Friday, Jul 11, 2003 at 02:24
Hi,
I may be wrong on this, so if I am please feel free to let me know, as I don't claim to be any sort of battery expert, but it's my belief that no such 'formula' exists.
The reason is that you can have a battery with great CCA rating but very low amp/hour optimised for turning a motor over - ie producing a very high current for a short period of time, and on the other hand you can have a deep cycle battery with poor CCA rating optimised to run accessories such as fridges and maintaining a relatively low current flow, but steady voltage over a log period of time. So based on this theory, if one value rises, then the other value would not necessarily rise, in fact in many cases it will go down! The way in which these batteries are optimised for different roles is in their construction - from memory, the deep cycle will have a greater number of plates, and these plates will be at least 4mm thick - thereby making a larger surface area available for chemical reaction to produce voltage.
These batteries may both be very high quality batteries costing alot of money, but are optimised for different things, this is why you might see many dual battery setups fitted with a good starting battery (high CCA number) for starting the vehicle, and a deep cycle auxilliary battery for running low current accessories over a long period of time.
Two examples:
Yuasa 68MF has 525CCA, and storage capacity of 68Ah
Optima D34 has 870CCA, and a storage capacity of 55Ah
(Thanks to 4WD Monthly for those stats found on page 130 of the Aug2003 edition)
The Yuasa has a larger storage capacity than the Optima, at the cost of it's cold cranking power whilst the Optima has excellent cold cranking ability at the cost of it's storage capacity.
Another example (also from 4WD Monthly) is:
CGB CB12100 which has a massive 900 CCA cold cranking amps, and a big 100Ah storage capacity.....
Yep, batteries are a science :-)
Cheers,
Luke.
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Follow Up By: chopper - Friday, Jul 11, 2003 at 07:13
Friday, Jul 11, 2003 at 07:13
I'm with Luke.
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Follow Up By: GaryInOz (Vic) - Friday, Jul 11, 2003 at 08:15
Friday, Jul 11, 2003 at 08:15
Ditto, It's more to do with the construction of the battery. CCA and A/H are two totally seperate aspects in the battery design.
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Follow Up By: Mick - Friday, Jul 11, 2003 at 08:29
Friday, Jul 11, 2003 at 08:29
I think you're on the money Luke. I have a portable battery/jump start unit. It is an 18amp/hour and claims 300CCA. Great little unit too I must say - runs lights starts cars and runs a "snore machine" for 3 nights!!
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Follow Up By: Steve from Drive Systems Victoria - Friday, Jul 11, 2003 at 08:51
Friday, Jul 11, 2003 at 08:51
Spot on, Luke. The other misnomer with batteries, is the falacy that you can run a deep-cycle battery flat without hurting it. Wrong. No battery likes total discharge state, including deep cycle types.
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Follow Up By: Patrol22 - Friday, Jul 11, 2003 at 12:35
Friday, Jul 11, 2003 at 12:35
Logic says that if CCA goes up and AH goes down or vice versa then there appears to be an inverse relationship between the two - I wouldn't be the least bit surprised if the physicists have derived a formula to calculate this relationship - begs the question however - why bother?
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Follow Up By: Luke - Friday, Jul 11, 2003 at 20:47
Friday, Jul 11, 2003 at 20:47
Mmmmm ...not sure Patrol22 - as you can see if you look at many different battery examples - I don't think if one goes up the other necessarily goes down...
check out example number three to see what I mean.
Cheers,
Luke.
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Follow Up By: GaryInOz (Vic) - Friday, Jul 11, 2003 at 21:08
Friday, Jul 11, 2003 at 21:08
CCA's are related to the total surface area of the plates in the individual cells. Starting or Deep Cycle relates to the thickness of the individual plates.
For a given volume, either the number of plates may go up (ie., Starting, high CCA battery, but not much metal to get through before the plates disappear altogether) or the thickness of the individual plates goes up (ie.,Deep Cycle, lower CCA but able to withstand continuous dischage without mechanically dissolving the plates away). The starting battery is capable of high currents over a very short timespan (= high CCA, and generally lower A/H capacity), related to the high surface area. Deep Cycle have a lower surface area but more "meat" in the plates (= lower CCA, but generally higher A/H capacity), enabling the chemical reaction to occur to a greater depth in the plate.
THERE IS NO CONVERSION RULE FOR CCA's TO A/H's. Apples and oranges.......
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Follow Up By: GaryInOz (Vic) - Friday, Jul 11, 2003 at 21:13
Friday, Jul 11, 2003 at 21:13
Before I get shot down, please take note. I said "FOR A GIVEN VOLUME...". There will obviously be differences in size and construction that will affect CCA and A/H ratings of indiividual batteries.
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