440v 3 Phase Rotary Converter Help

I am new to this forum and have read a lot of threads looking for solutions to an issue I am having with a phase converter. I obtained a 7.5hp rotary phase converter(autostart with capacitors, relay, etc.) from a guy who used it in his woodworking shop until he went to a VFD. It was wired in using 220/240 single phase and worked great. There are no tags on the RPC because it was removed to be re-painted and never put back on. The guy told me that it was a Baldor motor. For my shop I have a hoist that was removed from where I work. The hoist is a 440/480 3 Phase only setup. (That's what the diagram/tag inside the cover to the junction box on the hoist says) Along with the hoist from work came an ACME 10KVa general purpose transformer (model T-2-53516-3S). It is a 240 X 480 PRIMARY VOLTS — 120/240 SECONDARY VOLTS — FOUR WINDINGS — 1Ø, 60 Hz. I used this transformer backwards to step up my single phase input voltage to 480. I then re-wired the phase converter motor over to the 440 settings(there were 9 wires coming from inside the motor labeled T1 thru T9) using the following directions that I located on the internet:

For 440V, Leg 1 gets hooked to wire 1, Leg 2 gets hooked to wire 2, Leg 3
gets hooked to wire 3. Wires 4 & 7 are connected, wires 5 & 8 are
connected, and wires 6 & 9 are connected.

I left the capacitors and relay/switch wired the same way they were when wired for 220/240 and connected the single phase inputs to the same place. The way it ended up being wired was the incoming single phase connects to Leg 1 and Leg 2. Leg 3 is where the "third" phase is produced for the output.

The issue I am having is that when I apply power to the RPC it starts turning slowly, the relay in the start circuit connected to Leg 3 opens, disconnecting the start circuit. The motor continues to turn slowly until it kicks of my double 30 amp circuit breaker.

I have done some troubleshooting with a volt meter. In the knife switch box used to apply power to the RPC with the knife switch open(no power to RPC), I get appox. 475 volts on the two terminal lugs where the knife switch makes contact. If I go from each terminal lug separately to the neutral/ground bar in the box, I get approx. 275 on one and approx. 198 on the other. Could this single phase voltage difference on the input legs be the issue or is something wired wrong in the start circuit with the capacitors not starting the motor correctly or just something not wired right? I am sure I missed something in my explanation of the system, so feel free to ask questions and input your theories. Thank you.

The problem is the RPC capacitors and circuit have to be reconnected for 440vac ( the capacitors can be changed from a parallel circuit to a series circuit ) but the contactors and potential relay have to be changed or put voltage drop resistors in series with the coils.
Your best bet is to feed the RPC with 230vac single phase, than step up the output side of the RPC with three phase transformer to 440vac three phase.
The reason your RPC is turning slowly is the potential relay pickup voltage is being achieved as soon as you turn on the power to the RPC, the RPC will never build up speed at this point.

Is there a website that might have a schematic to reconfigure the capacitors/start circuit for a 440v setup? I know a 3 phase transformer would be easier (I have priced a few..$$), but I am currently working on a tight budget and was trying to use what I had on hand already. Thank you for your help.

"The reason your RPC is turning slowly is the potential relay pickup voltage is being achieved as soon as you turn on the power to the RPC, the RPC will never build up speed at this point"

Correct.

You could try connecting a modified Steveco 90-66 at an alternate point.

(The modification is to isolate the 90-66's internal contactor's connection from its "sensitive" coil).

Let's say your Y-wound idler has (1) to L1/A, (3) to L2/C and (2) to B.

Let's also say your Y-wound idler has (4) connected to (7), (5) connected to (8) and (6) connected to (9).

You could, for example, connect the 90-66's "sensitive" coil to (5)/(8) and (6)/(9) and then the isolated end of the 90-66's internal contactor to (2), and the remaining internal contactor terminal through the starting capacitor to (1).

The 90-66 should see one-half of the B-C potential, and should respond as expected, holding the starting cap in-circuit until it was "picked" at about 460 volts B to C, but about 230 volts (5)/(8) to (6)/(9).

Just a thought.

That's a good idea Peter, I will have to remember that one.

lounsbmw can you post the internal wiring of your control panel, so we can help you with the internal connections for 440vac

The way the 9 wires to the motor are wired are almost exactly like Peter listed. L1(single phase in) to Wire (1) of motor
L2(single phase in) to Wire (2) of motor
Wire (3) of motor goes to relay/switch and out of box to supply "3rd" phase.
Wire (4) is connected to Wire (7)
Wire (5) is connected to Wire (8)
Wire (6) is connected to Wire (9)

There are two run capacitors (silver metal) and one start capacitor (black plastic) in the circuit. I can't remember the specifics right now of where they are wired in. I am at work and not in front of the control panel... Thanks.

Just to be sure, is this the 90-66 that was referred to?

http://www.grainger.com/Grainger/wwg/itemDetailsRender.shtml?ItemId=1611630458

Thanks again.

Yes that is the correct grainger number, but you will have to remove the internal jump connection between the pickup coil and terminal 2. I will work up a diagram and post it for you.
I do need to know the MFD rating of the start capacitor?

Attached is a thumbnail schematic of what I disclosed, above.

Peter

Yes, the Grainger 4E655 is the correct part.

For 5 HP and less, the 4E655 is the one.

There is a GE "sub", but it is only good for 3 HP and less.

However, if you are making a larger than 5 HP RPC, then you are going to use the potential relay to control an auxiliary contactor, in which case it really doesn't matter which P.R. you select.

FWIW, a 90-66 can safety, and reliably switch about 550 µF at 240 volts. (The actual maximum is 552 µF; at 480 volts, this maximum is 276 µF).

The 90-66's contacts are rated 50 amps.

For a 480 RPC, you actually need 1/4 the capacitance of an equivalently rated 240 RPC.

While I have not personally put it to the test, this fact should mean you can use a 90-66, modified as disclosed, above, to make an RPC rated 20 HP at 480 volts.

Peter's diagram is correct, and he is right about using 25% of capacitor value as compared to a 240vac RPC design. And it does work, as I do have a few out in field right now

What about the voltage rating on the caps?

I see that Peter's diagram shows caps in series but what if one of them shorts?

"I see that Peter's diagram shows caps in series but what if one of them shorts?"

Always use caps marked "Protected with a series resistance".

That, plus install a 15 kilohm 5 watt resistor across each cap, both as a bleeder and as a voltage equalizer.

I do agree with the resistors, but I never seen a capacitor labeled "Protected with a series resistance"

Should he check the caps in his unit?

Since the RPC was set up for 230VAC operation they may let the magic smoke out if he tries to use them at 460.

What about the voltage rating on the caps?

The start caps will have a voltage rating of 250vac and the run caps will have a rating of 370vac.
Example would be two start capacitors that are rated 400mfd 250vac each, now if the two caps were wired in series the new total value capacitors would be 100mfd 500vac

Torque1st said:

Should he check the caps in his unit?

Since the RPC was set up for 230VAC operation they may let the magic smoke out if he tries to use them at 460.

Click to expand...

I dont think the start cap went bad, since is was removed from the circuit as soon as the RPC was power up. It would be a good idea to check the run caps, but since the RPC was not up to speed the B phase voltage would be alot lower than 460vac

"I never seen a capacitor labeled "Protected with a series resistance"

That's my term.

The industry-standard term is, "Protected".

I believe my term is more complete, and is more descriptive.

In the example I gave, above, the resistor provides both a voltage equalization function and a bleeder function.

It would be bad if he wired it all up then put power to it and had the caps fail explosively...

Torque1st said:

It would be bad if he wired it all up then put power to it and had the caps fail explosively...

Click to expand...

As I stated before, it might be a good idea to check them out. But I still believe the caps never seen 460vac across them.
The start cap was disconnected from the circuit since the pickup voltage is about 230vac on the potential relay. And since the idler motor was in lock rotor condition, the voltage across the run capacitor would be well below 370vac ( as the manufactured phase could not generate voltage at 0 rpm, I do think you would get a transformer action in the b phase winding, my guess would be 230vac )

I agree, they probably have not seen a large voltage yet...