Amp-Hours vs. Cranking Amps?

[Janey]

Automotive (marine, etc.) batteries are typically rated in (after voltage)
cranking amps.

Is there a simple way to determine Ah rating from this? How is cranking amps
determined?

Thanks.
pj

 

[Sjouke Burry]

Janey wrote:

Automotive (marine, etc.) batteries are typically rated in (after voltage)
cranking amps.

Is there a simple way to determine Ah rating from this? How is cranking amps
determined?

Thanks.
pj

cranking amps depend on internal resistance, which depends on
chemical composition, and actual plate area, none of which
actually determine AH, although some of them influence AH.
But the main parameter of AH is weight(in lead).
Divide AH and weight, and you get a sort of efficiency figure
for the battery.

 

[Tim Wescott]

On Wed, 08 Jul 2009 19:12:27 -0700, Janey wrote:

Automotive (marine, etc.) batteries are typically rated in (after
voltage) cranking amps.

Is there a simple way to determine Ah rating from this?

No. But you may find Ah listed somewhere, perhaps in very fine print.
Batteries sold for their capacity (like deep-discharge lead-acid
batteries) will list capacity.

Cranking amps will be very roughly proportional to capacity, because if
you just scale a battery up in a linear manner the cranking amps will
scale with capacity. But there are a ton of ways that you can trade off
cost, ruggedness, cranking amps, volume, weight, capacity, etc., so the
correlation isn't strong.

How is cranking amps determined?

However the manufacturer wants to. Honest ones will do it with some sort
of testing, hopeful ones will do it by analysis, dishonest ones will slap
a number on the battery that they think will sell without getting them
sued.

Cranking amps _should_ be _defined_ as the amount of current that the
battery can put out for a short period of time at some reasonable (but
significantly lower than "normal") voltage without permanent damage. I
don't know if any standards body (SAE?) has a published spec for this or
not, but you could do a web search.

--
http://www.wescottdesign.com

 

[miao yun]

On Jul 9, 10:24 am, Sjouke Burry <burrynulnulf...@ppllaanneett.nnll>
wrote:

Janey wrote:
Automotive (marine, etc.) batteries are typically rated in (after voltage)
cranking amps.

Is there a simple way to determine Ah rating from this? How is cranking amps
determined?

Thanks.
pj

cranking amps depend on internal resistance, which depends on
chemical composition, and actual plate area, none of which
actually determine AH, although some of them influence AH.
But the main parameter of AH is weight(in lead).
Divide AH and weight, and you get a sort of efficiency figure
for the battery.

http://www.51orders.com/

 

[BobG]

http://www.autobatteries.com/faq/index.asp
says CCA is amps at 0 deg F for 30 sec,
RC (reserve capacity) is minutes it will hold up above 10.5V at 25A
discharge