Does parallel connecting batteries double the CCA?

Submitted: Thursday, Jun 26, 2014 at 12:52
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If I parallel connect batteries in a 12v system does the CCA of each battery combine to equal the total just like the a/h do .....with the voltage remaining at 12v obviously

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Reply By: Allan B (Member, SunCoast) - Thursday, Jun 26, 2014 at 13:11

Thursday, Jun 26, 2014 at 13:11
Yes it does.
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Reply By: Robin Miller - Thursday, Jun 26, 2014 at 13:47

Thursday, Jun 26, 2014 at 13:47
Only if they are identical batteries in identical state of charge , and at the same temperature.

The current delivered depends on the internal resistance of the batteries and this is affected by the above parameters.
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Follow Up By: Allan B (Member, SunCoast) - Thursday, Jun 26, 2014 at 14:09

Thursday, Jun 26, 2014 at 14:09
Not so Robin.

If the batteries are connected in parallel you can reasonably expect that they will be at the same state of charge and temperature even with differing CCA ratings. Then under discharge their relative internal resistances will act to deliver current proportional to their relative CCA ratings up to their maximum delivery. So the total CCA will be the sum of their individual CCA ratings.

Just as their combined Ah capacity is the sum of their individual Ah ratings.

All give-or-take a small tolerance due to expected manufacturing deviation of course.
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Follow Up By: Robin Miller - Thursday, Jun 26, 2014 at 14:54

Thursday, Jun 26, 2014 at 14:54
Allan which part is not so ?

Batteries of different chemistries have different internal resistance which is why I said only if identical.

Same for each other factor.

Perhaps you are making the point that in practise they are close enough and results are therefore close enough, and that might be , but in practise we often get the case when someone has batteries on either side of engine bay with 1 hotter than the other, or that someone in a dual battery system parallels the starting battery with the deep dischagre type which causes a significant disparity.

In this later case the resistance of the leads can also play a significant part and prevent CCA being doubled or even added.










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Follow Up By: Allan B (Member, SunCoast) - Thursday, Jun 26, 2014 at 15:35

Thursday, Jun 26, 2014 at 15:35
The "identical" part is what I was referring to as "Not so" Robin.
The word "identical" is very specific. Even two brand new batteries of the same manufacturer and specs will not be "identical".

I was assuming that Bungarra has enough sense to consider connecting two batteries that are of the same class and reasonably similar in capacity. They do not need to be identical other than nominal voltage of course and for charging purposes they should be of the same chemistry but apart from that, if reasonably similar, parallel connection is satisfactory for discharge. Charging however can raise some issues, but that is not what Bungarra's question was about.

The very fact that the batteries have internal resistance and cabling resistance is what allows them to proportionally share the current delivery without issues. In fact, in constructing dc power supplies with paralleled diodes is is practice to incorporate a low resistance value in series with each diode to ensure that there is acceptable current sharing.

Paralleling of batteries for cranking large engines in trucks, ships and the like is common practice in order to sum the CCA.

Of course there will be some difference in contribution, but essentially the available CCA will be of the order of the sum of the individual ratings. Bungarra is surely not performing a scientific evaluation!

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Follow Up By: Robin Miller - Thursday, Jun 26, 2014 at 15:40

Thursday, Jun 26, 2014 at 15:40
Close enough is indeed good enough for many purposes Allan.

I think that people reading the post will now be aware of the factors that influence the result.
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Follow Up By: Member - Jim B8 - Thursday, Jun 26, 2014 at 19:26

Thursday, Jun 26, 2014 at 19:26
Robin, Allan
I reckon you'r both correct. Start with two equally rated batteries of the same brand, and you get double the CCA. Of course the easiest way to get this is to buy 2 "Identically Branded - same capacity" batteries, because its way too hard to try and match the impedance of differing brands, ratings etc.
Allen is correct when he says that when paralleled, then they behave as one, but having said that, you must get the ratings right, if 2 batteries are joined (paralleled) , with different internal impedances (different amphour ratings, sort of), then the battery with the biggest AH rating will do all the work, as it has the lower impedance.

Which is all Gobble-D- gook, yes it doubles your CCA, no don't do it without very close matching of the 2 batteries.
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Jim
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Follow Up By: mick v1 - Thursday, Jun 26, 2014 at 19:42

Thursday, Jun 26, 2014 at 19:42
it will help with your cranking capacity but if one is crook then you probably still won't be able to start your engine. our tractors have three or four batteries or excavators or trucks but it only takes one of those batteries to be stuff and they won't start regardless how batteries are in there
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Follow Up By: Member - Jim B8 - Thursday, Jun 26, 2014 at 19:51

Thursday, Jun 26, 2014 at 19:51
Mick
Oh yes, one dead battery in a parallel circuit, and nothing works. A shorted cell anywhere lowers the impedance, and that battery then takes the entire work load. And its ability to deliver, is close to Zero - 11.6 volts (when one 2.2 volt cell shorts out) shorted across a 12.8 volt circuit, with (very) low impedance, the whole system is too worried about shorting out, than actually doing its job

Never underestimate the complexities of a 12 volt system, they're tricky little buggers
Jim
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Reply By: luggy - Thursday, Jun 26, 2014 at 19:30

Thursday, Jun 26, 2014 at 19:30
Now now boys everyone likes to think they know about batteries !so I think he has got the correct answer to get himself out of trouble.
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Reply By: Michael ( Moss Vale NSW) - Thursday, Jun 26, 2014 at 21:32

Thursday, Jun 26, 2014 at 21:32
My Patrol has had parallel batteries for its 11 year life, on my third set of batteries now. Ive never had any charging problems and always change both batteries at the same time. I have a power thirsty 90 litre fridge, hence the parallel configuration. No solenoids to fail and less wiring this way! Michael
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Reply By: drivesafe - Thursday, Jun 26, 2014 at 23:38

Thursday, Jun 26, 2014 at 23:38
Hi bungarra and I ASSUME you are looking at improving you starting ability.

While adding another battery in parallel will increase the CCA by the amount the new battery is rated at, just as adding another battery will increase the total Ah by the amount of AH the new battery has.

But please note, the Ah of a battery has no connection to the CCA and you can’t use one to calculate the other.

The CCA rating of a battery is based on the amount of current that battery can supply at 0f ( -18C ) and the battery’s voltage does not drop below 7.2v.

Next, if a vehicle manufacturer requires a minimum CCA of say 800, this does not mean the vehicle will draw 800 amps while starting.

The vehicle might only draw 350 amps while starting but needs to have a minimum voltage of no less than 10 volts to be able to start, so the manufacturer will have established that a battery with a CCA rating of 800 amps, will not drop below 10v while supplying 350 amp needed to start the motor.

Back to your question, if you have a battery rated at 700 CCA and you add another battery, rated at 500 CCA, you will now have a total CCA of 1200 amps.

If your motor needs an 800 CCA rating to start, it will still only draw 800 amps while starting BUT, it will now be supplied that 800 amps at a higher voltage.

This has a number of advantages. The first is that a motor is easier to start when a higher voltage is applied to the starting motor.

Plus, because the batteries are not discharged to as low a voltage while starting, they will be recharged in a shorter drive time and spreading the starter motor current over a larger CCA means the batteries will probably have a longer operating life.

Last but not least, you do not need the same size, type, age, shape or colour of batteries to increase your CCA.
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Follow Up By: Member - bungarra (WA) - Friday, Jun 27, 2014 at 08:33

Friday, Jun 27, 2014 at 08:33
thanks for your answer...yes I understand all of that...the reason for asking was simply because the 200 LC has two batteries in parallel....and I intend to replace the cranking battery and isolate the other (and replace) as an AUX.............I was checking that the total CCA was within the engine requirements.......

It is really quite straight forward as the other posters have indicated
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Follow Up By: Member - Phil G (SA) - Friday, Jun 27, 2014 at 17:40

Friday, Jun 27, 2014 at 17:40
The VDJ200 comes with two 530cca crankers. But the V8 cranks perfectly on one 700cca battery (as did your VDJ79), so feel free to join the many thousands of 200series owners and isolate them. I've heard of some who just isolated the 530cca batteries and found it cranked fine on just one. I'm assuming you don't live in the snow country.
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Reply By: Ron N - Friday, Jun 27, 2014 at 11:47

Friday, Jun 27, 2014 at 11:47
Don't forget that the length and sizing of the cables used to link the batteries in parallel will affect the total amount of current drawdown ability, too.

Cheers, Ron.
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Reply By: Allan B (Member, SunCoast) - Friday, Jun 27, 2014 at 16:49

Friday, Jun 27, 2014 at 16:49
..


A one-sentence question, a one-word answer, and then.................!!!!!

I'm never, ever, ever going to answer another battery question!

Sorry chaps.





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Allan

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Follow Up By: Shaker - Friday, Jun 27, 2014 at 17:29

Friday, Jun 27, 2014 at 17:29
Don't forget this is ExplorOz, & hairs need to be split!

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Reply By: oldtrack123 - Friday, Jun 27, 2014 at 23:06

Friday, Jun 27, 2014 at 23:06
HI
I may as well add my 2bobs worth to Allan's & Driveafe's post
Both are totally correct
[[a] if you parallel connect batterries the CCA &/or the Ahrs are the sum of the individual ACTUAL capacities
This takes into account
[a] different manufacturing tolerances.
[b]Different RATED capacities
[c]Different actual capacitites due to aging'

There may be slight difference in SOC during charging & recharging due to different internal impedance. but these will balance out over time

It would be impossible for one to be flat & the other to be at say 20%SOC

BUT both batterries should have the same charging requirements regarding Max charge voltage , float voltage & depth of recommended discharge.

Where high current demands are possible, the connection configuration is important.
The battery interconnections should be the same length & the SAME sized cable
The load Pos & charge Pos should be taken from one battery & the load neg /charge neg connected to the other battery.

PeterQ
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