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1998 8HP 2-stroke will not charge the battery

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whitegreg56

Regular Contributor
It's a pull-start with a simple rectifier (4 diodes). All the diodes have been checked...forward and reverse bias. The alternator winding checks out OK, with no shorts to ground. When the engine is started, the battery voltage increases by maybe .01 volts even if the engine is "raced". I used Ancor marine cable between the engine and the battery. I used Ancor adhesive-lined heat-shrink terminals. Is this likely a high-resistance somewhere in the wiring? It's in a sailboat with perhaps 20' of cable between the rectifier and the battery. Oh yeah, I am an Electrical Engineer!
 
Measure the DVA voltage across the stator’s charge wires (typically Yellow wires) while connected
to the rectifier. At idle, DVA should be between 17-25V DVA. If not, disconnect the Yellow wires from the
regulator/rectifier and retest for 17-50V DVA at idle. If not, the stator is possibly faulty.
 
If its a black stator its only a 4 amp output at 6000rpm, so you wont see much increase if just racedasit has to overcome the internal battery and wiring resistance.
 
Regardless of which stator- you should should show an increase in VDC as the rpms increase. Typically, at 2500 rpm, you shoulld have a reading of 13.1 VDC (measured at the battery terminals) or better. What kind of rectifier is attached- Mercury (or Mallory or CDI aftermarket), or a DYI from Radio Shaft?
 
The cable between the engine and the battery is 16 AWG. It has a resistance of .004 ohms/foot.
With 40 feet of cable, that works out to 0.16 ohms. The stator resistance is supposed to be ~0.65 ohms.
The rectifier is a Sierra (aftermarket). I took out the original because I thought it might have been the
problem. In fact, the original tests OK. There should be an increase in voltage at the battery when the
engine is "raced". This should be the case even if the alternator is only putting out a couple of amperes.
I have a Fluke Scopemeter...I'll see what I can find out, tomorrow.
 
see if you have a voltage drop between the output of the regulator and the positive post of the battery at 2500 rpm... as you know you will not measure a drop if you are not pulling current so the motor has to be running...preferably above idle rpm..
 
Well, I checked all of the wiring between the engine and the battery...everything looks OK.
Seems that the voltage coming from the alternator is low...~5 volts at fast idle (battery disconnected).
It looks like, even when the engine is "raced", the voltage is insufficient (<12 volts) to cause
current to flow into the battery. I suspect that some of the windings in the stator are shorted.
Or, the air-gap between the magnets and the stator is "off" (not likely). It won't be easy to
get the recoil-starter and flywheel off with the boat/engine in the water. May just have to recharge
the battery using commercial power.
 
I'm not sure what a DVA reading is.....suspect it's the peak voltage.
I'm wondering where the 17V, 25V, 50V came from. My Mercury Factory Service Manual
doesn't mention any such test....just resistance and no shorts to ground.
My fancy meter has the capability to read peak-voltage (or, peak-to-peak voltage).
The two wires coming from the stator are yellow and gray.
There is no regulator....just the (full-wave bridge) rectifier.
It is definitely a 2-magnet flywheel.
 
the 17-25v (with the rectifier as a load) come from the stator and should be read on the two wires feeding the rectifier..the 50v is with rectifier disconnected (no load)....
 
  1. Some meters are capable of reading DVA or peak voltage pulses. Many ignition system components produce short AC voltage pulses. A peak-reading analog meter or DVA adapter plugged into a digital metercaptures and holds the peak value of an AC sine wave long enough for the human eye to see it displayed on the meter.
 
Its a 4 amp system, that rated at WOT. At idle or just racing it does not give the system enough time to overcome battery resistance. At idle you will be lucky to see a 1/4 to 3/4 amp output,at WOT its more like a trickle charger....
 
Well, as I said in post #9, I suspected that some of the stator coils were shorted out.
So, I bought a new one to the tune of $160. The new one came in at 0.1 ohm more
than the old one (on the same meter). I took the flywheel off (that's another story) and
bolted the new stator in place. I put a small capacitor between the rectifier (+) and ground.
It comes up to 6 V just cranking it over with the recoil starter. There should be no problem
getting to 12 V with racing the engine. We'll know for sure when I fire it up in the Spring.
I consider this problem SOLVED.

So, don't think your stator is good just because it's not open and not shorted to ground.
The enameled insulation on the wire can break down with vibration and heat.
It was real tempting to rewind the stator but it's pretty well gooped up with epoxy,
making it difficult to sort things out.
 
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