Another Rotary Phase Converter

I can't say that I have ever seen Power Factor correction capacitors used in a phase converter. That's a new one. Your values for your run caps are not shown. All I can say is watch overdoing it with the run capacitors on the RPC. Too much capacitance and you will get a wild leg in the 300 to 500 volt range with no load.
I have tuned most every one I have touched down to within 5% A to C and B to C voltage wise and they are typically very stable under load.

Now as far as the motor. Is it compressor rated or not?
If compressor rated, what type of compressor?
It's important to understand that rating. If it's rated for a screw compressor then your fine. It's 100% duty cycle.
COmpressor motors are typically NOT rated to be run for hours on end. Think about how your compressor works. You use air, it comes on and pressure builds up and it shuts off. It's off for a while then cycles again.
RPC's run and run as long are you are using them. You also give up some efficency for starting torque with a compressor motor. Meaning it will draw a bit more power, and generate a bit more heat than a pump or fan motor.

I'll be very carefully monitoring the voltage and Power Factor with built in instrumentation. Measuring leg to leg output parameters as will as input voltage, current, and power factor. The input and output will will be measured with separate devices attached across their respective legs. Like I said above, I tend to over engineer stuff. :grin:

The capacitors are roughly calculated by this formula:
CL1-L3 = 4 to 5 times the motor horsepower = 75 (20+20+10+10+10+5+5+5+5)
CL2-L3 = 10 to 15 times the motor horsepower = 180 (60+60+20+20+10+10+5+5+5+5)
PF COR = (10+5+5+5+5)
Where the capacitors will be switched in and out manually by toggle switches for now. Once I get the system running, they may be adjusted on the fly by a PLC if needed.

The compressor motor is a rotary screw driver, rated for continuous inverter duty, 12.5KW, 3600 RPM nominal. Also interestingly enough rated for 6700 RPM at 114 Hz. Would make a heck of a spindle motor If you had something big enough to run it on. :)
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CL1-L3 = 4 to 5 times the motor horsepower = ~75 uF
CL2-L3 = 10 to 15 times the motor horsepower = ~180 uF
Where L3 is the manufactured leg.

Question: Given the large difference in capacitance L1-L3 vs. L2-L3, how do you know which is which when first testing? Is this dependant on idler motor rotation direction? Connections at the motor?
 
Got some work done on the RPC today. Bet you have never seen a RCP with an oil filter on it. :grin: The compressor has been gutted, but the main screw is part of the motor armature shaft so I kept the housing intact to use the bearings. The pony motor is the fan motor from the compressor. It's a 1/2 HP, 3 phase, so I'll run it with a small VFD to start the system. I used the base from the compressor to mount everything on.

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The pony motor mounting is adjustable in all axes to get proper alignment on the coupling. I think a fan is going to go on the shaft to provide some cooling.
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Tomorrow I'll do the panel cutouts for the switches and instrumentation. Once completed, the whole assembly will go on a pallet rack to get it out of the way.
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Bet you have never seen a RCP with an oil filter on it. :grin:

No sir, that's the first RPC i have seen that has twin filtration!
(most other hyperdrive generators are single filter units :grin big:)

what weight of RPC fluid are you gonna use???
What brand???
can i get some RPC fluid too??? :grin::grin big:
 
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CL1-L3 = 4 to 5 times the motor horsepower = ~75 uF
CL2-L3 = 10 to 15 times the motor horsepower = ~180 uF
Where L3 is the manufactured leg.
Question: Given the large difference in capacitance L1-L3 vs. L2-L3, how do you know which is which when first testing? Is this dependant on idler motor rotation direction? Connections at the motor?

Hi Jim,
i'm not an expert, but here is how i get to doing it.
you'll test voltage from a-b{L1,L2} , b-c{L2-L3} , a-c{L1-L3}.
you'll see one leg that is very low in comparison to the others.
in a 240v system, you'll identify the generated leg pairing, it may come in around (a-c)205v or so (in the unbalanced state)
that's the pairing that should get the larger capacitance for balancing
the other pairings may appear as 240v (a-b) and (b-c)226v respectively during operation, all dependent on rotation. (also in the unbalanced state)
this b-c pairing will require less capacitance to balance.

yes, Jim rotation of the idler motor will be a factor as to which legs get which capacitance.
 
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Thank you Mike. You confirmed what I guessed at. :) I only want to wire this thing up one time, so all I have to do is reverse the rotation if my cap connections are backwards. The caps will be available to switch into circuit per the above formula. Since I'm starting the system with a 1/2 hp, 3 phase pony motor connected to a small VFD, all I have to do is flip the switch and start the system in the other direction.

I test ran the mechanical systems last night, the pony motor spins up the idler motor just fine. But I ran into a bit of a problem. I left the main screw in place, and it started seizing on me at 3450 RPM, ran fine at 2000 RPM. Not sure where that was coming from, but maybe it didn't like the grease I used in the bearings, couldn't find any scrape marks anywhere. So I spent today extracting the main screw. The system was designed to be non-serviceable so that was a bit of a challenge. But I was able to extract the screw without damaging anything that I need to use in the system.
 
I got a bit more work done on the RPC over the last couple of days.

Here is what the cabinet door is going to look like
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Here is a picture of the power meters. I found these on EBay, $14.00, supposed to be good for 100A and 250V. We'll see how accurate they are :cautious: These will be checked against my Fluke meters. If I can get comparative values between the panel meters I'll be happy.
https://www.ebay.com/itm/100A-AC-LC...814329&hash=item1c90f0f879:g:FPUAAOSwo-NZsPKK
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And what the door looks like right now. I know the top meter might be redundant, but it will be wired ahead of the idler motor contactors. The others will be wired at the output.
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And the back view
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And the cabinet back panel

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And a better view of the cap rack. Two pieces of 0.125 aluminum spaced 1 inch apart and 1 inch off of the back panel

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I still need to order the VFD for the pony motor and the wireway to keep things neat. So in a couple of days I'll start wiring it up. The VFD will be mounted just to the right of the 2 terminal power block.

So why would you put a VFD in a RPC? Well, the pony motor is a 3 phase, 1/2 hp motor so I need 3 phase power to run it. But the best part is that the VFD has a programmable relay output. I'll program it so that when the system ramps up to speed, about 10 seconds, the relay closes, switches in the main power to the idler motor and simultaneously turns off the run command to the VFD. From there the pony motor just coasts and the system is running on the idler. Starts with minimal load that way. :)
 
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Hey Jim,

I would have one main question/concern in using a VFD in this application, when the VFD gets a stop command, the pony motor will continue turning. The VFD may go into a fault mode from voltage regeneration. It is possible to program the VFD to free run or possible shut down with a timer circuit, but I still do not know if it will go into a fault mode when it receives the stop command because it expects the motor to be stopping. Also how this would affect the output section, or feedback into the line. I would run the vFD in the V/Hz mode. Might call the VFD company and speak to someone in tech. Another option might be to use a static converter and a timer relay. I use a timer relay in my mill to control the motor blower. They are SS and have a wide range of timing functions. This 822 has two channels each with a trigger.
 

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The VFD (AD GS1) can be programmed to Coast to Stop. In that stop mode, the output section just turns off when the run command is interrupted and allows the motor to coast. I don't know about other VFDs, but I have used AD VFDs with large flywheel loads and never had a problem doing this. This particular VFD is only V/Hz.
 
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