On another sail I also got some indication that regen may be occurring earlier than the speed of 6 knots. But, until I can get some type of current meter installed that I can view in the cockpit without opening a hatch and bending down to get the readings I'll have to wait to do more precise observations. But, at least I can now say that regen works and it is just another added benefit of having electric propulsion on board.
Thursday, September 29, 2011
ANOTHER ADVANTAGE OF ELECTRIC PROPULSION: REGEN
It seems every year I discover something new that my electric propulsion system can do. Last year there was the joy of sailing along double reefed at 7 knots SOG while my solar and wind generator were at the same time pumping energy back into the battery banks. Earlier this season I had another epiphany while electro sailing on a pretty windless day. I thought I should probably always electro sail when I sail the boat. Since the prop is going to be turning no matter what unless I install some type of shaft lock but, that would also increase drag and slow the boat down. So I might as well electro sail by turning the prop just enough to negate the prop drag. My boat would move faster through the water and I could also point up more since the motor was helping to push the boat slightly when the wind dies. Adopting this routine has led to another surprise. Something that I have not been able to see until now and that is to see my electric propulsion system actually regen. Regen is the concept of spinning and electric motor by it's shaft so that it becomes and generator and "regenerates" power back into the motor's power source. In the case of BIANKA the 48 volt electric propulsion battery bank. For example on a sailboat with electric propulsion in regen mode you are recharging the batteries while you are enjoying a nice sail. I had just about given up on this on board BIANKA since a lot of factors can influence the ability of a sailboat to actually regen. Things like the keel shape that might cast a "shadow" around the prop so that it never sees enough water flowing past the blades to turn the prop enough for regen to occur. Then there is the prop its self. It might not be big enough or have the right pitch to rotate enough for regen. Changing the prop and/or some of it's specs might help but, that will cost $$$. Since I was already very happy with my electric propulsion system as is I did not feel an urgent need to try and experiment with a new prop. I had the same three bladed prop that had propelled BIANKA when she had a Westerbeke diesel installed. But, a few weeks ago I was electro sailing BIANKA and took a look at the amp meter and was pleased to see that there was a positive indication on the amp meter. Which meant that the boat was moving fast enough so that it was spinning the motor backward enough and had actually achieved regen! It was only about about a quarter to a little over one amp but, that was enough to make me very happy. When the motor is in regen mode unlike a sophisticated battery charger there is no regulation. So you have the potential of over charging the battery bank if too much current flows back into the battery bank. You don't want too many amps flowing into an already charged battery bank. But, an amp or two over a few hours of sailing may be enough to bring the battery bank back to the same level as when you left the dock. In essence you would have the same amount of fuel when you come back as when you left. That's the beauty of regen. Here is some video of my electric propulsion system operating in the regen mode: