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Author Topic:   Voltage Regulator for Outboards
whalerron posted 01-01-2001 11:45 PM ET (US)   Profile for whalerron   Send Email to whalerron  
I was wondering if anyone has heard of a voltage regulator for outboard motors. Apparently, many outboards have no voltage regulation and this allows the voltage to run anywhere from 12 to about 18 volts depending on the engine RPM. I have been told that there is a voltage regulator that can be mounted somewhere on the boat and it will limit the voltage to the 12 - 15 volt range. But, the person who told me about this didn't know where to find such a device. I have a 1975 70hp Johnson and I need to limit the charging voltage so that I don't fry my new electronics. I would be happy with device that I could mount in the console and it would be used to regulate the voltage to my depth finder and vhf....

- ron

- ron

jimh posted 01-02-2001 12:25 AM ET (US)     Profile for jimh  Send Email to jimh     
What I would do:

Install an external voltage regulator, using an off-the-shelf part like a Motorola 7814 3-terminal regulator in a TO-3 Case.

Mount the case to a heat sink. Connect the unregulated (+) voltage to the input terminal, and the common to the case. Get the regulated output voltage (+) from the output terminal.

This type of regulator costs about $2 and is good for up to a couple of Amps. They also make higher current ones, too, for more money.

If you add an input filter capacitor you can smooth out some of that alternator whine and ripple, too.


whalerron posted 01-02-2001 11:03 PM ET (US)     Profile for whalerron  Send Email to whalerron     

I am a software engineer by trade but I have some electronics background too. This seems easy enough to build but where do I buy that regulator and what is a T0-3 case? Are these Radio Shack parts?


triblet posted 01-03-2001 10:05 AM ET (US)     Profile for triblet  Send Email to triblet     
Are you sure you got the part number right?

An Alta Vista search on
+7814 +voltage +regulator
got nothing but noise.

Also, watch out if you are going to use this
to supply your VHF. A VHF needs a little
over 2 amps when transmitting. You should
heat sink it real well, and I think I'd
test it (using a power resistor) for
half an hour or so.

Also, if you put a big capacitor on the
output side, it will help keep the electronics
from shutting down when you crank the motor.

All that said, the battery does a pretty good
job of regulating the voltage.

And check your service manual. That motor
is big enough that it may well have a
voltage regulator. My 90HP Evinrude does.

Chuck Tribolet

jimh posted 01-03-2001 07:48 PM ET (US)     Profile for jimh  Send Email to jimh     
7814 = 14 volt regulated output, harder to find than the 7812, 12 volt regulated.

Don't put the capacitor on the output of the regulator. If the output voltage is ever higher than the input voltage the regulator self-destructs. So put the filter on the input.

The recommended circuit includes a diode connecting input and output, cathode to input, so that if the output voltage rises above input the diode conducts.


triblet posted 01-03-2001 09:45 PM ET (US)     Profile for triblet  Send Email to triblet     
Near as I can tell from their website,
Motorola doesn't make DC voltage regulators.

Fairchild makes an MC7812 (12v) and an
MC7815 (15v) both rated at 1A. I found
other references to xx78x12s, all at .5A
or 1A. No xx78x14s at all.

It should be possible to use a 12v regulator
and a diode in the right place to shove the
reference voltage ground up a volt and a
half or so.

I'll check with the analog wizard at work
tomorrow. He just went through something
similar on his bicycle lights.


whalerron posted 01-03-2001 11:05 PM ET (US)     Profile for whalerron  Send Email to whalerron     
triblet - Nah, this motor has definitely has no regulator on it. Of course it has a rectifier but no regulator. Apparently this is a fairly common setup on outboards so I am kind of surprised that nobody makes a regulator that would go in a console.

If I build a unit, I am probaby going to need one that supplys at least 5 amps. That should cover the depth finder and the VHF.

- ron

triblet posted 01-04-2001 01:07 AM ET (US)     Profile for triblet  Send Email to triblet     
The reason nobody makes a regulator is
two fold:

- The battery makes a pretty decent
regulator. The excess current (and there
isn't much as most outboard alternators
are pretty wimpy) just goes into the

- Until recently, the chips to make an
external voltage regulator weren't too
common. At about the same time, the
manufacturers started putting regulators
on their new outboards (as I said, my
1997 Evinrude 90 has one). So no market.

Also, I just checked the manual on my VHF
(Standard Horizon Spectrum). It says 6A
while transmitting. But I remember that
my fishfinder is way less than 1A.

I'd suggest hooking up a battery to your
alternator and seeing what happens to the
voltage before I started building electronics.


whalerron posted 01-05-2001 12:35 AM ET (US)     Profile for whalerron  Send Email to whalerron     
triblet -

I checked the voltage right at the terminals on my battery with a voltmeter. We did this at idle, half throttle, and WOT. At idle and upto about 1/2 throttle, the voltage stayed under 15 volts which is good. At WOT, the voltage went to 18 volts and that shutdown my depthfinder. If I turn the lights on, the voltage pulls down to about 16 volts at WOT so I agree with you that the alternator is pretty wimpy.

My brother has a Johnson 65hp (1972) and his behaves identically and both act like the dealer told me they would. My brother has built a regulator but he hasn't had the warm weather necessary to test it. I was hoping to find an off the shelf unit but I guess that isn't going to happen. I would like to see a schematic and parts list for this if you have them. After checking on my equipment, I need a unit that will give me at least 10 amps regulated.


jimh posted 01-05-2001 09:07 AM ET (US)     Profile for jimh  Send Email to jimh     
According to the 1992 Edition of the "Motorola Master Selection Guide", they made all kinds of voltage regulator ICs, but maybe they don't any more in 2001.

The "MC" in the MC7812 came from Motorola.

The 7814 part is gone. So is the T0-3 case,
which was easiest to mount.

The most current you can get from these is 3.0 A. There are some specialty parts that can supply more current, but they tend to be much more expensive. The 78XX series costs less than a buck, usually.

triblet posted 01-05-2001 10:55 AM ET (US)     Profile for triblet  Send Email to triblet     
10 amps is going to be hard.

The analog wizzard recommended looking at
Maxim parts.
He says you want an "inductor-based stepdown
DC-DC powersupply"
like the MAX1745 or MAX724, but that's only a
5A part, and shuts down at 6.5A.

These are switching regulators and are
very efficient, unlike the MC7812 which is
a linear part.

There are schematics on Maxim's website.

I'll check with him later today to see if
he has an idea for more current. MMM, one
thought would be to use two, one for the
VHF and one for everything else. And check
the specs on your VHF -- some marine
electronics are quite happy with fairly
high input voltages -- I've owned something
that was happy to thirty-something volts.

Chuck Tribolet

Steve Leone posted 01-05-2001 12:54 PM ET (US)     Profile for Steve Leone  Send Email to Steve Leone     
Dear Sirs, The fellow that mentioned the battery being the regulator is correct. Although If you are really worried about excessive voltage going to ANY electronics there is the option of instaling an inline resistor before the aforementioned electronic. Ballast resistors were used on old style mag ignitions to reduce the voltage to the coil. I would think the same technology would work here. Your Pal in El Cerrito, Steve. PS Does anyone have a phone number for Mills (the canvas folks) ?
triblet posted 01-05-2001 04:07 PM ET (US)     Profile for triblet  Send Email to triblet     
A ballast resistor going to the VHF would be
a bad idea. The VHF pulls MAYBE an amp when
receiving, and 6A transmitting. When the
current goes up, the voltage drop across the
ballast goes up, so the voltage at the radio
goes down.

At least part of the reason for using a
ballast resistor on a Kettering (points,
capacitor, coil) ignition is that when
you are cranking the starter, the ballast
is bypassed, so the coil still sees a
decent voltage even though the starter has
pulled the battery voltage down around
6-8 volts.


triblet posted 01-05-2001 08:15 PM ET (US)     Profile for triblet  Send Email to triblet     
I couldn't find the analog wizard today.

I did a little more research.

My Standard Horizon VHF is rated at .5 AMP
standby, 1.5 amp receiving, 6A transmitting.
123.8V +- 20% (11.04 to 16.56V)

My Apelco 5200 (now Raytheon 5200) VHF
was rated about the same, except that the
voltage spec was +-15%. And add one more
spec: "don't get it wet". ;-)

My Garmin 162 is rated at 4W max (.29A at
13.8V), 10-40V DC (Attaboy, Garrmin).

I can't find the specs anywhere on my


jimh posted 01-05-2001 11:18 PM ET (US)     Profile for jimh  Send Email to jimh     
You can wrap a 3-terminal voltage regulator around a "pass" transistor to get higher current capabilities. A $1 transistor like a 2N3055 can handle up to 15 A.

These circuits are usually shown in the regulator data book.


lhg posted 01-08-2001 01:28 AM ET (US)     Profile for lhg    
My 1985 Merc 115's came without voltage regulators, but Mercury offered an optional voltage regulator kit for this engine. Back then they cost about $90 each. I installed them myself and they work just fine. Do not use a sealed battery without a voltage regulator installed. I'll bet OMC also offered regulator kits, but considering their situation these days, you may not be able to obtain one. Might give it a try, however.
Whaletosh posted 01-08-2001 09:03 AM ET (US)     Profile for Whaletosh    
Let me throw in my 2 cents. For the record I have made my living as an electronics/computer tech for the past 15 years.

First, the LM78xx series is a good regulator for most circuits. The problem is that it has a fairly high drop out voltage. Drop out voltage is the voltage level of when Vin -Vout will cause the regulator to stop regulating. On a LM78xx series regulator that voltage is usually 1.5 volts. That means that a LM7812 (MC7812 is the same) won't regulate if unless the input voltage is 13.5 volts or higher.

In this case the drop out voltage isn't really concern. Ron just wants to prevent overvoltage. Input voltages that would cause the regulator to dropout of regulation will just not be regulated. This won't harm the regulator or the GPS, fishfinder, etc.

If one wants to insure regulation then I would suggest looking at Linear Technology. They have a whole series of low dropout regulators, as well as some higher current units. Maxim has some as well.

another approach that could be used ist oinsert some common rectifiers in series with the positive lead. All diodes have a forward voltage drop, usually .7 to 1 volt. Put a couple in series and you have a voltage drop of 1.4 to 2 volts. The only problem is that the voltage drop is there alll the time, regardless of the speed of the motor.

Having said all that, using a seperate deep cycle battery for you electronics is a better option if you have the room. A small deep cycle unit has the following advantages:

1) Overvoltage is almost impossible unless a battery switch is employed. On a small, trailered boat I wouldn't bother with the switch. I have never had a problem with a fully charged battery lasting for a weeks vacation of fishing and boating. so I just charge the deep cycle when I get home.

2) electrical noise from the motor will be greatly reduced.

3) you don't need to worry about draining the starting battery.

If one does use a seperate battery, make sure that one runs a good stout cable from the negative terminal of the deep cycle to the negative of the starting battery. Use a 10 to 8 gauge marine grade wire. It is very important for all of the 12 volt "grounds" to be bonded to true ground. True ground on an outboard is established with the metal parts of the motor; although and actual grounding bar on the transom of the boat is better. This provides safety.

triblet posted 01-23-2001 11:04 PM ET (US)     Profile for triblet  Send Email to triblet     
Here's your answer.

Humminbird has a new product called Surevolt.
Put in 6 to 25 V, 13 V comes out. It puts
out 1.2 amps, so it won't run the VHF, but
it will run everything else. Details at



triblet posted 01-27-2001 03:38 PM ET (US)     Profile for triblet  Send Email to triblet     
I ordered up a Surevolt, (my fishfinder
shuts down everytime I start the engine)
and it arrived.

It's the ugly Hummingbird yellow.

I'm not impressed with the gasketing. The
base is gasketed and held on by the friction
of the gasket. Once you screw the box to
something, the bottom will be held on.
Anyway, when I install it, I'm going to put
some silicone on the joint. I popped the
bottom off, and they did seal where the
wire's go in and out with silicone or some


triblet posted 01-31-2001 09:56 AM ET (US)     Profile for triblet  Send Email to triblet     
I got an e-mail back from Humminbird about
my Wide 3D Paramount:

"The power draw will be 1/4 of an amp per
hour with the lights on."

Duh, "per hour" has nothing to do with it.


whalerron posted 02-01-2001 10:00 PM ET (US)     Profile for whalerron  Send Email to whalerron     
Couldn't you use the amp/hour rating to figure out how long a battery would last assuming that the battery was not been charged? They usually rate batteries in amp/hours I think. Of course, nobody really knows what they meant when they said 1/4 amp per hour. They could have meant this or they might be just goofed....
triblet posted 02-01-2001 11:27 PM ET (US)     Profile for triblet  Send Email to triblet     
If you want to figure out long the battery
will last, divide the battery amp-hours
by the device amps. 60 amp-hour battery
divided by 1/4 amp device means 240 hours.
(Kinda sorta, it isn't really that simple,
but that's the first order approximation).

amps per hour would be a rate of change
in the amperage.

Chuck, Electrical Engineer by training,
software engineer by profession.

triblet posted 02-03-2001 07:47 PM ET (US)     Profile for triblet  Send Email to triblet     
Since Neptune is throwing a small tantrum
today, I installed the Surevolt and
reorganized all the accessory wiring in
the console, which I'd been meaning to do
for a while -- it was suffering from wiring
entropy after replacing all the electronics
last spring.

The Surevolt has plus and minus input wires
and plus and minus output wires. I had a
hunch that the two minus wires were tied
together and my DVM says they are. This
simplifies installation because you don't
need a separate ground bus bar for the
Surevolted devices (three in my case).
I used the existing ground bus and it
runs fine.

It passed smoke test and an hour's burn-in
in the garage today. It looks like Neptune
is going to calm down tomorrow, so I should
get to try it for real.


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