1979 70HP Johnson putting out 16V while running open throttle

[Btmbass]

Hello everyone,

I have a 1979 70HP Johnson on my Spitfire V15. On my last two outings my console depth finder showed 16V while I was going full throttle. When the engine is off the voltage drops back down to 11.5-12.5V (depending on if I have bow depth finder on and various pumps). Once I've started the engine, sitting at idle it seems to remain at 12-13V. Once I get on the throttle, it'll slowly build up to 16V which is when I panic and begin turning on my bilge and making slight trim adjustments which temporarily drops the voltage back down to 14V.

The question stands is this normal? My googling searching is producing a very mix bag. Some reports say an engine so old doesn't have a voltage regulator and is normal, other reports say it'll fry all circuits on the boat and kill my battery (which I believe from my automotive electrical background).

Should I be concerned? I was really hoping to get another 2-3 trips out of her before putting it away for the winter. Thanks for the help

[ChampioNman]

C0087860:2010/CAT13/CAT13_43641.gif

Item 43 is your rectifier. This is what regulates your voltage on your particular motor.

[Btmbass]

Thanks, I saw that diagram while searching around for a voltage regulator. So 16V is definitely not good and I should replace the rectifier?

[Bassmeister]

Yes sir....

[Btmbass]

Hello everyone,

So I replaced the rectifier last week and it seems to have helped but the issue is still there to a degree. So before I replaced it, I was getting 16.5V after running full throttle for about 5 minutes. Now I'm still getting up to 15.5V after running full throttle for about 7-10 minutes. Any ideas? The old rectifier looked ok, but the wires were a bit corroded

[ChampioNman]

You'll be OK remember it is a rectifier not a regulator/rectifier. You want to make sure your grounds are clean and tight on both the cranking battery and the motor. It is more of a "load leveler".

[Btmbass]

Ok thanks. Remembering back, I had to rewire the battery connectors about 5-6 weeks back. I suspect the battery connections might have gotten loose or my solder jobs weren't as good as I thought they were.

[316jughead]

You must have a good battery and solid connections, a weak battery is a no no with your system.

[SEAHORSE]

That is an unregulated system so the battery capacity is what regulates the voltage. If you parallel 2 batteries or use something like a group 31 size, your voltage will stay in a better range. Back in the day, we would turn the running lights on to lower the battery voltage when it would rise too high.

CDI Electronics also makes a regulated-diode assembly for your motor that monitors the voltage and keeps it in line. Click on

Regulated-rectifier

[Bassmeister]

HOSS.....ya don't miss a beat old son!!!

[Btmbass]

That is an unregulated system so the battery capacity is what regulates the voltage. If you parallel 2 batteries or use something like a group 31 size, your voltage will stay in a better range. Back in the day, we would turn the running lights on to lower the battery voltage when it would rise too high.

CDI Electronics also makes a regulated-diode assembly for your motor that monitors the voltage and keeps it in line. Click on

Regulated-rectifier

This was a huge help. Thanks!

[316jughead]

HOSS.....ya don't miss a beat old son!!!

He said it so much better than I did, that has happened a lot to me.

[ChampioNman]

He is a finagler extraordinaire.

[316jughead]

He is a finagler extraordinaire.

That might be one of those "it takes one to know one" things.

[SEAHORSE]

He is a finagler extraordinaire.

Does anyone have a dictionary that I can borrow?