Rectifier Upgrade

[shadowrider]

I have a 73' Merc 850, tach not working, it is wired properly. The rectifier is rectangular shaped. I Also have a 72' merc 800, it has a different rectifier that is square. Is there an upgrade, or aftermarket ( possibly the 72 was upgraded?) for the rectifier ? I have 3 spares from part motors and all test bad, trying to find a good replacement, that will fit and not drain my wallet. Thanks

 

[Barnacle_Bill]

Re: Rectifier Upgrade

There are people that use a 25 amp bridge rectifier from Radio Shack. About 5 buck.

 

[swamp-fox]

Re: Rectifier Upgrade

A rectifier is $50 at the most. I picked one up on here for $39.

 

[bktheking]

Re: Rectifier Upgrade

Used one (radio shack) on my 90 hp johnson, worked great.

 

[shadowrider]

Re: Rectifier Upgrade

Thanks for the ideas, I would like to know if the small square rectifier is interchangeable with the larger rectangular stock type, and if it came with a mounting bracket to use in the original mounting position. It must have, as the one on my 72 has been changed at some point. I'm thinking it was from a later model --- 78' maybe? Are they the same amperage, and what is the amperage needed ( minimum or max). .............? 25 amp was mentioned as the radioshack version, I know Mercs went to 40 amp later. Can I use a 40 amp ? Thanks guys

 

[bktheking]

Re: Rectifier Upgrade

It's all based on amperage and connections, usually 2 AC wires from the stator, 1 DC red wire and 1 ground. The one I got was 50 amp, you can get all different sizes.

 

[Chris1956]

Re: Rectifier Upgrade

Your charging system is 9A. You may use any rectifier that has that capacity or more. A bridge rectifier has 4 connections. The Merc rectifiers have the - connection already connected to the case. When you bolt the rectifer into the cowling or cowling support it is automatically grounded. If you use aftermarket rectifier, you will need to ground the - pole yourself, and likely change out the ring terminals for spade terminals.

BTW the Radio Shack rectifer is much better than the Merc rectifier, and 1/10 the cost.

 

[shadowrider]

Re: Rectifier Upgrade

Thanks for all the help guys. I put on a 25 amp rectifier from radio shack and made a real neat clean installation in original location. Still need to try it out, but have high confidence. ............

 

[j_martin]

Re: Rectifier Upgrade

Thanks for all the help guys. I put on a 25 amp rectifier from radio shack and made a real neat clean installation in original location. Still need to try it out, but have high confidence. ............

Check your work. This is on a V6.

 

[shadowrider]

Re: Rectifier Upgrade

Just got back from river tuning newly rebuilt carbs. My tach is alive, it reads 700 at idle, wot 4150. Tach is a new teleflex set to 6p. Motor is 73' merc 850 with a jet pump. I never left the trailer, I beleive it should be turning 5500 wot. I have been told that a jet does not need to be under way to reach full rpm. Motor sounds like it is screaming but tach says 4150. Tach reads 50 rpm with key on motor not running. Throttle plates fully open in carb at wot. Link and sync done a year ago. Will recheck. Any thoughts ?

 

[Gomer50]

Re: Rectifier Upgrade

Maybe I did not understand your post (reading I never left the trailer) does this mean your motor was @ WOT on the trailer trying to push your boat,trailer,and your vehicle ?? At 4150 RPM, imagine what your motor will do if it didnt have to try and push all this.

 

[shadowrider]

Re: Rectifier Upgrade

You have it right, do you think it will unwind to 5500 out on the water ?

 

[Gomer50]

Re: Rectifier Upgrade

I cant answer that because I really dont know perfomance wise what a jet pump will do on your setup.I would guess however that it would bring you into the RPM specs for that motor.