Johson 70hp overcharging question.

[Tommy J]

Need some advice please. We have a 1991 22' cruiser with the original 70hp Johnson with about 700 hrs on it. It has been pretty much flawless over the years. This motor has a non regulated system (No voltage regulator). Hears my problem. last yr we replaced the stator/retifier and we can now get up to 16.6 volts of charging when underway. The motor has always charged high 14-15V but not this high. We use interstate vented marine batteries and ironically the tech at interstate could not tell me if this high of a charge would hurt the battteries. 2 knowledgable mechanics told me that it could be normal for this motor to charge this high. Questions 1) Will charging at 16+volts over time hurt these batteries? 2) How much trouble would it be to add a voltage regulator to this system? Thanks.

[Larry H]

Tommy,

I owned a 1991 70hp Evinrude and I was an outboard mechanic for many years.

That voltage is normal when the unregulated 70hp motor is trying to charge an already fully charged battery. That high a voltage is not good for any electronics or light bulbs and will boil the water out of the battery.

The solution is to turn on some electrical items like running lights, cabin lights, radios, or fans, until the voltage is down to 13.6 to 14 volts. This is a manual way of regulating the charging voltage.

Boats with that era motor should have a voltmeter installed on the dash to monitor the charging voltage. I don't know of any way to regulate that charging system other than to add electrical load as mentioned above.

[Tommy J]

Hi Larry. We have tried what you suggested i.e. turn on all electrical accesories and at first this will drop the voltage down to what you mentioned (around 14 volts), but then it seems to creep back up over time, so not sure what to do. Can a regulator of some sort just be added into the system?

[Adeline]

Hi Tommy,

You just described exactly the same thing that happened to my '89 Johnson 70. I remember the day it began. I had just started her up and noticed that the voltage was rising above 16 volts on it's way to 17+. At a fast idle ! It had never done that before. Even at full throttle the highest it had ever gotten was 14.3 volts. Without thinking I switched the battery selector from 1 to both. At that moment the control-box started to scream. Barely audible at first and then louder as the voltage continued to rise. As Larry suggested, I started turning on accessories...lights, stereo, etc. As I did the voltage started to lower along with the volume level of the control-box alarm (S.L.O.W.). That's been three years ago and it still does it. Since then I run all of my accessories or the box screams and my batteries boil.

I posted questions at I-Boats and Hull Truth but nobody had any suggestions different than Larry's. I think they thought I was crazy or lying it was so weird.

In my research I DID stumble onto a fellow (minitauk85) over at Continuous Wave.

When you read his thread you'll see that he had the same issue as us. Near the bottom he explains that he finally had his mechanic install a regulator.

I never did this. Maybe I should have...

Here is a related thread.


BTW, I never replaced any electrical components such as stator/rectifier before mine started acting up.
Please, if you learn anything more, post back.

[Larry H]

Another thought occurred to me. It is possible that you have a high resistance in one or both of your batteries. If the batteries are old that could happen.

The recommended batteries are ordinary wet cell lead acid starting or deep cycle with caps on top.

Not recommended are AGM, sealed lead acid, gel cell or any other new type of battery.

The acid level needs to be maintained with distilled water.

The total alternator output is 6 amps, so 6 ordinary bulbs like running lights or cabin lights should use up the entire output of the motor. If you have that much load on, and the voltage is still rising or high, something is wrong with the batteries.

[Adeline]

[Larry H]

That looks like a regulator from an Evinrude/Johnson and the part # is an OMC number. I don't have any experience installing that reg on a 70hp.

If that works, that's a solution. If it doesn't work, and does damage, the stator and regulator could set you back $$$$!

The only bottom line I have is that the total output is 6 amps, and using up those 6 amps to run some 12v device(s) should do the regulating. I think that 14 to 14.5 volts is tolerable on these electrical systems.

These voltages should be measured with a digital voltmeter, not just the analog gauge most older boats have. Those analog gauges are only approximate.

[Tommy J]

Thanks Larry and Pete for the comments. We are running interstate wet cell lead acid batteries and they are 2 yrs old. We have had our entire electrical system checked out by our local OMC mechanic and he says its A-OK. I have never had the control box alarm go off (did'nt know I had one). Interesting 6 lights = 6 amps. Now that I think of it I'm not sure we have had "all" our lights/accessories on at the same time - that should be our next step - to make sure "all" our accessories are on and double check the voltage. Also Pete, thanks for the regulator # and picture. I will research this. By the way I was also told that the 16 volts might be ok if the amperage was below 10? I never checked the amps and need to do this (we have an in dash volt/amp meter). Larry - had not seen your last post. It seems that if I can draw the 6 amps that would be the simplest solution.

[Adeline]

I just remembered that they began installing voltage regulators on the newer OMCs starting in '92. 10 amps! Looks like you missed it by one year Tommy.

Click on it.

[Larry H]

I just missed that regulated 12 amp output too. I looked into changing my 70hp over to the newer stuff, but it would have required a new flywheel, stator, regulator, and some wiring harness work. The total was just never in my budget.