Rectifier melted.... cause?

[Nick1818]

Went out to test my boat and I had to boast it to start. Tach worked fine for the first 1/2 hour then quit. When I got home noticed tar like substance below the rectifier. It had been replaced about a month ago. One of the yellow wires seems to be burnt. Should I just change it again or should I do some diagnosing?

 

[Dhadley]

Re: Rectifier melted.... cause?

What motor? We assume this is the small rectifier not the water cooled regulator / rectifier, right?

 

[Nick1818]

Re: Rectifier melted.... cause?

79 johnson javelin 100hp

 

[Nick1818]

Re: Rectifier melted.... cause?

any help would be greatly appreciated

 

[F_R]

Re: Rectifier melted.... cause?

Dirty or loose connections will blow the rectifier diodes. Check where they are attched to the terminal strip, and where the small red wire attaches to the same post on the starter solenoid as the battery cable, Finally, check the battery cables at the battery. Don't just look--take them off and clean them shiny bright. A rarity I found was a bad battery--the cell connectors were loose inside.

 

[Nick1818]

Re: Rectifier melted.... cause?

Thank you

 

[ezeke]

Re: Rectifier melted.... cause?

The rectifier melts like that when the wires short within. That is the more serious damage because it can harm other components. I would disconnect it before running the motor again - just make a wiring diagram so that you can get the new one wired back the correct way.

Rectifiers get cooked by many routes, but mostly by mistakes. Reversing polarity on the battery is most common, with instant fatal results. Others are: Disconnecting the battery with the motor running; Loose battery cables; Bad battery cables; and Bad ignition switch.

Most fellows here will tell you to lock those battery cables down with pliers at a minimum. A lot of people toss the wing nuts and use nuts and a wrench. I finally got smart and installed marine switches in my boats so that I could use regular automotive cable clamps and just leave them connected. [The switch and the rectifier are close to the same cost.]

http://www.iboats.com/mall/index.cg..._id=216621&list_time=1155295437&view_id=39407

http://www.iboats.com/mall/partfind...d_poid.109227/gd_row.69/session_id.834958650/

 

[Nick1818]

Re: Rectifier melted.... cause?

There is three wires on it, two yellow one red. does it matter if the yellows are reversed?

 

[Nick1818]

Re: Rectifier melted.... cause?

Thank you, hope to have 'er fixed in the morning

 

[Xcusme]

Re: Rectifier melted.... cause?

Nope, doesn't matter. The yellow leads are connected to the stator which is A/C voltage.....The recitfier converts this A/C voltage into D/C voltage....

 

[iwombat]

Re: Rectifier melted.... cause?

Overly simplified rectifier theory of operations.

Your rectifier contains four diodes AC, power in a wave comes in, and DC, straight steady power comes out. AC comes in from two leads one and inverted wave of the other. when the voltage is positive on the lead it travels one direction through the diodes, when negative it travels the other direction through the diodes. Since each AC lead is a continuous wave and inverted from the other, it really doesn't matter which AC lead goes where. The schematic for the rectifier is as follows:

AC comes in from the top and bottom. Pos DC out the left, and neg DC out the right.

These usually fail by one pair of diodes shorting out. Leaving only one side rectified. This is known as half-wave rectification. And, is essentially some amount of DC overlaid by a similar amount of AC. The acompanying circuitry in your regulator will throttle down DC to about a 12.5 volt level. However AC will generally pass right through. I've seen as much as 25V AC go through (plus a 10V DC offset) This will definitely begin to fry electrical elements.

Do not let this happen to you.

 

[Nick1818]

Re: Rectifier melted.... cause?

That really is a good explaination. I now understand how it works.

 

[iwombat]

Re: Rectifier melted.... cause?

No problem. Sometimes all that schooling comes in handy.