Automation or not ?

Pierre

Lifetime Supporting Member
Join Date
Apr 2002
Location
Montreal
Posts
1,669
We all brag about the fact that we are not just PLC programmers... to do the things we do... one need much more... neumatic, hydraulic, electrical, mechanical knowledge and on and on.

Well, here is one for the DickDV of this world (hope you can give me a few hints on this one)

My brother in law is a milkman. Nothing special about this.

He has a truck. A nice truck. The problem comes from the fact that it's Thermo-King compressor system is supplyed by a 208V 3 phases circuit. The power comes from a diezel motor included in the unit.

When he is working, this motor/compressor system starts and stops on demand.

At night, when he parks the truck at the depot... in the past he would connect to a 120 AC outlet and go home. Now, with this 3 phase system he has to let his system running.

They do not have 3 phases outlets at the company where he get his milk and stuff.

He tested the connection at a place where they have 3 phases and there is a detection and transfer circuit which detect the incoming power and switches from the diezel engine to an electric motor.

Today I looked at it and its a very nice system. Miniature diezel engine, compressor, fan, heat exchanger... just a nice setup.

I know that we could use an inverter to transfer this 2 phases outlet into a 3 phase system.
We could also replace the motor.

But could we convert the 2 phases into a 3 phase via a rotary converter or other devices?

This is a compressor system, its hard to start and will start often.

Anyone has recommendation for this. For me there is no money involved but the fun of solving this to the minimum price...

I have a 5HP inverter in the shop but with the 2 phase supply I would need a 10 HP to do the job... what could we do?

If anyone thinck this has nothing to do with automation... thinck again :)

Spec: Motor 5HP / 230 V / 3 ph - 14.xx Amps
 
If I truely understand what you are looking for (a stand-alone phase converter to genererate 3 phase from 2 phases), the answer is "yes" such devices do exist. One supplier is Phase-a-matic .

In the industry my company services, there are many customers who do not have 3-phase available to them but need to purchase and run 3-phase systems. They often opt to purchase this type of converter.

Steve
 
Tancks steve,

I know those systems exist but what I really look for is another "Cheap" Ho God not cheap... I meant less expensive way to do...for...

...the fun of solving this to the minimum price...
 
Cool. Hopefully someone will have something. I know a bunch of shop owners who would like to find less expensive ways to accomplish this.

Steve
 
For instance... I knew a guy a few years back whom was dealing with hoists, overhead cranes and PLCs.

In his shop... almost a garage operation, he did not have 3 phases... he was testing his systems with an arrangement of transformers...

It was working. How did he do it... I suppose the phase angle out of the transformer where not really good for full tork operations but what would be needed to make it so.

When there is a will... there is way...
 
Cheapest solution will likely be to change to a single phase 240vac motor. This presumes that they have a 240v main feeding the shop where he parks. He would need about 30 amp service.
 
Roll your own

Check out eBay. You can buy inverters or plans to build your own. IIRC, the build-your-own type generates an additional phase which is 90 degrees out from the original instead of the normal 120 degrees from the utility company.
 
Pierre,

I really love it when something "bad" can be turned into something "good"!

My Dad has been using a 3-phase generator in his 2-phase garage for years. He has had this system for as far back as... Oh, my God! As far back as into the last Century! The 19-Somethings!.

It's a simple arrangement that takes advantage of the fact that a 3-phase motor will continue running very well with only 2 of the 3 phases!

We've all seen it. You start a motor under 3-phase... fine. It starts and runs just fine. Then you lose a phase to an "open". It runs a little warm but the motor continues running, albeit, "single-phasing" (what a lousy term).

Everything is fine until you turn the motor off and try to restart.
It won't restart. It just sits there and hums until the overloads trip.

However, if you are foolish enough to do so, before the overloads trip, reach down and give the shaft a quick twist. Depending on the mechanical loading, you just might find the motor starting and running again! This works especially well on motors with clutches (normally disengaged, of course).

Glory Be! Imagine that! A 3-phase motor running on 2-phases! Do wonders never cease? (The best part is yet to come!)

Sounds pretty good except for the part about reaching down to "give the shaft a quick twist". Read on, McDuff!

The physical and electrical arrangements are as follows:
There are two electric motors. One motor is a 120-VAC single-phase motor. The other motor is a 220-VAC, 3-phase motor. The nominal speeds of the motors should be close if not the same.

The shaft of a single-phase motor is mechanically coupled to the shaft of a 3-phase motor.

The wires of the single-phase motor are connected to a 120-VAC contactor. (You could use a 2-phase 220-VAC motor, if you wanted.)

The two wires from the 220-VAC, 2-phase, house-supply are connected to TWO (2) of the input connectors on the 3-phase contactor.

The 3 wires from the 3-phase motor are connected to the output side of a 3-phase contactor.

Also at the output side of the 3-phase contactor, three (3) wires are taken out to the load. Like so...




SUPPLY

|<-220 VAC, 2-phase ->| nada

| | x
_|_ _|_ _|_
___ ___ ___
|\ |\ |\
| \ | \ | \
| \ | \ | \
| \ | \ | \
| \ | \ | \
MTR OUTLET MTR OUTLET MTR OUTLET
A A B B C C



.
The contactors are controlled by a 3-position switch.

Position-2 (middle) is ALL OFF.
Position-1 (left) is single-phase contactor ON.
Position-3 (right) is 3-phase contactor ON.

SEQUENCE:
Start with Switch in Position-2, all OFF.
Switch to Position-1, single-phase motor ON.
When motor comes up to speed, switch from Position-1 to Position-3.
The single-phase motor drops out and the 3-phase motor kicks in.

The 3-phase motor runs "single-phasing".

Now comes the magic!

Two house-phases are connected to 2 lines of the 3-phase motor and 2 lines of the outlet (Phase-A and Phase-B). The third leg to the outlet is "produced" by the third leg FROM THE MOTOR!

The third leg voltage is produced by the phase-angle difference and the imbalance between the other two legs. Voltage is "generated" in the third leg!

Certainly, this is not a TRUE 3-PHASE POWER, but, it is true enough to run and that is the quest, is it not?

To shut-down, change the switch to Position-2 (middle).

So, all you need is a discarded 3-phase motor and a discarded single-phase motor of the same nominal speed. Adding a coupler and a 3-phase outlet should do the trick!

Gotcha's:
You need to have room to install the single-phase & 3-phase motor. This can be done on the floor, somewhere. My Dad's setup uses about 3-4 Sq-Ft (1-Ft x 3 to 4-Ft).


Give that a think, Pierre. And give a rub and a "Hey" to Tin-Tin for me!
 
WOW!!!!!

Terry Ol' Pal, Where Ya Been?????

Glad to see you back. We've missed you! (Let me guess, those damned Keepers again?)... :D

beerchug

-Eric
 
Until DickDV steps in here and shows us the 'correct way' to do it, I'll offer up this idea. Note that this is NOT my writing. This is from "The Electrician's Book of Trade Secrets" from Hood St. Press ©1987. Quite similar to Terry's version, but it may give you some other ideas... :confused:

  • "Here is the easiest way we know to get good three phase power from a single phase; it has some limitations, but overall it works very well.

    To start with, you will need a standard three phase induction motor (Delta wound is preferable to Star) and a capacitor (an electrolytic type is usually alright, as it won't really be carrying the load current; it is needed for power factor correction).

    As you see in the accompanying schematic, you bring both legs of your single phase power to two leads of the three phase motor, and continue them into the three phase power system; the third leg of the three phase system will come from the last lead of the motor, as shown in the schematic.

    Your power factor capacitor will be connected betwen the motor lead which is not connected to one of the single phase legs and to the continuing portion of one of the single phase leads (see drawing for clarification). The best value of a capacitor to use is usually somewhere between ten and twenty-five mfd (micro-farad), but this value is not critical. You can start with a ten mfd capacitor, and then add additional capacitors in parallel until you get no more improvement in performance.

    The three phase motor will start by itself once power is connected to it if you use the proper value of capacitance. If it doesn't, you can switch some additional capacitors into the circuit momentarily. If you really have trouble getting the three phase motor started, you can use a small single phase motor with a belt drive to bring the three phase motor up to speed.

    The typical load that is usually run on a system like this is three phase motors, here are a couple of things to remember about using three phase motors on this type of system:

    You can usually start a motor up to the same horsepower rating as the motor you are using to convert the single phase power to three phase, but not larger. You can usually power a total load four times larger than the rating fo your converter motor. For example: if the motor you are using to convert the single phase power to three phase is 10 horsepower, you should be able to run 40 horsepower of load on the system.

    Because of the difficulty of getting balanced current on all three phases, you should not run motors at more than 80% of their rated load on this system; if you did you would run the risk of overheating any motors on this system. Starting torque for the first motor run on the system is usually not too good (about 60%), but if you add more motors, this figure will improve significantly.

    Remember that the voltage rating of your three phase motor should match the voltage of your single phase power."
[attachment]
beerchug

-Eric

P.S. I still can't believe Terry's back... Did Phil find you hiding at Disney or something?... :cool:

3phase.gif
 
Three Phase

Pierre

http://ecmweb.com/ar/electric_unconventional_transformer_connections_3/index.htm

I was in a terrible rush with my first post but have found more time,since,to locate the correct information.

The connection you are looking for is called a "Scott Connection".
The Scott Connection is a unconventional transformer connection, three phase to single phase, single phase to three phase.
I have worked with such transformer connections, in the steel mill.

Good luck
Roger
 
Pierre:

I have seen things like that when I was a bit younger ;) , mostly in machine shop-type applications (a circular saw, a grinder etc.) For a compressor - it might be a problem, but anyway... Here what I was able to dig at on of the sites in the domain .RU:

You may run a 3ph motor in a single phase system if you put a capacitor in series with one of the windings. The problem is, since motor windings' impedance is different for different speeds, one capacitor would not do. You may use a second cap in parallel just for starting; once at speed, this extra capacitor should be disconnected.

Using this method, the motor still should be derated down to 40 - 50% of its power, alas (there is no free lunch!)

The diagram attached uses european-style symbols so don't get confused. Switch SA1 allows to change direction of the rotation. SB1 is a manual contactor with spring-returned contact SB1.2 and latching contacts SB1.1 and SB1.3. R1 is a 2 Watt resistor (just to help C1 to discharge when disconnected) C1 is the starting capacitor and C2 is the run cap, both rated at about 400-500 VAC.

The "rule-of-thumb" formula for C2 is:

C2 = 4800 * I/V ,

where C2 is in uF, motor rated current I is in Amps and motor rated voltage is in Volts

The capacitance of C1 should be selected 2 to 2.5 times higher than C2. However, both C1 and C2 should be decreased about 20% if the motor is constantly underloaded. In your case, you are looking at about 300 uF for C2 and 600 uF for C1. Still, given the hard start conditions (a compressor!) this may not work at all! :(

If you try this, please be careful, observe the currents etc.; there is no warranty, implied or otherwise; void where prohibited; some restrictions apply; use at your own risk; some assembly required...

In short, good luck.

dvig.gif
 
My 2 cents

Get a VFD off of eBay, single phase in - 3 phase out. Cheapest and best (IMHO)......

And just to correct you non-electricians.... there is no such thing as 2 phase. 220, 230, 240 Volt, whatever you want to call it, is single phase power.

Cheers! beerchug
 
Your probably going to want to stay with the 3 phase motor for the strong starting torque needed to start and run the compressor. Its probably best that you step up your supply voltage to the motor voltage and than use a single phase to three phase transformer or equivalent. Just check with your local electrical supply house. The parts person should be able to let you know what is available.
 

Similar Topics

Hello, I have an automation direct d2 262 plc and C-more HMI EA9T6CL-R. I need to prepare a program, scheduled to be performed on a future date. I...
Replies
1
Views
22
Hello all- I have a unique challenge using a customers Direct logic 06 PLC. This customer has a DC motor operating at 10 RPM which is turning a...
Replies
1
Views
86
Hi, I have been trying to run drive via Sysmac studio. I can ping the drive. I can see the logic bits going on/off as per command. But, drive is...
Replies
21
Views
454
Hello Guys, I am using 1769-L36ERMS PLC by Rockwell which doesn't let me MOV or COP literal text into string datatype? i very well know the...
Replies
13
Views
350
Good Afternoon , Does Rockwell Automation have an Input Card , maybe in the 1734 series , or CompactLogix series that will receive signals...
Replies
15
Views
774
Back
Top Bottom