What's your AWG from Alt to Battery & Engine to Ground?

[StanL]

Wondering what size cables are used when replacing, and possibly upgrading the Alternator to Battery wire, and the Negative Battery to Engine Ground wire.


Planning to use Anchor pre-tinned cables, but also thinking of going with a larger
wire for my 3 cyl 30hp Yanmar diesel. The orig dealer used AWG 3 for the alternator and AWG 6 for the ground, but they weren't tinned marine grade wires.


The good stuff is expensive, and I'm wondering how big is too big. So, how big is your cable?

[rslifkin]

It depends. How big is the battery positive to starter cable? Does anything else ground to the engine? And how big is the alternator?

I'd say the engine ground should be at least as big as the starter positive. Alternator cable size will depend on alternator output.

[a64pilot]

I have 2 Ga from alt to my starter lug. I didn’t see the point of running a big cable to the battery bank, when I have a cable that is already run there.
Bank to starter and ground is I think 00. Makes no sense for ground to be smaller, as both carry the same load.

How far away the bank is and the engine size determine sizes of wire in my opinion.
Mine are 33 yrs old and aren’t tinned either, and have no problems. Tinned wire is better I’m sure, all the wire I have added is tinned, but as I said all the factory wire in my boat to include the factory Yanmar wiring harness isn’t tinned, so it makes one wonder just how essential tinned really is.
You can’t have too big, you can only have bigger than what’s minimally required, the bigger, the less voltage drop.
On edit, if you run alt to starter, then most likely the only bank charged will be the one selected at the battery switch. If you have a separate starter battery, something that I don’t understand, but if you do then it’s likely that only it will be charged

[StanL]

Oh, and there is this chart, which the boat builders seem to ignore when it suits them.


It's odd how the AWG size jumps from 4 to single 0

[Poche]

Originally Posted by a64pilot

Mine are 33 yrs old and aren’t tinned either, and have no problems. Tinned wire is better I’m sure, all the wire I have added is tinned, but as I said all the factory wire in my boat to include the factory Yanmar wiring harness isn’t tinned, so it makes one wonder just how essential tinned really is.

If you're re-wiring and expect it to last 100 years I would see the tinned need. Or a sub marine.
Over kill.

[BlackHeron]

I ran 2/0 between the starter and the fuse block hooked to the Blue Sea Systems Automatic Charge Relay. The Green Volvo-Penta Devil Beast cranks over with plenty of vigor.

From the ACR fuse block I ran #3 the final 14" to the battery post. #3 can handle the load and there is minimal voltage drop over just 14 inches and it is much more flexible and easier to connect than 3/0 and doesn't get in the way of the battery electrolyte caps.


Between the alternator.and the starter I think I ran #6 as it was the heaviest gauge wire that didn't seem to put too much stress on the tiny alternator lug. It's another 14" run -so again voltage drop is minimal here and we only have a 60A alternator so #6 has plenty of ampacity to handle the load in free air even derated for ambient temperature.

I don't see the point in running a separate alternator and starter wire since we never just charge batteries with the alternator and only run the engine to motor or motorsail. First priority is to recharge the starter battery after starting anyway for safety, so it can start it again readily. Once charge voltage meets the minimum the BSS ACR combines the starter and house banks until charging is over, then disconnects them again once finished.

I use a BSS dual battery shutoff switch so when switched on it connects the battery to the engine and separately the house banks to the house panel. It is the job of the ACR to combine start and house banks when charging voltage is sensed -by the alternator, the shorepower AC battery charger, the solar charge controller, or the wind turbine charge controller. Everything charges together and discharges separately all automatically.

Battery chemistry is all flooded lead-acid. Starter battery is basic group 34, so it is economical to replace and I do not worry much about over charging. I've got the alternator cranked up to run 14v by the alternator shop that rebuilt it. I believe in charging hard and adding distilled water as needed. House bank is four 6v golf car batteries. I can replace all 5 batteries for under $400 total, but so far in over three years they perform like new, and the electrolyte tests like new with the hydrometer. Levels are checked and filled monthly or more often if motoring every day. Simple 5-minute job.


There is a second position on the battery switch to combine manually in an emergency, but we've never needed to do that.

[Luna Loca]

Lots of confusion on wire gauge sizing and it's all dependent upon current, temperature, bundle size (heat dissipation problem), and length.


Here is my goto site whenever I need to select the appropriate size wire and cable: https://www.powerstream.com/Wire_Size.htm


I'm a retired electronic engineer and do everything myself.


A good site to purchase wire and cable: https://www.wireandcableyourway.com/


Hope this helps many!

[seabreez]

Originally Posted by StanL

Oh, and there is this chart, which the boat builders seem to ignore when it suits them. It's odd how the AWG size jumps from 4 to single 0

I have used this chart for the longest time... If you look at 60 amps alternator which never gets more than 35 to 45 amps going to the battery... in the chart... used #10 gauge wire. It is a short run from the alternator to the big lug on the starter. I would use copper thinned wire for that since there is always some humidity and this is prone to corrosion... then good marine grade copper thinned wire connectors that you crimp and heat shrink. Then you forget about it... tie up all loose wires and voila!

[seabreez]

Originally Posted by StanL

Oh, and there is this chart, which the boat builders seem to ignore when it suits them.


It's odd how the AWG size jumps from 4 to single 0

it is 4 to 1/0 not single 0. That is a big cable... it is like a welding cable. And the key to installing this size of cable is making sure you have good connectors and seal the ends very very good to prevent moisture from getting inside and corroding the copper. You will never see this corrosion until you have a no start condition... then you cut the cable open length wise and see the results...

[NorthCoastJoe]

On my Yanmar 3gm30f I used 6 Ga from the alternator to the + starter lug it is less than a 12-inch run.
From the starter + to batteries 30 inches, and the ground 18 inches, both are 2 gauge.
I used non-tinned cables and have had no problems in 3 years, the boat does not sit around much it gets used weekly. All of my terminal ends are sealed watertight.

[jmschmidt]

Tinned is undoubtable better if you have wire exposed to bilge water or other places where water might enter at the wire's terminals. Most bilge pumps, shower drain pumps, float switches, liquid level detectors and the like have a significant length of tinned leads so connections and terminals can be made well above any water levels.

"Marine Grade" is just a way to charge you double for what you could buy if for at the hardware store down the street.

[michaelratinter]

I use 4/0 welding cable for all connections. 690AH house battery.

[smac999]

That chart is bs. 140a with 10awg? Abyc is max 40 or 45a. And nobody would ever run more then 30a.

Use the bluesea chart. It has every wire size, and 3% vrs 10% drop table.

[mitiempo]

I agree with smac99. The chart in post #4 is the most bizarre wire chart I have ever seen. Dangerous if followed.