250 Pro XS Alternator Voltage

[MidniteTA]

250 Pro XS
12500033A
3B433854

Having what appears to be a low output from the alternator. When the motor was new, I would see ~13.8v at idle and 14.2-14.5v while cruising on both the dash volt gauge, Vsupply on graphs, and vessel view mobile. Now I'm only seeing ~12.8-13.0v regardless of operating condition.

Looking to see what is normal for these motors. Dealer is saying that anything over 12.6v is charging and nothing they can do warranty wise until it doesn't maintain 12.6v.

Thanks,
Dan

[mactlman]

takes 13V or more to charge a battery - should be 13.4 or more usually---12.6 is battery voltage and it is not charging?

[MidniteTA]

Correct, as a powertrain engineer dealing with engines all day, I have always known 13.3v minimum needed to effectively charge a battery. Just needing a sanity check as to why a dealership would say there is no issues when the alternator is putting out sub 13v. Screenshot on vessel view from Sunday shows 12.8v at 4280rpm while running on plane.

Motor has 84 hours on it now. When new it was just like every other 4 stroke 250 pro xs I've seen where you have 13.8ish at idle and 14+ while running. Issue arose in tournament late last season, got back to weigh in and smelled the lovely electric smell, and have had low voltage since then.

[mactlman]

if you look back through the history, there’s lots of talk on here about alternator failures and ground strap, failures, and fusible Link failures on these 250 mercs.

[PatriotAW4]

I thought mine was having issues because the voltage is kind of low like that sometimes but it's still charging. Did an amp draw and it was putting around 30-35 amps to the battery at 12.9-13 volts so it is working, I haven't had any issues with it.

[EuropeanAM]

250 Pro XS
12500033A
3B433854

Having what appears to be a low output from the alternator. When the motor was new, I would see ~13.8v at idle and 14.2-14.5v while cruising on both the dash volt gauge, Vsupply on graphs, and vessel view mobile. Now I'm only seeing ~12.8-13.0v regardless of operating condition.

Looking to see what is normal for these motors. Dealer is saying that anything over 12.6v is charging and nothing they can do warranty wise until it doesn't maintain 12.6v.

Thanks,
Dan

Still running the same battery, or have you since switched to LITHIUM? Due to the charging and voltage profiles of Lithiums, alternator output IS DIFFERENT when you change.

Need to test voltage at the large red output terminal, engine idling.

Also check the GROUND STRAP for the alternator. Moving it to the next bolt (the one for the BACK half of the case) helps to achieve a more consistent ground, and can improve charging.

[MidniteTA]

Still running the same battery, or have you since switched to LITHIUM? Due to the charging and voltage profiles of Lithiums, alternator output IS DIFFERENT when you change.

Need to test voltage at the large red output terminal, engine idling.

Also check the GROUND STRAP for the alternator. Moving it to the next bolt (the one for the BACK half of the case) helps to achieve a more consistent ground, and can improve charging.

Same battery, X2 Power 31AGM. Purchased July of 2024. Voltage on DMM at alternator terminal agrees with other voltage measurements. The dealership stating alternator is good moved the ground strap per the latest service bulletin. This had no change.

[EuropeanAM]

What is the voltage on the other wires connected to the alternator connector (key-on or engine idling)?

When using a DVM for measurements, there will almost ALWAYS be a difference in voltage between loads and supplies that are located on opposite ends of 24' of cable. The "devil" of the matter is often found in that difference (even if it's very small).

[lpugh]

Correct, as a powertrain engineer dealing with engines all day, I have always known 13.3v minimum needed to effectively charge a battery. Just needing a sanity check as to why a dealership would say there is no issues when the alternator is putting out sub 13v. Screenshot on vessel view from Sunday shows 12.8v at 4280rpm while running on plane.

Motor has 84 hours on it now. When new it was just like every other 4 stroke 250 pro xs I've seen where you have 13.8ish at idle and 14+ while running. Issue arose in tournament late last season, got back to weigh in and smelled the lovely electric smell, and have had low voltage since then.

bad or discharged battery voltage will not come up to 14.4- 14.6, test the battery

[EuropeanAM]

AND... if the battery is heavily discharged, it may take some time to bring the voltage back up (even when you're running at RPM's on plane).