OT Three phase motors

[OldRedFord]

I might have a chance to get a few three phase motors. Part of a clean up job I am involved with.

My questions are...

How can I tell for sure they are three phase?
Can I check them with a DMM to see if they are good?
If so how?

[fordman]

i think three phase means it has 3 hot wires a neutral and there should be a ground in there soem where. even if it is a case ground. that is about all i know. if you can run 3 hot from different circuts to the motors and they spin over then they work. usually motors liek that arent much good for regular people use. are are worth more as breakage at the junkyard. maybe someone else knows how to check them out a different way. and you may have a use for them i dont know. or you may find a buyer for them too.

[OldRedFord]

I would like to have one of them for future use as a RPC (rotary phase converter). To run 3 phase equipment at home.

http://www.metalwebnews.com/howto/ph-conv/ph-conv.html

[fordman]

mayeb if you build this converter you can test the motor in the converter. http://www.metalwebnews.com/howto/ph-conv/fig1.html not that i completely understand all of that. but i do the top part.

[R.Smith]

Do they have no tags? You'd want to know what voltage they are as well. You can't run a 440 3ph motor on a 240 3ph converter for instance.

[averagef250]

3 phase motors are far more efficient than single phase motors, but not much good if you lack 3 phase. An RPC is a real simple thing to build, small ones are uber simple. You get into the 100+ amp capacity range and they get a bit more critical, the power company may come knocking on your door if they're seeing a few 2 second 700 AMP spikes from a big cap start RPC on your residential power usage every day. Not just that, but residential lines aren't meant to feed thier rated capacity like commercial power is so if you're drawing 200 amps @240 on a regular basis your neighbors may start complaining about power issues.

The best design for an RPC for residential power I've found is a cap balanced pony start setup using a programmable VFD to ramp up a small 3 phase motor connected to a larger one with a one way sprag. There's no big voltage spike and the RPC windings last forever.

[R.Smith]

Ramp up a one way sprag? I thought this was a family forumn!

[MaxKlinger]

There are two types of three-phase systems, called Delta systems or Wye systems. A Delta System has three wires, phases A, B, and C, which usually have 208 Volts with respect to each other. A Wye system has four wires, where phases A, B, and C are all used relative to ground. Look for a nameplate with the voltage rating and look for the number of terminals that they use.

If you decide to build a rotary phase converter (these are way cool) plan ahead and see if you want to build a wye system or a delta system. You can also build a device called a Delta-Wye switch.

I don't know all the details of these things, I'm not an electrical engineer. But Wikipedia has some useful information:

http://en.wikipedia.org/wiki/Delta-wye_transformer

http://en.wikipedia.org/wiki/Three-phase_electric_power

Good luck!

[averagef250]

I've never heard of or seen this "wye system". I've always been told 3 phase motors run the load between phases, not to earth ground whatsoever so say you're running a 40HP 220V 3 phase motor you run your 3 gauge wire for A, B, C and run a 10 gauge wire for ground. Saves hundreds of bucks in copper over 4 wires needing to be the same gauge on even a small run.

Also, Fordman if you pull 120 from 3 different circuits it doesn't make 3 phase. Each leg of 3 phase power has a seperation angle of 120 degrees, not 180 like single phase. A rotary converter works by producing a half-assed dirty 3rd phase. The funny thing is a lot of RPC generated power is better than the crap the power company puts out. When I set up my 20HP DC spindle Mazak to run off a 30HP RPC I had problems with the control shutting down when my compressor would kick on (my compressor is 3 phase through the RPC as is most of my shop). An electrical guru friend of mine helped me get a handle on it and realize that no machine draws equally on all 3 legs and the Mazak was no exception. I needed to switch legs around in order without changing phase rotation until I got the highest drawing leg of the machine hooked to the strongest leg of my RPC. Got it first try and now I can run an intermittant 100+ amps @240V through that 30HP RPC (with a cooling fan on it) with my 150 gallon aqueous washer heating up and running, air compressor loaded and the Mazak taking a heavy cut.

RPC's are pretty cool. they aren't perfect, but it is truly amazing what a properly built one can do. My best advice is use NEMA parts. If you go off the manufacturer ratings instead of NEMA ratings you'll burn your place down if you overload it. The NEMA stuff might be 5-10 times the size, but it'll run twice it's rated load for 50 years and laugh it off.

[MaxKlinger]

When I was on the Formula SAE race team in college a couple of guys and I built a braking system dynamometer (measures performance of brake discs, calipers, and pads). We used a three-phase motor that worked on the Wye system, where it had four wires. We selected it because it was available on a shoestring budget, not because it was better. We got an ABB (Asea Brown Boveri) IGBT converter to turn the 480V 60Hz three-phase (I suspect delta type) into wye-type three-phase at a frequency we controlled. Pretty cool.

[Don H]

If you want to check if these are 3 phase motors there is typically a nameplate that will tell you. Also listed will be a wiring diagram for low voltage (230 V ) or high voltage ( 480V ). If there isn't a name plate then check to see how many leads there are to wire the motor typically 9 for a standard 3 phase motor. A quick check to see if the motor is good using a multi meter is to wire according to name plate except for the line leads and check resistance between the L1,L2,L3 and make sure all are the same. Also it would be wise to spin the motor real slow while checking this to see if there are any variations in the ohm reading- shouldn't be. A typical high voltage connection would be L1 to T1 L2 to T2 L3 to T3 tie T4 to T7 T5 to T8 and T6 to T9. If you feel any rough spots while turning the motor it will have to have bearings replaced. Hope this helps.

Don

[fuzzier1]

I too have built RPC for my milling machine (actually I have made 2 of them, one a buddy took on an agreement we had at the time, different story, doesn't matter). Each of them cost around $50 for a 5hp RPC. Very easy to do, the second one came out better than the first of course. I have it mounted to the back of my mill. I am happy with it so far and very reliable.

Fuzz

[OldRedFord]

Well that did not pan out as planned.

Calls were made to the truss manufacturing business there. They said the motors etc were not theirs.

We get my truck all loaded up and some guy comes running yelling that its their stuff.

Might I add this stuff was in another building about 150 yards away. Vacant.
Stuff had been sitting there for a while.

Something seemed odd about all that. Its not the the truss company did not have enough room to store it. They are only using half the building they are in.

Heck they were even asked why they were storing stuff in a building so far away.

Personally I think they figured out what was going on when they were asked if it was their stuff and at the last minute decided to claim it.

Turned out good in the end tho. I might have a full time job doing grounds keeping.

I would not have made the money I made today off the scrap that is for sure.

[papabug71]

I had the chance to buy a old old "The Cincinnati" bench grinder a couple of months ago at work. Navy builders tag on it dated 7/'43. The round house was cleaning out a bunch of old tools & had a employee only sale. This thing was MASSIVE !

I passed on it cause it was 220 3 phase & I have absolutely no room for it. It was the biggest bench grinder I have yet to see. It sold for $40 bucks.

[averagef250]

Tanusfarms, #$&#$# static converters, they are junk, nothing but a huge disapointment. The article says 80% power? Try more like 1/4 the power. Build a rotary, for next to nothing and run it. to run a 3 phase motor off an rpc you do not need to balance it at all. Seriously, all you have to do to run your saw on single phase is wire in a bigger 3 phase motor, kick power to it and pull start it with a rope around it's shaft. Violla! instant 3 phase. Single phase power won't start an RPC pony, but it keeps it going and generating the 3rd leg. apply common sense and you the sky's the limit for RPC's.