Moderated Discussion Areas
  ContinuousWave: Small Boat Electrical
  Bad Voltage Regulator - What's the Potential Damage

Post New Topic  Post Reply
search | FAQ | profile | register | author help

Author Topic:   Bad Voltage Regulator - What's the Potential Damage
newt posted 07-28-2005 07:02 AM ET (US)   Profile for newt   Send Email to newt  
Either I have a bad battery or the voltage regulator on my 1990 Johnson 150 is on the way out. Last time out in the boat my voltage guage would hit the peg at 16 volts when the engine was wound up over 3500 rpms. Several trips prior to that everything was normal, but one trip back in June I had some funny voltage reading also.

So, in if I do in fact have a bad voltage regulator, what is the potential damage to the engine and electronics if I go ahead and use the boat this weekend?

Chuck Tribolet posted 07-28-2005 09:21 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Or you have a bad gauge, though it's not likely because
reading high is not a usual failure mode for that type of

It's probably not a bad battery. Batteries fail with low
voltage, not high.

You could fry everything (though I suspect you would have
already). Replacing the regulator looks real easy.

All of this assumes that engine HAS a regulator. Some don't,
but they seem to be mostly smaller and older. If it doesn't
have a regulator it depends on the battery to absorb the
excess, and if there's a bad connection to the battery,
the voltage will go high.


jimh posted 07-28-2005 09:40 AM ET (US)     Profile for jimh  Send Email to jimh     
Continued operation of your boat with the engine charging circuit forcing the battery voltage to 16-volts will likely cause:

--reduced battery life from overcharging

--damage to electrical devices designed for 12-volt nominal operation, including your marine electronics, pumps, and lighting devices

Some modern electronic devices will shut themselves off if the voltage to which they are connected is too high.

I replaced the regulator on my 1992 OMC V6 after it began to put out more than 14-volts intermittently.

I believe the regulator on your engine is similar to the one used on mine. Mine was an integrated assembly which included some circuitry related to the engine tachometer and alarm/shut-down circuits. The OEM replacement was about $230.

The regulator is mounted into the engine block water jacket to receive cooling. It is a bit of a chore to replace it as there are some other components which are mounted above it that have to be removed, too.

The regulator assembly is a sealed unit and there are no serviceable parts inside. You have to replace the whole unit. I would retain the old one as an emergency spare, since the engine will still run with it in use.

Buckda posted 07-28-2005 10:08 AM ET (US)     Profile for Buckda  Send Email to Buckda     
Wouldn't your fuses on your electronics protect them in this case?

I just replaced my voltage regulator on my 1986 Merc 150 and had the same bad (high) readings within a couple of weeks when running over 3,000 RPM.

The electronics are behind two protective measures: the first is the power distribution panel/circuit breaker that is supposed to "throw" at 15 AMPS, and the second is that my electronics (GPS, VHF) are protected by the appropriate in-line fuse.

Right now, I think I'm just working my batteries really hard, until I figure out just what is going on (or perhaps not going on) with the regulator.

phatwhaler posted 07-28-2005 10:25 AM ET (US)     Profile for phatwhaler  Send Email to phatwhaler     
If you are looking for an alternate source of supply for an OMC regulator look here.

You might have to call Rapair and ask them who distributes their products in your area.

My Merc has two regulators that are listed at $150 bucks a piece. I ended get them both for $156.00.

phatwhaler out.

newt posted 07-28-2005 12:45 PM ET (US)     Profile for newt  Send Email to newt     
Thanks for the advice. I mentioned that I may have a bad battery for two reasons. First, while surfing thru Google results for "Johnson Voltage Regulator" I came across several posts on other forums where the authors indicated that a sulphated battery or bad battery connections could cause high system voltages. Second, the high voltage readings are not consistent from outing to outing and since I alternate batteries each time out, it is possible that I only have high readings with one of the two batteries.

I will probably take a chance and run the boat this weekend and hopefully rule out a battery problem, then order a new regulator.

frostbite posted 07-28-2005 01:12 PM ET (US)     Profile for frostbite  Send Email to frostbite     
Leave your electronics off when you run your next voltage check, just to be cautious. Fuses protect from high current, not high voltage.
jimh posted 07-28-2005 01:19 PM ET (US)     Profile for jimh  Send Email to jimh     
Fuses protect against OVER-CURRENT, not against OVER-VOLTAGE.

If a device acts as a resistive load, increase in voltage will cause a proportionate increase in current. Unfortunately, in most cases the fusing of a branch circuit in a boat will not be done with a fuse whose over-current rating is sensitive enough to react to a small increase in current. Fuses usually only blow quickly if the fault current is two or three times their rating.

A new, strong battery will tend to hold down its terminal voltage and act as a regulator when a charging current source tries to drap the battery to higher voltages. This is the basis of operation of many small outboard motor's that have unregulated battery charging output.

Jerry Townsend posted 07-28-2005 04:29 PM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
Newt - With your charging system performing differently with each battery - your regulator and meter are probably OK and the problem is probably with a battery. Clean the contacts to that battery, check those cables and your problems may just go bye-bye. If not, you are probably looking at a new battery.

Another indication of a battery problem is the high voltage - because a battery is a pretty good self regulator. ---- Jerry/Idaho

LHG posted 07-28-2005 05:52 PM ET (US)     Profile for LHG    
I had the same problem a few years ago. Chances are you are going to have to replace both the battery and regulator. I had to.
JOHN W MAYO posted 07-30-2005 12:26 PM ET (US)     Profile for JOHN W MAYO  Send Email to JOHN W MAYO     
The fuse protects mainly against high [current] that is in excess of the rating of the fuse; unless the voltage was very extreme I do not think they would protect the system.
Liteamorn posted 07-30-2005 05:16 PM ET (US)     Profile for Liteamorn  Send Email to Liteamorn     
Most quality electronics have a window that will read your voltage (my old Lowrance fish finder and now my Garmin gps does just that). Double check your voltage that way. The volt meter on my Montauk is almost always pinned but my electroncs read the correct 14.7.
Freeport Alan posted 07-31-2005 12:42 PM ET (US)     Profile for Freeport Alan    
My 1994 40 Merc 4 cylinder doesnt have a voltage regulator, came from the factory this way as did all Merc 4 cylinder 40's & 50's over the decades.
You need the proper marine deep cycle battery & not a bad idea to keep the running lights on often while running { this keeps the voltage down a bit } .
Also keep an eye on the water level in the battery.
Granted I only have a 12 V port for my handheld & spot & running lights & horn but have had no issues from this condition Year & 1/2 60 + hours I've owned & run the boat.
newt posted 07-31-2005 06:28 PM ET (US)     Profile for newt  Send Email to newt     
Here is the latest. I started the day on battery #2. The in-dash voltage guage was pegged at 16 volts, while the fishfinder indicated 13.7 volts. I switched to battery #1 which apparently was not fully charged and the in-dash guage started at 14 volts and slowly climbed until it was pegged. The fishfinder started at 12.4 volts and evened out at 13.6.

At home in the driveway with the key on and motor off, the in-dash guage read 14 volts, and the fishfinder indicated 12.5 volts. Switching batteries gave the same readings.

I think I can rule out a bad battery, and I am starting to suspect the in-dash voltage guage. Is it possible to have battery voltage of 14 volts? When I get a chance, I will check battery voltage with my multimeter.

Chuck Tribolet posted 07-31-2005 11:49 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Newt: I agree that it is smelling like the guage. I'd check
it with at least two multimeters. Borrow a couple from your buds
and neighbors.


kaige posted 10-25-2009 01:09 PM ET (US)     Profile for kaige  Send Email to kaige     
A battery under ideal conditions will only give you 2.2 volts per cell thus giveing you 13.2 volts and the normal is about 12.6 volts

Post New Topic  Post Reply
Hop to:

Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.