Phase converter/autotransformer 220 in / 440 out

[Jacin]

Hello, I am new to the group and after reading several posts I appear to be in the right place. First off I am NOT electrical, but rather mechanical so PLEASE go easy on me.

Problem in Nutshell:

I have a piece of machinery that is 440V 3 Phase (6hp).
I have 220V Single phase service.
I have a 220/440V 10hp that i wanted to use as my rotary converter.
I was TOLD that I could have this motor be BOTH the phase converter and the step up transformer if I wired it for the 440V configuration and center tapped the 220V coming in. Whatever that means.
FWIW I plan on using both a Start cap as well as run caps from both lines to generate a makeshift 3rd leg going into the idler motor. Given all this all's I can make out of this would be to hook up the motor (which is "Y" configured BTW)

Something like this:

T1 connected to Load 1
T2 connected to Load 2
T3 connected to Load 3

L1 connects to T7,T4
L2 connects to T8,T5
L3 connects to T9,T6

But after looking at this I am not so certain I am heading in the right direction.

This seams theoretically possible, btu I am tripping over the actual connections.

Any help is greatly appreciated.

 

[busbar]

In various phase-converter discussions, I don’t remember anyone mentioning use of the converter motor as an autotransformer. It may likely require additional derating of the converter motor.

There has been a fair amount of discussion here, that should show up with a search.

 

[DanDel]

I'm assuming that your 220/440V 10hp motor is single phase. Any chance you can simply substitute this motor for your 6HP 3-phase 440V motor? (Because your plan as described does not induce confidence from my point of view.)

Yes, you could get 220V out of a 220/440V motor by tapping the connections. It's the current you need for your load that is the problem. What do you think inrush current for the motor you are trying to start will do to the windings of the motor from which you are trying to get it? (Let's not even talk about your 'makeshift 3rd leg' from capacitors.)
The truth is, if I were given these components and your plan for a dare, I might be able to make your 3-phase motor start(once, anyway...or at least begin to start once, anyway).

 

[Jacin]

Dan, I am NOT the inventor of this theory, but rather was told of it by someone who has had good success with it. Unfortunately I am unable to again contact them so I was looking for assurance on connections here before trying it out. Seems like an interesting concept. I can always just use a step up transformer worst case so it's not a huge deal, but rather more of a neat way to minimize my components especially since the size/derating will very likely NOT be an issue for my application.
FWIW the Idler motor IS 3 Phase as I know no other way to make a "make shift" phase converter using a single phase motor.

 

[DanDel]

The easiest(and cheapest) way to make this work continuously and reliably is to replace the 3-phase motor with a single phase motor. The next best thing is to use an electronic single-phase to 3-phase convertor.

 

[Jacin]

Dan- fair enough - I get your point. BUT... (you knew this was coming right?)....The 10 Hp 3 phase motor I already have (free) - the machine motor which is a 2 speed motor is 5hp at 1750rpm and 6hp at 3500rpm. The contacts are all 440V coils. Given all this I figured IF (big IF) I could actually use the 10 Hp motor as BOTH the converter AND the transformer then it would certainly be cheaper than anything else - at least in the short term since I already have all the stuff to potentially make it work. I MIGHT be able to scrounge up a transformer and step up after the converter, but until then I am curious if this method would work or not (given my particular parameters). A VFD would sure be nice as well, but they are cost prohibitive for me. The single phase motor may also be an eventuality, but I will first NEED to scrounge up a cheap one.

 

[Lewish]

Take a look at this website...

http://home.earthlink.net/~ojmsmith/indexd.html

and then go and get a copy of Smith's patents. They will tell you how to do what you are asking how to do. It is really a very clever use of the magnetics in the motor. It is all about how to run any 3 phase motor from a single phase supply. Voltage adjustment included. It may elimiate your need to use the 10HP motor as a phase converter.

Please post the results of what you decide to do.

 

[DanDel]

Jacin, you say your motor is two-speed and 220/440V? How many leads does it have?

 

[Jacin]

Hi Dan, The 2 speed motor has only 6 wires in the connection box. I think I know where your heading and I had considered "opening" it up to see if I couldn't pull out the additional leads if present. I may still do that, but what made me stop was that I would still need to get a (albeit small) transformer for the contactor coils or just replace them. If that's where you are headed - then I will say it IS STILL a possible option. The motor itself is from Sweden made to run on "our" (US) service, but I don't know what the insides look like just yet - that may change!

 

[Jacin]

Hello all, Here's an update to my motor dilema with slight recap:


I wired up a 10 Hp 3 phase motor to put 220V single phase IN and got 440V 3 phase out (Well actually idle voltage is closer to 480 but drops down to 440V when the machine is running).
Currently everything is "jerry rigged" just for testing, but it is wired like this:
L1 to L3 has a 40mfd Run cap
L2 to L3 has a 80mfd Run cap
L1 to L3 has right about 900mfd Start cap
Motor wired 440 w/220 fed into the "center" of the windings.
"old" inputs now output 440-480 (T1 T2 T3)
Initially I am running a 5Hp 440V 3phase Nibbler - It starts (full speed) in less than a second or two.
I ran it for about a 1/2 hour - neither motor got hot - both were barely warm.

That was the good news -yea!

The bad news is that I cannot start the motor in "high" speed. The nibbler has a dual speed motor and it worked great (start/stop) at the low speed 1750rpm, but when I tried to start it (from a dead stop) in the high speed (3500rpm) it stalled my converter motor. I am considering adding a flywheel to the idler or maybe even some circuit to sense voltage and have the start caps kick back in when needed, but before any of that I first need to do some more checking out of the current motor and contactor set to make sure that they are NOT the culprits.

Just thought you guys might like to know how this is going so far.

 

[busbar]

Try wiring the two {or more} run capacitors in parallel on one side; id est, everything L1-L3 and none L1-L2.

 

[jbartos]

Suggestion: There are additional challenges to be faced, namely, the protection, the quality of such voltage supply, a type of load that the supply will be suitable for, efficiency, power factor, maintenance and life-cycle.