Enging/starter battery pretends to be good but.... - Page 3 - SailNet Community
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post #21 of 29 Old 09-05-2012
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Re: Enging/starter battery pretends to be good but....

Just wanted to mention my experience last weekend - the engine started great on bank 1, but not on bank 2.

I check the bank 2 batteries, they measured fine. But still the starter went grrrrr grrrrr.

So I selected bank 2, and switched on every light in the boat, so I was pulling about 20 amps. I then started measuring voltage drops. Luckily, I started at the battery end.

I had a drop of 0.5V between the battery post, and the the cable clamped to it. Also feeling the cable clamp showed it to be getting distinctly warm, just at 20A draw.

So a drop of 0.5V at 20A would be a drop of 5V at 200A starting current. So that's why the engine was not starting. BTW, at that kind of resistance and voltage drop, something in your system should be getting VERY hot.

A cleanup of all the battery connections and application of some dielectric grease and it starts up perfectly.

BTW, a good habit when working on 12V systems especially around batteries is to take your watch off, especially if it has a metal strap.

Bristol 31.1, San Francisco Bay

Last edited by MarkSF; 09-05-2012 at 02:29 PM.
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post #22 of 29 Old 09-05-2012
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Re: Enging/starter battery pretends to be good but....

"A cleanup of all the battery connections and application of some dielectric grease and it starts up perfectly."
It took me a while but I've gotten in the habit of greasing all sorts of connections, including the battery contacts in flashlights. When they leak it makes the cleanup way easier. So far the cheapest cource for dielectric grease that I've found is the auto parts store. "High temperature brake grease" about $4 for a toothpaste-tube size.

"take your watch off, "
Heheh. We won't mention the bezel that almost got welded in place here. Welcome to the club.
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post #23 of 29 Old 09-05-2012
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Re: Enging/starter battery pretends to be good but....

I used Permatex anti-sieze grease, on the basis it has copper and aluminium in it, which should be conductive. Yes, it was the only thing that was handy.

Bristol 31.1, San Francisco Bay
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post #24 of 29 Old 09-06-2012 Thread Starter
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Re: Enging/starter battery pretends to be good but....

Update and thanks to all for inputs.

Got "Dave" from the yard to come aboard and we sorted it out in about 3/4 of an hour. The PO made a mistake when putting in the new house batteries; fixed that and that solved the alternator issue to the house bank. There is/was something pulling .1 amp/hr off the starter battery so moved that to the house and will run that down later. Today the engine would not start off the "starter" battery even with a full charge so Dave thinks it is the starter. It would start off of the "all" setting of the Perko(s). Dave gave me a starter he had lying around to try that and see if it fixes the problem. Tomorrow's project along with engine mounts, should be a fun day.

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post #25 of 29 Old 09-06-2012
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Re: Enging/starter battery pretends to be good but....

Did Dave measure the voltage AT THE STARTER SOLENOID under both conditions?

Changing out the starter before you do this -- to eliminate the (very real) possibility of a faulty battery switch and/or connections -- is the last thing I'd want to do.

A flaky solenoid is another possibility; the starter itself is not necessarily the problem, especially since you can start the engine under certain battery/switch positions.

Bill
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post #26 of 29 Old 09-08-2012
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Re: Enging/starter battery pretends to be good but....

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Originally Posted by btrayfors View Post
A flaky solenoid is another possibility; the starter itself is not necessarily the problem, especially since you can start the engine under certain battery/switch positions.

Bill
I assume he means starter battery when he says starter. I was confused the first time reading it as well.
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post #27 of 29 Old 09-08-2012
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Re: Enging/starter battery pretends to be good but....

No, bill usually means exactly what he's said. I read it that when he says the STARTER he means the starter, especially in the context. No reason to read it as meaning the starting battery, that seems clear if you understand how starting systems misbehave.
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post #28 of 29 Old 09-09-2012
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Re: Enging/starter battery pretends to be good but....

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No, bill usually means exactly what he's said. I read it that when he says the STARTER he means the starter, especially in the context. No reason to read it as meaning the starting battery, that seems clear if you understand how starting systems misbehave.
I wasn't questioning bill...I was questioning his interpretation of what F15EWSO said which I think was confusing. I agree with Bill 100% that if the engine starts under some battery conditions then the problem isn't likely the starter. That's why I think F15EWSO meant starter battery when he said "Dave" from the yard had one "lying around".
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post #29 of 29 Old 09-09-2012
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Re: Enging/starter battery pretends to be good but....

What was that .1 amp draw?
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