New rectifier blown

[recess]

I just picked up a 1990 175 Black Max. After hooking it up, noticed that I was not getting a tach reading and voltage was only on battery. Usual cuplrit is the rectifier. Changed that out and everything back up and working. But, after a few times starting it, problably no more that 15 mins running time over the last 3 days on mufflers, now my tach stopped again, and the battery is powering the motor. After checking the wiring diagram and reading up on the Merc manual, I followed the wires to the voltage regulator (yellow and red wires). Here I noticed only 1 screw securing the regulator to the block, and upon removing, found the contact surfaces dirty and corroded.
Could this be the problem with blowing a new rectifier? Since the contact surface is the ground, I'm thinking the regulator may have caused the problem. I metered the 2 yellow wires from the stator and they check out per manual specs.

 

[j_martin]

Re: New rectifier blown

You might notice the regulator is NLA in the parts listings. That's because it's more trouble than useful. It still shouldn't be able to blow the rectifer, except that the stock Murkery rectifier is junk. Lightly loaded it'll last OK. Fully loaded, bad battery, regulator short, etc. will take it out in a New York minute.

I use this instead.

 

[recess]

Re: New rectifier blown

Got it. Going to Radio Shack tomorrow to pick up the 2 they have in stock. $$$$ sure beats a new one. Looks like a simple wiring mod (spade to screw) and mount the ground. Thanks for your input. As always, this forum is GREAT!

 

[j_martin]

Re: New rectifier blown

The Rad Shack one is theoretically marginal. In practice it usually works. Reason is that minimum back voltage rating should be around 200. Rad shacks is 50. In practice they substitute any part available, which usually is a much higher voltage.

There's a gazillion of them available, 20 amps or better, 200V or better. Usually you can find them at Mouser or another electronics wholesale outfit for under $3 one at a time.

On mine, I fashioned loops of 14G solid wire and soldered them to the blade terminals. Then connected the original terminals with screws and nuts. You could probably just drill holes in the blades.

 

[Faztbullet]

Re: New rectifier blown

The 1990 175 came with either a 16 or 40 amp charging system. From what you describe you have the 16 amp system and The Rad Shack should work fine a J posted. If you have the 2 wire 40 amp rect/reg installed in divider plate, I do not recomend the Shack unit as this thing generates a TON of heat. A weak impeller,low cooling flow from city water supply along with bad ground due to o-ring seal can cause the 40 amp units to fail.

 

[recess]

Re: New rectifier blown

I know it's not the 40amp charging system. Rectifier and regulator are all in one on those. I'm going to rig it as suggested for now, and find the heavier duty rectifiers on line. I've used them before in other applications and they hold up great. I'm stilll a bit puzzled about whether it blew because of the bad ground on the regulator, or just junk from Merc.
I'm going to set it up tomorrow afternoon and try it. I'll post and report. Thanks to all.

 

[Faztbullet]

Re: New rectifier blown

Make sure you clean aluminum under the rectifier and use some heat sink compound.If you mount it back in original location make sure grounds on ignition bracket/plate are good. I use the MES replacement rectifier as it has the heavier diodes than the Merc,Sierra,Mallory and CDI replacements and are around $33

 

[recess]

Re: New rectifier blown

Thanks for the replies. Yes, clean and grounded is the name of the game. I just went and picked up a Radio Shack rectifier and figured I might as well test my batteries since I'm near a NAPA. 1 good, 1 bad. The bad one was reading 12.8 volts, and even started the motor yesterday, but apparently under test load, it failed. Perhaps this is my "overcharge" that caused the new rectifier to blow. I remember starting the boat with the good battery, and all went well. Later in the day I tried switching batteries to the "house" battery and shortly after is when I lost the tachometer and charging. Thanks to your help and replies, I think I found the problem. Better now than out on the water. Getting ready to hook up the rad shack replacement. I'll check back later.

 

[recess]

Re: New rectifier blown

UPDATE: New rectifier in, bad battery out, all seems well. Charging at 14.4 volts at 1500 rpms, drops down to about 13.7 at idle. Tach working again. Never would have thought a battery with 12.8 volts, and enough to crank over a 175 would be bad. Can't say enough about corroded terminals and connections. What a difference.
Hope to splash this boat on tuesday and see what she'll do. Thanks to all for the input.

 

[j_martin]

Re: New rectifier blown

Bad battery connections will blow a stock rectifier in a heartbeat.