Wire Size from Battery to Shunt

[Capebuild]

Hello. Can anyone suggest what size wire I'd use to connect a 100Ah battery to a shunt used for a battery monitor? (I'm using a Victron BMV712 monitor and the shunt that comes with it)
Also.... whatever wire size that winds up being, would the same wire size be used to connect to the loads? I can post an image of my planned set up if that would be helpful.

Thank you for the help.

John

[lfhoward]

I would match the gauge of wire you’re using to come off the positive terminal to go to your fuse panel. The wire gauge needed will depend on the length of the circuit and the total amperage that needs to go through the wire.

This article includes a wiring chart to help with that.
https://www.bluesea.com/resources/1437

[tony.latham]

Can anyone suggest what size wire I'd use ...

I used 12 AWG multi-strand for mine –-which of course can handle 15 amps which I'll never come close to using. And yes, both wires coming from the battery need to be the same size.

Tony

[flboy]

Battery to Shunt wire and Shunt to ground bus needs to be the same gage. 0 gage is more than plenty for most RV applications using a modest 1500W inverter and with typical appliances such as a small microwave. Can go smaller, but then refer to wire gage/amp charts.

On the positive side to positive bus, I'd use the same gage as negative. Then from the positive bus bar to various loads, use wire charts. Keep inverter close to batteries and if you can, use same gage wires as Shunt just to ensure best performance.

Sent from my SM-N970U using Tapatalk

[saltydawg]

You can go look up some charts, or just read below.

no inverter, just lights, fan usb plugs etc. I would use 12 or 10 gauge if a longer run ( personally i would do 10 gauge )
if the run is over say 20 feet going to 8 might not be a bad idea, I used 8 to go to my fuse panel, which is a 5 foot run yes its over kill, but my solar and shore charger both go to my fuse block so it could see 20 amps of charging.

if you have a 4-500 watt inverter go with number 6
500-1000 watt inverter number 4 unless its a long run then go to 2 gauge

edit, you need a main fuse and/or switch in there so you can shut it off. size the wire to fuse, ie 50 amp fuse number 8, 20 amp fuse number 12 ( i would still use 10 gauge )

[featherliteCT1]

I would you this Blue Seas wire guage calculator to reduce the guess work. Remember, use the total round trip wire length for the calculator. It is also recommended to size the wire for the inverter based on peak wattage rather than continuous wattage.
http://circuitwizard.bluesea.com/#

[Capebuild]

thank you all for the helpful suggestions. I was originally thinking to go from battery to shunt I might need 2 or 4 gauge but I now get the feeling that is way overkill. I'm not too experienced with this field (setting up an electrical system)....so proceeding slowly. Scott, what you've described in your post is very close to what I've got planned. No inverter..... the components will consist of fan, fridge, some lights, USB-12 volt receptacles ...
and that's about it. LFHoward, the article and chart you suggested looks great, I need to read it over more closely to get the full gist of it.

I kind of get the feeling if I add up all the amps I'll be drawing (like the max load if everything were on at one time) and use that as a "go by" for wire size to go from battery to shunt (maybe make it a size or 2 larger to accommodate any future electrical additions down the line that would be a good go by.... yes?

I'll post a drawing of what I've got planned just to make it more clear for myself and to bounce it off all of your experience.

Thanks very much for the help.... I appreciate it!

John

[tony.latham]

(maybe make it a size or 2 larger to accommodate any future electrical additions down the line that would be a good go by.... yes?

That'll work fine.

Tony

[saltydawg]

If I turn everything on in my trailer, all lights, fan, radio and usb I draw like 5 amps unless I turn the radio up loud.

I did a simple wire job of an old little guy, with a 35 amp battery, a few lights, usb and a small fan, charged by a 50 watt panel. The owner over night with the fan on, some lights, charging her phone and having her ipad ruinning for a little used about 7 ah. so her average was about 1 amp an hour. I ran number 10 for the short run to the battery from the breaker and fuse box, and by short I mean 12 inches.

[John61CT]

BSS' Circuit Wizard app is better than static charts for wire sizing.

Allowable voltage drop quickly becomes the critical factor.

[Capebuild]

Attached is an image of my first attempt at laying out my device's power consumption. The amp draw on some of the devices is accurate as noted on the sell sheets of the devices, others are best guesstimates.
If I include the laptop and phone charging (guesstimates, really)... I'm getting total consumption, if everything were on at one time) of around 10 amps. Without those, maybe like 4 or 5 amps per day's use.
Does all this seem like I'm in the ballpark? As noted, the only real high draw devices are the Dometic fridge and the Maxxair fan. So if I use 10 amps as a max draw per day, and add 20% to that, making it 12 amps....
I'm thinking the wire from battery to shunt could be size 10..... or if I wanted to be safe (and "overbuild" a bit) it could be size 8.

All the electrical components (fuse boxes, 100 Ah lith batt, bus bars, etc) will be located in the same vacinity and I don't see any wire runs to the consuming devices being more than 20 feet, round trip

Does this all sound (and the image), look "correct" (in that, I'm figuring this correctly)? Any comments would be welcome.

Thank you all very much for the help.

John

[TimC]

Not a bad thing here to over estimate draw for your wiring purpose.

Double check your wattage for your fridge. I have a 12v fridge, 35L, and through multi day tests it has consumed an average of 14 aHr per day and ~45 watts. 15 watts seems really low and 32 aHr per day seems very high. Your Dometic, I would guess, is a little more efficient than my Alpicool. Your numbers may be right since I'm not familiar with the Dometic, but have been told it is a Dometic clone.

The others look good.

[Capebuild]

Thanks for your thoughts, Tim. I had gotten those numbers from (as far as I can remember) various sources, googling and such. I'll double check and make sure. Unfortunately the Dometic site doesn't provide any hard numbers.


On another note, I've attached my electrical layout. I'd surely welcome any comments, especially about the wire sizing. I'll also reattach the spreadsheet showing the intended draw.
Thanks again. (just thought I'd mention if you click on the wiring diagram, it will open to full size..... )

John

[saltydawg]

you can eliminate the fuses on the chargers just by taking them to a fuse on the fuse block. dont muddy the waters with fuses all over the place.

edit the only thing you really need 14 gauge for is the usb's and a 12 volt jack if you have one, lights can easily be 18 gauge.

[Bezoar]

Don't you need a jumper from the battery positive to the shunt?

Also, I put an in-line circuit breaker between the PV panel and the solar controller, it will function as the switch and fuse, simplifying things a little bit.