1996 Merc 250 EFI Charging System Question

[srq_fl]

When at idle speed (700 rpm), alternator does not seem to be charging. I get 12 volts. Less that 12 volts when accesories are tured on.<br /><br />At above 1500 rpm, I get 14 volts. Is this normal for this engine? If not, what could be the problem?<br /><br />Thanks - Vic

 

[WillyBWright]

Re: 1996 Merc 250 EFI Charging System Question

That would also be true of your car. There's a lot of demand with the electrical system on that motor. Add accessories and the alternator is doing double duty. It's not going to keep up at idle. No alternator is. That's why the motor flares a bit at start-up, to get the alternator alternating. But if you leave it at idle for extended periods ... well, it's just Physics. Below 800rpms the alternator current will eventually drop out.<br /><br />I take it you want to troll with that motor. Bad choice. Even though it runs better than most conventional 2-strokes at idle doesn't mean it's supposed to be operated that way for extended periods. It doesn't matter what kind of induction you have, a 2-stroke is still a 2-stroke. They LIKE rpms.

 

[marinegrh]

Re: 1996 Merc 250 EFI Charging System Question

12.56 is a norml charge on your battery, about 14.1 to 14.3 when your engine is running, just like your car, that alt. maintains a positive charge on the battery, if you are suspecting problems, take a voltmeter and put it on ac volts and go across your battery, any indication of ac voltage going to a dc component is a bad thing. you may want to look futher into the charging system possibly the reg/rec has a shorting diode in it??????????keep us posted

 

[rodbolt]

Re: 1996 Merc 250 EFI Charging System Question

hello<br /> test your charging system. if its the 40 amp system it will have 2 regulators and the stator is double wound. its basically two altenators with a common rotor. if one side fails those are the symptoms.

 

[rodbolt]

Re: 1996 Merc 250 EFI Charging System Question

hello again<br /> I actually cant remember and not going to look it up but I think the 250 used a belt driven alt similar to automotive use. in any case an EFI motor should read 13.5 v or higher at idle.<br /> the older not regulated 9 amp system did not have much output at idle. modern systems with EFI have a large capacity system. most with 35-60 amp systems with 3 phase altenators.<br /> good luck and post back what system you have

 

[srq_fl]

Re: 1996 Merc 250 EFI Charging System Question

rodbolt:<br />The 250 EFI does have a belt driven alternator. According to specs, it should deliver 30 amps @750 rpm and 60 amps @ 2000 rmp. I do not have the means to check the amps output. (you need to put the amp meter inline!)<br /><br />Do you know if the voltage regulator/rectifier on this model are build into the alternator or external? Are they servicable or need to replace the alternator?

 

[rodbolt]

Re: 1996 Merc 250 EFI Charging System Question

hello<br /> the regulator is part of the altenator. but check your service manual. Mine is 30 miles from me today. I have been sitting here with a broken hand for the past week. boredom is killing me. take the altenator to a reputable starter/altenator shop. most dealers dont have the tools to properly repair and test them.

 

[srq_fl]

Re: 1996 Merc 250 EFI Charging System Question

FYI:<br /><br />Got the charging system fixed. Took the alternater to a shop. They replaced the Stator and the regulator/rectifier ($110 job).<br /><br />Now, the voltage shows ~14 volts at idle and at WOT.<br /><br />Thanks for all replies.