Why Two Rectifiers?

[dwparker99]

I recently bought a 94 Ranger 481V with a 94 Mercury 175 XRI. While changing the starting battery I noticed sparks when I connected the last terminal going to the motor. Measuring the draw, I usually got ~8mA with an occasional higher 12 -18mA. I disconnected the motor harness going to the switch and the cable at the starter. Still had the 8mA draw. Disconnected the 4 red wires from the solenoid and lost the draw. Connected each, one at a time, and 1 had no draw, 1 going to a module at the front of the motor had 1.5mA draw, the two remaining go to two rectifiers 1 had 3.5mA and the other had ~4mA draw. I assume this is ok/not problematic since it would take many moons to draw a good battery down at 8mA.

I?m curious as to why two rectifiers. Do they have different functions? My bottom rectifier has a red wire and a yellow wire going to it that has gotten hot (bullet connector has burn marks). My tach is working and battery voltage rises once I come off idle. I?m of the philosophy that if it ain?t broke it don?t need fixing. Could one of the rectifiers be bad and not noticeable?

 

[Faztbullet]

Re: Why Two Rectifiers?

The engine has 2 rectifier as its a 40 amp system, 20 amps per rectifier. These regulator/rectifiers will cause a small spark when you reconnect the battery and will draw a very small amount of current from the battery (Less than 0.001 amp). Clean the connectors and install a dab dielectric grease to ends as this is a common problem with this system....

 

[sschefer]

Re: Why Two Rectifiers?

To be a little more clear the 40 amp stator is actually two 20amp circuits producing alternating (a/c) current, so you need two recitifers to convert both of them to 12 vdc. Those are then combined to create a single 40 amp circuit. You can actually split them and charge two batteries separately and it seems like it brings them up faster. Might have been my imagination and I only did it for fun when i was messing around one time. You could also wire them up in series and double your voltage (24v) if you wanted. Theres all sorts of tricks you can do but it's best to leave them as they are designed.

 

[jimbo_jwc]

Re: Why Two Rectifiers?

Replace the crimp on female connectors as they have lost tension connection hence showing signs of heat /lost current from poor connection , this is common on all loaded battery charging circuit rectifiers on mobil equipment. See alot on motorcycles .

 

[dwparker99]

Re: Why Two Rectifiers?

Thanks for the comments. A few more questions. Is it possible for one of the rectifiers to be bad and not noticeable? If so, is that bad for the stator. Also, 40A seems like a lot of current to charge the battery. Does the system have a current limiter that limits the amount of charging current going to the battery?

 

[Faztbullet]

Re: Why Two Rectifiers?

Is it possible for one of the rectifiers to be bad and not noticeable? If so, is that bad for the stator

Yes and yes...

Does the system have a current limiter that limits the amount of charging current going to the battery?

Yes .. these are what you could call a combo unit as its a rectifier and regulator in same housing.

You could also wire them up in series and double your voltage (24v) if you wanted.

You got me ......I would like to see a diagram on how to do this.

 

[Chris1956]

Re: Why Two Rectifiers?

Doesn't that motor have the twin voltage regulators? My '93 Merc 135HPV6 has them. I would think a higher HP newer motor would also have them.

If you do have the VRs, look for burn marks on the boards under the potting material. CDI makes replacements. I think it would be strange to have a 40A unregulated charging system. You could have a fire....

 

[dwparker99]

Re: Why Two Rectifiers?

Doesn't that motor have the twin voltage regulators? My '93 Merc 135HPV6 has them. I would think a higher HP newer motor would also have them.

If you do have the VRs, look for burn marks on the boards under the potting material. CDI makes replacements. I think it would be strange to have a 40A unregulated charging system. You could have a fire....

It does have dual VRs. They are located behind the power packs plate. I can see that the upper one is a CDI but I'm going to have to remove the plate to get a good look at both of them. At a minimum, I'm going to remove the plate and do a visual on the potting compound and also replace the bullet connectors that show signs of over heating. Also clean all connections and apply dielectric grease as Fastbullet suggested. Even though I don't have a noticeable problem, I'm probably going to do a CDI bench check (resistance reading) and an op check (hooking one at a time up to see if I get charging voltage). I would also like to build a DVA adapter and check input and output voltages.

Questions for anyone

Can I harm the stator by running the motor with one VR disconnected?

In my research, I understand that my dual VRs are capable of providing 40 amps at peak (somewhere around 3000-3500 rpms). At idle, the VRs provide enough power to run a reasonable electronic load and maybe provide a minor charge to the battery. At peak, with minimum electronics on it will put 30+ amps to an almost discharged battery. As the load demand decreases, power not needed is shunted to ground. Is this close?

Thanks for helping me understand this.

 

[j_martin]

Re: Why Two Rectifiers?

Questions for anyone

Can I harm the stator by running the motor with one VR disconnected?

Nope.

In my research, I understand that my dual VRs are capable of providing 40 amps at peak (somewhere around 3000-3500 rpms). At idle, the VRs provide enough power to run a reasonable electronic load and maybe provide a minor charge to the battery. At peak, with minimum electronics on it will put 30+ amps to an almost discharged battery. As the load demand decreases, power not needed is shunted to ground. Is this close?

Thanks for helping me understand this.

Not very.......

Each will put out about 20 amps, but they will hit peak output at about 1500 rpm. These are switching regulators, so the extra available just isn't tapped from the stator. It isn't shunted to ground. If it were, they would require one humongous heat sink. That, by the way, was the failure in the single water cooled 40 amp regulator. The actual current limit is a design factor in the stator.

You can run either one, or both in parallel, or each to a different battery provided they share grounds. Theoretically, if you isolate the mounting electrically from the motor, you could run them in series, or to different not connected in any way batteries. The stator windings are floating, so the regulator mounting ground is the only limitation.

BTW, I split the system in my bass boat. One goes to the starting battery, and one goes to the trolling batteries.

Weak link in these regulators is the fact that they run 20 amps through 10 amp bullet connectors from the stator to the regulator. They overheat, lose tension, overheat some more, and often get enough heat down the wire to toast the regulator itself. Best bet is 6 wire (newer) or CDI's with the stator wires soldered and sleeved.

hope it helps
john

 

[dwparker99]

Re: Why Two Rectifiers?

Nope.



Not very.......

Each will put out about 20 amps, but they will hit peak output at about 1500 rpm. These are switching regulators, so the extra available just isn't tapped from the stator. It isn't shunted to ground. If it were, they would require one humongous heat sink. That, by the way, was the failure in the single water cooled 40 amp regulator. The actual current limit is a design factor in the stator.

You can run either one, or both in parallel, or each to a different battery provided they share grounds. Theoretically, if you isolate the mounting electrically from the motor, you could run them in series, or to different not connected in any way batteries. The stator windings are floating, so the regulator mounting ground is the only limitation.

BTW, I split the system in my bass boat. One goes to the starting battery, and one goes to the trolling batteries.

Weak link in these regulators is the fact that they run 20 amps through 10 amp bullet connectors from the stator to the regulator. They overheat, lose tension, overheat some more, and often get enough heat down the wire to toast the regulator itself. Best bet is 6 wire (newer) or CDI's with the stator wires soldered and sleeved.

hope it helps
john

Thanks John, this helps a lot. It has been a long time since I went thru the Navy's electronics training (late 70s) and have many cobwebs. I googled "switching regulators" and have a better understanding as to how they work.