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  #1   IP: 71.98.36.232
Old 03-28-2009, 02:51 PM
baileyem baileyem is offline
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Question Cold cranking amps vs Amp hours

This is not an A-4 question, but it is closely related:
When shopping for a new battery I find that non-marine suppliers only list Cold Cranking Amps and don't have the faintest idea how to calculate Amp Hours......but then neither do I. How does one calculate Amp Hours for a battery?
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  #2   IP: 142.68.117.65
Old 03-29-2009, 05:03 AM
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rigspelt rigspelt is offline
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I use Cold Cranking Amps (CCA) to tell me about engine start batteries (lighter and smaller), and amp-hours to tell me about deep cycle batteries (heavier and larger) used for house loads. CCA indicates how much voltage a start battery can deliver to an engine starting motor in a very short period of time, while Amp-hours tells me how much amperage can be drawn from a deep cycle battery for a certain period of time. Start batteries do not get deeply discharged in regular use, unlike house batteries. If a battery is not rated by amp-hours, then it may not be designed for frequent cycles of slow deep discharging.

Basically, amp-hour measures the maximum number of amps that can be drawn from a battery until the battery is dead (about 10.5 volts) over a fixed time period, say 20 hours or 100 hours. Not all amp-hour statistics are apples and oranges, because there are different ways to calculate and measure amp-hours while controlling for variables like temperature in different ways.

Compromise economy batteries, often labelled "marine", have mixed features: both cranking and deep cycle. This type of battery is a compromise for certain types of boating. They may provide enough cranking amps to start lower demand engines, but usually don't provide sufficient deep cycle capability for serious cruising. The term "Reserve Capacity" is another measure used to describe batteries: number of minutes a battery can maintain a useful voltage at a certain amperage discharge rate. Some of these economy batteries are also rated using Marine Cranking Amps (MCA), which is not the same as CCA. See http://www.exide.com/faq/faq_marine.html.

These might be of interest:
http://www.windsun.com/Batteries/Battery_FAQ.htm
http://www.dcbattery.com/faq.html
http://www.windpowerunlimited.com/ba.../Amp_Hours.htm
http://www.sailnet.com/forums/gear-m...amp-hours.html

The books by Calder or Wing are useful in understanding how to design a boat battery system for house loads.
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Last edited by rigspelt; 03-29-2009 at 07:07 AM.
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Old 03-30-2009, 11:01 AM
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msauntry msauntry is offline
 
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For what its worth, I've been using a pair of deep cycle Trojan 6v batteries for years. I only have one bank and this does it all. For my long cruise, I threw in a second "bank" which consisted of a cheap lawn tractor battery. That was rated 300 cca and it turned the A4 over just fine, but I've since yanked it and am back on the Trojans.
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Old 03-31-2009, 12:29 PM
baileyem baileyem is offline
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Smile Cold Cranking Amps vs.....

Thanks, rigspelt and msauntry, for the responses. It looks as though I have some reading to do. Thanks again.

Mike
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Old 04-10-2009, 05:35 AM
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rigspelt rigspelt is offline
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Quote:
Originally Posted by msauntry View Post
For what its worth, I've been using a pair of deep cycle Trojan 6v batteries for years. I only have one bank and this does it all. For my long cruise, I threw in a second "bank" which consisted of a cheap lawn tractor battery. That was rated 300 cca and it turned the A4 over just fine, but I've since yanked it and am back on the Trojans.
I've heard others talk about just equipping a small sailboat with deep cycle batteries when the auxiliary is a relatively low starting current engine like the A4, roughly 135-150 amps, from what I can tell reading the net. It's an interesting thought. A cruiser wants lots of house electricity when sailing/anchoring, and the suggestion is that perhaps A4s may not strain deep cycle batteries with that kind of starting motor amperage. I haven't found any technical discussion of this option. Weight becomes a factor for the Monday-Wednesday racer who cruises less than races and can't stand being down the results page.
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Old 04-10-2009, 09:09 AM
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msauntry msauntry is offline
 
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You can certainly add a lot of complexity and money to the charging system, but I had to go with something cheap and simple.

For race weight, I'd probably avoid the double Trojans. Each one is a slipped disk waiting to happen. I think a decent single 12v deep cycle will survive the starting loads of the A4 just fine. Its such a low compression engine that its easy to turn over. If you really want light weight, a motorcycle battery will start this engine.
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Old 07-27-2009, 07:18 PM
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Mephisto, a C&C 29 Mk. 1 Mephisto, a C&C 29 Mk. 1 is offline
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Cold Cranking Amps Required by an A4

Can someone tell me the cold crank amp requirements of a late model Atomic 4, please? I cannot find that in any of the specifications that I have in hand. I ask because I'm about to replace my two existing batteries - 1 starting battery and one deep cycle battery - and I'm wonder if the CCA requirement is low enough that two deep cycle batteries in parallel would do a sufficient job of turning over the engine. Thanks very much!
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