Batteries! How weird they are...

[Fuddy1952]

Mind blowing...
I have my granddad's Economy Power King tractor he bought brand new and a Cub Cadet garden tractor, both have same Kohler engine and about same vintage (1976,1979).
Economy came with a car battery, by that I mean a top post (12"x8"x7"). For years it's been hard starting, so I installed a new 700CCA battery. Still hard starting (I rebuilt carb, all new ignition, no help). Basically choke...crank, fiddling with throttle finally it will start. Many times out somewhere I'd park so I could get it rolling & pop start it.
Although battery was new, I had it professionally checked, it was good and actually measured 717CCA.
All ground connections cleaned, cables fine, solenoid & starter fine, the charging stator ok, I even replaced the diode/regulator module. Motor wide open I was lucky getting 13 volts at battery.

Cub Cadet has a new mower battery. It's a 300CCA (8"×6"×5"). It starts fantastically, choke and fires right up then choke off.

OK...today my GLOVES came off .

Both tractors haven't been run in a few weeks, so the surface charge was a little low. Here are the measurements at the battery using Fluke meter:

Economy, 700CCA battery:
12.45v static
11.30v cranking
12.70 full throttle (slowly climbing to
about 13v max. after 10 minutes)
Cub, 300 CCA battery:
12.14v static
9.91v cranking
14.20v full throttle
Then I put the little battery in the Power King:
Economy, using the 300CCA battery:
12.17v static
11.12v cranking
14.13v full throttle
With the small battery it starts, runs better. Of course lights are brighter.
I understand now it's more of a match to the charging system. Apparently the more than double cranking amp battery just wasn't able to spin motor over like you would think which doesn't make sense.
Everything has to match. The larger 70's top post car batteries must have been available with about 300CCA. How weird is that?

 

[CausticUrbanCoast]

What brands and model batteries? Not everything various manufacturer say is true... especially low end brands, if they briefly hit the benchmark they are "in spec".

 

[K5lwq]

That was a very good experiment that proves bigger is not always better. May have to share that with my wife.

 

[Doughknob]

Yeah...... i think something else is going on there. "Match" as you describe does not work like that with batteries for starting. Just as you said, not only does it not make sense, it almost certainly is not the issue.

Charging is another story, and indeed should be "matched." Right off the bat, i wonder if the terminals on both your batteries are the exact same size and shape/profile.

 

[WranglerX]

Battery match is not a science, it will either spin up starter respectably and provide enough voltage for ignition (if is has points and coil ignition). BUT most small engine are magneto...

I use a not to expensive 230 CCA battery to spin up my JD with a 22.5hp 2 cylinder B&S..... Battery issue is not the problem its the carburetor, and usually a shot of carb cleaner eases "dry" starts.... Carb cleaner is less volatile than "starting" fluid and less like to hurt engine... And magneto on B&S only charges battery a something close to 13.2 volts....

Your ignition and hard starting if not fuel may be the magneto output for firing plugs...

 

[Fuddy1952]

Yeah...... i think something else is going on there. "Match" as you describe does not work like that with batteries for starting. Just as you said, not only does it not make sense, it almost certainly is not the issue.

Charging is another story, and indeed should be "matched." Right off the bat, i wonder if the terminals on both your batteries are the exact same size and shape/profile.

Terminals are different. Economy as I said was top post, Cub is not, but installed right and clean using 1/4" bolts...so that didn't matter.

 

[Fuddy1952]

Changing battery solved the problem though! Changing back to large battery the problem reappeared.
What's going on is the stator+diode/regulator system is not able to keep the 700CCA battery charged and running like that voltage is low.
Using 300CCA battery the stator+diode/reg module is matched. It now runs at just over 14 volts, keeping battery charged and since the voltage is a little more cranks better.
I've spent many hours of experimentation and if I were to use large battery in Cub it would act like the Economy over time. Battery is so large I'd have to fabricate some way mounting it. It would crank Cub fine at first, but the Cubs same charging system wouldn't be able to restore that battery. Over time same thing, lower voltage gradually, lower running voltage (dim lights), until hard starting. Higher voltage means faster cranking, hotter spark, brighter lights, etc.
I'm telling all this hoping it may help someone. Over the years I've discovered some things you think would be an improvement like higher CCA battery may have opposite effect.

 

[Oaktree]

I'm telling all this hoping it may help someone. Over the years I've discovered some things you think would be an improvement like higher CCA battery may have opposite effect.

Thanks for the info. I never would've thought a bigger battery would give poorer performance, but the charging theory makes sense.

 

[rScotty]

Changing battery solved the problem though! Changing back to large battery the problem reappeared.
What's going on is the stator+diode/regulator system is not able to keep the 700CCA battery charged and running like that voltage is low.
Using 300CCA battery the stator+diode/reg module is matched. It now runs at just over 14 volts, keeping battery charged and since the voltage is a little more cranks better.
I've spent many hours of experimentation and if I were to use large battery in Cub it would act like the Economy over time. Battery is so large I'd have to fabricate some way mounting it. It would crank Cub fine at first, but the Cubs same charging system wouldn't be able to restore that battery. Over time same thing, lower voltage gradually, lower running voltage (dim lights), until hard starting. Higher voltage means faster cranking, hotter spark, brighter lights, etc.
I'm telling all this hoping it may help someone. Over the years I've discovered some things you think would be an improvement like higher CCA battery may have opposite effect.

"Matching" is not the answer to charging a battery.
I'm sorry. It's an innovative idea, but probably incorrect.

There is a minimum size (ampacity) battery required to turn the starter and start the engine. Any larger capacity battery will simply do the same thing for a longer time. "Matching" the charging system to the battery capacity is not real.

Everything you are seeing and measuring could also be due to a large battery that is able to develop cell voltage, but is not able to store much of a charge (amperage) in those cells. A possible cause for that is something in one or more cells is not allowing the plates to use their full area to store charge. The plates may not be properly isolated, there could be uneven sulphation due to how it was stored, or it may simply be one or more cells have a low amount or acidity of electrolyte.

Science starts with the simplest theory that explains the facts. A poorly built battery makes more physical sense than the electrical matching idea.

rScotty

 

[LittleBill21]

sounds like the larger is sulfated. you would need a load test, your testing shows the smaller battery trying harder, but may be able to release more amperage.