My OMC almost barbecued me - need some help, please.

[Steve2ManyBoats]

No kidding!!!

Background - With help from a number of kind folks here, I got a '79 235 Johnson together with the ignition system from a 91 150. Wanted the 35 amp charging for my 20' Sea Ox. Thing's been running great for the entire summer...'till yesterday.

Running out to the fishing grounds on the Chesapeake yesterday - about a 10 mile run - all was well. When I throttled down to start trolling, I noticed white smoke pouring out of the the engine cover vents. Not black smoke, but white smoke. First thought was steam, but my water pressure gauge read steady pressure @ 4 psi @ idle.

Stopped the motor, took off the cover and there was a fire under the flywheel. Cut the 12V power and had to drain a fire extinguisher putting out the fire. Smelled like hell - a typical electrical fire. After the fire was out, checked the engine temp by hand - block and heads were just warm, not overheated.

Got towed home without further drama and popped the flywheel today. Stator has some black soot on it but looks OK otherwise. Voltage regulator has a hole melted in it.

Trying to diagnose, key off, power on causes an arc in the hole - an obvious short. Didn't try anything past that.

Obviously the voltage regulator is toast. Anyone got any ideas why it failed?

Any tests I can perform that would help?

Anyone got a spare 35 amp OMC voltage regulator?

Thanks as always.

Steve2manyboats.

[flabum1017]

Sounds a lot like a loose connection. A loose connection will heat things up in the charging system just as well as it would right at the bad connection. It could also have been either a bad regulator or an overload.

[baja200merk]

check the positive voltage regulator wire that runs to the solenoid, might be worn and grounding out on the block somewhere.

[THEFERMANATOR]

What regulator were you useing? The 79's used an air cooled 9 amp regulator, the 91 uses a 35 amp water cooled regulator IIRC. I've heard of a 9 amp regulator melting and doing funny things hooked to a 35 amp stator. Remember that an outboards regulator works by sending excess current to ground whereas in alternators they regulate the output by fielding it. The regulator has to dissipate the heat, and if it can't meltdown will occur.

[Steve2ManyBoats]

When I swapped over the ignition system, I swapped the flywheel and water cooled 35 amp voltage regulator as well. The engine never lost cooling water pressure so the voltage regulator should have had no reason to meltdown from lack of cooling water.

I'll check grounds tomorrow.

Thanks...Steve2ManyBoats

[racer]

I would take a close look at the battery if it has a plate shorting out it will take out the regulator

[EMDSAPMGR]

I have seen a number of these 35 amp stator fires. It is not uncommon on these higher output systems. There is a lot of black smoke, charred pcs, but little actual damage to the powerhead. You will probably need a stator, timer base, and new regulator. I'd also check the magnets under the vented flywheel. They may have loosened in the fire. You may want to replace it to insure you don't have problems in the future, esp if you are doing a claim on your insurance.

[Steve2ManyBoats]

EMDSAPMGR:

I dont think the stator or pickup got taken out. The voltage regulator sure did. I got to the fire nearly enough that the regulator was the only victim. I have liability only on all my boats. Frankly, there's no one around here that I'd trust with my motors. I feel better doing all my work myself and knowing I did it right. It was getting dark yesterday so I didn't get too far diagnosing things. I'll look for the obvious tonight - bad ground, chafed wires, battery short, etc.

I assume that the voltage regulator could have decided to melt down all on its own, but I've never heard of that one before. I thought that when voltage regulators failed, they let all power through and didn't shunt any, so that you cooked your battery, not your regulator.

Is there anything significant in the fact that it shorts/arcs now with the key off, but the 12 power on?

Thanks again for your post. You were a big help in getting both this 235 and my 140 sorted out.

Thanks...Steve2ManyBoats.

[LineItUp]

I have a comlete 150 system i think that it is off 91 Everything from flywheel to coils and harness if you need it let me know

[EMDSAPMGR]

The keyswitch has nothing to do with the charging system. The charging system works on it's own as soon as the flywheel starts moving. It is independent of the electrical system that drives the ignition. Probably why the engine was running as the fire was going on. The arcing is probably because the battery is still connected and feeds through the regulator. I'd disconnect it till the regulator is replaced. You may be lucky if it is just the regulator-maybe a cheap fix. When you pull the flywheel to put the regulator in, you will get a good look at everything...

[clanton]

You need the regulator without the purple wire, latest version. 4lbs water pressure seems low. You can also vent the top of block to insure no air in top of block. DHadley iboats will give you info for the vent, may not apply to this motor.

[Steve2ManyBoats]

Tested both batteries - both @ 12.5 volts at rest and all terminals clean and shiny.

Checked all wires from the voltage regulator - all were perfect. No chafing, no signs of shorting and the positive connection to the starter solenoid looked brand new. The stator looks fine, just a little black soot. No melted insulation and all wires look fine. Terminal block looks fine too. The flywheel looks brand new - all magnets are in place and nothing looks amiss.

What happened? Do voltage regulators like this just decide to meltdown for no apparent reason? I can't find any reason why it failed.

I'm reluctant to put in a new or new/used regulator until I can determine why the first one failed.

Is there a better or later model regulator I can run if this part is failure prone?

Thanks again for the help.

Steve2ManyBoats.

[EMDSAPMGR]

The rectifer/regulator typically will fry for two reasons. The battery got hooked up backwards or loose engine terminals on the battery posts. This will fry the diode and cause an overheat condition in the regulator. It can lead to the fire you mentioned. Typically, you just replace the rectifier/regulator and check all connections. You should be good to go. make sure you get the 35-amp replacement regulator.

[Steve2ManyBoats]

Two batteries and a switch have been hooked up for years. Both batts read 12.5volts. All terminals are clean and tight. Everything is perfect...except for the hole burned in my regulator.

Do these things just melt down on their own? I'd like to know before I toss another one in and melt it too.

Thanks...Steve2ManyBoats

[CharlieB53]

One thing I don't see anyone mention........

DO NOT, repeat, DO NOT switch battery connections while the engine is running.

That includes, DO NOT switch the battery isolator switch positions while the engine is running. Doing so leaves the charging system disconnected for that heartbeat of time while the battery switch is in between poles, this affects the rectifier in two ways, momentarily allowing the unregulated voltage to surge/rise, totally uncontrolled, then slams it back into full load. The sudden voltage/amperage 'shock' will shorten the rectifier life, if not smoke it outright.

[Steve2ManyBoats]

This thing just decided to melt down. Ordering a new rectifier. Hope the same thing doesn't happen...

[seahorse]

Newer 35 amp regulators have a thermal safety shut-down circuit in them. Make sure you use hex nuts on the battery terminals, no wing nuts.

Check the stator carefully. Any blackened or discolored copper wires are suspect as is any evidence of melted insulation from the black plastic coil assemblies on the stator.

[200VEGAS]

Cause They Need To Be Tight?

[THEFERMANATOR]

Cause They Need To Be Tight?

Wingnuts are VERY well known to back off and cause electrical problems(even fires) in offshore boats.

[powerabout]

what did your voltage gauge say during all this?

[Steve2ManyBoats]

After I got home and checked, 12.5 Volts across each battery at rest and disconnected. Both batteries were hooked up (selector set to "All") at the time of the fire.

Thanks...Steve2ManyBoats.