Rectifier replacement

[marcus_human]

Can I replace my rectifier on my Mariner 90 6-cylinder model 1981 with a commercial bridge rectifier which is a much cheaper solution and if so will a 10Amp bridge rectifier do. There is no regulator involved and the output go straight to the battery.

 

[SlowlySinking]

Re: Rectifier replacement

conjor, the big problems with boats appear to be the possibility of explosions from non-marine stuff and corrosion, since bridge rectifiers are sealed units this should do the trick, maybe someone else has a different thought,you might consider a higher amperage unit if it fits, good luck.

 

[John Reynolds]

Re: Rectifier replacement

I wrote a little about the Radio Shack full wave bridge rectifier (p/n 276-1185 handles 25 amps 50piv). for $2.99 about 2 or 3 weeks or so ago on this forum. Any time you have AC (alternating current, like out of an alternator) and there are two wires going to the rectifier assembly, the rectifier is a full-wave bridge, which contains 4 diodes. If the alternator output consists of three wires, you probably have a full-wave rectifier (not a bridge) containing two diodes. You can see a schematic of a full-wave rectifier here: http://www.infodotinc.com/neets/book7/27c.htm <br /><br />The "triangle" part is an arrow, pointing to the cross-bar or line at the tip of one of the triangle's points. It's pointing to the bar because if current flows that direction (current flows from negative to positive) it is blocked. so for current to flow, negative must be at the wire connected to the bar, not the other end of the triangle. You can trace it out so that you can see that at the AC inputs, it doesn't matter whether or not an AC input at any point in time is positive or negative, it works out that the negative DC output is always negative, and the positive is always positive. THAT BEING SAID, A full-wave bridge rectifier is a full-wave bridge rectifier, no matter what the package it's in, only difference is the amount of power it can handle, and the peak-inverse-voltage (PIV) which is how high the voltage can be in the opposite direction from normal flow, and the current still be blocked. SO, if originality doesn't matter as much as price, go for the $2.99 radio Shack. It probably has a higher current rating anyway! But if you get close (maybe withing 20%) to it's maximum rating, better put a heat sink on it or mount it to something with heat-conductive grease. This full-wave bridge rectifier has a hole in the middle for a bolt to go through.

 

[jee70611]

Re: Rectifier replacement

John beat me to this one. It will work fine like he says. I used one on a '79 model 70 horse evinrude and it still works great to this day. That was about 4 years ago . I used the same one he suggested. Just make sure that you hook the wires to the right connectors and follow his advice for the heatsink info and you shouldn't have any problems. Just don't disconnect the battery with the engine running. It might overload the rectifier and fry it and possibly the lights or other electrical system components. Good Luck and let us know how it goes.<br /><br />James

 

[John Reynolds]

Re: Rectifier replacement

I did my own 40 hp mercury, and also a friends motor. But I was thinkin'; if a person was to connect more than one together (they're cheap, after all) say three in parallel, then you're talking about a robust 75 amps there. If the old rectifier is mounted on a heatsink, you can use the little hole in the center of the new rectifier(s) to mount the rectifier(s) to the heatsink. Use a little heat sink compound on it (also available at Radio Shack). You could almost weld with it. if one was to go bad by opening up, the other two would still work and you won't be stranded. If you fuse (fuse rating equal or less than the max alternator output in amps) all three rectifiers individually, then if one was to go bad by shorting, then the bad one will be taken out of the circuit by a blown fuse, and you'll still be good to go. With three in parallel, there should be enough robustness there I think to keep you from losing rectifier due to a disconnected battery cable.

 

[marcus_human]

Re: Rectifier replacement

I went and bought a bridge rectifier and fitted it. Works 100 %. I am only concerned with the voltage on the battery. For the best charge you must maintain 13.6V on the battery. With the bridge rectifier it pushes the voltage up to 15.5V when reving the engine and the battery is charging like cracy. I was thinking of maybe fitting a voltage regulator to the output of the bridge, any comments? Thanks for all your help.