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Discussion Starter #1
I have the old faithful Yanmar 3 cylinder 3GM30? diesel on my cat. The starting battery probably needs replacing (won't charge over 12.7 volts) but I thought I would just take the battery from my car as a spare.

The CCA on the car battery is fairly high - 720 CCA.

My question is whether the car battery might damage the starter or other systems? Any ideas? Does the CCA have to do with amps available or amps delivered?

David

PS - I like the new discussion topic
 

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Sailboat Reboot
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My question is whether the car battery might damage the starter or other systems? Any ideas? Does the CCA have to do with amps available or amps delivered?
First - there are only DC Amps and DC Volts - not car or boat or airplane or whatever. So no, using a car batter to crank a marine engine will do no damage. In fact many of us, myself included, use golf cart batteries in their boats. Usually they are used as house batteries but if you have a big house bank as many cruisers do the fact that they are not optimized for starting the engine is of little consequence.

CCA, MCA (marine cranking amps) are just specifications. They all relate to how long you can crank the engine at a particular current before the batter is exhausted. Every battery could be rated as CCA and MCA etc. It is just what process is used to rate the battery's ability to deliver current.

Of greatest importance is how much you draw down a battery. Batteries have lives calculated in charge - discharge cycles. It is generally a bad idea to discharge a battery more than 50% so usually the charge discharge "life" is based on a 50% discharge followed by a recharge cycle - lets say 1000 cycles is the life. But if you only discharge the battery 10% each time you are going to get a lot more cycles.

Cranking is also temperature senstivie. No only does the battery current and charge parameters change (not usually enough to care about) but cranking a cold engine full of thick oil takes a lot more current than a warm engine.

So, the bigger the battery the longer the life. Most batteries on casual use boats die because they have been cooked (left on the charger too long) or dry out. So a sealed no maintenance battery can be worthwhile.

Summary:
1. Use your car battery (then what, push start the car down the hill and pop the clutch to jump start it?) Did that a while in my youth.
2. Bigger is better but the constraint is usually the size of the battery box. You should enclose the battery in a box so that if it leaks it can't damage the boat.
3. Most of all - fair winds and following seas. :)
 

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Discussion Starter #3
Thanks for the information Roger. That is a great answer and just what I needed to know.

I thought I could swap the boat battery to the car and check if it will charge up there. The boat starter battery is over 5 years old so might be over the hill anyhow. I did get it to start the motor but it didn't seem to charge up very well. Process of elimination - I hope it is not a problem with the alternator.

I will do the swap and see how it all goes.

Thanks again,
David
 

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Sailboat Reboot
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I hope it is not a problem with the alternator.
David
Before you do anything with the alternator check the drive belt tension. A loose drive belt can make it look like the alternator is failing. This is true much more often in a boat since in a car you are usually just topping off the battery where in a boat you can be recharging from a deeper level. This requires more power into the alternator (the engine drive belt) so it is more likely to slip.

I would just take the battery to a West Marine or Auto Zone (since you were taking it out anyway.) They have a machine that will tell you if the battery is any good for free. :)
 

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Closet Powerboater
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I agree with pretty much everything Rodger says. Also, I believe the difference between CCA/MCA etc is how many amps they can deliver at a given temperature.

From the interstate website here:Interstate Batteries

MCA:
Marine Cranking Amps - The amount of amps a battery can produce at 32°F.


CCA:
Cold Cranking Amps - The number of amps a battery can deliver for 30 seconds at 0°F and maintain 7.2 volts.

RC:
The amount of minutes a battery can be discharged to 10.5 volts by 25-amp discharge at 80°F.

Amp Hour (Ah or ah):
A unit of measure for a battery’s storage capacity obtained by the amount of amps a battery can be discharged (typically 1.75vpc) multiplied by the amount of hours @ 80F (26.7C) . Most auto/marine and light truck batteries are tested at a 20-hour discharge rate. Example: A 12-volt 100ah rated marine battery means that 5 amps can be discharged for 20 hours at 80°F (26.7C) before falling below 10.5 volts (6 cells X 1.75v)
 

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Boatswain
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The wrong battery can cook your alt. You need to use the battery that is specified for your boat. The battery has a certain resistance to charge and the Alternator and regulator is matched to that. Wrong battery can ruin your alternator or cause the battery to over charge and off gas.
Just FYI.
 

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The wrong battery can cook your alt. You need to use the battery that is specified for your boat. The battery has a certain resistance to charge and the Alternator and regulator is matched to that. Wrong battery can ruin your alternator or cause the battery to over charge and off gas.
Just FYI.
While any dumb regulated alternator, with no internal temp compensation, can cook itself when attached to a large bank, where it will be asked to produce full output for hours on end, alts are not "matched" for a particular battery. Alternators are specified by amp output and voltage not by the battery they should be connected to.

If you have a large bank of flooded, AGM or GEL batteries they may over work and cook your alternator. However, that same alternator converted to external regulation with a temp sensor can run for years charging that same bank because it will run cooler being temp compensated...
 

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Boatswain
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By the OPs original post I am assuming we are talking in simple term, no conversions or temp sensors.

I am just posting for the benefit of the OP. I have cooked alts and destroyed brand new batteries by Willie nilly battery swapping. And I am not talking about huge banks. My experience has mostly been in diesel trucks and tractors.

But everybody can judge their own ability and research their application... or you can just follow the Manufacturer suggestions.
 

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By the OPs original post I am assuming we are talking in simple term, no conversions or temp sensors.

I am just posting for the benefit of the OP. I have cooked alts and destroyed brand new batteries by Willie nilly battery swapping. And I am not talking about huge banks. My experience has mostly been in diesel trucks and tractors.

But everybody can judge their own ability and research their application... or you can just follow the Manufacturer suggestions.
I've replaced a lot of batteries and alternators, even old generators, including replacing the brushes in 6 volt systems over the years and have never "cooked" an alternator or destroyed a brand new battery in the process.
 

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Boatswain
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But when you changed them did you use a random old battery from a car? We are not talking about replacing batteries with the correct one... we are talking about using an unknown battery from a car on a boat and only comparing CCAs.
 

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But when you changed them did you use a random old battery from a car? We are not talking about replacing batteries with the correct one... we are talking about using an unknown battery from a car on a boat and only comparing CCAs.

Using an "unknown" battery can get you into trouble if you don't first test it first. Could have an internal short or was so sulfated it just won't take any current. The only things I have ever seen "cook" alternators, other than just plain old age and the marine environment, is running them too long at full output, direct shorts in the wiring or owners passing the battery switch through OFF with the engine running.. Big banks and AGM's have a tendency to do overheat alts but no "car battery" should ever cook a marine alt unless you have six to ten of them in parallel and depleted....
 

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Boatswain
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Okay well I am bowing out of this one.

Batteries are dangerous, just use your head... Hydrogen gas is both flammable and deadly toxic...
 

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But when you changed them did you use a random old battery from a car? We are not talking about replacing batteries with the correct one... we are talking about using an unknown battery from a car on a boat and only comparing CCAs.
Oftentimes they were replaced with anything that would hold a charge. It wasn't until I had a bit of money that I worried about such esoteric concepts as the "recommended" battery. :)
 

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Okay well I am bowing out of this one.

Batteries are dangerous, just use your head... Hydrogen gas is both flammable and deadly toxic...
Dat's da troof, I was walking down an alley near my work once, years ago when I noticed 3 guys jump starting a small BMW in a parking lot about 100 feet away. All of a sudden I heard a loud, hard BANG and looked over to see them all jumping back from the Bimmer. A good six seconds later I heard the clunk of the battery top hitting the ground - it must have spat it more than 100 feet in the air.

Pretty scary.
 
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