Battery CCA/amp hours formula

Submitted: Friday, Jul 11, 2003 at 00:50
ThreadID: 5920 Views:100081 Replies:8 FollowUps:12
This Thread has been Archived
Does anyone know the formula to convert CCA (cold cranking amps) to amp/hrs please.
Back Expand Un-Read 0 Moderator

Reply By: Phil R - Friday, Jul 11, 2003 at 01:23

Friday, Jul 11, 2003 at 01:23
John try this

Amp/hour = CCA / 6

I havn't checked this. so good luck
AnswerID: 24664

Reply By: Luke - Friday, Jul 11, 2003 at 02:24

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.
AnswerID: 24667

Follow Up By: chopper - Friday, Jul 11, 2003 at 07:13

Friday, Jul 11, 2003 at 07:13
I'm with Luke.
0
FollowupID: 16591

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.
0
FollowupID: 16593

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!!
0
FollowupID: 16594

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.
0
FollowupID: 16598

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?
0
FollowupID: 16613

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.
0
FollowupID: 16635

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.......
0
FollowupID: 16636

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.
0
FollowupID: 16638

Reply By: paul - Friday, Jul 11, 2003 at 12:20

Friday, Jul 11, 2003 at 12:20
Fromm an earlier post in which I took an interest:

"Mark, Dug this formula up using Google [wanted to know myself seeing you asked] Cam from a University of Hawaii electronics website. hope it is of use: Many batteries today are rated in CCA or RC. CCA is Cold Cranking Amps. CCA is approximately equal to the RC of a battery times five. [1000 CCA is about 190 RC]. RC is Reserve Capacity. You can convert RC to amp/hours by the following formula: Amp/Hours = (Reserve Capacity / 2) plus 16"
AnswerID: 24687

Follow Up By: Luke - Friday, Jul 11, 2003 at 21:09

Friday, Jul 11, 2003 at 21:09
Hey Paul - that's interesting about the formula you have supplied.

It seems to work quite well for the CGB battery I mentioned - only 1.5 Ah out.......but it doesn't seem to work for many other batteries when applied to them using manufacturer stated specifications.

What are people thoughts? Does this mean then that the manufacturer's specifications are not accurate, or that the formula only applies to some types of battery?

Interested in your thoughts,

Cheers,

Luke.
0
FollowupID: 16637

Follow Up By: GaryInOz (Vic) - Saturday, Jul 12, 2003 at 02:20

Saturday, Jul 12, 2003 at 02:20
See above. Apples and oranges........

VERY loose connection if any at all.
0
FollowupID: 16654

Reply By: ThePublican - Friday, Jul 11, 2003 at 17:23

Friday, Jul 11, 2003 at 17:23
John have a good old look in the archives here you will find the formula , an overlander 700 / has a cca 600 / rca 130 / is actualy rated at 68 amp hrs /the ducks guts for the info is the university of Hawaii web site.
AnswerID: 24714

Reply By: Eric - Friday, Jul 11, 2003 at 23:49

Friday, Jul 11, 2003 at 23:49
John.

There is no relationship between cca and ah. the type of construction is the only determinate of these two parameters. the cca is limited by internal resistance of the cells not the capacity. Eric.
AnswerID: 24752

Follow Up By: Patrol22 - Saturday, Jul 12, 2003 at 09:07

Saturday, Jul 12, 2003 at 09:07
Too many variables for me - I think I'll stick to fishing and 4WDriving where one can always think about the variables over a cold beer.
0
FollowupID: 16657

Reply By: Luke - Saturday, Jul 12, 2003 at 22:21

Saturday, Jul 12, 2003 at 22:21
Interesting thread indeed!

It seems, as I first thought that the general consensus is that there is no direct relationship between CCA and AH, and that those merits are dependant on battery construction techniques.

This is certainly the idea that I've always been familiar with....

Maybe someone from the University of Hawaii will come over and explain their "Formula".

Cheers,

Luke.

:-)
AnswerID: 24796

Follow Up By: tex1972 - Monday, Jul 14, 2003 at 22:44

Monday, Jul 14, 2003 at 22:44
Food for thought peoples depending on wich country batteries are tested in changes the cca ratings etc.different countries use different temperatures in thier tests for benchmarking, bit like the japanese horsepower its only a pony.
0
FollowupID: 16827

Reply By: CirclingVulture - Monday, Aug 11, 2003 at 18:17

Monday, Aug 11, 2003 at 18:17
link text
AnswerID: 27471

Reply By: CirclingVulture - Monday, Aug 11, 2003 at 21:49

Monday, Aug 11, 2003 at 21:49
Just a test pic

[ View Image]
AnswerID: 27517

Sponsored Links

Popular Products (13)