Tag Archives: pwm

Frugal Boater: Keeping it Cool

Although we have air conditioning on Pearl Lee we don’t often go to marinas and don’t want to run the generator and air conditioner 24×7. Any HVAC (Heating, Ventilation, and Air Conditioning) professional worth his salt will tell you that three factors effect our comfort. Air temperature, humidity and velocity. Without running the air conditioner we can’t control the first two, so we work on the third, velocity.

Pearl Lee has four hatches and 21 opening ports, all with screens. In the summer,  inside temperature is rarely more than a degree or so warmer than the outside air, unless we have to close up due to rain. When there is just a light breeze our Davis Windscoop helps a lot.

We also have fans, lots of them. We’ve installed six of these little oscillating fans in strategic locations. We have two more that clamp on for temporary use. They work well, even though they only have one speed, but the oscillating action can be turned on or off. Our oldest fans are about 5 years old, with one year of full time living aboard, and still going. We also have a 10″ O2Cool fan in each stateroom. They work well, but I can’t recommend them because a recent revision has made them 9 volt fans instead of the older 12 volt model.

Our biggest problem was a lack of ventilation where we sleep, the aft stateroom. Hatch airflow is mostly blocked by the cockpit and mizzen mast. Although there are six opening ports, they don’t catch much breeze either. So, inspired by another cruiser, I built this hatch fan.

It’s a 16″ radiator “pusher” fan rated at 1400 CFM (Cubic Feet per Minute) of airflow. That’s a lot of air, but at the price of noise and power (about 10 amps). So I added a PWM (Pulse Width Modulation) controller. This little device controls fan speed by turning power on and off 15,000 times per second. Speed is controlled by regulating the ratio of “on” time vs “off”. The box is just a plastic project box, shown here open. I drilled the side holes for ventilation because PWM’s do give off a little heat.

With the fan dialed back from “landing helicopter” to “pleasant breeze” the fan only draws about one amp and is whisper quiet. We can dial in any speed we like, and even flip the whole thing over for use as a whole boat exhaust fan. Our retractable internal screen still works, so bugs stay out.

We use a two conductor trailer plug for quick connect/disconnect, and the entire thing can easily be deployed from inside the boat. One last tip, when buying from Advance Auto Parts you can usually get a discount by purchasing online and then picking up the order (often right away) at your local store.

Here’s to summer breezes, both natural and artificial!

Frugal Boater: Solar Charge Controller Basics

With all but the smallest of solar panels, you’ll need a charge controller. A charge controller goes between the solar panels and the batteries. It’s job is to limit, or control, the power your panels put into your batteries.  This keeps you from destroying expensive batteries by overcharging. There are two types charge controllers.

Power Width Modulation (PWM) controllers are relatively inexpensive. They work by literally switching the panels on and off very rapidly. That works fine as long as your panel voltage is fairly close to your battery voltage. If you’re a weekend boater who just wants a small panel to keep your battery topped up while you’re away, a PWM controller might do the job. Using a PWM controller will limit the size panels you can use because they don’t have the capability to change the voltage, only turn it on and off.

Multi Power Point Tracking (MPPT) charge controllers are a big step up in performance  and price. These controllers actually adjust voltage/current in an attempt to wring the most power out of your panels. They also have the capability to step the panel voltage down to whatever your batteries need. An MPPT controller takes the 60 volts coming in from our panels and steps it down to our battery charging voltage (around 13.5). When the voltage comes down the amps go up, so very little power is lost in the controller.

Beware of cheap “MPPT” found on Ebay and the like. Some are actually PWM  controllers with “MPPT” printed on them. Since the charge controller is the heart of your system, and could prove dangerous to you and your batteries, it’s best to stick with a quality unit from a reputable manufacturer.

A standard system with one MPPT controller is striving to optimize all panels, meaning that during partial shading some panels are running higher and some lower than optimum. No panels are really performing their best because the controller is working with an average. This is where MPPT optimizers on each panel can be useful. In an environment where shading is unavoidable, this allows each panel to work independently for optimum results. Obviously no two systems and shade scenarios are identical, but tests with optimizers show that during partial shading power output can be increased by 15-25%. In an environment where partial shading can’t be avoided, and space is limited this can be important. That sounds a lot like a sailboat doesn’t it?

Related articles:

Solar Panel Basics

Pearl Lee Solar 1.0

Pearl Lee  Solar 2.0