CCA = Ah?

boisblancboy

Is it possible to convert Cold Cranking Amps to Amp Hours? Or even a rough estimate to the batteries capacity?

BB.

Re: CCA = Ah?

They are not really directly related (other than with a physically larger battery--both will be larger than a smaller battery).

If you have the battery name/model number--search the web for the specification sheet.

If not, you can find either the battery manufacturer, or a similar manufacturer for the same "type" CCA rating of battery (flooded/agm/gel/etc.; , deep cycle, RV/Marine, or starting/ignition battery; of roughly equivalent size/weight/construction, etc.).

Problem is that Batteries with a CCA rating (Cold Cranking Amps) are designed to start car/truck/boat engines. These are not storage batteries. Starting batteries are designed for a maximum discharge of ~15% maximum (85% State of Charge)...

Deep cycle batteries are designed for an 80% maximum discharge (20% state of charge), and are not designed to provide short bursts of high current (and be of lightweight design--as need for a car). And even then, 80% cycling is still very hard on deep cycle batteries.

There are some specialized lead acid "Storage Batteries" that are designed for very long life, but cannot deep cycle either (typically used by the telephone companies in their central offices with generator backup). They may only cycle ~15%-20%--but they will have a 40 year life while doing it.

In the end, pick the right battery for your application--don't go by price alone (unless it is near free--then all bets are off ).

-Bill

boisblancboy

Re: CCA = Ah?

Great, thanks. Pretty much answers my question. I didnt think they were related in anyway, but I thought I would make sure.

dagr51

Re: CCA = Ah?

Actually, I thought it was a great question in light of my recent discovery of the Blue Seas "Nifty Circuit Wizard for Wire Sizing" wire selection link I found at NAWS. When attempting to enter a number in the battery DC Circuit Protection Selection slot (apparently for breaker sizing), the only number it will accept is a Battery CCA. Therefore, I too was looking for a way to compare my battery bank size (660 ah) to CCA so that I could use the Wizard.

They do say that it is in beta, so maybe we can expect it to change?

Dale

Cariboocoot

Re: CCA = Ah?

Generally speaking, if the battery is being promoted by its CCA it's the wrong kind of battery for solar anyway. That's pretty much a rating of its ability to start an engine, a quite different function from supplying the continuous draw of an inverter.

So if they don't tell you the 20 hour amperage rating, its probably the wrong sort of battery.

BB.

Re: CCA = Ah?

Blue Sea is for marine applications--so the standard battery bank is used to start the boat motor--as well as to run the "house loads".

CCA is the maximum current a battery can output and therefore the minimum current a fuse/breaker must be able to interrupt if there is a short:

Cold Cranking Amperes (CCA)/Marine Craking Amperes (MCA)

CCA and MCA measure the power capacity of a battery. CCA is the discharge load in amps which a battery can sustain for 30 seconds at 0°F/–18°C without falling below 1.2 volts per cell (7.2V on 12V battery). MCA is similar, but is measured at 32°F/0°C and results in a higher number for the same battery.


The amount of current that a breaker or fuse can interrupt without malfunction is its Ampere Interrupt capacity (AIC). The required AIC for a circuit breaker or fuse is determined by the power capacity of the battery.

For wiring on cars and smaller boats--they just use heavy enough gauge wire that it is designed such that it will not catch fire/fail if there is a short circuit on the starting circuit. It is assumed there is not the big a difference between the load of a starter motor vs that of a short--the battery outputs a similar amount of current in either case.

The marine industry is starting to see the bigger issue that off-grid systems have. The larger battery banks that can provide power for hours or days of use while the generators are turned off and are also used for starting--are capable of supplying much more current that a single starting battery by itself. And they have/will need to install fuses/breakers on circuits that run to the starter motors too.

If you need the CCA of a battery--as good as estimate of any would be to use the weight of the battery... If a 30 lbs starting battery can output 300 CCA--then the worst a 30 lb storage battery can output is, most likely, less than 300 amps.

From the Battery FAQ:

Using a deep cycle battery as a starting battery

There is generally no problem with this, providing that allowance is made for the lower cranking amps compared to a similar size starting battery. As a general rule, if you are going to use a true deep cycle battery (such as the Concorde SunXtender) also as a starting battery, it should be oversized about 20% compared to the existing or recommended starting battery group size to get the same cranking amps.

So, a deep cycle battery CCA capability would be about 80% of a similarly Amp*Hour rated starting battery.

The other thing to remember though... CCA (0F) and MCA (32F) is defined for cold weather conditions... Shorts can also occur in hot weather too--and batteries supply much more current when warm.

Hmmm--looking around, there is an HCA rating too (Hot Cranking Amperes at 80F for 30 seconds, and even a PHCA--Pulse HCA, 5 seconds at 80F). This battery company lists the CA, CCA, HCA, and PHCA ratings for their batteries... And the PHCA can be 3x the CCA for there smaller batteries. For their larger batteries the ratio can be less than 2x PHCA vs CCA.

As always, the devil is in the details.

-Bill