Small Engines (Lawn Mowers, etc.): rectifier, bridge rectifier, voltage chargers

Question
Hello, my 25hp merc outboard is burning up rectifiers. When I replace it motor works fine.
Then I will go ahead and put it back together,
throw the battery on charge. Then when I go to start it again another fried rectifier. I feel that maybe could be the onboard 3bank charger that is shorting these out, allthough this unit is new. Could another electical part be causing this to short, stator, ect... All parts are in like new condition no fraying, corrosion ect...
Any help in running down this problem would be much appreciated. Thanks.

Answer
Hi Bob
I really haven't much outboard motor experience, but one thing I do know, you have to make really really sure that you're using the right kind of rectifier (this is a mercury standard part yes?)  reson I ask is a buddy of mine ran into this, and he was substituting a different rectifier, turns out the reverse voltage rating of the units he was using was lower than the original, and on a bridge rectifier, two are exposed the twice the input DC voltage (its the ways they're used) so the ratings for this have to account for the additional voltage chargers put out (about 13.8-15 volts).  You may want to consider a battery isolator (a big knife switch).
lemme know - ok?