Stator Voltage

billmcc1280 · Aug 9, 2003

I am attempting to help a friend diagnose a charging problem on a 79 Johnson 150. Tach had quit working and also had quit charging. through searching the forums here we replaced rectifier. Now the tach works and I get only 12.5 volts WOT. Checked voltage at rectifier wires. Only get about 6.2 on both yellow wires WOT and 12.5 or so on the red wire. I am assuming 6.2 volts is low for yellow yellow/gray. also voltage drops to 11 at the battery when you turn on the spotlight at WOT. I want to know if you guys think the stator is the fault and what the proper voltages should be. BTW the voltage at idle was 11.3 or so and then 12.5 at WOT at the battery. Other problem

I also replaced the bendix on this engine because when it hits it would always kick out and spin. Making starting this engine a real pain. Replacement of the bendix did not help this problem. I heard that johnson engines as they get older would develop this problem. do you guys concur??? Thanks for the help,

billmcc1280 · Aug 9, 2003

Re: Stator Voltage

Bump! C'mon guys I know you know the answers.

Joe Reeves · Aug 9, 2003

Re: Stator Voltage

Bill.... A 1979 150 V/6 incorporates a 10 amp charging stator. The 10 amp output is achived at approximately 4500 rpm. I have no idea what the actual voltage output might be. Rule of thumb is that if the tach is working, the charging system is working. Another rule.... don't be using a imperfect battery but rather have a good high amp hour battery and make sure that all (ALL) connections are wrench or plier tight, not finger tight. Rectifiers fail due to loose or non existent connections, and reverse polarity. The starter bendix problem is caused by either a weak battery or starter which is causing the bendix to flick up into the flywheel rather than to slam into it. This (as you found out) wears the bendix teeth down. However, the major problem is that this condition also wears out the bottom portion of the teeth on the flywheel ring in (usually) a specific area. Check the flywheel teeth closely. Unfortunately, the cure is to replace the flywheel.

billmcc1280 · Aug 9, 2003

Re: Stator Voltage

I agree with you that it is charging somewhat. I read somewhere on this forum "can't find it now of course" that the 2 yellow wires should have around 16 to 18 volts going into the rectifier which should output 13.8 or so to the red wire coming out of it. I have 6.2. going into the rectifier. Maybe I am misunderstanding how this works. Maybe the 6.2 volts on each yellow is combined to make charging voltage output on the red wire. I am going to test the amperage now. Thanks again for the help,

wilde1j · Aug 9, 2003

Re: Stator Voltage

Bill, is that 6.2 vdc or vac? Let us know.

billmcc1280 · Aug 9, 2003

Re: Stator Voltage

It is 6.2 vdc at WOT. Around 5.5 at idle. That is only testing the yellow and the yellow grey stripe. not the brown brown black. Have not tested them yet but I probably need to since it will only go to 4500 rpm now instead of 5200. We lost 700 rpm and 15 mph. the 4500 is on the water. it will rev freely to 5200 in neutral. Thanks

nitsuj · Aug 9, 2003

Re: Stator Voltage

Shouldn't the wires going IN to the rectifier be putting out AC power? Every other motor I've ever tested had AC going into the rectifier, which was converted to DC needed to charge the battery. I thought that what rectifiers did, change the voltage from AC to DC and regulate it down to 12 volts, or, 13.8 actually.

billmcc1280 · Aug 9, 2003

Re: Stator Voltage

You know what. I did have multimeter setup for 20 volt dc. I am assuming I should set it up for ?? how many volts ac?? That is the primary question for this thread. How many volts ac or dc should I expect on the yellow wires at idle and at say 4500 rpm's? I am testing from the busbar to ground. Sorry to be such a pain but I have been browsing and searching these forums for four days. and applying what I have learned but I have read so much I am starting to get confused

Thanks again,

Droll · Aug 9, 2003

Re: Stator Voltage

The charging on a outboard is very similar to an car alternator, you got ... 1# Stator winding ,from here the current goes to the rectifier diodes and to the battery as DC. 2# Field winding ,this one is funny ,when you feed it whith a light current , you make a magnetic field, when the engine is turning ,the flywheel breakes the magnetic, field and you got AC current on the stator winding . If you adjust the voltage to the Field winding ,we can adjust the output on the stator winding , this jobb goes to the powerpack. On my engine ( se signature ) I got a separate voltage regulator . If you don´t get what you want on the output (low voltage ) , the voltage on the input ( field winding ) is to low . Check powerpack I hope some of this make any sense

long time since school .

wilde1j · Aug 9, 2003

Re: Stator Voltage

Bill, the stator output that feeds the rectifier is AC. You shouldn't rev the motor over 2000 RPM in neutral (unless you want to buy a new powerhead. Let us know the stator voltage to the rectifier as well as the dc voltage at the batt terminalswith the motor running.

billmcc1280 · Aug 9, 2003

Re: Stator Voltage

Thanks for the tip about reving. Will not happen again. I will retest tomorrow. One more time though. What is the average AC voltage I should be looking for on a working stator? Thanks, Bill

nitsuj · Aug 9, 2003

Re: Stator Voltage

Not to hijack the thread, but why wouldn't you want to rev it past 2000 in nuetral? You can do it with any other engine.

wilde1j · Aug 9, 2003

Re: Stator Voltage

nitsuj, not any other two cycle, unless you don't care if it runs away and blows the powerhead. Bill McConkey, you really need a shop manual ... I don't know the specific voltage for your motor, but it's almost always > 20 VAC and sometimes > 100 VAC.

nitsuj · Aug 9, 2003

Re: Stator Voltage

I still don't understand. The power head doesn't know if the boat is moving or not, to the pistons zinging up and down in the bore, 2000 rpm is 2000 rpm. What part of the power head will you hurt? Well, nevermind, that would take this thread way off topic, maybe I'll ask the question in it's own thread.

billmcc1280 · Aug 9, 2003

Re: Stator Voltage

I believe the over reving in neutral has something to do with not having a load on the engine. Engines are designed to pull or have a load on them not to "freewheel". I thank everyone again and will continue testing tomorrow. I have enough information now pursue this further. Thanks,

seahorse5 · Aug 10, 2003

Re: Stator Voltage

Bill, Joe Reeves is the only one here giving you accurate information. You do not have an automotive alternator or a field circuit on it. You have a stator and moving magnets inside the flywheel and a rectifier assembly, that is all. The stator resistance and any shorts to ground should be checked, probably around 1.1 ohms but check the service manual. The rectifier has four internal diodes that can be checked per the manual. The easiest test is to put an ammeter in series with the red wire from the rectifier and read the charging amperage at various rpms, per the manual. That's all there is to it.

billmcc1280 · Aug 10, 2003

Re: Stator Voltage

Thank you Seahorse. It is raining here now. But I will eventually get to it this afternoon. No one lives near Chattanooga - Decatur TN do you

? Thanks,

nitsuj · Aug 10, 2003

Re: Stator Voltage

Ok, seahorse, now you got me confused. Was I wrong about the juice coming out of the stator being AC? I know we're not dealing with an automotive system, but I though on this type of charging system, the stator made AC that needed to be converted to DC that could charge the battery. If the stator is making AC and he tried to measure it with his meter on DC, that would explain why he got a low reading now? My point being, maybe replacing the rectifier fixed Bill's problem and he just doesn't know it because he has his multi meter set up wrong.

billmcc1280 · Aug 11, 2003

Re: Stator Voltage

Ok retested. 7.7 volts "AC" on both yellow wires. 12.3 volts at battery idle. 12.7 volts at around 4500 "With boat moving"

. Have not tested amperage. Another question that may be related. this engine WOT now will only reach around 4500 RPM. Before we had the charging problem this engine would run up to 5200 RPM and 55-60 mph in a 16'9 Procraft. Also it would "yank a knot in your butt" on takeoff. Now starting off WOT it takes off slowly and takes a while to climb to 4500 rpm. No torque whatsoever. I am going to buy a service manual for this engine. All of these problems have to be related in some form or fashion I would think because it all happened at once.

Very confused. Thanks,

seahorse5 · Aug 11, 2003

Re: Stator Voltage

Nitsuj, There are no specs for AC voltage on OMC outboards. You check the output amperage to see if you need to troubleshoot the system. >>I thought that what rectifiers did, change the voltage from AC to DC and regulate it down to 12 volts, or, 13.8 actually.<< The rectifier only changes AC to pulsing DC voltage, it does not regulate any voltage.

Stator Voltage

Cadet

Cadet

Supreme Mariner

Cadet

Vice Admiral

Cadet

Chief Petty Officer

Cadet

Chief Petty Officer

Vice Admiral

Cadet

Chief Petty Officer

Vice Admiral

Chief Petty Officer

Cadet

Rear Admiral

Cadet

Chief Petty Officer

Cadet

Rear Admiral