Starter battery seems dead, yet.....

[macbeth]

It runs the anchor windlass and shows 12.5 volts. But nothing when I try to start the diesel. The only way I can get the starter to operate is to turn the twin circuit switch handle to the combine position. The starter battery is connected to the starter and thence to other items, eg starter solenoid. The house battery is connected to the output of the alternator. Any suggestions as to how I go about finding the problem ?


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[macbeth]

I also have a battery combiner connecting the two batteries, for charging purposes.


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[DeepFrz]

Start at the battery. Check every connection, follow every inch of cable to starter. Check and clean every connection between battery and starter.

[smac999]

Are you sure then windlass isn't of the house?

[macbeth]

Windlass is definitely on starter battery. This situation only began this spring after replacing the batteries after the winter. Strangely the starter battery worked fine without the house battery. I am going to undo the house battery and see what happens.


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[bobnlesley]

Battery good, but starter won't work, unless house-batteries (more amps) added into the circuit, so I presume the starter spins, but too slow a spin, to fire the engine?

As suggested earlier, check all the wiring/connections, but also get the starter-motor itself checked out: We had a similar problem last summer and eventually discovered that there was a break in the starter-motor's winding; it just chugged slowly around on the start battery, but with the extra amps of the house batteries added, there was then enough to 'jump' this break and spin normally.

[hellosailor]

If your starter battery shows 12.5 volts, surely, you have a way to show voltage for the house bank alone? And that would be?

[MarkSF]

Test the voltage at the starter, while cranking. Anything below 10V is suspect. If low, then start measuring the voltage drops in the wiring. Most likely is a bad connection. I've had this problem caused by bad crimps on battery cables. Genuinedealz.com is an excellent source for custom cables, and they use the best 4 jaw crimper.

[mcgann454]

Originally Posted by MarkSF

Test the voltage at the starter, while cranking. Anything below 10V is suspect. If low, then start measuring the voltage drops in the wiring. Most likely is a bad connection. I've had this problem caused by bad crimps on battery cables. Genuinedealz.com is an excellent source for custom cables, and they use the best 4 jaw crimper.

I would also check the solenoid on the starter. If is is going bad, it will require more amps to kick over.

[Old Swampy]

Don't forget to check the ground connections between the battery and the engine, etc. flexible ground straps can have hidden faults.

[macbeth]

No charge is seen on the ammeter with the engine going and the alternator working. Hmm, I wonder if the voltage is higher on either battery when it is. Something to check.


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[Boatyarddog]

Look for a hidden resistance in a battery + cable or ground - cable.
Here's what I found in my battery cable, hidden under insulation, barely noticeable. O/2 gauge cable, about 8' long.
But as one started to probe the insulation you can see the trouble. It was about 18" long, and stared at the positive terminal.
This corrosion created so much resistance that it absorbed all current of two new batteries, so the starter motor would not operate.
All other components worked fine.
It's probably been there for years




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[TomLewis]

May be losing a cell on the starter battery. Diesel may take more current than the windlass. I had a similar issue.

[mitiempo]

Originally Posted by macbeth

.......This situation only began this spring after replacing the batteries after the winter.

I would look at the connections you replaced.

[FatBear]

If none of those other things turns out to be the problem the battery switch itself can be. It was once for me. Could be that a cable pulled on it while connecting batteries, bending something or loosening a terminal nut. Mine was very easy to take apart, clean, tighten, etc. Once I got it off the bulkhead, anyway.