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Running a 2000 70 HP 2/C Johnson...

Replaced what I thought was a bad battery just prior to hauling out the boat last fall. This spring finds me with a battery that isn't charging. If I put a booster box on the motor it fires up and runs great and I am reading 14.6 volts at on my depth finder. I did notice though if I operate the power tilt the reading drops down to 8.5 or 9 volts on the depth finder. Trickle charged the battery and it seemed okay and I would think if it was stator /rotor problem I wouldn't be running at all. So... I am thinking a replacement regulator/rectifier is needed?

Any thoughts?

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How many volts does your depth finder show when the ignition key is turned ON but the engine is not running?

It should read about 12.5 to 13 volts.

If the depth finder shows 14.6 when the engine is running, then your charging system is charging.
If that is the case, your battery is bad.

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Checked this evening. Depth recorder showed 10.5 volts. Used the booster box again to start up the motor, took off the booster and took a ten minute ride at speed. Voltage on the depth recorder was showing 13.5 volts. Trimming the motor or even keying up the VHF microphone cause the voltage to drop 2 volts or so.

After running 10 minutes or so, the voltage was reading 12.5 volts with the motor shut down. And I was able to start up the motor with no booster.

I pulled the battery off and will trickle charge it over night and load test it in the morning. I'm going to assume if it flunks the load test then maybe it is the battery...

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Battery is reading almost 13 volts and holding a load just fine after charging overnight. Two questions: 1) I thought I read somewhere that a bad rectifier could actually drain the battery. Is this correct? 2) I forgot to mention in my last post I found one of the two bolts holding the rectifier to the block missing, although the remaining bolt was snug, could this be an issue? Does the body of the rectifier act as the ground?

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Many years ago I had an inline Merc 115 . When the rectifier went bad on it my tach was screwy, thats how I knew something was wrong. I was running about 4200 rpm but my tach said 2500.

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Pull the positive battery cable and put an ammeter in series. Anything more than a few tens of milliamps is too much. If you have a drain you can pull fuses, or disconnect accessories, one at a time until you find the culprit.

A bad rectifier can drain the battery. It's easy to damage a rectifier accidentally (momentary shorting of the battery cables for example). It's a relatively inexpensive part and easy to replace. And I believe you're right about the body of the rectifier acting as ground, at least in some cases. It may also need intimate contact with the block for heat sinking. On the other hand, seems like the rectifier on my 60 Merc is isolated from ground and has a ground lead instead. Depends I guess.

The heavy voltage drop when you run the tilt motor is a worry. I think it's possible to damage diodes in such a way that they work better under light load than under heavy load, but I'm not sure. If so the voltage drop could be caused by a damaged rectifier. If not, it's possible you've lost good ground contact on the tilt motor.

A few thoughts is all. HTH.

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I like to start "simple" when trouble shooting, Are the battery post's in good cond. (no corrosion) ? Did you check the wet cell's on the battery w/a "Hydrometer" ($5 auto store), check ea. battery cell with the Hydrometer, the number's themselves are not all that important as long as they are all "about" even in the Hydrometer, if one cell has way lower numbers on the "specific gravity" test in the Hydrometer than the other cell's, it's a bad cell, and a bad battery.

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A bad cell should cause the battery to fail a load test. Seems like he's beyond the battery at this point.

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My assumption was if the battery charged off the boat and passed a load test that I could rule out the battery. I'd love to think it's the battery which is still under warranty. But I think it's either the rectifier or something drawing a load but for the life of me I can't imagine what. This evening I will put the battery back on board, polish up the terminals even more, refasten the rectifier to the block, put a meter inline on the positive side and see if there's any draw with the motor off.

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You can also check the stator coil with a ohm meter to see if it has an open or short in it.

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Two years ago I put a new battery in my boat. Well after a day or two of sitting, it would drain and die on me. I didn't think I had a battery problem at first because it was a new battery. So out of frustration I took the battery out and brought it to Pep boys for them to test. Well come to find out it was a bad battery after all. I traded it in for a new one (as it was under warranty) and I haven't had a battery problem since.

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I am not that knowledgeable about the electrical aspects of 2 cycle motors... what would the procedure be to check the stator coil? My assumption (and we all know what happens when assume..) was that if I had a stator/rotor problem I would not have spark and thus not be able to run the engine.

Just for laughs I called my local OMC repair place: No rectifier in stock, order tomorrow "maybe" it's in Friday, for 236 frogskins plus tax... I can order one on the web for about $100 less...

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The stator has windings that you can test for continuity and impedance. You need to follow a written procedure from a service manual but it's a simple test if you have a multimeter. There will be a specification for resistance through each of the windings. You would also be looking for short to ground and for open (broken) circuits. Hopefully you can get access to the wires without a lot of disassembly.

I can't believe a rectifier is 240 bucks. I shouldn't have been so flippant about just replacing it. Sorry.

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This a great reference site and has good pricing for parts too. I got the rectifier for my 90 'rude 88 for 43 bucks through him.

Highly recommended.

http://www.maxrules.com/index.html

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It's only $240 if I buy it from the local "authorized" OMC guy. There's a half dozen places online to buy it for $130 or less. Which is a shame because I'd rather support the local guy and would gladly pay a little more to do so provided they can provide the service and the benefit of their experience. Would you believe they are asking $3.73 a piece for the mounting scews?

Put the charged battery back on board and put the meter inline on the posi side. No draw to speak of. 4 mili-amps which is I attribute the LED's in my switches.

Started up the motor and it showed charging at 13.5 volts and no appreciable voltage drop when operating the power trim, radio, etc.

So... maybe all that was needed was a good deep charge on the battery. At this point I will wait and see if the charge holds.

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A good charge plus fresh cable connections at the battery terminals maybe? (Matt nailed it. :D) Hope that's all it was. I'm going back to my cage now.

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Brother in-law and nephew are passing through on their way from Ithaca to Florida after Nephew's college graduation. They were taking the boat and my rods this morning to go find some stripers and blues. While I am stuck in the office. I am sure I will hear the fish were everywhere.:o

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Installed new rectifier. Problems solved. With the old rectifier voltage readings were all over the place going from 12.5 V to 14.7 to 13.5 back to 14.7 etc. continously. And then the tach cut out but came alive again... Now with the new rectifier the voltage readings make sense, the battery's charging, and the tach's reading correctly... thanks all for your help.

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Well done. Thanks for letting us know how it turned out.