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Author Topic:   Excessive voltage during operation - OMC V4
Jeff posted 07-27-2010 01:48 PM ET (US)   Profile for Jeff   Send Email to Jeff  
Lately I have been noticing while my 1974 Evinrude 85hp V4 is running I am seeing voltage readings in the 16.7 - 17.1 range. Is this out the operating range and would this be a sign of an impending regulator replacement?

I have checked all of my battery connections and they are clean and tight. I have no fluttering RPM readings from the tack either.

jimh posted 07-27-2010 11:16 PM ET (US)     Profile for jimh  Send Email to jimh     
With a modern outboard and charging system, the battery voltage should be limited to about 14.5-volts maximum. i don't know off the top of my head what the specifications are for a 1974 OMC charging output. It might be that higher voltage was tolerated back then. The concern for high voltage is that the battery will be overcharged, turning its electrolyte to gas. If you are using a sealed battery, you do not want the charging voltage to go above 14.5-volts.

Perhaps an OMC expert can help with this 1974 engine's charging specifications.

seahorse posted 07-27-2010 11:47 PM ET (US)     Profile for seahorse  Send Email to seahorse     
Your 1974 engine does not have a voltage regulator, it only has a rectifier. The battery size determines the final voltage.

Do not use sealed or maintenance free batteries with your motor as they will have a short life and high voltage. You need a flooded cell battery where water is easily added.

Running with the lights on helps absorb excess voltage and a group 27 deep cycle/starting battery or even a group 31 will keep the voltage down to tolerable levels.

A quick fix is to wire 2 batteries in parallel.

home Aside posted 07-29-2010 02:33 AM ET (US)     Profile for home Aside  Send Email to home Aside     
Is this a great site or what?
Jeff posted 07-29-2010 11:28 AM ET (US)     Profile for Jeff  Send Email to Jeff     

Thank you for the feedback. It mirrors the same as what I got from Lockeman's yesterday.

I currently run a group 27 open / wet battery. The typical load on the system is the VHF, depthsounder and a small GPS unit. I will start running the lights as well to see what that does. The only problem with the current set up is my VHF has a high voltage alarm that goes off at readings >15 volts. This is rather annoying and I have not found out if it can be turned off.

So another question I then have is, Am I harming my electronics at this voltage?

Buckda posted 07-29-2010 11:57 AM ET (US)     Profile for Buckda  Send Email to Buckda     
Continued exposure to voltage above parameters can cause minor damage to semiconductors, degrading their performance. This damage is cumulative and eventually reaches a point where sudden and complete failure of the component could result.

In short, high voltage is not exactly good for your electronics. You should see if you can get it fixed, or install a device that will dissipate excess voltage as heat.

jimh posted 07-29-2010 05:43 PM ET (US)     Profile for jimh  Send Email to jimh     
To protect the electronics from higher voltage you could install a separate regulator. To make it economical, you'd have to build it yourself.

I wonder if there is a later model component that could be fitted to your older OMC V4 engine which would provide better regulation of the charging voltage. I have to think that eventually OMC improved the charging circuit. If they did, and the parts could be added or retrofitted to your engine, it would solve the problem.

contender posted 07-29-2010 11:13 PM ET (US)     Profile for contender  Send Email to contender     
Have you checked the gauge? hook up another one for a check or get a meter...
Jeff posted 07-30-2010 12:10 AM ET (US)     Profile for Jeff  Send Email to Jeff     

These readings are not from a gauge but, from both my Garmin Sounder and VHF. They both display system voltage.


I was thinking the same thing and would likely make it a winter project.

L H G posted 07-30-2010 06:00 PM ET (US)     Profile for L H G    
Mercury in-line 6's also came with an unregulated charging system. When purchased new, I installed Mercury's optional voltage regulator kits (about $90 at the time). I would assume OMC has a similar voltage regulator accessory to install, which I would do to avoid damaging electronics.
cjmiller posted 08-01-2010 10:08 AM ET (US)     Profile for cjmiller  Send Email to cjmiller     
I had a high voltage issue with a yamaha 100 4 stroke; battery terminals seemed tight, etc. However, there was some corrosion on the threads and what appeared tight, wasn't; the wing nuts and hand tightening didn't do it. Cleaned terminals and wire terminals, tightened with pliers (carefully), voltage back to normal.

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