Charging system fail?

[saltlife97]

I'll let y'all catch up with me:

I have an Ariens 46in lawn tractor with a 22hp B&S Intek V-Twin/Twin Cylinder engine. The model is: 407777-2217-G5. Bought the mower brand new in 2012, since then it's been having hard-start/no start issues. You'd turn the key and it would hesitate before turning over or sometimes you'd have to turn the key multiple times to get it to start. The battery is brand new replaced, the solenoid is getting 12.5V in and out to the starter. The starter checks out. Well every time you'd charge the battery after say 15 minutes, the engine fires up instantly. Therefore I know the issue must be with the charging system because the battery isn't being charged fully even though it claims it has 12.5v on the multimeter. As the service manual states, I have either a 10amp or 16amp charging system. The owner's manual says in the spec box that the charging system is: "16 @3600rpm" and I'm assuming 16 is amps. The output of the stator is only 16-17v AC but the service manual says it shouldn't be lower than 30v!!!! The only way to tell if it's a 10 or 16 AMP system (other than the owner's manual saying so), the flywheel magnets are small for a 10 amp and large for a 16amp. My flywheel has a ring of square magnets and IDK if that's the large or small. Either way even for a 10amp system the output is low(should be no lower than 20v). I replaced the stator with a brand new one from B&S and it still only gives me 18v. What is going on?

 

[cpurvis]

Check the charging system where it matters the most--at the battery.

Check the voltage of your battery with the engine off. Start the engine, rev it up. Check the voltage across the battery terminals again.

If the voltage is the same (or lower) your battery is not being charged. Typical value for a charged battery is ~12.7 volts. Typical reading for a working charging system is 13 to 14 volts. ( edit: A 12.5 volt reading with the engine running is not indicative of a battery being recharged.)

If it's charging, something may be draining your battery when the mower isn't being used. Most multimeters have an amp meter function that can check this by removing a cable from the battery (with the engine off) and putting the multimeter between the battery post and the cable. Amp draw should be zero or very close to it.

Another possibility is a bad battery that simply goes dead by itself.

 

[bertsmobile1]

And if it is not charging, check the earth strap on the rectifrier. It is the usual suspect.

 

[saltlife97]

Typical reading for a working charging system is 13 to 14 volts.

So you're saying the 18v given from the stator is good enough at 3600 rpm even if it shouldn't be lower than 30? I'll check the charge on the battery with the engine running too.

And if it is not charging, check the earth strap on the rectifrier. It is the usual suspect.

I shall look at that as well.

 

[cpurvis]

So you're saying the 18v given from the stator is good enough at 3600 rpm even if it shouldn't be lower than 30? I'll check the charge on the battery with the engine running too.



I shall look at that as well.

18 volts at the battery is actually too much. Batteries boil off their electrolyte if the recharge voltage is too high. 14 volts at the battery is more than enough to recharge 12 volt batteries.

 

[saltlife97]

18 volts at the battery is actually too much. Batteries boil off their electrolyte if the recharge voltage is too high. 14 volts at the battery is more than enough to recharge 12 volt batteries.

The 18v AC is coming directly from the stator I mean. Before it enters into the rectifier to be turned into DC. The output voltage from the alternator is below the specifications mentioned in the service manual (30 volts at 3600 rpm).

 

[cpurvis]

That is all well and good, but what is the voltage at the battery with the engine running? That is what ultimately matters.

 

[bertsmobile1]

18 volts at the battery is actually too much. Batteries boil off their electrolyte if the recharge voltage is too high. 14 volts at the battery is more than enough to recharge 12 volt batteries.

Only on a open toped flodded cell battery.
The maximum recharge voltage depends upon the state of charge of the battery and the chemistry of the grids and grid paste .
The current available and the current ( Amps ) rate of charge depends principally upon the surface area of the plates.

To charge properly you need both volts & amps.
Week magnets will always put out full volts as that is a function of the actual windings and the speed that the magnets energise the coils.
But it is very common to find an old Pommie motorcycle alternator that still puts out 14.5V but only at a paltry 2 or less Amps because the magnets have become weak. That is why we went to field energised alternators for general use & not permanent magnet alternators.

And as an aside, pressure valve regulated batteries are no where as sensative to over voltage as open topped batteries another good reason to spend the extra $ 10 on a sealed battery for mowers which do not have a particularly good charging regulating system.

 

[saltlife97]

I'll still check the voltage across the battery at wide open throttle, but could a defective regulator rectifier be the issue too? Like with the mower off, could the rectifier allow voltage to leak back through the rectifier and into ground?

 

[cpurvis]

As I said, 18 volts going into a 12 volt battery is too much. Open cell, closed cell, it makes no difference.

Once you figure out what is happening, then you can start diagnosing why.