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Old 21-06-2013, 13:22   #61
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Join Date: Feb 2012
Boat: Pearson Ariel, 26 feet
Posts: 127
Re: Water Generator Concept Thread

Here are my measurements of the actual output from a Hamilton Ferris WP-200 generator. My hull speed is 5.8 knots, so the measurements cut off near that speed.

The numbers below were derived with a Fluke laboratory averaging ammeter and with speeds computed with GPS by taking two sets of readings while sailing on reciprocal headings to compensate for any current (no differences were observed).

Here are my results:

<3.0 kts: zero output
3.5 kts: 0.2 amp
4.0 kts: 1.0
4.5 kts: 2.0
4.7 kts: 2.2
5.0 kts 2.5
5.2 kts: 2.8
5.3 kts: 4.0
5.5 kts: 4.5
5.6 kts: 4.8

The results above were obtained while charging a 400 amp/hour lead/acid battery bank with a terminal voltage of 12.5 volts.

The graph shown on the product's brochure displays an output beginning at 1 knot, which is impossible, and leads me to believe that either short-circuit current was measured instead of practical charging current, or that the person producing the graph attempted to extrapolate the current at 1 knot while neglecting the non-linear electrical characteristics involved. The generator cannot produce charging current until its loaded output voltage exceeds the sum of the battery terminal voltage, plus the forward voltage drop of the series steering diode (1.1 volt when using the diode provided by Hamilton Ferris) and whatever voltage drop occurs in the series resistance loses in the generator-to-battery wiring.

At a speed of 5.6 knots, one can expect 115 amp/hours per day (24 X 4.8). While that's a little more than half the 200 amp/hours/day claimed on the product's web site (no speed is stated for that output number), it's still not too bad for the claims made by wind and water power products -- which in my experience tend to be wildly exaggerated industry-wide.

I built my own diversion load to alleviate hockels in the tow line when switching away from the batteries at a state of full charge. I used Schottky steering diodes to improve efficiency and 14 volt zener diodes to balance the diversion load to the generator output at the switching threshold. I also used a large value electrolytic capacitor to damp fluctuations in rotation speed to maintain a more stable torque on the tow line, and installed a ferrite toroid RF interference suppressor near the generator. If you'd like a schematic with a parts list, send me a private email.

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