CCA may not matter

Posted by jdemaris on October 31, 2006 at 06:06:43 from (66.218.17.210):

In Reply to: 8volt/6volt battery posted by n8terry on October 30, 2006 at 21:23:37:

The cold cranking amp rating may, or may not have any affect on how well your tractor starts/cranks. The #1 issue that will determine how fast your engine cranks it the voltage when cranking. That is, more or less, determined by battery size versus starter demand. The bigger the battery, the higher your cranking voltage will be. Most 12 volt systems are designed to crank at 9.5-10 volts, and most 6 volt systems are designed to crank at 4.5 volts. If the battery size is increased in any system, cranking speed also increases as long as there is rise in voltage under load.
My point is - e.g. - if the 8 volt battery is able to maintain 6 volts at cranking, and your old 6 volt battery only maintains 4.5 volts at cranking - then the 8 volt will crank it over faster - even though it has a lower CCA rating.
When you are looking at batteries - to buy - a general rule of thumb is - to look at the weight. That because some companies - will use the same amount of material to make a 6, 8, or 12 volt battery - they just use smaller cells and thinner plates as the voltage goes up. Batteries are just boxes with little batteries hooked in series.
For example - Interstate 6 volt 575 CCA battery weighs 33 lbs. Same physical size battery in 8 volts is 525 CCA and 31 lbs, and the 12 volt is 525 CCA and 34 lbs. To maintain the same physical sizes the cells get smaller as voltage goes up.
Many small 6 volt tractors will crank faster with an 8 volt battery - but I've never found it to be worth the bother and expense. Since 8 volt batteries are oddities - they are expensive. 12 volt batteries are always the best buy. Yes, most 6 volt charging systems can be turned up enough to just barely charge an 8 volt battery properly - but if you care about good cranking and expense - 12 volt is a better deal all around.
Or - if you really want to be cheap? I've got several 6 volt tractors - that will never start when it's 20 below zero with the 6 volt battery. But - for winter - I unhook the charging systems and stick in a 12 volt battery for the winter. But - I don't have lights on them and ignition is by magneto.

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