How to test a rectifier

[Matysiak]

Hello All,<br /><br />Firstly, I finally got my boat going (Replaced one power pack and all of the coils) this weekend and she flies!!!<br /><br />When i got back home i noticed that the red wire coming from the rectifier was loose, i re-joined the wire right at the rectifier base (The rest of the wiring was very brittle). Now before i go on the water again, i want to check if this rectifier is working, how do i check?<br /><br />The motor is a 115hp 1980 Johnson.<br /><br />Stephen

 

[Joe Reeves]

Re: How to test a rectifier

(Small Rectifier Test)<br />(J. Reeves)<br /> <br />Remove the rectifier wires from the terminal block. Using a ohm meter, connect the black lead of the ohm meter to the rectifier base (ground), then one by one, connect the red lead of the ohm meter to the yellow, yellow/gray, then the red wire (some rectifiers may also have a yellow/blue wire. If so connect to that also). Now, reverse the ohm meter leads and check those same wires again. You should get a reading in one direction, and none at all in the other direction. <br /><br />Now, connect the black lead of the ohm meter to the red wire. One by one, connect the red lead of the ohm meter to the yellow, yellow/gray, and if present, the yellow/blue wire. Then reverse the leads, checking the wires again. Once more, you should get a reading in one direction and none in the other. <br /><br />Note that the reading obtained from the red rectifier wire will be lower then what is obtained from the other wires. <br /><br />Any deviation from the "Reading", "No Reading" as above indicates a faulty rectifier. Note that a rectifier will not tolerate reverse polarity. Simply touching the battery with the cables in the reverse order or hooking up a battery charger backwards will blow the diodes in the rectifier assy immediately.

 

[rickdb1boat]

Re: How to test a rectifier

Or, just check the voltage of the battery when the motor is not running, then compare it to the reading when it is running. For example, if your battery reads 12 volts across it with a voltmeter when it's not running, but at idle or above it reads 12.5-13 volts or better, it's working. Of course, this is if you have muffs to run it on now..

 

[tntwalker]

Re: How to test a rectifier

Joe Reeves... Along this same topic... Will a "blown" rectifier have any impact on how a motor runs?

 

[Joe Reeves]

Re: How to test a rectifier

TNT.... Actually a blown rectifier will not have any effect initially on the running of the engine as that simply disables the charging system.<br /><br />However, continuing to run the engine with the charging system disabled will in time cause the stator, under the flywheel, to overheat as the voltage, current, power, whatever one wishes to call it, cannot obtain passage through the circuit to charge the battery, and in plain simple terms..... has no place to go!<br /><br />The power (whatever) continues to back up at the stator, eventually overheating it to the point whereas the larger black coils of the stator which provide approximately 300 AC volts to the powerpack fail and start to melt down, dripping a sticky substance down on the block.<br /><br />This results in a voltage drop to the powerpack(s) which results in erratic and eventually no ignition (spark).<br /><br />The above pertains to the OMC "Magneto Capacitance Discharge Ignition" system that came into existence in 1973 and which continues to this day.<br /><br />On the "Battery Capacitance Discharge Ignition" system that existed with the OMC 1968 55hp model and all of the 3cyl and 4cyl models from 1969 to 1972, a blown rectifier also disabled the charging system. The stator on these models had nothing to do with the ignition system BUT this type ignition system demanded a top notch battery of at least 70amp hour rating. As the battery dropped in voltage due to the disabled charging system, it usually caused the battery powered powerpack to fail... a rather expensive item!