More RPC questions

Ok, I am planning on using this method to assemble a rotary phase converter, I already have the idler motor and the static phase converter, but I have a few questions if I can get help. Here is the schematic of how to hook up the RPC:



Questions:

1. With this method it shows using the same wires T1, T2, and T3 on my idler motor to input power from the static converter and to output to the load motor, my question is if I should use different wires to output from the motor? My idler motor has 9 wires in the box.

2. On the 3-pole switch, should I use a magnetic switch, or should I use a standard 3-pole switch?

3. It was mentioned in my first thread that I may want to balance the load using capacitors, where would they go in the mix? What type should I use and how do I test for balance? Is there a good resource where I can read more on balancing the phases?

4. Should I run wires right from my lathe to the idler motor, or should I run the idler motor to a circuit breaker, and then from the circuit to the lathe?

Thanks for any help you can give, I know I am new and have little understanding of terminology, but feel with the right guidance I should be able to hook this up without any problems.

Thanks!

Dave

I bought a facory-built RPC on eBay. It's rated 5 hp. The hookup diagram shows a two pole switch to feed the 240 VAC single phase into the machine. It has a relay that starts the idler motor which then generates L3 to provide three phase.

There are capacitors on the three output lines to balance the voltage. Sorry I don't know the values as I couldn't get a true schematic from the company, just a hookup diagram. Across L1-L2, I'm getting 240 VAC. When underway, I get about 260 across L1-L3. It works very well and startng is almost instantaneous. The only thing is, if it ever breaks, I'll have to reverse engineer it to fix it since they don't give out their values because they apparently don't want people making their own. It is guaranteed for a year, though. I could have probably built one if I'd tried but I was sort of in a rush to get my mill running. I do know that the idler motor is 3,600 rpm and it's a TECF, made in China, of course, although they removed the motor plate. The box has a tag showing a 5 hp rating.

I have it on a 20 amp 240 VAC line with a breaker. Downstream of the RPC, power goes through a 3 pole 20 amp breaker and also though a three phase on-off switch on the back of the Mill that I just leave on since I can't reach it anyway. Right now I'm using a 20 amp breaker for an RPC start switch until I can find a proper switch. They seem to be very expensive.

I'm curious about the use for the static converter within your RPC design. Is that used to start the idler? I was told that those will cut your power but I don't know for sure. Thanks in advance.

Here's a picture of the wiring hookup that came with my unit. The box on top of the idler motor (Rotary Phase Converter in the Picture) has three capacitors and one startng relay.

The static phase converter in the diagram I posted is to start the idler motor, since it doesn't use much power when not under a load, it doesn't matter, basically I only use the static converter to start the idler motor, then it is switched off as soon as the light comes on in the static converter. I don't plan to do a fancy self start or switchless design, so this should work for now, I am still confused on how to balance the phases, but I keep reading so hopefully I will figure it out. From what I can tell that isn't necessary, so I may just run it like the diagram shows for now, and then see what I get.

Thanks for the input!

Dave

DebosDave said:

The static phase converter in the diagram I posted is to start the idler motor, since it doesn't use much power when not under a load, it doesn't matter, basically I only use the static converter to start the idler motor, then it is switched off as soon as the light comes on in the static converter. I don't plan to do a fancy self start or switchless design, so this should work for now, I am still confused on how to balance the phases, but I keep reading so hopefully I will figure it out. From what I can tell that isn't necessary, so I may just run it like the diagram shows for now, and then see what I get.

Thanks for the input!

Dave

Click to expand...

I see. Well, it looks like it ought to work fine.

Ideally you will use a magnetic contactor to bring
power in to the idler motor. This is because a contactor
like that will drop out during any sort of power failure
or dip.

That way the idler cannot try to start, when it is at
a dead stop when the power comes back up.

Jim

So that would be a 3-pole magnetic contactor instead of just a switch?

Newman109 said:

I bought a facory-built RPC on eBay. It's rated 5 hp. The hookup diagram shows a two pole switch to feed the 240 VAC single phase into the machine. It has a relay that starts the idler motor which then generates L3 to provide three phase.

There are capacitors on the three output lines to balance the voltage. Sorry I don't know the values as I couldn't get a true schematic from the company, just a hookup diagram. Across L1-L2, I'm getting 240 VAC. When underway, I get about 260 across L1-L3. It works very well and startng is almost instantaneous. The only thing is, if it ever breaks, I'll have to reverse engineer it to fix it since they don't give out their values because they apparently don't want people making their own. It is guaranteed for a year, though. I could have probably built one if I'd tried but I was sort of in a rush to get my mill running. I do know that the idler motor is 3,600 rpm and it's a TECF, made in China, of course, although they removed the motor plate. The box has a tag showing a 5 hp rating.

I have it on a 20 amp 240 VAC line with a breaker. Downstream of the RPC, power goes through a 3 pole 20 amp breaker and also though a three phase on-off switch on the back of the Mill that I just leave on since I can't reach it anyway. Right now I'm using a 20 amp breaker for an RPC start switch until I can find a proper switch. They seem to be very expensive.

I'm curious about the use for the static converter within your RPC design. Is that used to start the idler? I was told that those will cut your power but I don't know for sure. Thanks in advance.

Here's a picture of the wiring hookup that came with my unit. The box on top of the idler motor (Rotary Phase Converter in the Picture) has three capacitors and one startng relay.

Click to expand...

Your drawing shows that the generated leg is not protected with a fuse.
That is not good!

Kevin shows...

and I'll tell.

Hi Dave!!

The picture Kevin shows you is a common style of magnetic contactor.

A contactor is a type of relay. There's an electromagnet coil pulling in an arm that has at least 3 shorting-bars on it... these shorting bars connect large contacts on each side, to switch three power leads on and off.

Contactors are designed to carry substantial power.

Jim's comment is a major point-of-concern... Standard practice for industrial safety, is to wire a contactor in line with the machine, and use two pushbuttons to start and stop the machine's power source... wherin you push the START button, applying power to the contactor's coil. Once pulled in, an auxiliary contact of the contactor bypasses the 'START' button, holding the contactor's arm in. To STOP the unit, a second pushbutton (with normally-closed contact) interrupts the coil circuit, causing it to 'drop out'... so push to start, push to stop.

IF your shop power is somehow interrupted, the coil naturally drops out, and will not restart until you press the START button.

Reason for this: IF you lose power, and the machine shuts down, you DON'T want it to restart on it's own... not only is it hard on the grid, and your shop power system, if someone happens to be in the vicinity of the machine, they could become part of the machine's work.

In response to your other questions:

It's always wise to include protection on the input and output... for safety of your converter, equipment, power system, and person. Surplus 3-phase breakers, contactors, etc. are easy to find, easy to mount and work with if you do some careful hunting.

Balancing and static converters... A Rotary converter uses an idler motor, and can be performance-enhanced by placing balancing capacitors between the phases. A STATIC converter is nothing more than capacitors... by connecting them across the legs of a 3-phase motor, it allows the 3-phase motor to start and run on single phase power, albeit with a substantial power penalty.

A Rotary Converter is nothing more than a static converter (capacitors) with an idler motor. The rotary converter grants much more power to the tool, and it's not very complicated... they're so cheap and easy to build, that most guys won't even consider buying a commercially-made unit.

For more info on balancing, look at the "sticky" threads... the plans for Fitch-Williams and others identify the ballpark capacitance values... what you hafta do, is get a double-handful of various motor-run caps, three voltmeters, and experiment. Measure voltages across the three phases, and add or subtract one at a time to get the closest voltage balance. What'll happen, is that you'll find one leg WAY high, and as you get closer, the others will get a little strange. Try to get 'em fairly close, but don't drive yourself crazy to get it perfect, because it's not possible to make it (and keep it) perfectly balanced... just get it closer than raw, and it'll be fine.

DaveKamp said:

and I'll tell.

For more info on balancing, look at the "sticky" threads... the plans for Fitch-Williams and others identify the ballpark capacitance values... what you hafta do, is get a double-handful of various motor-run caps, three voltmeters, and experiment. Measure voltages across the three phases, and add or subtract one at a time to get the closest voltage balance. What'll happen, is that you'll find one leg WAY high, and as you get closer, the others will get a little strange. Try to get 'em fairly close, but don't drive yourself crazy to get it perfect, because it's not possible to make it (and keep it) perfectly balanced... just get it closer than raw, and it'll be fine.

Click to expand...

I disagree with the comment about balancing. I got my RPC lines to balance
within a volt of each other. 247v, 247v, 248v. Just take your time and use a
chart. If you really want to get into it you can solve a few network equations.
If you are running the RPC for multiple machines then it is better to adjust
your capacitor network for the machine you use most often.

wherin you push the START button, applying power to the contactor's coil. Once pulled in, an auxiliary contact of the contactor bypasses the 'START' button, holding the contactor's arm in.

Click to expand...

There needs to be one *teeny* correction to that schematic - I know for a
fact, you didn't wire it that way!



Jim

wippin' boy said:

Click to expand...

A auxiliary contact is supposed to be across the start switch.

I think if you wired it that way, the thing would wind up as a relaxation
oscillator. Until the contact smoked out, anyway!



Just swapping the coil and the NO start switch, that would put it right.

Jim

you know
this is about the 3rd time i have put up that pic
and every time you guys catch that
need to get that drawing updated
fact is i did wire it that way
the first time
and the damn thing didn't work (doa!)
i really need to remember to change that (fat chance)
sure is pretty though
gotta love that Visio
i submit (as allways) to the engineers
us blacksmiths don't have to be as good in the "debugging stage" as we are the ones
that catch our mistakes, so no one knows but ourselves
(unless of corse you post them on the webs largest manufacturing and technology forum )