Correct size wire for 3GM Battery Bank?

[Gone2long]

Originally Posted by Dave Lochner

The instantaneous load on a starter will be around 200-250 AMPs for a fraction of a second. Once everything starts spinning the actual load will drop significantly. My starter is fused at 250 amps and it has not blown the fuse.

As others have mentioned bigger is better when it comes to wire size, especially on things like starter motors, refrigerators, and windlasses. Anything with a motor will have high instantaneous loads, it takes a lot of energy to get things moving, but once the motor is turning the actual load decreases.

If you have the 1 ga wire, then that would be a better choice than 6 ga.

Cold cranking Amps only 250? Seems low from what I have read. What engine do you have? As noted originally, mine is a 3G 30 yanmar.

Starting batt is a group 27, 70Ah car battery.

G2L

[Gone2long]

Originally Posted by rwidman

It doesn't matter to the engine or starter what size the wire for the house bank is.

Why not use the starter cable for the starter circuit?

Understood. As noted above, 1 Gauge starter cable is being used from controller to starter. 6 AWG is being used from E bank to controller.

Has always worked ok, so far. No heat or starting probs.

G2L

[Gone2long]

Originally Posted by Roger L

That wire seems at the small end for this engine - however the run is short, and so the total heat caused by the resistance of having slightly smallish wire may be OK. If in doubt, simply feel of the wire when you are using a lot of battery power or charging the batteries at a high rate. If the wire is perceptibly warm then it is time for larger wire.

As to your question about using larger wire, there is no electrical problem with using the larger wire to connect the last battery - or to any battery for that matter. The only caveat is that if you are running two wires to the last battery - as I suspect you are - good practice says that you should use the larger wire for both of those wires.

Anytime that battery wiring varies in diameter, the resulting losses - as well as any local heating of the wire - are always going to be controlled by the smallest and longest wire (or worst corroded connection!) that you are using to connect to the bank.

Larger wire is difficult to bend, more expensive, and it can be hard to find proper fittings for it....those are the only noticible downsides to using larger wire where you can.
Keep your connections clean and tight!
rScotty - old sailor & retired engineer

Yes. Using two wires for the last batt. Both are 1 Gauge, Belden Starter Cable. Put it in last night. No probs.

Thank you for your advice.

G2L

[Gone2long]

Originally Posted by a64pilot

6ga will work fine for your starter, proof is it has. However if your bank is a little low, the bigger wire will start it where the smaller won't. Plus any motors brushes will last longer with less voltage drop that you will get with bigger cable.
If you have the wire, already and it's just laying around, I'd replace the starter cable.

Understood. As noted above, 1 Gauge starter cable is being used from controller to starter. 6 AWG is being used from E bank to controller. This is the configuration I inherited when I bought the boat, and it has worked OK for last 2 years.

Don't have enough 1 Gauge to use it instead of the 6 AWG from the E bank to the controller. Am using the 1 Gauge on hand to connect the 3rd house battery to the house bank.

All seems OK at this point.

Thanks again,

G2L

[GordMay]

Originally Posted by Gone2long

Cold cranking Amps only 250? Seems low from what I have read. What engine do you have? As noted originally, mine is a 3G 30 yanmar.
Starting batt is a group 27, 70Ah car battery.
G2L

Yanmar (3GM30) specifies a minimum 70 A/Hr, 385 CCA, or 455 MCA starting battery.

[Gone2long]

Originally Posted by GordMay

Yanmar (3GM30) specifies a minimum 70 A/Hr, 385 CCA, or 455 MCA starting battery.

Thank you,

Much appreciated.

G2L

[Dave Lochner]

Originally Posted by Gone2long

Cold cranking Amps only 250? Seems low from what I have read. What engine do you have? As noted originally, mine is a 3G 30 yanmar.

Starting batt is a group 27, 70Ah car battery.

G2L

G2L,

Take a look at this site.

Battery Bank Fusing Photo Gallery by Compass Marine How To at pbase.com and

https://youtu.be/8hX7NMiV_Gc

RC has measured the inrush amperage at 316 amps for a Yanmar 2QM and only 225 amps for a Universal M-25.

I might have been a little low in my estimate, but not out of the ball park.

[mitiempo]

One concern is the voltage the starter sees when cranking. Wire size, if too small, will reduce this voltage. Starters do not like low voltage.

I usually wire batteries and starting circuits with 1/0 or 2/0 for this reason. Faster starts result.

In my opinion all battery wiring as well as the starting circuit should be the same gauge.

[Gone2long]

Originally Posted by mitiempo

One concern is the voltage the starter sees when cranking. Wire size, if too small, will reduce this voltage. Starters do not like low voltage.

I usually wire batteries and starting circuits with 1/0 or 2/0 for this reason. Faster starts result.

In my opinion all battery wiring as well as the starting circuit should be the same gauge.

Yeah, 1/0 definitely seems to be the trend from what I have lately read, even with manufacturers. Mine is a sailboat, which had been used primarily for weekend racing, and I think the previous owner wanted to keep her light as possible.

G2L