I agree with Dave. Vfd and induction motor is only very slightly less efficient than PMAC/ BLDC. That is the slippage required to magnetize the rotor. No need for overload between vfd and motor. The motors rated current is programmed in and vfd acts as a virtual thermal overload.
Now what is really needed by this community is a VFD that can take 24 or 48volts and buck boost it to the vfd bus dc voltage 600v typically for 400v motor.
If you cut out the need to turn 12v or 24v dc into 230v single phase a.c. and then rectify it to bus voltage you have removed 2 processes and the associated losses.
Anthony
Frequency drives are taking over the commercial AC motors market. Convenience stores here in Chicago are replacing their motor 'starters' (typically a simple contactor w/control circuit arrangement) with variable frequency drives on 3-phase HVAC fans, compressors, pumps, etc.. The CTA (commuter trains aka 'Elevated' trains) are replacing their trains' older brushed DC motors with three phase AC motors and inverters, yet still running the 'third rail' on 600VDC. They are not doing this for no reason. It's being done for _efficiency_ and maintainability.Again, this is not only my opinion, but 7-11, Chicago Transit Authority, etc. deciding this. An estimated savings of 30% on the electric bill is (I'm told) typical of switching from straight 3-phase AC (on/off type 'sinewave' control) to VFDs with complex control waveforms used with/for standard inexpensive 3-phase squirrel cage induction motors. (Note: three phase motors are inherently more efficient to start with.) There's a LOT of control theory developed at electrical engineering schools over the last 50 years that got us here. I must admit I've been confused why boaters would even look at these oddball boutique motor types when standard off-the-shelf parts are now available.Think about it. In food processing they need motors you can literally hose down for cleaning. And they need a spare handy so the line can be brought back running ASAP if something breaks. _And_ they need it to be cost effective. _And_ efficient so they keep the electric bill down. Someone want to debate the virtues of specialty 'Marine' rated devices against that? Be my guest. The control and safety side of these systems are well understood by most competent industrial maintenance techs too. Short ckt protection=>VFD=>overload protection=>motor. Done. Off the shelf parts. Industrial grade.DaveOn Monday, May 31, 2021, 09:45:47 AM CDT, 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
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