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2002 MFS25A not charging?

S

snookwhaler

Regular Contributor
Like the title says. It's not charging.

When I first got the engine, I could put a meter on the battery and the voltage would slowly increase over time. Now I put a meter on there and nothing happens and the voltage is low to begin with. Today I had to pull start it to get it going.

The weird thing is that every minute or so, the RPM's drop just a little, like it is charging, but the voltage is just not making it to the battery?

Any ideas on where to start troubleshooting?
 
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Voltage is only an indication of state of charge of the battery -- not whether you are charging or discharging. Over time (as you noted), a change in voltage should indicate an increase or decrease in state of charge.

There is a 20-amp fuse that should be checked. If it is blown, you won't charge.

If that looks good, and the battery will charge with a conventional charger, then you need to whip out the Factory service manual, and run the ohm meter checks for the charging system. The MFS25/30 uses a rectifier/regulator that comprises much of the charging system.
 
Thanks for the quick reply guys! Battery is on the charger right now and it looks good. I will have it load tested later.

I checked the 20 amp fuse and it does not appear to be blown (didn't know it had one). I used a meter to verity this.

The rectifier has always gotten very hot when the engine is running as is the case now, so no change there. Can I disconnect the battery and hook up the meter to the end of the battery cables to verify that it's charging? Or do I need to do that a different way before I start ripping things apart?
 
If rectifier keeps getting very hot your engine might be running hotter than normal. Check your telltale stream, does it burn?
 
Those recrifier/regulators do run pretty warm. You can use an ohm meter (with battery of 3v or less) to test the rectifier. The procedure is in the Factory service manual.
 
Engine temp. is 140F at idle on the hose and checked with an infrared thermometer at the thermostat housing. Pee stream is warm and normal.

Rectifier temp. is 250F at idle as well. It has always run hot. So, it must be working? I just need to figure out where to look and what to check.

Battery is fine and it is still not getting charged. I'm having to put it on the house charger now to keep it charged.
 
If the fuse is OK (you can change it even if it looks OK -- there may be a spare in the fuse holder), then your options to troubleshoot are the alternator (big and expensive on that model -- and it runs the CD as well), or the more-common failure, the regulator/rectifier.
 
OK... So, I'm pretty sure I found the correct wiring diagram for my engine. It's a little confusing because I converted it. It used to be tiller with electric start and not trim. Now, it is remote with electric start and no trim.

The wiring looks ridiculously simple though. So, aside from all the grounds, there are 3 yellow wires coming from the magneto to the rectifier and then a red wire going from the rectifier to the starter solenoid. This red wire should have lots of DC voltage with the engine running correct?

I have been reading on how to test "a rectifier" with it removed from the engine using a meter across the 3 yellow leads. I plan to do that here in a little while once I get the boat pulled around front.
 
OK... Sorry for the late reply. Between the hurricane and all the wind for weeks on end this thing has been parked anyway. So, today I finally pulled the rectifier to test it and found this! It's obviously toast. What would have caused this? Are there other things I should be checking before installing a new one?

I found a video on youtube on how to check the diodes on this type of regulator/rectifier. It looks exactly like the ones used on lots of Jap motorcycles. It passed the diode test. But, obviously something wrong because it is melted.

The bakealite material is cracked and some molten metal oozed out of the crack.rect.jpg
 
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Your motor has a 3-phase alternator, so the rectifier/regulator is more complex than just a bridge rectifier. Yes, it appears your rectifier has failed, based on the solder leaking out of the potting.

Use your Factory service manual as a guide, and test the alternator (which is probably fine), and then feel free to install a new regulator. The current part number for the regulator is a revision (new version) from what was originally on the 25/30A, probably a more durable version.
 
Thanks for the input again! I found the revision part on ebay for $45 used. $52 delivered. I bolted the new one on there and it is charging properly again. The new one does not get hot like the old one.

Also, when I cranked the engine up with the new one connected, a large puff of smoke came out the exhaust and the engine was immediately running smoother with no more wandering idle! So, I wonder if that old rectifier was causing other gremlins besides just not charging?

I plan to take it out on the water in a couple hours to see how it runs after all of this. Last warm day of the season.
 
It's fixed!

I ran it for over 3 hours today without a hicup around Ft. Pierce Inlet! Works like a champ. No issues at all.

The engine definitely runs and idles better. Hopefully nothing else did not get screwed up having that bad part on there for so long.
 
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