Mercury 650 rectifier

[andy77]

hey guys.. I have a 74 650 outboard mercury that is not charging. It left me stranded at the lake at 3 in the morning. I guess that is when i decided that i should have paid for the full size paddle. I got a new marine battery, hooked it up and it had 12.6 volts. started engine and the voltage stayed the same 12.6 at both idle and higher rpms. I read a few forums on here and decided to look at the rectifier. Rectifier looked really good. no corrosion or anything. Removed it and too it to an electrictian i work with to shoot for omhs. He said it seemed ok. shot 400 ohms from stator post to power post both sides. I put the rectifier back on and started boat to check voltage at rectifer to make shure i didnt have a bad wire from rectifer on. It shot 12.6 volts at + post dc. Shot between both stator post and it read 14.2 ac. It seems to me the rectifer is messed up somewhere. I just want to make sure that it what it is. nothings worse than buying a part and it didnt fix anything. let me know what you think. thanks guys!

 

[Laddies]

Re: Mercury 650 rectifier

Yup, you need a rectifier

 

[j_martin]

Re: Mercury 650 rectifier

The ohms is insignificant, depends on the individual meter dealing with the nonlinear characteristics of a diode. Trick is, it should read one way, and not the other. And also to ground, but reversing the leads on the meter.

Electrician's half educated.

John

 

[andy77]

Re: Mercury 650 rectifier

thats correct on the ohms. it would only read 1 way and not the other way. it was a digital fluke meter and it read 400 ohms from stator post to power on both post. it read only 200 ohms to ground. i dont know anything about ohms or much about a multimeter im just a diesel mech on locomotives. the final test of starting the motor and reading voltage tells me the rectifier cant be right.

 

[Yachtzee]

Re: Mercury 650 rectifier

Which kind of rectifier. Plate, Thunderbolt ignition or diode?

Plate and thunderbolt seem to be full wave bride rectifiers, acutaly 4 diodes.
for the plate type The ratios should be 10 to 1 forward to reverse accross each pair of connections. The thunderboat style should read continutiy one way and open the other.
I have seen the rectifiers for sale for 50 bucks on the web,

I bought a 5 dollars bridge rectifier 25 amp 50 PIV from radio shack that has been working well. Make sure you have continuity from the + terminal on the rectifier to the battery. Not being hooked to a battery while the engine is running tends to fry the rectifier.
On another note I get about 45 volts AC on my 650 across the stator wires motor running at idle

 

[chuckb]

Re: Mercury 650 rectifier

Yachtzee is correct. A $5 (even that's expensive) simple bridge rectifier will be a suitable replacement for the $50+ Merc part. You need to find the 2 wires from the flywheel alternator and hook them up to the two rectifier inputs marked with a sideways "S". The other two got to the positive and negative (normally engine ground).