Re: [OMC-Boats] Historical Info on Ballast Resistors

Hi Jeff,

I'm not clear what you mean by "called it quits?" Can you more accurately describe the malfunction? I'm pretty certain the early OMC/Johnson 17's used the potted or sealed device you speak of for multiple purposes. (Don't have a wiring diagram handy to check). What have you done to measure or test the unit?

So from your description I think it does a lot more than simply act as a resistor to reduce voltage from 12 to 6 volts. The OMC/Johnson 17 used an innovative automotive-inspired instrument panel, which required some innovative design accommodations, not typically seen today.

a) It was pretty common in the late fifties-early sixties timeframe to use external voltage regulation on fuel gauges and temp gauges in automotive applications. This was done so the accuracy or reading of the gauges did not vary with the output of the alternator. You wouldn't want to see the gauges changing as a function of engine RPM!

b) Also Tachometers essentially measure ignition (or alternator in some cases) pulses over time to determine engine RPM. The original OMC 17 came with a 2-stroke engine, not 4-stroke I/O.. And it had 4 cyl not 6 or 8. So the device you speak of also has internal circuitry to accommodate different engine configurations, but still allow a common instrument to accurately read back. Later model (from about 65-66-onward) OMC boats used tachometers that could accommodate these settings without the external device that you boat used.

c) This is a specialized part that you won't easily come across. The solution is to reverse engineer it and built your own from common electronics parts available at your corner Radio Shack. Basically you need to drive the tachometer pulse signal properly and supply the regulated voltage to the fuel gauge. (The current measuring ammeter does not require regulated voltage.) Or alternatively you can replace the original instruments which would ruin the character of your 17's unique instrument panel.

________________________________
From: heavy [mailto:heavy@...]
Sent: Thursday, June 10, 2010 11:34 PM
To: Lee Shuster
Subject: re: [OMC-Boats] Historical Info on Ballast Resistors

Hi Lee,
I'm aware of the Ballast resistor located on my 64 Johnson Deluxe's engine (v6 155hp), but it seems now the voltage regulator under my dash has called it quits after 50 years. It sits up next to my fuse panel and takes a 12v to 6v. It has settings for a 6cyl or 8cyl and has 4 wires going into the instrument panel (fuel gage etc.) It has numbers of 7666H91 and looks like a little clay brick.

Question is, what can I replace this with, it seems a little different than the VR on the engine. Will any 12v to 6v VR do?

thanks,
Jeff

________________________________
From: "Lee Shuster" <Lee.Shuster@...>
Sent: Thursday, May 13, 2010 9:38 AM
To: "Evinrude & Johnson Boats of the 1960's and 70's" <omc-boats@...mate.com>
Subject: [OMC-Boats] Historical Info on Ballast Resistors

Actually you are all making good points here about ballast resistors but there is additional historical information that may be interesting and insightful.....I

n the early-to-mid fifties Detroit began introducing more powerful engines. Chrysler had their famous Hemi, while GM and Ford also introduced high-compression OHV V-8's. The horsepower race was on and many of the ideas were gained from the engine advances of Word War II (piston-powered) aircraft.

When you increase the compression and number of cylinders it becomes a more difficult challenge to start engines, using the traditional Kettering 6-volt starter system. (BTW, Kettering is the same guy who pioneered the battery-Ignition-using coil-points-distributor to replace the magneto.)

 the 1954 - 1956 timeframe most Detroit engineers began upgrading electrical systems from the traditional 6 volt systems to the now standard 12-volt systems. If you understand Ohms Law, ( E = I * R, see: http://www.the12volt.com/ohm/ohmslaw.asp ) increasing the potential voltage offers several significant advantages.

When automotive electrical systems were moving to 12-volt designs, some bright engineer discovered you could continue to use existing 6-volt coils in combination with a relatively inexpensive ballast resistor. Adding the 'BYPASS" circuit to the starter also gave the beneficial short-term "BOOST" for lighting off the higher compression engine. After the engine was done cranking the coil and points could revert to operating closer to it's earlier 6-volt design limits. Since the ballast resistor acts to limit electrical current to the primary side of the coil and thru the contact breaker points before returning to the battery via the common ground path, the life-cycle of all components in the chain is extended. But not all Detroit manufacturers used external ballast resistors -- some incorporated the resistor inside the coil.

Once you move into the early to mid-seventies when long-term emissions began to be a concern we started seeing the adoption of breaker-less or electronic ignition (EI) systems. The famous GM HEI system incorporates the coil and distributor into one unit. And permits higher secondary voltages, which allows greater spark plug gaps,

The Pertronix breaker-less EI products (Ignitor, Ignitor II, Ignitor III) can be combined with their various Flame Thrower Coils. see: http://www.pertronix.com/prod/ig/flame/coils/chart.aspx<http://www.pertronix.com/prod/ig/flame/default.aspx>

I've used the Ignitor II EI with an internally ballasted Petronix 45,000 volt coil for the past three-seasons, with excellent results. I have retained the original Mallory (marine-rated) distributor, but no longer have a need for the OE ballast resistor. The system retains a stock look, but provides modern HEI efficiency and long-term, hassle-free reliability,

History class is now dismissed......;-)

Lee
Received on Friday, 11 June 2010