Electrical advise needed Regulator Rectifier or Stator or Both

[Blade]

Hello Raiders, 

I am seeking some advise from relating to some electrical diagnosis.

Problem statement:

Motor is a 2001 3 cyl 90hp 2 stroke Mercury

When I did a visual inspection under the cowling I noticed that three wires have been getting hot to the point that the connectors melted.  X2 yellow and X1 Red wire had burnt the others showed no sign of heat.

 

Potential causes:

Based on an online search the most likely issues are either the regulator rectifier or the stator. 

I have done a diode test on the regulator rectifier voltage flowed in the correct direction with an OHM reading of 000.2 OHMS

The Grey wire to red wire registered a higher output.

I then did a test on the stator results were (note the multimeter has 000.2 OHMS reading when the probes are touched as such this must be deducted from the below readings)

Yellow to yellow = 000.4 OHMS

White and green to Green = 0.668 KILOOHMS

I checked the AC voltage output (yellow wires) with the motor running, the readings were bouncing around 23-24v the voltmeter then flashed overload. 

 

Advise needed:

The thing that has me concerned is the AC voltage check on the stator with the voltmeter registering a fault, and the higher reading on the grey to red wire reading on the rectifier.

I have tried to look online to see if these readings are in range, but the documents are too technical for me, I am hoping that there is a raider that can advise me on this.

Thanks in advance.

 

 

 

[JonD]

Had the same with a 90hp 2003 mercury. A reputable mercury mechanic and good friend (now passed away) said it was be a common issue if the battery isolation switch is turned on and the outboard key is in the on position. The key needs to be fully in the off position when the battery isolation is turned on. 

[Blade]

Thanks @JonD I have been told that previously as a result I always ensure the key is in the off position before I switch the batteries on, so I am confident that the burnt wires are as a result of something else. 

[Blade]

I have been doing some further reading based on what I have seen online there are two more potential causes. 

1. Bad battery/ batteries 

2. Bad connections 

The last time I checked the connections they seemed okay all I did then was add some dielectric grease nothing else looked to be an issue. 

I will take the batteries for testing. 

 

[slothparade]

11 hours ago, Blade said:

Thanks @JonD I have been told that previously as a result I always ensure the key is in the off position before I switch the batteries on, so I am confident that the burnt wires are as a result of something else. 

The burnt wires are probably a loose connection that has ended up shorting. I've had something similar happen. 

Another thing if they're getting hot they're getting to much current through them. Therefore thicker wire helps. 

Sorry I can't speak for your particular situation with regards to marine, but I have been wiring up a 12v system in my rig and have had a bunch of fires due to the previous owner not fusing things or incorrect guage wire. 

[slothparade]

Just now, slothparade said:

The burnt wires are probably a loose connection that has ended up shorting. I've had something similar happen. 

Another thing if they're getting hot they're getting to much current through them. Therefore thicker wire helps. 

Sorry I can't speak for your particular situation with regards to marine, but I have been wiring up a 12v system in my rig and have had a bunch of fires due to the previous owner not fusing things or incorrect guage wire. 

Has this been a one off or have you tried rejoining the wires and they over heat again? Because if it was a one off might be worth getting so e inline fuses to stop this from happening again. 

[noelm]

There's a whole lot of things at play here, first off, a 2 stroke charging system is quite primitive compared to a 4 stroke which is more "car like" a simple moving magnet charge system produces a big range of voltage and current, a simple bad connection will cause an over heat situation. Add to that the rectifier is also pretty simple, excess voltage/current is just "shunted" to ground and produces lots of heat, if the rectifier has a ban ground, or not secured to the engine block (heat sink) it will over heat, just like your photos. Engines like the e-tec have the most stupid system of all, the regulator/rectifier is built into the EMM, a simple charge fault fries your $1000+ EMM, why anyone would build a high heat device internally is beyond me......but anyway. Testing the components is quite simple, but you need a service manual, checking "stuff" with a meter is useless unless you know what the result should be! Buy a genuine manual, not a cheap generic manual, copy or an online CD. Mercury are notorious for weak charge/ignition components.

[noelm]

2 hours ago, slothparade said:

Has this been a one off or have you tried rejoining the wires and they over heat again? Because if it was a one off might be worth getting so e inline fuses to stop this from happening again. 

You don't want fuses in that location! But, you are correct, simply having bad connections will heat up wire/joins, but unlikely for them all to be bad, certainly possible. My advice is repair manual and testing, either that or guess and throw parts at it, you might get lucky before your wallets empty......

[Blade]

15 minutes ago, noelm said:

You don't want fuses in that location! But, you are correct, simply having bad connections will heat up wire/joins, but unlikely for them all to be bad, certainly possible. My advice is repair manual and testing, either that or guess and throw parts at it, you might get lucky before your wallets empty......

The empty wallet is what I am trying to avoid, it's an old motor so I can expect things to break every now and then but this is easier to diagnose on the mechanical side of things vs the electrical. 

Based on what I can see in the service manual and online the rectifier is within the allowed limits. 

The tests I did with the stator still installed but disconnected all seem to be in spec too.

Noted all tests were done with the batteries disconnected so there is no way there is interference from the batteries. 

This leaves me to think it could be either a bad battery/ batteries which places extra load on the system as it is trying to charge a bad battery. 

Or 

It is a bad connection. 

I will take the batteries to be tested, if they come back good then I will re run the tests on the stator and rectifier to be 100% sure. 

 

 

[XD351]

My money is on a corroded connector , the wires on either side of the connector look ok so maybe moisture has got in through the plastic sleeves and got trapped in there . I would replace the connectors then run the motor for a little while and see if the new connectors are getting hot, while it is running check your battery voltage to see if it is charging then shut it down and let it sit for half hour and check the voltage again to see if you have dropped a cell - voltage will drop below 12v very quickly.

[Blade]

Did a battery check on both batteries and they are both in good condition. 

 

[BaitDropper]

Regulator /rectifiers are an absolute pain in the @@@@..

My only take, as mentioned above, go over every earth possible, follow every wire, track it's common earth. At least you can do what you can. before having to shell coin for a sparky to get in there. I deal with the same issues on older british motorbikes, there a disaster of a set up and prone thru vibration to cause headaches. most of the time I convert them using a podronics Typanium system and remove the rectifier all together, however I'm not sure that's possible in your situation. Sometimes you feel as though your just chasing your tail trying to diagnose,, but as mentioned, loose connections and definitely crook earths will reek havoc there, so hopefully that's your solution...

Edited May 1, 2023 by BaitDropper

[dunc333]

i had a 2004 merc and there was a recall on the rectifier as recall said it could catch fire mercurys solution was to put a fusable link before it they just supplied a waterproof fuse block i cant remember what size fuse .it was put on my motor and i never had a issue  im sure if you look up recalls for merc in australia it would come up cheers dunc333

[Blade]

I re did the tests on the regulator rectifier 

When trying to forward bias the diodes across both circuits I go a 0 reading so it seems like the rectifier is not allowing anything to pass through.

When I touched took the reading from the yellow wire (would normally be connected to the stator receiving AC current) to the earth of the regulator rectifier I got a 2.9v reading, this makes me think that there is a short (It just seems odd that the unit would allow AC current to pass through the earth) This only occurred on one of the circuits i.e the 2nd yellow wire to earth did not allow any voltage to pass.

I also did an OHM test and the reading was not stable it started high and dropped steadily

It seems to me that the regulator rectifier is the issue, or am I doing something wrong?

 

[XD351]

When testing a rectifier or diode you need to use the diode function on the meter and the reading will be the forward voltage drop across the diode - typically 0.6 volts then reverse the leads and the reading should show an open circuit . If you unit is all in one package rectifier& regulator you are better of testing the output voltage on DC setting of the meter with the motor running and the rectifier still in circuit ( should show 13.7-14.4v)  then switch the meter to AC to see if there is an AC component to the reading - the meter should read near on zero for AC- this men’s the rectifier is working and there is no AC ripple .If the voltage test ok the unit is good . Turn the motor off the disconnect the rectifier output leads and put the meter to read a high range resistance and test the DC output leads for leakage between the two then do the same for the positive lead to engine ground - should be infinite resistance - if not then something is leaky or has a dead short - maybe a capacitor , maybe a transistor but either way not repairable. Usually these things just die and stop charging or at worst give a high output voltage which generally kills batteries. 

Edited May 1, 2023 by XD351

[dunc333]

dont know how to repost it but recall is still there product safety recall australia mecury the one i found was for 30 to 60 hp but im sure they are all the same rectifiers

[dunc333]

glad you can do the tests another sign your rectifier is caput your tacho needle will start jumping around 

[Blade]

Replaced the regulator rectifier, redid all of the connections. Took the boat out on the weekend, was reading just above 14v at the batteries.

Will keep an eye on the connections to see if they show signs of excess heat.