Symptoms of bad rectifier?

[nphilbro]

1980 Johnson 140hp J140TLCSA

I'm not sure if this is a post about the rectifier, battery amps/voltage, or something else.

I had been troubleshooting tach problems with this motor from day one but I didn't see any posts addressing a bad rectifier until I finally stumbled across one a month into my efforts. It seemed like posts to my question were met with exactly the same answer - bad tach or it's wired wrong, set to 6p, etc. To be fair, often this settled the post even though I knew mine was wired correctly and already replaced the tach.

Anyway, I'm going to jump to the wild conclusion that I have a bad rectifier due to the fact that when I connected the send wire to to adjacent yellow wire to on the engine terminal block the tach response was instantaneous (after reconnecting the battery and hitting the ignition with a quick flick). I have an in-dash voltmeter and voltage reading on my fishfinder and neither one shows the voltage increase with increased RPMs, although I think it has dropped from 12.4v to 12.1v (maybe more?) over the course of a couple of days with many hits of the trim and some time running the bilge and radio and one harder start at the launch after I forgot to prime it. Before this weekend I had always dropped it on the charger the night before to make sure I always started with a fresh battery. I also don't recall if the voltage would climb at acceleration before getting the tach working.

The tachometer worked really well for about 3 hours on the water that first night and then *almost* all day (7 hours) the next day with numerous starts between drifting, starting (starts in an instant after carbs have fuel) again to get to new spot with intermittent episodes of running it 3200 to 4000 . As we were pulling in to the marina I noticed the tach had flatlined at 1200. I took it out yesterday and the tach still never responded and sat at 1200 just like the night before but there was still enough juice for multiple starts even when a few other issues started to come up.

1. Within a half hour I had a hard time getting moderate to fast acceleration, if not outright die, when kicking up the throttle. I could get it going, just had to ease it up yet after revving it in neutral for a few moments I could jump on the throttle without it hesitating. I didn't have this issue a week or so ago.
2. I was running an estimated 3k rpm and adjusted the trim and the motor lost power then recovered after I let off the trim (I always see a huge voltage drop with trim adjustment anyway).
3. The throttle has always been too sensitive when backing off but yesterday I backed off from 3/4 throttle to 1/2 (it's just very small movement) and it stalled out completely. It started right back up but something like that is always unsettling on the water.

My question then - if the battery isn't getting charge then what are some of the symptoms of a low battery while in operation? Am I experiencing it?

I suspect a bad contact in the remote since the first start of the day is always tough, jiggling the throttle back and forth until the ignition connection is finally made (for some reason all future starts after it's warm are easy).

Also, it idles way too high: 1200 in neutral and 900-1100 in gear (in the water) so I think the extreme drop in rpms when backing off the throttle is likely more a symptom of the timing so hopefully a sych and link will fix it.

I'm not clear what the relationship between the rectfier/battery charge/spark strength is since I thought the coils drew from the motor's ignition system independent of the battery.

One last question. Am I risking any damage to ignition components by hooking up the battery to the charger without turning off the battery switch? It's a 2-10amp charger and I know I've connected/disconnected it many times without turning off the battery but all my accessories are independent of the control box on their own circuits. I've never run the engine with the charger connected.

 

[Joe Reeves]

Re: Symptoms of bad rectifier?

The stator under the flywheel is a two fold component. A series of small coils pertain to the battery charging system and of course are also pertinent to the tachometer's operation. There are two larger coils, one located at the front of the stator, the other at the rear portion, which provides approximately 300 AC volts to the powerpack in order to engage the ignition.

Note that the engine must crank over at least 300 rpms in order to have the stator provide that voltage to the powerpack.

Should the stator overheat bad for any reason (usually a shorted rectifier) it may start to melt down. Those black coils would be dripping a sticky looking substance down on the timer base and powerhead area. This would result in a voltage drop to the powerpack which in turn would result in weak, erratic, and eventually no ignition.

Examine the stator closely. Usually the melting and dripping can be seen by simply looking closely under the flywheel. If this problem exists, replace the stator.

The rectifier can be easily tested as follows:

(Small Rectifier Test)
(J. Reeves)

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 fourth 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.

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.

Note that the reading obtained from the red rectifier wire will be lower then what is obtained from the other wires.

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.

Symptoms of a low battery are that it simply will not crank the engine fast enough to have the stator engage the ignition properly.

The fast idle may simply be a misadjusted throttle cable at its clamping area at the engine or other misadjustments... something to be looked at later.

There is no intended relationship between the rectifier and the igniton system.

The battery charge question.... That creates no problem UNLESS you accidently hook the charger up backwards. Reverse polarity will blow the rectifier instantly.

 

[nphilbro]

Re: Symptoms of bad rectifier?

Thanks, Joe. I'll hit it with the gauge today to confirm and get it on order.

So, to be clear, running with a bad rectifier can do serious damage to other ignition components over time?

Am I safe to assume the sudden power loss at cruise speed when adjusting the trim correlates to a bad rectifier-large power draw the battery can't support on its own - steals power needed by the coils.

 

[Joe Reeves]

Re: Symptoms of bad rectifier?

So, to be clear, running with a bad rectifier can do serious damage to other ignition components over time?Am I safe to assume the sudden power loss at cruise speed when adjusting the trim correlates to a bad rectifier-large power draw the battery can't support on its own - steals power needed by the coils.

Running with a shorted rectifier will prevent the voltage being generated within the stator for completing the circuit to charge the battery. This results in a backup of voltage and overheating at the stator which in turn results (in time) a melt down of the stator. Since the two black coils within the stator are the beginning of the ignition system.... this you could say would be damage to an ignition component due to running with a faulty rectifier.

If you're enountering a drop in rpms when you press the PTT switch in either mode at the instant you press that switch, you have the PTT switch or the PTT system itself wired incorrectly. That should have absolutely no effect on the engine's performance whatsoever. However, correct the problem(s) that you're aware of first as it's always possible that a weird feedback of some kind could be taking place.

 

[nphilbro]

Re: Symptoms of bad rectifier?

Good stuff. They have the part in stock locally that I can pick up tomorrow. I just took a good look at the coils and there is no visual evidence of meltdown and my hope is there wasn't enough overall run time to cause other damage.

I'll also use the downtime to adjust the idle, check timing, examine the plugs and cylinders and do some other preventative maintenance on the fuel system. When fishing season hits it's hard to trade dry lines for bench time so I may as well get it all done in one day. I'll do a trial run on a small nearby lake that I can get to shore by oar power if necessary while I run it through its paces. I have no desire hail the coast guard with the sun setting on the outgoing tide.

 

[nphilbro]

Re: Symptoms of bad rectifier?

A bit late...but problem solved with new rectifier and a full overnight charge...it's been a month and everything is running well. No overnight charges required beyond the first. About 10 launches so far.

 

[Joe Reeves]

Re: Symptoms of bad rectifier?

Glad to hear you solved your problem(s) and are once again a happy boater. Hopefully you do not have other boating problems in the near future... but when/if they do pop up, come back and see us.

 

[Looperdoo]

I believe I'm gonna have to replace rectifier on my Evinrude 115,,

 

[Looperdoo]

Be sweet if just checking voltage,, But has to be measured by ohm's.