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  • lakeside53
    replied
    I would not be upsizing breakers without some in investigation as the real issue. Masking a problem is a great way to burn out a motor (either the idler or the target). BTW.. by NEC all these motors - idler and press should have OC protection - not just the source breaker.

    As I suggested before - just put a voltmeter on the t3 leg (t1/l1-t3, t2/l2-t3); that will tell you pretty much everything. In the absence of real data, it's pretty good bet the T3 is sagging, the motor isn't getting to its rated speed and is hogging current. It's a VERY common problem with undersized rpcs.

    Also... in an early post the OP mentioned that the idler has no capacitors. While there are a few motors that will produce close to the rated t3 voltage without corrective capacitors, it's unusual. The last two I made produced 212v and 192v respectively without correction (242v input). You should try to get within 5% at load. However... even 5% difference requires a significant derating of the target motor.
    Last edited by lakeside53; 11-19-2013, 09:12 PM.

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  • PStechPaul
    replied
    If the 50 amp breaker takes 5 seconds to trip, it is probably seeing 150-250 amps for that time, and unless there is a huge inertial or static load on the motor, it should be up to speed and drawing nominal current by then. A clamp-on ammeter would be a wise investment to see what is going on. You might also measure the currents on the three phases going to the press from the RPC, to see if one (or more) is drawing a lot more than the others, which would indicate an imbalance situation, or a defective phase in the motor.

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  • Ironwoodsmith
    replied
    From what I am hearing you are popping the 50 amp breaker feeding the RPC. But before that happens the press starts and runs for 5 seconds. If the press can start then the RPC is at least close to adequate size. I would try a 60 amp breaker before I did anything else. I run my shop with a 20 hp RPC. One of the machines I run is a 15 hp Woodmizer sawmill. It has no problem starting the mill in gear or out. I occasionally start the mill in gear by mistake. I run the RPC off a 100 amp breaker. One other thing to look at is wire size and run length. Excessive run lengths or undersized wire will add resistance and pop the breaker sooner than it should.

    Try the 60 amp breaker first, I think it may solve your issue.

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  • RichardG
    replied
    You said that the press will run for a short time before it trips out is the bypass valve working? I would think that if it runs for a short time and then dumps that there is a big load some where. Just my two cents
    Richard

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  • rdhem2
    replied
    I have a silly question. Why is the hydraulic press starting with a load on it? I believe it should just be spinning bypassing oil until the valve to the cylinder opens, then basicly free running until the ram contacts the load. Just a thought.

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  • J Tiers
    replied
    Originally posted by PStechPaul View Post
    The very high starting current is mostly due to the full voltage starting which was the norm before VFDs became commonplace and inexpensive. Most 3 phase motors have locked rotor and breakdown torque of 2-4x nominal, and current is generally proportional to torque. A VFD uses reduced voltage starting while maintaining maximum torque and thus the current drawn from the single phase mains will be much lower than the current supplied to the motor. If the PhasePerfect must accommodate full voltage starting, it needs to be oversized by 2x to 4x, so you are paying for a 20-40 HP VFD when all you really need is 10 HP. I think it would be worthwhile to try a dedicated VFD for the press, and perhaps smaller ones for the other tools. The total cost would be less than the PhasePerfect, and provides better control of motor startup, speed, and torque, with better efficiency and safety.
    AS mentioned, of course the P-P supplies a single (3rd) phase of 230VAC to complete the 3 phase, which is the same job the RPC does. A VFD supplies THREE phase outputs, so for equal current capability the VFD must have THREE TIMES the amount of expensive output devices, rectifiers, heatsinks, and filter capability.

    Then also, the VFD in this size will likely need to be derated due to using single phase input. So even if a 10HP was OK, it might have to be rated at 20HP just to get the 10HP capability on single phase input.

    You CAN use a VFD set to 60Hz (50 Hz for others) to act a bit like a phase perfect. But you need it to be rated at the starting surge of your largest motor, plus the FLA of everything else, AFTER derating for single phase input.

    Then also, either an RPC or the P-P has an ADVANTAGE vs a VFD, in that both the RPC and P-P can return energy to the power line, where the typical VFD cannot. (we are not discussing "system drives" here.) The P-P is fully bidirectional, where an RPC is about 3/4 to 7/8 effective on bidirectional power flow, due to impedance on the generated leg. Returned energy is from an overhauling load, or certain kinds of braking setups.

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  • WilsonT
    replied
    Michael,
    You may have missed the almost incidental mention of the three phase generator by PStechPaul in his first response. He said that I might use the generator along with a VFD to power the shop. Although, I am not sure that the generator would be more reliable and less expensive than the grid. We do occasionally have blackouts (usually during the worst weather), but for the most part the grid is pretty reliable. As far as expense is concerned, the units that I have seen that will generate three phase and large enough to power the shop are diesel. While I realize that diesel engines will run for a long time with proper maintenance, they run best if run frequently. Also, diesel seems to be the most expensive fuel currently available. (Although, I have looked into Bio-diesel, and if diesel goes back to where it was a couple of years ago, I might start making some.) Who knows, maybe using the genset with a battery bank would provide the a good, even three phase without the grid.

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  • mike4
    replied
    I have read this thread and am interested that no replies mentioned a three phase generator.
    The RPC approach seems like an electricity waste to me and the VFD means the shop is still totally dependent on an increasingly unreliable and expensive grid.
    The genset would supply all of the required power and possibly a little more , give him immunity from blackouts etc .

    Just my approach.
    Michael

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  • PStechPaul
    replied
    I was surprised at the 53.9 amps for the 7.5 HP on 230 VAC, as 5.6 kVA should draw only 24.3 amps. But if there is no power factor correction, then that seems about right, because of the large capacitive load. However, I searched for phase converter drives with PFC and I found this interesting device that not only incorporates PFC but also can boost the 240 VAC input so that the drive can directly supply 480 VAC three phase. The 10 HP version needs a supply rated at 58 amps, and has a PF of 0.98:


    Interestingly, the email address is phaseperfect.com!

    The other hits I got were for foreign sources or much smaller VFDs.

    I wonder if the power factor for the rotary phase converter is lagging (inductive), in which case it may provide PFC for the capacitive load of a standard three phase VFD? But you need to be careful when you combine inductance and capacitance, as resonance can create huge voltages. I built a static phase converter using a 100 mH 10 A reactor and something like 70 uF capacitors, plus some large power resistors (heaters), transformers, and Powerstats. At one point I did not have the resistors connected properly and the voltage meters spiked and there was some arcing until the line breaker tripped.

    I'm approaching this from an electronic engineering perspective and not so much from that of a machinist who just wants a reliable system to run his machines, so my suggestions might be somewhat "outside the box" and inappropriate for the purpose at hand. But if I wanted to provide three phase power to my shop, I would definitely try to use a standard VFD and provide PFC, or add the battery bank which would also provide the function of a UPS and emergency power.

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  • lakeside53
    replied
    I would not consider the problem PP or VFD for just your press. Only consider it to replace your RPC with a more capable device, and the press problem goes away.

    To run the press without going the vfd route you'd need a larger RPC anyhow - 15-20hp. That will require an update of your breaker and maybe wiring anyhow. The combined current drawn with large idler and smaller motor is complex (no pun intended) as the idler power factor will be lousy when the smaller motor is running at full load; power consumption isn't vastly increased, but breaker doesn't see power- only current. If power is important to you, a 10-15hp large idler will draw 750-1200 watts at "idle" - a PP is about 100 watts.

    Adding a vfd to your press may not be as simple as you think - I assume it has control/safety logic that needs to be accommodated. Sure you can work around it, but do you want to?

    Current for single phase 7.5hp vfd? - 53.9 amps at 230v for the rated output... 71 amps for the 10hp version. No free lunch - that's only a small amount more than the PP will also draw at that output. http://www.polyspede.com/pdf/spedestarb.pdf

    The PP gives you a lot of flexibility for the future - I don't worry about how to deal with three phase issues on machines I buy now - so long as it's less than 10hp. I plug it in and it works. And.. I can add three phase vfds to machines if I desire (which is why I added a 480v transformer to use the stuff nobody wants!).
    Last edited by lakeside53; 11-19-2013, 03:14 AM.

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  • WilsonT
    replied
    These are the points as I understand them to this point. Please correct me if I am wrong.

    A 10hp Phase Perfect
    ---Uses single phase to create 3 phase of the same voltage.
    --Will replace the rpc that I now have and will be able to run the 7.5hp press without tripping a breaker.
    --Will allow all my machines to be attached to the same circuit (as they are now)

    A 10hp VFD
    --Will need to be dedicated to the press and require that I have other phase conversion for the other machines.
    --Will convert single phase to 3 phase albeit not as cleanly
    --Allow for a softer start of the press to reduce required amperage draw.
    --Is significantly cheaper than the Phase Perfect.

    I currently have a 50amp service to the RPC. If I use a Phase Perfect, I may need to upgrade wiring to a 60amp circuit. If I add a VFD for the press, I will need to add a circuit or at least add double lug with the rpc circuit. How much current should the vfd be supplied with?

    The cost of the Phase Perfect is doable, but is it worth 4 times the price of a VFD? The real question is whether I will use the press enough to justify the price of either the PP or VFD. I bought it several years ago from CL, had it at a friends shop (wired up and working) then brought it to my shop when I got it built. I have never actually used the press. It is rated at 100 tons. I would like to get it usable but it is hard to justify the price.
    Last edited by WilsonT; 11-19-2013, 02:42 AM.

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  • lakeside53
    replied
    But a Phase perfect supplies the entire shop with real three phase; not just one machine. And you don't have to worry about the machine control systems. The OP can ditch the RPC... that's what the PP replaces. Yes, it's oversized, but only for surge; it's continuous rating is still only 30-36 amps. That has a cost but considering what it does it's not unreasonable.

    As much some think every HSM wants the cheapest solution no matter, not all think this way. Sure, vfds per machine is one solution, but they are not for everyone. Some of us like to rewire the machines, program and fine tune vfds, some just want a power switch. For many the vfd programming is a huge challenge and all they really want to do is make chips. The only thing you have to do with PP is turn it on.

    I of course have both PP and VFDs
    Last edited by lakeside53; 11-19-2013, 02:43 AM.

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  • PStechPaul
    replied
    The very high starting current is mostly due to the full voltage starting which was the norm before VFDs became commonplace and inexpensive. Most 3 phase motors have locked rotor and breakdown torque of 2-4x nominal, and current is generally proportional to torque. A VFD uses reduced voltage starting while maintaining maximum torque and thus the current drawn from the single phase mains will be much lower than the current supplied to the motor. If the PhasePerfect must accommodate full voltage starting, it needs to be oversized by 2x to 4x, so you are paying for a 20-40 HP VFD when all you really need is 10 HP. I think it would be worthwhile to try a dedicated VFD for the press, and perhaps smaller ones for the other tools. The total cost would be less than the PhasePerfect, and provides better control of motor startup, speed, and torque, with better efficiency and safety.

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  • J Tiers
    replied
    Originally posted by lakeside53 View Post
    However... a 10hp vfd is not a Phase Perfect.
    Truth........

    A P-P rated for 30A continuous output will be able to supply something much more like 200A or 250A as a motor start surge, without any limiting or tripping off.. A VFD with a similar rating MAY be able to supply as much as 60A for a very short time.

    That high current capability takes much heavier duty devices than the VFD and a good heavy duty power supply as well. Plus the control circuits to do it without a hiccup. That ain't cheap, and the P-P pricing reflects that.

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  • lakeside53
    replied
    However... a 10hp vfd is not a Phase Perfect. The PP puts out a single channel of precision sine wave continuously phase referenced to the pass-though L1/l2 of the single phase input, and in the process creates 3 phase delta. It doesn't care what you connect to it. A VFD "expects" that it is connected to a motor. Although they share similarities, they are quite different in operation.


    Maybe I missed them, but...I find it interesting that after many years there aren't other brands of "phase perfects" to buy...
    Last edited by lakeside53; 11-18-2013, 11:26 PM.

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