Starting Battery Problem

[Dionysus]

Boat is a 1986 # 218.  My starting battery (from previous owner) is located in the space forward of the starboard water tank and that's a long way from the panel..longer yet from the engine.  Needless to say, it won't start the engine; I assume because of the voltage drop. It's new it tests OK at the posts and has 860 MCA, whereas Universal says I only need 500 MCA.   I thought about placing it on the starboard side in the space forward of the holding tank.  Closer to the panel, but the negative run back to the other batteries (3 deep cycles placed forward of the galley sink)is still long. This is where the common DC ground is.  Where else can I place it, and/or how can I re-wire it?  

Also, the DC ground in the battery compartment seems small to me.  It looks like a 10 gauge wire to me.  Is this reasonable?  

Thanks guys,  Chris   DIONYSUS #218

chp

[Charlie P.]

I just checked West Marine's wire advisor and #10 wire is below the chart.  I have 2/0 cable for my starting battery.  Recommend you upsize (is it hot to the touch currently?).

Charlie Pearsall
Delirious #1515

[malgase]

If the #10 wire you refer to is the DC ground to the electrical panel, my expectation is that is adequate for your use.  #10 wire in a conduit is rated for 30 amps minimum, and is actually rated a little higher in "free air" where it can exchange heat better.  

On my boat, there is large wire (same size as positive wires to engine) for a ground wire back to the engine (the return path for the large cranking load), and a smaller wire, #10-#8 to the DC service panel.  Tally up the typical working loads you put on the DC interconnect, and you'll likely find they rarely exceed 30A, even with a Fridge and Autopilot running at the same time.  Add some serious pumps on for steady duty, and you might have a problem, but most pump usage is "intermittent" and not constant.

Just some thoughts . . .

Michael

[howard armstrong]

My starting battery is on a platform that was built, next to the lift muffler, behind the engine. I ran separate cables to the starter using 2/0 cable. Also with the glow plugs on a silinoid the engine starts very quickly.
Howard

[jmnpe]

I had a dedicated battery for starting mounted in the same position (forward of the starboard water tank) for several years without experiencing any problems with starting the engine. Sounds like you have more of a problem with high resistance in the starting circuit wiring. If both the ground and positive wire are at least #2 AWG cable, and your terminals and connections are all tight, it should start fine. Check the quality of the attachment of the ring terminals to the cables, and verify the size of the cable. If you are running the 2 battery banks through the standard battery switch, also verify that the battery switch hasn't developed a high contact resistance in the circuit that carries the starting current of the starting battery to the starter. (You can check this by reversing the #1 and #2 connections on the battery switch and see if the problem follows the switch position or the circuit path.) Finally, make sure you have a good ground connection all along the ground circuit from the starting battery all the way to the engine block, and that the positive feed to the starter is also good all the way back to the battery.

Your problem is probably someting pretty basic in the starting circuit path rather than the actual placement of the starting battery.

As noted, the #10 wire is the negative feed for the DC distribution panel. While it is of "legal" size, it is also too small to prevent winky blinky lights whenever the water pump cycles on and off. I would add at least a second #10 or even #8 wire in parallel with the existing ground wire.

Joh