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  200 Merc stator or rectifer/regulator?

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Author Topic:   200 Merc stator or rectifer/regulator?
TampaTom posted 03-08-2004 08:47 PM ET (US)   Profile for TampaTom   Send Email to TampaTom  
Got the lower unit back on, new thermos, new popet valve, new flush hose. I think the overheating problem is solved (just had to pull the powerhead to get to this point.) Installed a new tach today so I can figure out how things are working. Wasn't getting a good signal which comes from one of two regulator/rectifers (40 amp 2x20 in series). Switched to unused tach signal output from lower r/r and tach worked. I therefore suspect that the upper r/r or part of the stator feeding it is not working. I was thinking it would be easy to troubleshoot this by switching the 2 yellow wires feeding each r/r (top to bottom, bottom to top), then testing the signal from each tach output. If the signal from the top r/r starts to work, then its the stator. If not, its the r/r. Correct? I don't think I could screw up anything trying this. Yes? No?

Can I get by for awhile with 20amps from the charging system?

LHG posted 03-08-2004 09:37 PM ET (US)     Profile for LHG    
A bad tach signal by itself is usually just a rectifier, about a $100 part. With a bad stator, the engine won't turn up anywhere near it's rated RPM.
captreils posted 03-08-2004 10:16 PM ET (US)     Profile for captreils  Send Email to captreils     
your stator has a "high" and "low" RPM windings. If one winding goes bad you will only have RPM's on the other winding. Also check the wires comming from the stator to the r/r with an ohm meter to make sure they are not shorted to ground. If that checks out I would say your r/r is bad.
Pete
TampaTom posted 03-11-2004 09:30 AM ET (US)     Profile for TampaTom  Send Email to TampaTom     
To follow up, I switched the stator leads to the two seperate regulator/rectifers and still had no signal from the upper r/r and still received a signal from the lower r/r. Therefore I assume the stator is working and the upper r/r is not. In fact, I trust this method more than I would if I used the ohm meter (I talking me, not you guys.)
tuna1 posted 03-11-2004 10:00 AM ET (US)     Profile for tuna1  Send Email to tuna1     
You correct with your thinking and execution.You can save money on the regulator/rectifier by going with after market parts by CDI/Rapair in Madison Alabama 1-800-467-3371 and going thur a local distributor.Good parts,priced right,and MADE IN USA.
jimh posted 03-12-2004 05:20 AM ET (US)     Profile for jimh  Send Email to jimh     
Typically the windings of the stator are floating above ground. A simple resistance measurement can confirm continuity. A good stator will typically have a resistance of only a few ohms.

Most stators are a single phase or just one coil with two leads coming from it. (The yellow leads you mention above.)

The rectifier is typically a bridge rectifier with four terminals: two marked AC (alternating current) and a positive (+) and negative (-) output. In some devices the negative output is connected to the metal base of the rectifier assembly and is carried to ground/chassis that way.

The tachometer pulse signal is typically derived from one stator lead and referenced to ground through the rectifier. This provides a pulsating DC signal that varies from ground to about 16-volts.

The rectifier consists of four diodes. Depending on what diode fails and whether it fails to an open circuit, to a short circuit, or to some intermediate resistance, all sorts of different symptoms can be observed with respect to the charging output and the tachometer pulses. It is too tedious to describe all the possible variations, but anyone with a basic understanding of electrical circuitry can see how various diode failures produce various effects.

The regulator is downstream of the rectifier. In simple engines there may not be a regulator at all. I am not familiar with what types of devices are typically used in the regulator on a Mercury outboard.

My guess is that the components are very inexpensive and off-the-shelf devices, but they are just assembled and potted into the OEM housing with attached leads or connectors. If you could remove the potting material you could probably re-use the OEM housing and just replace a couple of dollars in parts. If the replacement part was $200, I would certainly give that option a look.

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