cancel
Showing results for 
Search instead for 
Did you mean: 

12v wire thickness

timelinex
Explorer
Explorer
I have a 2kw inverter and will be getting a 100a converter for my 2 100ah lifepo4 batteries. Currently I'm just using whatever ga wires came with everything (a bix of 4/6/8).

I am planning on changing everything to connect through a BUS BAR and upgrade all the cabling to heavier ga. I want to future proof it to handle a 3kw inverter.

It's been REALLY confusing figuring out what wires I need. ALMOST everything online "(forums and articles) tell me I need something like a 4/0 guage, which is HUGE. That makes sense considering 3kw can reach 200-250 amps. Except the fact that no OEM items come with something nearly this thick.

I think the reason all these recommendations may be wrong is they do not account for length of wire being very short in our use cases.

Can anyone confirm?

I've found this site, which DOES take into account length:

http://www.offroaders.com/technical/12-volt-wiring-tech-gauge-to-amps/

It looks like considering everything is definitely under 4ft, I won't need anything over 4ga. On the other hand, I'm pretty sure that ampacity is over max 4ga rating when you look it up.

Using this calculator: https://baymarinesupply.com/calculator I get 2ga for my 2kw and 1/0 minimum for the 3kw. If this is the case I would likely go with 2ga to save money and more importantly because I don't even think the 1/0 would fit in the current inverters lugs.

Can anyone make any recommendations based on actual knowledge and not just heresay or making best guesses?
32 REPLIES 32

CA_Traveler
Explorer III
Explorer III
Goog suggestion but I've never seen 4/O jumper cables, maybe from a tow truck?

Check jumper cablles as you want solid copper and notf copper coated alumiinum,

4' will limit the cost,
2009 Holiday Rambler 42' Scepter with ISL 400 Cummins
750 Watts Solar Morningstar MPPT 60 Controller
2014 Grand Cherokee Overland

Bob

valhalla360
Nomad
Nomad
The cable length and amperage determine the wire size needed. Online calculators are available. Search or voltage drop calculator. If you plug in 3000w, that should be a bit conservative for you 2000w inverter but if not significantly more, look at going on size larger.

At 3000w, you are pretty much up around what the starter on a car will pull, so yes, you need a thick cable.

You might look for a heavy duty set of jumper cables to sacrifice. Much smaller 50amp charger installed recently but the 6ft 4 gauge wire was running $30 per cable (ie: I needed 2). Set of jumper cables was $15. I cut the ends off and used the wire.
Tammy & Mike
Ford F250 V10
2021 Gray Wolf
Gemini Catamaran 34'
Full Time spliting time between boat and RV

CA_Traveler
Explorer III
Explorer III
Boomerweps wrote:
I would not route inverter power via the shunt or buss bars (extra connections between the battery and inverter). Make it as direct & short as possible, just protection.
Without the inverter on the shunt the battery monitor would not be very accurate.

My shunt is rated at 500A 50mV hence very limited voltage drop considering its 25mV at 250A. Plus connections of course.
2009 Holiday Rambler 42' Scepter with ISL 400 Cummins
750 Watts Solar Morningstar MPPT 60 Controller
2014 Grand Cherokee Overland

Bob

Boomerweps
Explorer
Explorer
timelinex wrote:
Boomerweps wrote:
Read the reviews on Amazon. Most complain about the wires supplied with inverters is TOO small, mostly 4 AWG.
Use at least 1/0awg or better yet, 2/0awg. If making your own, ask for the given gauge welding cables at your electrical supply store. Welding cable is very flexible with many smaller wires.
Another consideration is that many, myself included, decide that a given inverter is a little small and get a higher power unit. If the wiring is extra thick for the smaller inverter, it can support the larger unit.
IMO, the inverter should be directly connected to the battery bank with only a fuse or circuit breaker on the positive cable.


I plan on adding a BUS bar. Should I connect the negative end directly to my shunt and positive to my batteries...Or should I go through the Bus Bars, which add distance.


I would not route inverter power via the shunt or buss bars (extra connections between the battery and inverter). Make it as direct & short as possible, just protection.
2019 Wolf Pup 16 BHS Limited, axle flipped
2019 F150 4x4 SCrew SB STX 5.0 3.55 factory tow package, 7000#GVWR, 1990 CC Tow mirrors, ITBC, SumoSprings,

enblethen
Nomad
Nomad
Make sure whatever size you decide on, it has multiple strands. Building wire is not the best. Welding cable works but so does power wire available at fancy radio installation shops.
Cables can have up to 400 strands.

Bud
USAF Retired
Pace Arrow


2003 Chev Ice Road Tracker

pianotuna
Nomad II
Nomad II
timelinex,

be sure to wire the batteries in a balanced manner.

This is what is balanced and best for twin twelve volt batteries.



As it often doesn't cost a dime more to do this, I think it is worth the trouble.

If you wish to understand the "why" surf here:

correctly interconnecting multiple twelve volt batteries

Others may say it doesn't matter--but unless there is a compelling reason to not optimize charging and discharging why not do it the best possible way?
Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp-hours of Telcom jars, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

CA_Traveler
Explorer III
Explorer III
At 250A direct and short as possible. BTW 250A is marginal for 4/O wire.
2009 Holiday Rambler 42' Scepter with ISL 400 Cummins
750 Watts Solar Morningstar MPPT 60 Controller
2014 Grand Cherokee Overland

Bob

timelinex
Explorer
Explorer
Boomerweps wrote:
Read the reviews on Amazon. Most complain about the wires supplied with inverters is TOO small, mostly 4 AWG.
Use at least 1/0awg or better yet, 2/0awg. If making your own, ask for the given gauge welding cables at your electrical supply store. Welding cable is very flexible with many smaller wires.
Another consideration is that many, myself included, decide that a given inverter is a little small and get a higher power unit. If the wiring is extra thick for the smaller inverter, it can support the larger unit.
IMO, the inverter should be directly connected to the battery bank with only a fuse or circuit breaker on the positive cable.


I plan on adding a BUS bar. Should I connect the negative end directly to my shunt and positive to my batteries...Or should I go through the Bus Bars, which add distance.

ktmrfs
Explorer
Explorer
go to a welding shop and buy the length of welding cable in the gauge you want and have them put logs on it for you. Many shops can do that.

Otherwise you'll need a hybraulic crimper. And based on what I've done I'd suggest and least 2/0 wire if not 3/0. Most inverters have a low voltage shutoff and a few tenths of a volt drop can make the difference in inverter running and inverter shutting down.

And make sure you use the correct fuse to the inverter. they are big, bulky but meant to protect under the high load conditions.

Welding cable has lots of very fine wire so it is very flexible and easy to route.
2011 Keystone Outback 295RE
2004 14' bikehauler with full living quarters
2015.5 Denali 4x4 CC/SB Duramax/Allison
2004.5 Silverado 4x4 CC/SB Duramax/Allison passed on to our Son!

Boomerweps
Explorer
Explorer
Read the reviews on Amazon. Most complain about the wires supplied with inverters is TOO small, mostly 4 AWG.
Use at least 1/0awg or better yet, 2/0awg. If making your own, ask for the given gauge welding cables at your electrical supply store. Welding cable is very flexible with many smaller wires.
Another consideration is that many, myself included, decide that a given inverter is a little small and get a higher power unit. If the wiring is extra thick for the smaller inverter, it can support the larger unit.
IMO, the inverter should be directly connected to the battery bank with only a fuse or circuit breaker on the positive cable.
2019 Wolf Pup 16 BHS Limited, axle flipped
2019 F150 4x4 SCrew SB STX 5.0 3.55 factory tow package, 7000#GVWR, 1990 CC Tow mirrors, ITBC, SumoSprings,

Grit_dog
Nomad III
Nomad III
For a short run, to power a 3000W inverter, 1/0 is sufficient.
4/0 is ridiculous unless you were hooking it up across the street.
2016 Ram 2500, MotorOps.ca EFIlive tuned, 5” turbo back, 6" lift on 37s
2017 Heartland Torque T29 - Sold.
Couple of Arctic Fox TCs - Sold

CA_Traveler
Explorer III
Explorer III
Especially unseen corrosion on connectors near flooded batteries.
2009 Holiday Rambler 42' Scepter with ISL 400 Cummins
750 Watts Solar Morningstar MPPT 60 Controller
2014 Grand Cherokee Overland

Bob

Chum_lee
Explorer
Explorer
timelinex wrote:
I have a 2kw inverter and will be getting a 100a converter for my 2 100ah lifepo4 batteries. Currently I'm just using whatever ga wires came with everything (a bix of 4/6/8).

I am planning on changing everything to connect through a BUS BAR and upgrade all the cabling to heavier ga. I want to future proof it to handle a 3kw inverter.

It's been REALLY confusing figuring out what wires I need. ALMOST everything online "(forums and articles) tell me I need something like a 4/0 guage, which is HUGE. That makes sense considering 3kw can reach 200-250 amps. Except the fact that no OEM items come with something nearly this thick.

I think the reason all these recommendations may be wrong is they do not account for length of wire being very short in our use cases.


It looks like considering everything is definitely under 4ft, I won't need anything over 4ga. On the other hand, I'm pretty sure that ampacity is over max 4ga rating when you look it up.

Can anyone make any recommendations based on actual knowledge and not just heresay or making best guesses?


Look at the cables/connectors from your chassis battery to the starter motor. What size/material/insulation are they? It's quite normal for your starter motor to draw well over 250 amps @ 12 volts (nominal) to start the vehicle. Granted, it's usually for only a short time, but when you need it, . . . . you need it. It's not just the size of the wire, the connectors are important too, since over time, often (not always) they initiate the failure of the wire.


Chum lee

CA_Traveler
Explorer III
Explorer III
You adapt to the situation. For example my 3x serial solar panels at 92V and with 62' of 10ga wire have a 0.4% voltage drop to the controller. One of the reasons I didn't wire them in parallel.

The second major reason is shadow performance which is another topic.
2009 Holiday Rambler 42' Scepter with ISL 400 Cummins
750 Watts Solar Morningstar MPPT 60 Controller
2014 Grand Cherokee Overland

Bob

CA_Traveler
Explorer III
Explorer III
deleted
2009 Holiday Rambler 42' Scepter with ISL 400 Cummins
750 Watts Solar Morningstar MPPT 60 Controller
2014 Grand Cherokee Overland

Bob