Hi Ken,
On the subject of using 2 of 240v generators to produce 460v. A.C. doesn't work that way. If you series connect them you will get anything from 0 to 480v, probably slowly cycling from one to the other, the difference in the generator frequencies.
I am going to try cheap 3 phase industrial motor on small sailing boat, 23 foot. 3hp. That's 12volt batteries to 230v inverter (3kw rated) to VFD, variable frequency drive, 230v 3 phase to 2.2kw motor. All very cheap.
Nothing wrong with using a generator to feed the VFD, instead, but rumour has it that one should have a light bulb connected to the generator before switching on the VFD to stabilise the voltage. Otherwise spikes may kill the electronics.
380rpm took 3.8a and 36a, 12.2v respectively. Still 50hz.
I was using 6mmsq wire x about 2m altogether which cost me a volt at the high current.
I hooked up the 2 cables from the original lever to a forward and reverse switches and a potentiometer for the throttle well out of the splash zones.
I had been planning a homemade 12v generator to extend the motoring range but have been inspired by your post to simply use a 230vac off the shelf and plug the VFD in direct. Long VFD ramp up times, 3 to 5 seconds, mean very gentle loading. A little suitcase generator would do my boat at 900w.
You will have 2 big VFDs and 2 big motors I presume?
I don't know about the Americas but here in Europe the larger 7hp upwards motors come 700/400v star/delta so you need a 3 phase generator and 3 phase input VFD.
If you aren't intending battery power or solar then doesnt your usage profile suggest outboard ice? A big generator is expensive and bulky too, although might have an advantage for a live aboard.
Research the economics and fill us in.
Regards Anthony
On Sun 8 Aug 2021, 8:17 PM Ken Winokur <kenwphoto@gmail.com> wrote:
Hi All
My name is Ken Winokur and I have been a long time lurker on this mailing list but I don't post much.
I'm a yacht broker, marine technology advisor and more and have worked with power boat manufacturers on high speed hybrid electric (Siemens electric motors and Styer engines / generators) which for new power boats is an excellent solution but of course are nearly the same if not more expensive then traditional diesel power.
I was wondering if anyone here has experience or experimented with a different more simple approach.
This would be for older boat that's would mostly be used as a live aboard but needs to be moved occasionally and at only hull speed.
My approach would be for say a 39 foot 1980's Searay express cruiser for which I have many for sale dirt cheap.
I would rip out both engines and generator and replace them with a pair of AC industrial motors and run the off a single at AC240/240 or perhaps a pair of generators to get AC 460.
I see motors from 10 to 40 hp at Grainger and on eBay which may be suitable.
Any one who has explored this path I would be interested in talking to.
Thanks so much.
Ken
Btw my personal boat is a Sabre 28 sailboat with an atomic 4 that I may replace with electric some day.
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