93' Mariner 20hp not charging

[Leonard5977]

[FONT=&quot]I've got this Mariner outboard (OD265831) that will not charge. The old deep cycle marine battery was complete toast. I put a new battery in it, checking voltage first (12.64v) fired it up, and again checked the voltage at the battery (12.59v) while revving to maybe 3,000 rpms. I checked the rectifier, with all leads removed, using a DVM and confirmed one of the diodes was open.
I also had a lower unit leak and took it to a boat shop. I asked them to also repair the charging problem. They said the stator was bad and replaced it. They also put a used rectifier on it and told me it was fixed. As soon as I got it back, I hooked up the water hose and fired it up to find it still wasn't charging.
It seems like a pretty simple system, a revolving magnet that induces an a/c voltage in the stator that then goes to the rectifier which clips the negative swing of the a/c signal and provides a slightly pulsating d/c voltage.
I pulled the leads from the stator and fired it up again, checking the a/c output, expecting to get something like 16v a/c from the stator. I got about 8v a/c. I checked the resistance through the stator and got about what I would expect, .9 ohms. I pulled the leads from the rectifier and found one of the diodes open again. So I bought another new Sierra rectifier, installed it, and still no charging voltage. Upon checking the new rectifier, I found both legs open on it.
It looks like I have 2 problems. One, the stator isn't providing sufficient a/c output and, two, it keeps eating rectifiers. I did look up at the stator as it was running and there does appear to be what I think is a proper air gap between the flywheel and the stator.
Does anyone have any advice?
Thank you so much for reading.[/FONT]

 

[flyingscott]

That motor has separate charging coils not much under the fly wheel except the trigger and the charging coils. Is it wired correctly no need to replace the stator when all it is is charging coils.

 

[sam am I]

Hmmmm, seems odd to be not "[FONT=&quot]providing sufficient a/c output" [FONT=&quot]and[/FONT][/FONT] yet,[FONT=&quot] "keeps eating rectifiers"[/FONT]? This make no sense, esp. if you're hooking up the rectifier properly. Few ways to go about it, guess i'd go this route........

The AC voltage on the stator seems too low esp. since it was unloaded.........As a quik and dirty (and not continue to dump in part$), I'd firstly load the stator alone(no rectifier attached yet) down with like a junk drawer spare car's head light bulb (55/60 watts low/high beam type). Hook up the low beam element, fire up the engine, quickly pop/bump the rev's up 3K ish.......That'll give, according to the Merc spec, around 2 amps @ 12'ish VAC on the 4 amp black stator and give about 5 amps on the red 6 amp stator...

The low resistance of the bulb will be able to saturate those lower 4 or 6 amps stator windings, limiting their output voltage's to around their spec'd (around 15 volts) levels and will quickly reflect whats going on under a/the load condition on the AC side of things.

i.e, should light up sorta dim'ish if you have the black stator and should light up pretty bright if ya have the red stator. Black or red, it'll at least tell you if your stator can produce current at a load similar to a real load but, isolating it on the AC side of the rectifier.

From there, if AC things seem okay..........Well, the diodes in the bridge rectifier opening up is quite odd. Any smoke come out?

Typically the PN junction in diodes will open with over current and they'll short out when their PIV (over reversed voltage potential) is exceeded. Given that and If there truely open, we'll assume over current.

So to prove (or dis-prove) this ^^^, and save you from possibly buying even more rectifiers and also after you know the above bulb test above seems to be okay, put an inline fuse (10 amps should do) on the AC side, fire it up and run it. If the fuse blows, then something down stream is in fact drawing too much current.

Report back and we'll go from there

 

[sam am I]

No text

 

[sam am I]

Oh God, not this again..........

 

[Leonard5977]

Well, I've been working so much overtime that I haven't had an opportunity to check it and I finally decided to just take it back to the place that charged me to fix it to begin with. They just called today and said they didn't find a problem with it. I will ask them to show me before I leave with it this time.

 

[flyingscott]

They may be right you can't use deep cycle batteries on unregulated systems Like you have. You need to use starting batteries that are not maintenance free. These systems use the battery as the regulator so try a battery that can be filled.