Single phase to three phase conversion:

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rattus

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Friend of mine claims to have seen a home built one to three phase converter which halved the electric bill of a small dairy.

He has no idea how it works, and neither do I. I am skeptical that such a rig would be that efficient.

Anyone have any ideas along this line?
 
Re: Single phase to three phase conversion:

rattus,

My guess is they are using a rectifier with charging caps to create a DC supply and then using SCR's or IGBT's to provide a 3-phase pulse width modulated output. Just about every VFD sales guy is doing the same thing with his demo case. They use a standard VFD powered off single phase and drive a small 3-phase motor. Watch the spinning wheel, my product is the best, you must buy it, you must buy it. :eek:

No, it is not the most efficient set up.

Tony
 
Re: Single phase to three phase conversion:

Isn't that the Scott connected transformer?

Halved, yeah, ok. :D

I would believe some savings because, let me see if I have this right:

Three phase doesn't have the zero crossing and motors will have an increased efficiency, not because of reduced heat loss, but because of reduced inertial loss. Which I suppose would still end up as heat loss, but a lot of it would be in the attached load instead of the motor.

I'm just thinking out loud, or in print. Does that sound crazy or plausible?

But halved, :D ha ha hee. maybe, but I don't think so. :D
 
Re: Single phase to three phase conversion:

Sam,

A Scott connected transformer goes from 3-phase to 2-phase. There is no transformer that will go from 1-phase to 3-phase.

Most people use static phase convertors (sometimes solid state but usually just capacitors) or rotary phase convertors (specially wired 3-phase motor and capacitors or a combined 1-phase and 3-phase motor).
 
Re: Single phase to three phase conversion:

That's right.

Edit: Used to use a plug in generator for 400 or 440 Hz. (I forget which) for airplane stuff back in my OEM days.

[ July 14, 2005, 12:40 PM: Message edited by: physis ]
 
Re: Single phase to three phase conversion:

My guess is that he is using solid state inverters. Don't think he is using a motor-generator. Wish I could see it.

Jim, how would you generate 3-phase with just capacitors?
 
Re: Single phase to three phase conversion:

I'd think you could get the three phase with somewhere around 95% efficiency. But the question is where are you gonna get the 55% increased efficiency from?
 
Re: Single phase to three phase conversion:

I can believe that he cut the electric bill but I don't think the converter had anything to do with it. I've used rotary phase converters when 3 phase was not available ( people get a deal on some used equipment), but there is going to be a certain amount of loss and another piece of equipment to maintain. I know of a old engineer that builds these in his garage and will sell at a good price. I would think that the energy savings come from buying newer more energy efficient equipment. Motors & compressors. Even caps for power factor correction could help if they have enough of a motor load. You have to ask are the savings worth the installation cost. The best thing for customer to do is get an energy audit. There are some cheap repairs that save more than expensive equipment.
 
Re: Single phase to three phase conversion:

Rattus,

One method is to not really get 3-phase as much as simply "kick starting" a 3-phase motor.

Here is one manufacturer with a better method, RONK Industries.
 
Re: Single phase to three phase conversion:

Originally posted by rattus: Friend of mine claims to have seen a home built one to three phase converter which halved the electric bill of a small dairy.
Click to expand...
The (asserted) fact that the electric bill went down does not mean that the new configuration is any more efficient. The three-phase machines are going to draw the same amount of power over the same amount of time (i.e., kilo-watt-hours), no matter where the power source comes from. My guess is that the electric bill went down because the electric company has a lower rate for supplying single phase power, and a higher rate for supplying three-phase power. But to give a useful comment, I would need to know the "before" and "after" configurations.
 
Re: Single phase to three phase conversion:

Originally posted by rattus:
Friend of mine claims to have seen a home built one to three phase converter which halved the electric bill of a small dairy.
Click to expand...
It sure sounds fishy, watts is watts as far as I understand it. :p
 
Re: Single phase to three phase conversion:

You can not create power this way.He may be tricking his electric meter somehow, but watts are watts.Its like trying to convince someone that 240 water pumps don't run cheaper than 120.They only see lower amps.If someone can out smart my meter please tell me how.
 
Re: Single phase to three phase conversion:

Who knows the relative efficiency of single phase and three phase motors in the 1 to 5 hp range?
 
Re: Single phase to three phase conversion:

Using the tables in article 430 for a 5 HP motor I came up with about 6400 watts single phase and 6000 watts 3 phase.
 
Re: Single phase to three phase conversion:

Just that 3 phase motors are more efficient.

It's not much though. I thought there was more benefit than that.

Don't panic Bob, I don't believe Rattus' friend either. :D
 
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