Re: Battery life and does size really matter?

Posted by Texasmark1 on January 04, 2017 at 06:26:41 from (198.45.240.17):

In Reply to: Battery life and does size really matter? posted by Geo-TH,In on January 04, 2017 at 04:02:00:

We're talking about horsepower here or watts if you will......1 hp = 746 watts (volts x amps in a dc circuit, considered to be the period of a second, unless time is involved, like hours for watt-hours or the more familiar term: kilowatt-hours for household power consumption).

To spin a certain engine at a certain speed under certain conditions for a certain length of time takes a certain amount of "work" measured as HP or kW x time required.

A battery stores "work" as "unconsumed" energy (which is the definition of work when consumed) in the form of watt-seconds meaning it will supply x number of volts x amps x time.

CCA makes no mention of the other two elements of energy storage: At how many volts, for how long. If we were to take the time to look up the definition of how the CCA rating is to be determined, we would see "the rest of the story" (Paul Harvey).

Starters in my corral require approx. 10v across the starter to spin up and when considering connectivity losses, which increase drastically when larger engines are involved due to higher amperage requirements, at least 11v needs to be at the battery terminals.

Sulphate is an oxide scale forming on the conducting plates of the battery as a result of the electric charge and the Sulphuric Acid-water (H2SO4+H20) solution. When it gets thick enough and enough vibration is present, some of it falls to the bottom of the battery case and in time piles up.

Sulphate amounts to a resistor in the circuit, inside the battery. Current flowing through the battery develops a counter voltage across this "resistance" which subtracts from the terminal voltage under the cranking load. Since the starting circuit is a "series" circuit, resistance anywhere in the circuit acts the same in limiting available current flow for a given voltage. Static battery voltage value does not take this into account as there is no current hence no counter voltage drop.

This is where the battery tester comes into play. It forces the battery to deliver whatever current you select and tells you the terminal voltage of the battery. (I have a HF unit and works great) If the battery is under charged or sulphate coated plates, the terminal voltage falls off fast as the current is increased.
Using a reference from my Mercury 90 hp outboard motor service manual, the stated starting current is 120 amps. I use 12.75V year around as my benchmark value for a fully charged lead acid battery, rather than a Hydrometer which I don't have.....todays digital multimeters makes this possible.

If I need 10V at the terminals of the starter at 120 amperes for as many seconds as it takes for the engine to light off, then the total circuit resistance can't be greater than (12.75v-10v)/120 amps = 0.023 ohms which is hard for the connectivity to measure with suitable wire and the connections clean, and bright, and tight, much less any resistance in the battery. So yes, sulphate matters as does size (surface area) and number of plates.

One thing I found (conventional "old school" LA batteries) is that the lower the CCA for a given battery size (24, 27, whatever) the shorter are the plates. The shorter the plates, the more room at the bottom of the battery for sulphate to collect before it shorts out a cell.

I don't know what happens when you put a fiberglass mesh between the plates like some current battery technology. Seems to me it improves the life span and maybe that's why I just got 9+ years out of the battery that was in my 2007 Branson 6530c. I never got that much service out of a battery.

Well, I didn't have anything else to do this morning. It's a "cabin" day and "cabin fever" is quick to set in. Hope I remembered it all correctly. I do things like this to keep what mind I have left active.....I think. Grin

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