Announcement

Collapse
No announcement yet.

Home built rotary phase convertor

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • #16
    Originally posted by dvo
    Can someone explain the power up and power down sequence when using a machine that is plugged into a rpc? Another word what do you do when you want to use the machine?

    You simply start the RPC and then turn on the machine that you wish to power. When finished, shut off your machine and then shut off the RPC. If I am doing several different things on the Mill like moving a part or changing a collet, I just let the RPC run. It doesn't hurt a thing.

    It's best to try to build an RPC that is reasonably quiet. That's why I suggested a 1,750 rpm motor. They are usually quieter than a 3,600 rpm motor. Some people will mount the idler outsiide to isolate the sound.

    Comment


    • #17
      I have a 10HP RPC, which is very quit just a low hum & just got a 7.5HP, a 440 transformer & the guy built me a panel to switch to 440 when needed. I can use them seperate or together.This guy will build you one that works & looks Great just like it's out of the factory cheaper than you can buy the parts. PM me & I'll send his number. He really knows his stuff. I bet he's built 500+

      Comment


      • #18
        Originally posted by gnm109
        You simply start the RPC and then turn on the machine that you wish to power. When finished, shut off your machine and then shut off the RPC. If I am doing several different things on the Mill like moving a part or changing a collet, I just let the RPC run. It doesn't hurt a thing.

        It's best to try to build an RPC that is reasonably quiet. That's why I suggested a 1,750 rpm motor. They are usually quieter than a 3,600 rpm motor. Some people will mount the idler outsiide to isolate the sound.

        Thanks, just what I was looking for. Thanks for the build info too.

        Comment


        • #19
          It's not always true that larger motors don't need balance caps. I have two motors that put out very low L3 (195-210) at low load that raised somewhat as the load increased.... and needed caps to raise that. As Jerry points out - balancing is only for a specified load so you need to figure out how to "load up" your destination motor(s) while adjusting. You can use Fitch's method to get "close enough" but even 5% unbalance at full load requires significant derating of the target load motor. If you want to worry yourself, put two cheap 300 volt panel meters (the type with needles!) and mount them L2-L3 and L1-L3. Watch them out of the corner of your eye as you work, then cover them up forever

          Another aspect of "balancing" is to reduce idle (or low output current) current with power factor correction. On 240 volt single phase a 15 hp idler motor (or my 8 pole 10hp) will have about 25 amp idle current without power factor correction caps. Place caps across L1-L2 near to the motor, and it goes down to about 3 amps. This of course has no effect (for most users...) on your domestic electricity bill as the power company doesn't penalize you for power factor, but it make wiring and breaker calculation easier.
          Last edited by lakeside53; 10-23-2011, 11:19 AM.

          Comment


          • #20
            Originally posted by 1937 Chief
            I would like to build my own rotary phase convertor. I have a 5 hp 440 v three ph motor, and can probably find a pony motor. Problems is I have no idea how to connect the whole thing, and end up with three ph to my lathe. I guess I need making a rotary phase convertor for dummies. Anything out there? Stan
            Don't build your phase converter larger than the motor you want to run, it wastes electricity. It is best to use equal size motors. If you want to run a 1.5 HP Bridgeport mill use a 1.5 rotary motor. You can buy used 3 ph motors for scrap metal price at most electric motor repair shops. Get one with a damaged or bent shaft or broker motor mounts. If the shaft is bad I like to cut them off with a hacksaw.

            There are several ways to build a phase converter. A static converter will make your equipment motor run at 2/3 it power rating. A rotary converter will many your equipment motor run at full power.

            How to build a manual start static phase converter. Wire your equipment motor for 240 volts AC. Connect power to L1, L2 with a ON/OFF switch. You will need a start capacitor of 60 uf per HP. A 2 HP motor needs 120 uf. A 5 HP needs 300 uf. Connect the start capacitor between L2 and L3 with a momentary ON push button switch in series with it. To start your equipment motor hold down the push button switch then turn on the 240 VAC. When the motor comes up to full speed about 3/4 of a second release the push button switch. This is a manual type static converter it will make your equipment motor run at 2/3 power. A 3 HP motor will produce 2 HP.

            How to build a manual start rotary phase converter. Wire your equipment motor for 240 volts AC. Connect power to L1, L2 with a ON/OFF switch. You will need a start capacitor of 60 uf per HP. A 2 HP motor needs 120 uf. A 5 HP needs 300 uf. Connect the start capacitor between L2 and L3 with a momentary ON push button switch in series with the push button switch. To start the rotary motor hold down the push button switch then turn on the 240 VAC. When the motor comes up to full speed about 3/4 of a second release the push button switch. L1, L2 and L3 of the rotary motor needs to be connected to L1, L2 and L3 of your equipment motor. Turn on your equipment motor it will run at full power. L3 of each motor act like a generator and generator electricity to each other that is how it runs at full power.

            In both of the above you can replace the push button switch with a relay to take the phase converter be automatic start.

            If you use a pony motor to start the 3 phase rotary motor you don't need any capacitors or a push button switch.

            This rotary phase converter motor runs at 2/3 power until it is connected to another motor like a mill or lathe. When the machine is turned on then L3 of both motors generate power to each other and both motors will then run at full power. When your machine is turned OFF the rotary motor continues to run a 2/3 power. If you connect your mill, lathe, and other machines all to this rotary then you can turn on any machine you want L3 will always generator power to L3 of the other motors and both motors run at full power. You can also turn on several motors like the Lathe and Mill at the same time all 3 motors generate power to each other through L3.

            Your rotary motor needs to be sized close to the largest motor in the system. In my home shop I have a 1.5 HP bridgeport mill, 2 HP surface grinder, 1.5 HP lathe and a 1.5 HP rotary motor phase converter. I start the rotary motor then I can run any machine in the shop even the larger 2 HP surface grinder. The 2 HP surface grinder works good most of the time but some times it is a little short of power so all I have to do is turn on the Mill or the Lathe and just let it run and not use it. The extra motor in the circuit generates the extra power the 2 hp surface grinder needs. If I were to us a 2 HP rotary motor the surface grinder would always have all the power it needs but running a 1.5 hp mill on a 2 hp phase converter all day would waste a lot of electricity being over sized by 1/2 hp. There are several crazy tricks to make this work I could have 2 phase converter motors one being 1.5 hp and the other being 1/2 hp. I could use the 1.5 hp motor on the lathe and mill then if I need to run the 2 hp grinder I flip a switch that connects the 1.5 and 1/2 together this will equal 2 hp for the rotary. 2 rotary motors running in parallel add HP. If you need a 10 hp rotary phase converter and all you have is a 5 hp, 3 ph and a couple of 1 hp motors connect all 4 motors together and you get 10 hp. You could even connect TEN 1 hp motors together to make a 10 hp rotary converter. LOL.

            I use to use a rotary phase converter but I removed it from my circuit. I use a static phase converter and my 1.5 hp bridgeport mill does fine running at 1 hp. I have no problem with my lathe either. My 2 hp surface grinder is the only problem and if I turn on the mill and let it run the 1.5 hp mill motor acts like the rotor for the 2 hp grinder and the grinder runs fine, no problems at all. It saves electricity not having that rotor motor running all day plus I don't have to listen to it run. The 2 hp motor is probably running at about 1.95 hp from the reading I get on my amp clamp.

            Photos show an automatic start rotary phase converter.







            Last edited by gary350; 10-23-2011, 03:21 PM.

            Comment


            • #21
              For the record, the RPC idler should be somewhat larger than the motor to be operated on three phase. If you use an idler that's the same size as the driven motor, you will not have enough power due to the electrical issues mentioned above in other posts.

              Furthermore, a larger RPC idler can be used later to power larger machines.

              Comment


              • #22
                Originally posted by gary350
                Don't build your phase converter larger than the motor you want to run, it wastes electricity. It is best to use equal size motors. If you want to run a 1.5 HP Bridgeport mill use a 1.5 rotary motor.


                >>>>>>>>>>>>>

                There are several ways to build a phase converter. A static converter will make your equipment motor run at 2/3 it power rating. A rotary converter will many your equipment motor run at full power.

                >>>>>>>>>>>>>>>>

                The 2 hp motor is probably running at about 1.95 hp from the reading I get on my amp clamp.


                There are many problems with what you posted, but I just snipped out 3.

                1) You need an RPC motor 1.5 to 2X larger than the target motor to start anything but the lightest loaded machine. OK, you can "start" with a lower rated idler, but how long does it take the target to get up to speed, and what is it doing to the target motor in the ramp-up period? I have seen many cases where you cannot start a 5 hp target with even a 7hp converter because the motor starters pop due to overload caused by a sagging T3. Bypass the current trips, and it will likely get there in some time, but that's trashing your motor. A lathe in high gears is a classic test -it will start in lower gears, but not in the upper speed ranges. Another great test... in a higher gear, snap your lathe from fwd to reverse and see how the rpc handles it.

                As for "electrical waste" your lights likely use more than the RPC at Idle... A 5hp idler uses maybe 200 watts. Sure, you'll measure a high input current, but that's at a power factor of 0.1 to 0.2.

                2) A static converter does not "make your equipment run at 2/3...". Your target motor will quite happly draw as much power as you load it until it stalls (all motor are like this, whether driven from a static converter or otherwise). If you USE more then 2/3 of the rated power, you will overload and overheat the motor. And...2/3 is theoretical ; in practise it's closer to 50%. This is the problem with static converters - although they have their place, if the target motor was just sized for the intend use (most are), then it's very easy to overload it.

                3) Measuring the current of a three phase motor to determine power output is fraught with problems. Even full power (how are you determining that - did you load the grinder to develop 2hp?) the power factor is maybe 0.8...
                Last edited by lakeside53; 10-23-2011, 03:54 PM.

                Comment


                • #23
                  While the experts are on tap, could someone please explain both 'power factor' and 'service factor'?
                  Thanks.
                  Southwest Utah

                  Comment


                  • #24
                    Originally posted by chipmaker4130
                    While the experts are on tap, could someone please explain both 'power factor' and 'service factor'?
                    Thanks.
                    I found Power Factor on Wikipedia. Check it out for explanatioin. I know longer do Wikipedia links.

                    Here's a nce short explanation of Service Factor. I sort of knew what it was but I this is better than my explanation.

                    http://www.engineeringtoolbox.com/se...tor-d_735.html

                    P.S. I'm no expert.

                    Comment


                    • #25
                      Power factor is just a number that relates the "actual" power drawn to the "apparent" power drawn. It is the fraction of the "apparent power" that is actual power.

                      Actual" power is power that can do heating or other "actual" work.

                      Because a motor has an "inductive" character, current is not drawn exactly "in phase" with voltage. Current is drawn related to "how long" a voltage has been applied (mathematically there is some calculus involved).

                      As a result, maximum current flows somewhat later than at maximum voltage. And current is still flowing when voltage is zero.

                      In a resistor, voltage and current are exactly in-phase, the maximum of one is the maximum of the other. Current changes instantaneously when voltage changes. In an inductor, current takes some time to change after voltage changes.

                      Power is the product of voltage and current. A current of 1A at 100V is 100W, but a current of 1A at 10V is only 10W.

                      So, with a resistor, you can measure the current with one meter, and voltage with another, and get actual power. The "apparent power" is equal to the "actual power".

                      With an inductive load (or a capacitive load), when you do that same measurement, you get "apparent power", but it is NOT the same as the actual power, because the current is delayed, it has a "phase shift".

                      As a result, the voltage is lower when the current is flowing. The voltage you measure is not occurring at the same time as the current you measure. The "apparent power" is larger than the "actual" power. One has to multiply the "apparent power" by the cosine of the phase angle between currrent and voltage. That is what the power factor is.

                      In an unloaded motor, the inductive characteristic is the main effect, so the current is "phase shifted" quite a bit. The "power factor" or fraction of actual power, can be quite low, like 0.1 or 0.2. Only 10 or 20% of the power the motor *appears to be drawing* is actually being used.

                      As you load the motor, more actual power is drawn, and the "power factor" goes up. It can reach anywhere from 0.6 to 0.8, meaning that 60 to 80% of the "apparent power" is actually being used.

                      With a resistor, the power factor is 1.0, all the "apparent" power that you get by multiplying measured current by measured voltage is actually power being used.
                      Last edited by J Tiers; 10-23-2011, 09:59 PM.
                      1601

                      Keep eye on ball.
                      Hashim Khan

                      Comment


                      • #26
                        Thanks, Jay.
                        I think I actually followed that!

                        Thank you too, gnm109.
                        The S.F. link was very clear as well.
                        Gordon
                        Last edited by chipmaker4130; 10-23-2011, 10:50 PM.
                        Southwest Utah

                        Comment


                        • #27
                          The simple one I did was based on the advice of a local motor rebuilder. His advice was, first, to run at least once size larger than the motor you need to power. The second thing he recommended was to use an old sleeve bearing motor, the older the better. At one time you could pick up old motors like this for a song, since they're obsolete and unwieldy, but a big old motor will be smooth and quiet and have lots of copper in it.

                          Comment


                          • #28
                            As you guys have correctly decided my Idler was 2hp as was my driven. The VFD is sweet beyond words, but if I had to go bigger then the RPC would make the most sense. Used 3 ph motor seem readily available.

                            Comment


                            • #29
                              Originally posted by chipmaker4130
                              Putting a little time into balancing the output with capacitors will do a lot to reduce all of those problems.

                              This is what I did and it both starts itself and is well balanced just on a motor and some capacitors. The capacitors also force it to start in the same direction all the time.

                              I think it depends on your motor, mine would self start from 240 single phase so I just need capacitors to balance things and influence start direction. No relays, no startup motors, its simple. I'd try your motor on single phase as a quick test to see what it does.

                              Be safe, these are scary voltages.

                              KEJR

                              Comment


                              • #30
                                Which potential relay should I look for or what spec do I need to look at? Will universal potential relay work?

                                Comment

                                Working...
                                X