Re: [electricboats] Electric Powerboat

As usual, your mileage may vary.

Technically, given generators can be synchronized to deliver power while tied in parallel, there is no unachievable technical reason that generators could not be "stacked" to deliver synchronized peak voltage equal to the sum of their peak voltages.  In either case, the frequencies and phases must be locked.  So sure, it's challenging and likely no vendor offers a design that allows that, but AC surely can be made to "work that way".  If not, then synchronized parallel EU2000i gensets would not be a reality, yet they are and abundantly in use.

 

From: electricboats@groups.io [mailto:electricboats@groups.io] On Behalf Of julie Lynch
Sent: Monday, August 9, 2021 10:45 AM
To: electricboats@groups.io
Subject: Re: [electricboats] Electric Powerboat

 

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.

 

I tried the setup on a small 3hp lathe which already had a similar VFD. Spun it at 1200rpm which took 3.8amps at 230v 3phase, 50hz = 77amps at 11.8v. That's about 900w dc.

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.