Voltage while engine is running

[Uthud]

Battery was dead when I went to start engine about 2 hours after shutting down following 2 hours of mowing.
Suspect battery is junk (it is at least 3 years old).
BUT…when I charged it overnight, it came up to 12.5V and started engine, and here’s the thing, when I measured V at battery while running, still only 12.47V. If my charging system is healthy, shouldn’t it measure around 13.x V??

 

[Uthud]

Update: I removed battery. It is 42 months old. Out of the machine it measures 13.4 V. Why?

 

[StarTech]

Need to know which engine you have so we which charging system you have. Some some system are very slow about recharging after the initial restart especially the 3 amp systems. Also posting the mower model from serial number tag will also help as you might an electric PTO clutch going bad.

Now if the charging wasn't working then a current draw will cause the battery to read lower while in the circuit due to the battery's internal resistance.

 

[Uthud]

Need to know which engine you have so we which charging system you have. Some some system are very slow about recharging after the initial restart especially the 3 amp systems. Also posting the mower model from serial number tag will also help as you might an electric PTO clutch going bad.

Now if the charging wasn't working then a current draw will cause the battery to read lower while in the circuit due to the battery's internal resistance.

Thanks. It’s aKohler CH 20S.
So, after being thoroughly confused, I got my other digital VOM.
Battery out of mower, reading 12.5, dropping to 12.27 in 25-30 minutes.
I have an old Sun load tester and it’s saying battery is weak: replace.
On my way to fetch new battery.
I also cleaned terminal wire ends and sprayed the regulator connector (it was oily).
Thanks again for your advice.

 

[bertsmobile1]

Take some voltage readings at the regulator, engine off & mower turned on
The regulator has 2 wire the same colour and one wire a different colour ( red or purple )
Battery - to red/ purple = battery voltage
battery + to regulator metal body = battery voltage
Because it is mounted into plastic Kohler use a brass ground strap to connect the regulator case to ground which can be hard to see .
If it breaks then there will be no voltage reading battery + to regulator body .
The 2 same coloured wires are the alternator stator and the regulator connects these via diodes
So when unplugged one of those terminals will have continuity to the + terminal
The other will have continuity to the regulator body (-)
If you swap your meter probes over then they should be open circuit where previously there was continuity
If both was have continuity or neither way has continuity then the rectifier is kaput .

 

[Uthud]

Take some voltage readings at the regulator, engine off & mower turned on
The regulator has 2 wire the same colour and one wire a different colour ( red or purple )
Battery - to red/ purple = battery voltage
battery + to regulator metal body = battery voltage
Because it is mounted into plastic Kohler use a brass ground strap to connect the regulator case to ground which can be hard to see .
If it breaks then there will be no voltage reading battery + to regulator body .
The 2 same coloured wires are the alternator stator and the regulator connects these via diodes
So when unplugged one of those terminals will have continuity to the + terminal
The other will have continuity to the regulator body (-)
If you swap your meter probes over then they should be open circuit where previously there was continuity
If both was have continuity or neither way has continuity then the rectifier is kaput .

Thanks Bert. I plan to spend some time on it tomorrow. I will update here as I discover more.
The mower is a CubCadet 2206, circa 1999-2000. The engine is Kohler CH20S.
I am suspicious that there may be a short somewhere. One day last year while mowing, the engine wound-down and died. It would turn over, but wouldn’t start. I found the 25(?)Amp fuse had blown. I replaced it, but never found out why it blew.
You’ve given me a great direction to start looking. Thanks!

 

[Uthud]

Thanks Bert. I plan to spend some time on it tomorrow. I will update here as I discover more.
The mower is a CubCadet 2206, circa 1999-2000. The engine is Kohler CH20S.
I am suspicious that there may be a short somewhere. One day last year while mowing, the engine wound-down and died. It would turn over, but wouldn’t start. I found the 25(?)Amp fuse had blown. I replaced it, but never found out why it blew.
You’ve given me a great direction to start looking. Thanks!

The part about terminals while connector at regulator is unplugged, I don’t follow.

When everything is connected as normal, I measure battery voltage (12.47 VDC) at the purple wire on the regulator connector with the key on . I measure around 30VAC between the two white wires with engine running at WOT.
When engine is running at WOT, I still get only 12.47 VDC on the purple wire; should I be getting around 13V (charging?).

 

[Uthud]

The part about terminals while connector at regulator is unplugged, I don’t follow.

When everything is connected as normal, I measure battery voltage (12.47 VDC) at the purple wire on the regulator connector with the key on . I measure around 30VAC between the two white wires with engine running at WOT.
When engine is running at WOT, I still get only 12.47 VDC on the purple wire; should I be getting around 13V (charging?).

UPDATE:
I ordered a replacement regulator/rectifier. Amazon, $13.99. Hope it arrives soon.
I verified that the existing regulator frame is grounded.
I left everything connected a usual, then added a jumper wire from battery + to the purple wire at the regulator. Still only 12.47 V at battery and purple wire connector. I didn’t find any shorts.

 

[Uthud]

Oh, I did finally understand what Bertsmobile1 meant about the diodes.
The + terminal of the (unplugged) regulator has continuity with only one of the stator terminals. None of the three has continuity with the regulator body. The regulator body does have continuity to battery - , though.

 

[Freddie21]

You should consider replacing the battery. Just because it charges to 12v, doesn't mean it will have the amperage to run the starter. An internal short in the battery cells reduces the output capability, just as your load test showed. At WOT, I would expect close to 14v.