Light Dimmer and Motor Controller


Occasionally, there are times when you would like to control the lighting brightness in the cabin-intimate settings, night sailing without adequate red lights in the cabin, or just to conserve batteries.

To understand how light dimmers work, first we need to understand how voltage affects light bulbs. The light output from incandescent bulbs decreases with lower voltage (voltage ratio to the 3.5 power). In addition, the lifetime of the bulb goes up with reduced voltage (by the voltage ratio to the 12th power).

A conventional household AC light dimmer will not work with the DC electrical system on your boat. For DC systems, the traditional way to reduce light output is to place a rheostat in series with the lamp. The rheostat introduces additional resistance into the lamp circuit, thereby lowering the voltage at the lamp. However, the additional resistance creates heat that wastes power from your batteries.

Another technique is to chop the voltage to the lamp. One technique, called Pulse Width Modulation (PWM), uses a fixed chopping frequency, but varies the duty cycle (i.e., the ratio of on time to off time), thereby controlling the available power at the lamp. The advantage here is little wasted heat, thereby saving battery power at low illumination levels.

Reddford Technologys DC Dimmer/Controller is an aluminum heatsink that uses a PWM to allow you to control the brightness of one or more lamps that are on a single circuit breaker or fused circuit. The 3.50″ x 2.88″ x 1.32″ module is inserted in series with either the positive or negative circuit feed. All you need is to cut one wire and connect the two wire ends to its screw clamp terminals.

For controlling the brightness, the module has two switch inputs. One input controls the lamp brightness and the lamp on/off. If the second input is used, it works in conjunction with the first switch to give additional lighting options.

In addition to lighting control, the module will also control speeds of DC brush-type motors, such as a cabin fan. The module will not control the brightness of fluorescent lamps.

The module does have some peculiarities. We found the two-input switch concept difficult to get used to (where one seems to work just fine in home light dimmers). The good news is that the module will work fine with just one switch input. Secondly, the module does not remember the last level setting. When power is first applied to the module (such as switching on the cabin lights circuit breaker), the module comes on with the lamp intensity set at full power.

PWM circuits, especially those switching power, have a tendency to produce electromagnetic interference (EMI). A quick cursory check of EMI emissions from the module with an AM radio showed that there is interference at low lighting levels at the low end of the AM radio band. This EMI may interfere with RDF or Loran equipment. We recommend not mounting the module near any radio receiving equipment. Price is $119.95. (Reddford Technology, Inc., PO Box 1316, Coeur dAlene, ID 83816; 208/666-1955.)

Cycle Flush
Few problems aboard boats are as common, and offensive, as the odors of human waste in the head. Its enough to keep some people off boats altogether. Over the years, weve written about many products that can help, including replumbing with rigid PVC and in-line deodorizers.

Russell T. Tritico, Sr., believes he has solved the head odor problem with his CycleFlush. Disappointed with in-line hose deodorizers (see our test, March 1, 1996, of the Earth Safe, Tank-Ette and Mar-Flush), he came up with an electronic box and small in-line pump that flushes the toilet for six seconds every six hours. It does not operate the toilet pump nor fill the holding tank. Features, according to Tritico, include a microprocessor control, dual relay for reliability, on-off switch, built-in test mechanism, flashing light to indicate operation or status, and easy installation.

Head odors emanate from a variety of sources, including toilet bowl, hoses and holding tank. Bowl odors are mainly offensive in saltwater, due to the thousands of critter corpses floating therein. Perhaps the major cause, however, is that waste stuck in hoses, usually at low-points, eventually permeates the walls. Periodically moving water through the system is bound to help. Generally we like to test each product before writing about it, but in this case we didnt, mostly because our head doesn’t stink. It should work. We all know that when on the boat, with the toilet being used and flushed at least several times a day, head odors are minimized. (It doesn’t hurt that the hatches are open, too.)

Drawbacks include having to leave the seacock open (we like to close ours when we leave the boat) as well as an electrical source on.

Price is $129.95 with a 90-day warranty. Feedback from readers who have or may use this product will be appreciated. (Tritico Enterprises, 714 Pujo St., Lake Charles, LA 70601; 318/436-6648; [email protected].)

No-Foul Sonic Transducer
How long does your knotmeters paddlewheel operate freely before fouling? Ours lasts but a few weeks after launching each spring, then barnacles and other marine organisms attach themselves and the wheel comes to a screeching halt. You notice this while sailing with friends when one calls your attention to the display. Hey, it says were doing zero!

Transducer manufacturers (Airmar Technology in Milford, New Hampshire, is the principal maker) expect this, so give you a plug to jam in the through-hull tube while you pull out the paddlewheel for cleaning. Its an anxious moment, wondering how much water will enter before you slam the plug in place. And if youre inclined to paranoia, you might also wonder what happens if a) the plug doesn’t fit, or b) you are suddenly incapacitated by a seizure or cardiac episode. Your boat is going to fill with water and you might drown, thats what.

Due to the difficulty of accessing the paddlewheel from inside the boat, we sometimes cleaned ours by diving, but thats not always feasible.

There is, as well, the issue of drag, which drives racers crazy. Hence, there are several flush-hull transducers available, one from B&G, which is part of an integrated instrument system, and another, the VDO Doppler, which we tested in the June 1, 1995 issue. The VDO Doppler worked fine, but is better suited to powerboats as it doesn’t have very good resolution at slow, sailboat speeds.

Then we noticed a small company called Kaytek Marine advertising the flush-mount Kaytek K-200 Speed Sensor. We called and talked with Karl Masreliez, who said hes sold a number, including one to an Americas Cup contender. We ordered a sensor and installed it on Viva, our Tartan 44 test boat, replacing the paddlewheel transducer that came with our Navico Corus knotmeter.

The K-200 consists of two components, the transducer and an electronics box. Standard cable length connecting the two is 20 feet. If you have an existing knotmeter and transducer, tell Kaytek what you have and youll be supplied with a new transducer that simply fits into the existing through-hull. Its a snap.

The cable has three twisted pairs of wires with a common shield; each wire goes to a terminal inside the electronics box. Instructions in the Kaytek manual are clear.

A bit more problematic is grounding the transducer (or, alternatively, the electronics box) to a seawater ground. Fortunately, we had a keel bolt that was already drilled and tapped for a small machine screw to ground the Loran.

The electronics box should be mounted on a vertical surface. We mounted ours on a bulkhead under a dinette seat. Positive and negative wires are connected to a 12-volt power source, such as the electrical distribution panel. This, too, is easy.

The more challenging part of the installation is connecting the existing knotmeter display to the electronics box. This is done by cutting the old paddlewheel transducer cable and leading the five wires to terminals in the electronics box. The manual has good instructions and a diagram.

The last step is to program the speed output pulse rate by setting the five dip switches off or on. A table in the manual shows you which combination of switches approximates the nominal output pulse rate of your old paddlewheel sensor. If you don’t know this figure, check the old manual, or call and ask Karl. Overall, we found installation easy.

There is a test speed function to verify the correctness of the settings. Your actual knotmeter can be calibrated for any errors according to its usual procedure. We used a GPS, but another method would be to run a measured mile, in both directions, and average the results.

The Kaytek sensor did not foul during the entire sailing season in New England. You can coat it with antifouling paint.

Price of the K-200 Speed Sensor is a hefty $695, but this is an extremely well-made, high quality product that should provide years of trouble-free, accurate service. (Kaytek Marine, 14606 SE 50th St., Bellevue, WA 98006; 425/644-2638.)

Darrell Nicholson
Practical Sailor has been independently testing and reporting on sailboats and sailing gear for more than 50 years. Its independent tests are carried out by experienced sailors and marine industry professionals dedicated to providing objective evaluation and reporting about boats, gear, and the skills required to cross oceans. Practical Sailor is edited by Darrell Nicholson, a long-time liveaboard sailor and trans-Pacific cruiser who has been director of Belvoir Media Group's marine division since 2005. He holds a U.S. Coast Guard 100-ton Master license, has logged tens of thousands of miles in three oceans, and has skippered everything from pilot boats to day charter cats. His weekly blog Inside Practical Sailor offers an inside look at current research and gear tests at Practical Sailor, while his award-winning column,"Rhumb Lines," tracks boating trends and reflects upon the sailing life. He sails a Sparkman & Stephens-designed Yankee 30 out of St. Petersburg, Florida. You can reach him at