isolator. The folks at Renogy recommended a 60 amp in-line prior to the van battery and a 50 amp in-line fuse from the van battery to the battery isolator. 4g Neutral and Hot from the Battery Isolator to the secondary Lithium battery. The 4g wire will come with the 1000w inverter albeit they recommended a 150a in-line fuse prior to. The 1000w inverter has a 2000w surge. Is 150amp in-line enough? From this point, from the Lithium battery, I would run 4g to/fro the fuse block and I will most likely run either 12g or 14g for the feeds/returns off the fuse block (i have multiple spools/colors of both). The Renogy monitor relies on an Ethernet cable but I do not think the one included will be long enough for where I need to mount it. I should be able to use any Ethernet cable to connect, no? Sorry for the long post but I'd just like to wire this once correctly off the bat. Am I missing anything here? Do you have any other suggestions or recommendations? Thanks in advance for your time and patience. Take care. Be safe.

 

[Weight]

Fuses protect wires. Select fuses to the awg of the wire. Select awg to the voltage drop of the combine length and amperes. There are many tables that can help decide. Blue Sea has a easy one. http://circuitwizard.bluesea.com/ I use another, but an example; 4awg marine grade wire safe to 160 amperes, so 150 - 160 amp fuse is good to go. I would up the size of the fuse for the 4 awg at the starter battery and at the house battery. The reason is to reduce voltage drop across the smaller fuse. Remember rule #1 fuses protect wire.

 

[MrAlvinDude]

First, I agree with every piece of advice that Weight has just given.


About the inverter surge:

A 2000W surge on the inverter will draw 2000W/12V =  166A

A 150-160A fuse is very likely to survive just fine, as most fuses in this range are "slow"  fuses.  And the inverter will only allow this level of power draw for some seconds, and then it will shot-down, in order to self-protect. 

So the fuse is NOT set in order to protect the equipment. The size of the fuse is chosen, only to protect the wires and connectors, from overheating.
The protection of the equipment it self, will be a part of the internal design choices of the equipment.


My testing of a series of different types of fuses (2 amp to 30 amp fuses - car blade fuses, round glass enclosed fuses, 1808 style fuses) show, that they will typically function for hours at +30-40% overload.  But they WILL get very hot after a few minutes of being loaded at or close to capacity. 

So it is always a good idea to use wires that are one size better than what is an okay size wire.  Both sizes of wires will work just fine, but the 'one size better', will live a 'cooler' life.

Fuses are after all typically based on melting a thin piece of metal - and metal gets hot when melting.

A good connector, and a beefy wire, will function as a heat sink, for the heat generated by a fuse, so the fuse will not get too hot under normal operation.
I try to not push my choices of wires to the limits of most charts. So there is some surplus ability in the wire to also function as a heatsink for the fuse (and the connector).



Fuses are super good at protecting wires and connectors, when there is a short circuit condition. 

A shout circuit condition will typically only be a very short lived situation, so the only thing that has time to heat up, is the fuse.  Then the fuse blows, and the circuit is broken, and not further heating can occur.

This is one good reason to place a main fuse as close to the plus of the battery as is physically practical.



If the Renogy monitor uses an internet plug for the wire, then it is indeed possible to use an internet cable.



Shorter wires in the main power path will ensure lower voltage losses in the wires.
If your main power wires are long (typically a foot or more), it can be beneficial to use a wire that is one or two awg steps better.



12 awg and 14 awg wires sound fine, as wires after your distribution fuse block with individual fuses for each cable run.

This chart shows how many amps one can usually safely draw with 12 and 14 awg wires:
https://www.powerstream.com/Wire_Size.htm

The column: "Maximum amps for chassis wiring" is based on the wires mainly having free air around them, so any heat that may build up in the wire, when it is used at or close to capacity, can easily escape into the air.


The column: "Maximum amps for power transmission" can be used as a guide in two situations.

a) if the wire is long (say, above 5-6 feet), so voltage lost in the wire is kept at a minimum.
(The ohm value per 1000 feet / 1000 meters, can be used to do a more precise voltage drop calculation of longer wires)
and 

b) if the wire is tightly enclosed.
As it typically would be in a house - where the wire would be inside a wall. A wall can be considered an enclosed space, and might even be filled with insulation.

The numbers in the above mentioned chart are however VERY conservative, if being considered as a guide for enclosed spaces.


According to this page: https://www.thespruce.com/common-types-of-electrical-wiring-1152855

These limits are used in houses:
14-gauge (15-amp circuits)
12-gauge (20-amp circuits)
10-gauge (30-amp circuits)

So I would say that you are very fine with using 12 awg and 14 awg wires in you conversion build, no matter how tight the wires might be enclosed.

 

[fixedweasel]

Thank you Weight and MrAlvinDude.

Weight, I punched in my numbers to the linked calculator you gave and it recommended 6g albeit I am already using 4g, so that sounds good. My longest run will be about 6'. This will be from the van battery to the DC to DC/Battery isolator. The Lithium battery will live between the front seats of the van in a custom box with the battery isolator mounted just outside that same box. From there everything else (fuse block, inverter) will be 18" or less from that Lithium battery. So, you were saying I should size up my fuses in-line before both batteries? They recommended a 60 amp prior to the van battery (from the alternator) and a 50 amp in-line from the van battery to the 40amp DC to DC battery isolator. What amp do you think I should go up to for both? Thanks in advance.

MrAlvinDude, thanks for that bit of info on the fuse load. I was not aware that they could take 30%-40% over the max load for that long. I knew they got hot but did not know that extended time frame for all those different fuse types. It's good to know from both of you that I can safely use a 150amp for the 1000w inverter. Also, the short 4g run from the Lithium battery to the 12v fuse block, do you recommend an inline fuse there and if so, how many amp? Thanks in advance.

I really appreciate the help with this. I am an old ICU nurse and always try to help others, so I will pass it on. Thanks again. Take care. Be safe out there.

 

[MrAlvinDude]

The wire in-line, between the two sets of batteries determines how big the fuse CAN be.
In this chart https://www.powerstream.com/Wire_Size.htm 4 awg says max 135A.

Leave a little head room, and use a max of 100-125A fuses.



About the size of fuse, for the wire going from the battery to the fuse block, you again have a max of something that will fit (and protect) the wire size between the two.
If this wire is also 4 awg, then a 100-125A fuse CAN be used.

The minimum of the fuse size should be,  so that you can operate all the gadgets that you expect to have running at the same time.

As an example, with some likely but random watt numbers:
if you operate some LEDs (5W, is about 0.5A),
a laptop (35W, is about 3A)
a 12V electric cup heater (120W, is about 10A)
a TV (15W is about 1.3A)
a 12V fridge (maybe 4 amp when running = 48W)

Each item may have its own 5, 10 or 15 amp fuse to protect the wires. But the total is 5W+35W+120W+15W+48W = 223W
At 12V then 223W is  about 19A

So in this example a 20A fuse between the battery and the fuses block, is the minimum, if you happen to use all of the gadgets at the same time.


So in this example, using a 4 awg wire your fuse can be any size between 20A and 125A
Both sizes will protect the wire. And both sizes will allow for ALL of the gadgets to operate simultaneously.

A practical choice, that will give a low voltage loss, could be something about twice the minimum requirement, so 30-40A  could be a good practical choice.  Though the 125A fuse will give the absolut lowest voltage loss for this particular fuse. 

So the choice between 30A and 125A (or any number in between), in this particular situation, is about a gut feeling of how likely it is that something will could accidentally be drop, in a fashion so it would penetrate the plastic protection of the wire, and at the same time also make contact with some metal that is grounded.  


Does the idea of max, is something that matches the wire
and min is something that machtes the combined load

And if you then double the minimum (so long as this is under the max option), is a good practical value/size, that will give a low voltage drop, make sense to you?

 

[Weight]

I always use marine grade wire and cable. That cable is rated for 105 C. In all the charts I have it lists 4 awg at 160 amps if out side engine rooms. very hot place on ship. I would be very comfortable fusing at 160 or 150 amps. If you are using 4 awg on both sides of your combiner you can use 160 or 150 amp fuse at each positive battery terminal. That will protect the wire and offer less voltage drop than a 50 amp fuse. Of course if you use different grade wire you must match the ampacity to that insulation.

 

[MrAlvinDude]

Just for some clarification, as someone might perceive  it as if Weight and I are saying something different,  like; when we refer to max loads on wires.

To me we are however in agreement.


Here is for instance a chart that shows typical temperatures of singe strand wires (the wires used in houses), when they are exposed to a constant amp load, with the kind of plastic shield that is normal for such wires:
https://www.lapptannehill.com/resources/technical-information/ampacity-chart

On this chart it says:
4 AWG -- 70A (60°C - 140°F) --  85A (75°C - 167°F)  -- 95A (90°C - 194°F)



If you do however use a multi strand wire, these temperature numbers will be different.
Among other things because multi strand wires have a different surface area. And surface area makes a difference for ability to let heat leave the wire, and get into the air around the wire.

And for marine gade wires, it is likely that each strand is also tinned.

Both of these details makes for a wire that can better handle higher amp loads, despite being the same awg size.

Also the plastic (or silicone) sleve protecting the wires, will be able to fully function, at different max temperature levels.  So some wires are rated to be able to function at 105*C, for years on end, without the sleve being degraded.


All of this is something to understand about wires. And something to consider when looking at charts that give recommended max loads.


Some wires will have some of these details printed on the outside of the sleve, like max temperature ratings.  And awg size. 


Here is for instance a chart that shows some details about marine grade wires
https://www.westmarine.com/WestAdvisor/Marine-Wire-Size-And-Ampacity
At the bottom of the page is a chart showing reccomendations of 4 awg wires to have a max amp load at 160A


And on the rest of the page it shows many details about why some specific type of marine grade wire is wise to use.


And after all of these details, it is worth remembering that none of the wires in fixedweasel 's setup are likely to be operated at max amp loads for more than a few seconds at a time. 
Most of the time the load will be at a max of 50% (and less) of these max limits. So really nothing to worry about.

And in this (marine) chart it shows some details about 4 awg wires being used at 200Amp.
http://assets.bluesea.com/files/resources/newsletter/images/DC_wire_selection_chartlg.jpg

My point being, that wires out there in real life, actually operate and live on a scale. But for convenience, we make charts, and mathematical models, that can help us predict a very high likely hood of a safe level of functionality. 



I hope these comments has brought clarity and understanding.  Otherwise please feel free to ask for further details - or for simplifications

 

[Weight]

Yes. MrAlvinDude and I are in agreement. He is just better at expressing himself. I am too old to have the patience for detail explanations. Thank you MrAlvinDude.

 

[fixedweasel]

Weight and MrAlvinDude, yes, it brought clarity and is helpful for sure. Looks like I will get Marine grade 4g for the run from the van battery to the Lithium battery. about 3' of this will be under the hood, so it's obviously hotter there. Depending on the price per foot of the Marine grade, I may use standard 4g for the rest of the runs inside the van. Looks like I'll go with 150a in-line before each battery and before the inverter. I think I'll go with a 50amp prior to the fuse block. I wired my house with stranded.* I never use solid, habit. For 110, always run 14g on a 15a breaker for light and 12g on a 20a breaker for power. So my runs off the 12v fuse block will be stranded for sure since I have multiple spools of it. Also, my set-up is not intended for high watt use. I will not be running anything with a coil or that will have a big pull. The only things I will have are a 12v water pump, 3 sets of 12v lights on dimmers, a 12v 44-quart fridge and the 1000w inverter. So I think the 50amp prior to the fuse block will be good. Thank you again, and if you see anything else I am missing here, please let me know. Take care. be well and be safe out there.



*our code here also has everything run in electrical conduit, so no Romex.**
**I also run my travelers for 3-4 way switches in completely separate conduit runs. they prefer that here.

 

[highdesertranger]

they want 12v wire run in conduits? that's outrageous.
what do they do about all the vehicles?
Romex is intended for 120VAC
what is,

"I also run my travelers for 3-4 way switches" ????

highdesertranger

 

[B and C]

He is probably using thhn wire in conduits for 120VAC. Thhn wire is pretty stiff even if it has a couple (7?) of strands. It may hold up ok in conduit as it is supported and not vibrating up and down a lot that way. I wouldn't use it unsupported, it will aneal and break with road vibrations otherwise.

Best to use marine grade wire, second best is automotive grade wire.

 

[Weight]

I want to clarify something. Fuses must be close to each positive battery terminal. (Not meaning interconnecting cables on series or parallel battery.) Also at any positive buss bar where the wire changes size.

 

[highdesertranger]

"He is probably using thhn wire in conduits for 120VAC."

but what about all the RV's they don't use conduit's. hell they even use solid core wire, how they get away with using solid wire is beyond me.

highdesertranger

 

[B and C]

I don't know either. Romex is cheaper and is probably the reason. My rig is 20 years old and no problems on the 120VAC side (yet?). Mine is sandwiched between the inside wall and the insulation (I had one inside panel off) and is probably what keeps it from annealing and breaking. IDK (I don't know) for sure though.

 

[fixedweasel]

Ah, highdesertranger......110/220, sorry 'bout that. Code here for homes call for everything to be run in metal conduit. We cannot run Romex here. I wouldn't run Romex anyway. I prefer bending my own conduit and having the ability to pull extra circuits if I need to. You always have access with conduit, and there's something very comforting about that for me. Travelers are 14g run between all 3 or 4 way light switches. They do not like you to run them in the same conduit as the hots/neutrals, so I always run mine separately. It takes more work, but I'm retired, what else have I to do? I also always color my wire as below for 110.............

Hots..............black, red, blue
Switch legs......yellow, orange
Travelers..........pink, purple
Neutral obviously is always white or you can use a light gray
Ground is obviously green.

Also, we don't need to run green to ground with metal electrical conduit as it is already grounded. We are allowed to run "whips"* of 6' or less, but I always ground those. Sorry for the confusion. My bad.




*basically Greenfield (flexible metal cable) with wire fed through it

 

[highdesertranger]

oh this is for a residence. did I miss that? sorry if I did. highdesertranger