Anthony: I did confirm with one manufacturer (Danfoss) that their VFDs _do_ have integrated limiting. And DC bus input capability. They had good tech support too. You _could_ look at that limiting as 'overload protection,' as defined by NEC but the systems I've examined in detail that were actually designed and implemented by the pros (the local POCO office hirise HVAC systems no less) _still_ had overloads post VFD. However, they did also have some building automation stuff in there as well, in addition to a 'bypass' to switch the motor directly to incoming line voltages (in the event of a VFD failure, I'd expect.) So that may have been the motivating factor there.
As for the particulars of energy supply, there are about no end of options. Personally, I'm looking seriously at higher voltage battery configurations for a 'local reservoir,' and the charging systems required. DC/DC switchers are certainly an option for this, as they can be quite efficient. Please let me know if you come across some reliable switching supplies that can do the required voltages/currents/power. I drew a blank looking for those. Isolation is probably a good idea too...IMO
Also, at hundreds of volts, rectifier losses are basically negligible. It's low current. You just need a good diode. (1000V reverse voltage? 2kV? IDK. How reliable do you want? How much current?) An inverter and transformer setup will likely have a fairly predictable efficiency too...but we'd have to spell out each particular model number, voltage, current, power, etc. to start putting real numbers to it. Switchers _are_ usually a bit more efficient than transformers tho. Probably about the same reliability as the inverter too all things considered. Again, we'd need particular part numbers.
However, having said that, the 460V systems _will_ still be inherently more efficient than 230 or 115 by simple virtue of running the same power at a much lower current. Thus their popularity. I'd tend to think running a 5hp VFD and motor at 2.5hp, similar to what someone suggested earlier, would get those same kind of benefits as well...if the tradeoff vs added weight of the larger motor doesn't cost too much. That's because the motor windings' DC resistance is yet another efficiency hurdle. BTW, that really doesn't change with BLDC or PMAC either. Again, we'd need some specifics, and some real-world testing to verify. These suggestions are just based on the 'governing equations' if you will. The devil's in the details, as always.
As for the need for a pro electrician? I'd say if you aren't confident in your electrical skills then, yes, you should get you someone that is good to hook that system up. 480V tends to fail rather spectacularly when something goes wrong. The IBEW local by me won't let you work on 480 until you're a journeyman, and then you still aren't allowed to work on it alone...if that gives you any idea of the safety concerns. You'll want a UL rated enclosure, proper (tinned, stranded) motor wire, solid connections, etc.
You'll want someone that knows what they're doing, if such a person can be said to exist for what we're talking about. It's kind of uncharted waters. But that's always where you find the treasure...and the shipwrecks.
Good luck! :-) I'll keep the group posted if I actually build something.
Dave
P.S. FYI: I came across a pile of 460V Danfoss drives. 20, 30, 40, and 50hp...if anyone's interested. They're used, but low hours. I'm planning to use the 5hp drive on a 2hp motor for my 30' Alberg...someday...perhaps, but if someone maybe nearby wanted to do some experimenting, I might be convinced to part with a few for cheap. This is how I came to know this stuff BTW, if you were wondering.
Oh yeah, I also teach the motor control class at a trade school :-)
On Thursday, June 3, 2021, 10:35:21 AM CDT, Carsten via groups.io <carstensemail=yahoo.com@groups.io> wrote:
Right, Anthony, that would be nice !
A question :
Does this setup eliminate the need for a pro electrician, so we can do DIY on such a system ?
On Thursday, 3 June 2021, 23:28:29 GMT+8, julie Lynch <anthonyandjulielynch@gmail.com> wrote:
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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