SkipperColin
New Member
Hi all, I'm hoping that you can help with some design ideas.
I have a sailing boat that I have fitted a Lucas Marine 45 amp alternator to the prop shaft.
Here are some of the specs.
The prop shaft spins @ about 200rpm when sailing.
I have a pulley ratio of 9:1 so get approx 1800rpm at the alternator
This all works well giving between 6-10amps at 12 volts depending on boat sailing speed.
However my problem is that when motoring I have a shaft rotation of about 2500rpm so close to 18500rpm at the prop alternator.
I do not want to use the prop alternator when motoring so have a switch on the field wire so the field is open circuit.
However I think I am blowing diodes and possibly the field is self exciting when in open circuit due to the high rotation speeds, but I'm guessing.
My question is, how do I ensure the alternator is 'off' with the field wire switched open and not self exciting
Secondly should I fit bigger diodes to cope with the open circuit voltages at the higher speeds. If so could you give me a spec for the diodes I should use in the bridge rectifier.
If you can think of anything else that is may have missed i'd be grateful
Hope you can help. This is a great project for us and means we are entirely green when under sail as we can generate enough power to mean the boat is energy independent.
Many thanks
Colin and Nichola
Yacht Emerald
www.yachtemerald.com
I have a sailing boat that I have fitted a Lucas Marine 45 amp alternator to the prop shaft.
Here are some of the specs.
The prop shaft spins @ about 200rpm when sailing.
I have a pulley ratio of 9:1 so get approx 1800rpm at the alternator
This all works well giving between 6-10amps at 12 volts depending on boat sailing speed.
However my problem is that when motoring I have a shaft rotation of about 2500rpm so close to 18500rpm at the prop alternator.
I do not want to use the prop alternator when motoring so have a switch on the field wire so the field is open circuit.
However I think I am blowing diodes and possibly the field is self exciting when in open circuit due to the high rotation speeds, but I'm guessing.
My question is, how do I ensure the alternator is 'off' with the field wire switched open and not self exciting
Secondly should I fit bigger diodes to cope with the open circuit voltages at the higher speeds. If so could you give me a spec for the diodes I should use in the bridge rectifier.
If you can think of anything else that is may have missed i'd be grateful
Hope you can help. This is a great project for us and means we are entirely green when under sail as we can generate enough power to mean the boat is energy independent.
Many thanks
Colin and Nichola
Yacht Emerald
www.yachtemerald.com