Voltmeter reads 16 at speed?

[skyguy.r]

It is a 1990, 40 HP Mercury, serial number ODO19542. How might I tell if the charging system shoud be around 14 Volts, or is 16 OK. I see, not measure, 16 volts at speed. I undersand that 16 is expected on some systems. Is there a rectifier/regulator combination I can identify without disassembly or a rectifier only I can identify without assembly? I'm worried about 16 volts on the gage and I assume the battery as well. I did not think that was allowed on a 12 volt battery.

Firstime poster,
Ray

 

[sam am I]

For that serial number, the parts houses say for the stock motor, it has the separate rectifier, voltage regulator setup. Therefore, assuming this info is correct, It should w its regulator properly functional, not exceed 14.5'ish volts.

BTW, :welcome:

 

[skyguy.r]

Good news, Bad news. Bad: gotta problem to fix. Good: I know I got a problem and can correct it. (Thanks sam I am)

From the links on this site, the regulator looks square, with 3 leads, mounted on something that can sink heat. Is it hidden in the motor control box? Do I need thermal paste?

 

[sam am I]

yvw, not sure where it's at, could just follow the yellow brick.......errr, the yellow wires from the stator. Thermal paste? Well, I don't think it's a "critical requirement", but I'd slap some on just for grins if ya got a tube laying around. Can't hurt eh?

BTW, do you have a known good volt meter you can double extra check it w before, ya know, before ya start buying parts? Perhaps you see 12'ish volts w the motor off is sufficient enough.

 

[skyguy.r]

I found the location of the regulator with the help of this post: 96 40HP Merc bad rectifier/regulator

sam i am, I will use my voltmeter and check if the voltatge measued at the batery matches the voltmeter gauge with engine off and key turned. If I get a match, I dig up an inspection procedure I recall seeing.
Before I suspected 16 V was bad, I ran it for an hour at 16 volts and may have taken out my gas gauge. The gas gauge bounced alot then began to read way below empty.

 

[skyguy.r]

My digital miltimeter reads either "off the scale" MOhms or 1 to 3 MOhms depending on the polarity I check with.

I gotta assume 1 to 3 Meg ohms indicates "continuity"? If so, I'm stumped cause it checks out good.

 

[sam am I]

I will use my voltmeter and check if the voltatge measued at the batery matches the voltmeter gauge with engine off and key turned. If I get a match

What are you checking on ohm scale? I thought you were checking voltage?

If the gauge and voltmeter are saying same thing(i.e., 16V running, 12V not).......The regulator is most likely toast. You can get a rec/reg all in one package to replace the separate rec, reg gig. Probably good idea'r to replace both bout now anyway eh?

 

[skyguy.r]

sam i am, I disconnected the ground on the battery. It reads almost 13 volts, btw. I disconnected the wires on the regulator, and leaving it in place, checked continuity between terminals per "internet" instructions on how tho check an outboard motor voltage regulator. All the instructions I found so far use the phrase "check continuity". My question is whether 3 Meg ohms indicates there is "continutiy". I believe it does, even tho I expected much less resistance. Maybe that is expected when putting an ohmmeter accross diodes.

If that high of resistance is expected, I got nothing to go on cause the regulator tests good. All I can do is other put it all back together and see if I still get 16 volts at the battery terminals.

 

[sam am I]

ahhhhhhhhhh, i see i see said the blind man.

Does your meter have "diode check" fuction? If so

http://www.youtube.com/watch?v=dqkT6hF0O3E

and yes, 3 Meg is "continuity" sorta. and yes, you can test diodes on just ohm scale, BUT problem with just "ohms" scale, is the current amount used is so low that the diode won't forward bias too well and ya see that higher resistance. A crapped diode can exhibit that exact thing.........The better/best practice method is,

Use "diode check" and that'll tell ya what the forward voltage drop (Vf), with silicon diodes, ya see around 0.5/0.6V at the meters diode check currents in one direction and "open/OL" when reversed as shown above.

With the package of the full wave bridge rectifier I believe you're testing, the "-" terminal is the metal mounting base

 

[enginepower]

The check continuity instructions is probably referring to check from point A to point B in your wiring. Checking across rectifier is better to use diode check as suggested. Might have missed it during scrolling but did you actually verify that your charging voltage is 16? Could just be an inaccurate gauge.

 

[undone]

And 16 volts shouldn't hurt the gas gauge, they do tend to fail in the exact way you mentioned though.

 

[skyguy.r]

Did not check voltage with multimeter with motor running.
Diode checks show regulator good as confirmed by continuity (3MOhm=OK) checks.
I'll put it back together, put it in a tub and see what I can find out below about 2000 RPM.
Possible clues are flakey gas gauge and a potential flakey volt gauge.
If the battery voltage was truly 16 V for the 90 minutes I ran the motor, I wonder if I toasted the battery? I like the bad gauges theory!
Thanks everyone for making the new guy feel at home.

 

[sam am I]

Put her together, fired it up, run around 1000-1500, turn a few lights on etc to load it a tad, wait a short bit for things to settle .............If meter reads 16V, the reg(and possibly the rec as well) w pre-boiled battery or not, is bad, plain and simple.

 

[undone]

While long term 16 volts isn't good for the battery, running for an hour isn't going to hurt it. There are many motors out there that don't have voltage regulators and they don't kill the battery even after several years of use.

 

[skyguy.r]

Had it idling in a tub of water and measured around 14 Volts at the battery terminals. Increased the RPMs and quickly exceeded 16 Volts at the battery terminals. My conclusion is that even tho my tests showed the regulator good, it is not. I wonder how I killed the regulator? Perhaps on old battery charger is to blame.

 

[sam am I]

24 yr old reg? Hmmmm, I think we'll let you off this time with just a warning

BTW, as I said above, replace the rec while yer there or, get the rec/reg "all in one" package.

 

[skyguy.r]

Yikes. When I thought I was testing the regulator, I was testing the rectifier. So it is the rectifier that tested good and my questions about "continuity" in the posts above were in reference to the testing of the rectifier.
Turns out, I don't even have a regulator. (1990 40-HP Mercury)
At this point I can only suspect the battery. My boat uses two dual purpose marine batteries, two or three years old, with poor maintenance practices. I'm thinking the battery internal resistance is going up and is no longer able to deal with the unregulated charging voltage. I switched to the larger, group 27, battery to start the motor and am hopeful it can better deal with the higher measured voltage at the terminals. My thoughts are that even thou the I will report back any findings/improvements.
Sound good? Make Sense? Safe?

 

[skyguy.r]

Ran 90 minutes with the larger group 27 dual purpose marine battery. With motor running, measured battery voltage started near 14 V, and after fifteen minutes worked its way up to 16 and stayed there. (Pretty much the same as with the smaller battery.) I felt the battery to see if I could notice any warming. No difference that I could tell.
So far I have learned what a rectifier looks like, how to test it and what it takes should I need to replace it. I learned my system is unregulated and to watch what I connect to the starting battery. And, perhaps the biggest thing, the system is running as expected for an unregulated system!
Thanks All

 

[sam am I]

Sounds right on!! As stated earlier, if you're so inclined, it's quite easy to change it over to a regulated system. Might make your present and/or future electronics perhaps happy as some can auto off on ya at certain "over voltage" thresholds, and at the least, probably make your G27 last just a bit longer too!!

 

[inthedirtagain]

Rectifier will only change the signal from the stator from AC to DC, then it gets regulated to 12 +/- volts. A fully charged battery, with no-load, should read approximately 13.2v after the initial charge has settled. Above idle, your charging system shouldn't exceed 14.5-ish volts on a regulated system. On a system that does not have a regulator, the battery and electrical load (demand) of the boat should keep the charging system in check. That is the way many smaller systems are designed.......they need to have a load on the system. If you fully charge your battery prior to heading out, there isn't a load on the system, so an over-charge state occurs. Unless you want to convert to a regulated system (not difficult, nor expensive), you will need to induce a load on the charging system whenever you go out. I've found that keeping the lights on creates enough of a load on the system to mainain 14-ish volts almost all the time when cruising. Watersports and multiple restarts creates enough of a drain on the battery to properly load the charging system, too. I don't like to see north of 15v on my charging system. I had a bad regulator on my old car in high school and had a battery explode due to over-charging. Lesson learned.