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ContinuousWave: Whaler Repairs/Mods
Voltage Regulator for Outboards
|Author||Topic: Voltage Regulator for Outboards|
posted 01-01-2001 11:45 PM ET (US)
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....
posted 01-02-2001 12:25 AM ET (US)
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.
posted 01-02-2001 11:03 PM ET (US)
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?
posted 01-03-2001 10:05 AM ET (US)
Are you sure you got the part number right?
An Alta Vista search on
Also, watch out if you are going to use this
Also, if you put a big capacitor on the
All that said, the battery does a pretty good
And check your service manual. That motor
posted 01-03-2001 07:48 PM ET (US)
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.
posted 01-03-2001 09:45 PM ET (US)
Near as I can tell from their website,
Motorola doesn't make DC voltage regulators.
Fairchild makes an MC7812 (12v) and an
It should be possible to use a 12v regulator
I'll check with the analog wizard at work
posted 01-03-2001 11:05 PM ET (US)
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.
posted 01-04-2001 01:07 AM ET (US)
The reason nobody makes a regulator is
- 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
I'd suggest hooking up a battery to your
posted 01-05-2001 12:35 AM ET (US)
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.
posted 01-05-2001 09:07 AM ET (US)
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,
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.
posted 01-05-2001 10:55 AM ET (US)
10 amps is going to be hard.
The analog wizzard recommended looking at
These are switching regulators and are
There are schematics on Maxim's website.
I'll check with him later today to see if
posted 01-05-2001 12:54 PM ET (US)
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) ?
posted 01-05-2001 04:07 PM ET (US)
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
At least part of the reason for using a
posted 01-05-2001 08:15 PM ET (US)
I couldn't find the analog wizard today.
I did a little more research.
My Standard Horizon VHF is rated at .5 AMP
My Apelco 5200 (now Raytheon 5200) VHF
My Garmin 162 is rated at 4W max (.29A at
posted 01-05-2001 11:18 PM ET (US)
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.
posted 01-08-2001 01:28 AM ET (US)
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.
posted 01-08-2001 09:03 AM ET (US)
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.
posted 01-23-2001 11:04 PM ET (US)
Here's your answer.
Humminbird has a new product called Surevolt.
posted 01-27-2001 03:38 PM ET (US)
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
posted 01-31-2001 09:56 AM ET (US)
I got an e-mail back from Humminbird about
my Wide 3D Paramount:
"The power draw will be 1/4 of an amp per
Duh, "per hour" has nothing to do with it.
posted 02-01-2001 10:00 PM ET (US)
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....
posted 02-01-2001 11:27 PM ET (US)
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
posted 02-03-2001 07:47 PM ET (US)
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
The Surevolt has plus and minus input wires
It passed smoke test and an hour's burn-in
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