Re: [electricboats] Silly question - powering with a 120V AC motor?

There are several advantages to electric over an ICE:

Quiet - remember how it sounds when you have the sails up and you turn off the engine?

Water Pollution: you don't blow exhaust into the water

Torque at any prop speed:   can turn the prop really slow

Trim: position the battery to help trim the boat

Space and positioning:   electric motor is usually pretty easy to position and align.  Engine takes up little space 


Caveat Emptor

Not for everyone.   If you are cruising on engine for long periods of time ICE is more practical.  If you can't remember to keep batteries charged up then go ICE.

Peter S. Ford
petersford@hotmail.com

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From: electricboats@groups.io <electricboats@groups.io> on behalf of julie Lynch <anthonyandjulielynch@gmail.com>
Sent: Monday, May 31, 2021 9:54 AM
To: electricboats@groups.io <electricboats@groups.io>
Subject: Re: [electricboats] Silly question - powering with a 120V AC motor?

 

Hi Mike et al.,

With regard to running a VFD straight off of a generator:

Generators are a bit spiky on voltage when they have no load. For instance, I fried the 12v dc power supply for my wifi receiver when I ran the house on a genny during a power cut. The man who supplied the wifi told me that having a 100 Watt bulb on the genny before you connect anything electronic would give it enough drain to let it regulate the voltage properly. 

A vfd is rectifying the input ac to a 330V ish DC bus and then chopping that into 3 230v ac phases. It may well be very tolerant of spikes, dumping it through a brake resistor if fitted. Also there is normally a slow start which slowly fills the dc bus at startup. You would have to have some other resistive load on the genny for when load comes off the vfd.

 I wouldn't chance it at sea. But they are so cheap now it might be an interesting experiment on a river. With an outboard handy. 

Bit circular though, using petrol to rotate a motor, 20% efficiency,

to rotate a generator to produce 230v ac, ~93% efficient

to power a VFD to rectify to 330v DC, ~98%

to produce 3 phase ac, ~95%

to drive a motor, ~87%

to rotate a propshaft.

Overall efficiency 15% to the gearbox, about half that of a diesel inboard, all the noise and smell.

Only advantages over an ICE inboard, you can use the genny for other stuff when not boating, no winterising and maintenance is easy, on the bench.

Anthony

On Mon, May 31, 2021 at 3:45 PM Mike hurley via groups.io <redwood1957=yahoo.com@groups.io> wrote:

Perhaps what might be a way to do this is use a 220 /240 volt generator run that into a VFD to make 3 phase to run a motor. 

You will need to calculate the KW or HP needed then double the size of the drive. An example would be a drive that's good for 5 hp would be able to run a 2.5 hp motor. 

I don't know how to calculate gearing or if you would need any. 

On Tue, May 25, 2021 at 10:21 PM, john via groups.io

<oak_box=yahoo.com@groups.io> wrote:

This is probably a really silly question, but....

Is it possible to find a 120V AC motor that can be speed controlled (and maybe even reversed??) for at least a proof of concept on a boat?

For those of us that prefer electric motors to gas or diesel engines, but are challenged by the investment of a huge battery bank, wouldn't it be cool if we could run an AC motor off an inverter from whatever battery bank we have handy, and use a generator to supplement - or just run off the generator entirely at first?

We've discussed the efficiency gain of running off a higher voltage / lower current.

I'm guessing that there just isn't a suitable way to control and/or reverse an AC motor??

John