Boat Show Blues
When this mailing goes out we will be exhibiting at the Miami Strictly Sail, which is part of the mega Miami International Boat Show. Now don’t go thinking that we do this just to buff up on the tan during a bleak Maryland winter, oh no. No, this is purgatory. This is some form of evil punishment hoisted on us, probably for being so slack and slovenly during the slow winter sales season.
Our German suppliers refer to boat shows as “fairs”, which to me conjures up images of riding prettily painted uppy-downy horses on a glittering merry-go-round while eating cotton candy, but sadly that is mere fantasy.
OK, so it is nice to get away from the office, pull on a pair of shorts and give the old pins an airing, but “doing” these shows is expensive, takes a lot of organizing and planning, and they are physically and mentally exhausting.
So why on earth do we bother?
Serious Solar for your boat or RV
A while ago I debunked some common misconceptions about solar panels in another blog here, but it seems I missed one that has come to light several times recently, i.e. the myth that to have proper, serious, useable solar power on a boat one must use residential panels, as marine solar panels are just itsy-bitsy wimpy battery top-up trickle-chargers.
Nothing could be further from the truth!
It's that darn flasher again!
Inner Secrets of the Danfoss/Secop BD35/50 Motor Controller (aka Module)
Well I can't actually give away any real secrets, because I don't think anyone really knows what goes on under that mysterious black plastic shell except for the manufacturer, but I do know a fair bit about what can and does go wrong with them.
But first let's take a step back and recap on what the little black box actually does.
The current generation of small, mobile refrigeration compressors from Secop (formally Danfoss) utilize a very simple motor with just three equal windings and no brushes or slip-rings. These three windings terminate in three pins that protrude from the compressor shell and connect to a push-on plug connected to the controller.
It's the controller's job to take the 12v or 24v DC input and spit it out in sequence to each of the windings in turn, causing sufficient torque to turn the rotor and so push the piston in and out compressing the refrigerant gas. So the motor actually gets a modified DC signal, a form of AC in fact, and by varying the rate of delivery of the signal to each winding and effectively altering the frequency, we can make the motor turn at different speeds.
That's it. All pretty simple in theory. As a means of altering compressor speed, the controller uses the switched input from the thermostat, and by adding resistance to this circuit it alters the speed at which the compressor will run.
So what could possibly go wrong?