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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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#1
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25 hp Phase converter
Ive been using a 25 hp phase converter for several years now and it's worked
perfectly except with no load there is "ghost voltage" on the generated leg. As soon as a load is applied, the voltage is quite even. The ghost voltage is twenty or thirty volts higher on the generated leg and is no problem for motors but cnc equipt is very sensitive. To be safe I would turn on a bridgeport or band saw before applying power to a cnc. I just bought a new 30 hp cnc safe converter for around $1900. If anyone is interested, I feel my old one should be worth $800. I'm in W. Mich and to lazy to arrange shipping, so if anyone is interested and within driving distance, let me know. Dixon |
#2
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25 hp Phase converter
"Dixon" wrote: (clip) with no load there is "ghost voltage" on the generated leg. As soon as a load is applied, the voltage is quite even.(clip) ^^^^^^^^^^^^^^^^^^^^^ Just a suggestion: might you put a little resistive load on--just enough to kill the ghost? |
#3
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25 hp Phase converter
On 2008-01-14, Leo Lichtman wrote:
"Dixon" wrote: (clip) with no load there is "ghost voltage" on the generated leg. As soon as a load is applied, the voltage is quite even.(clip) ^^^^^^^^^^^^^^^^^^^^^ Just a suggestion: might you put a little resistive load on--just enough to kill the ghost? My guess is that the RPC has unequal capacitance between legs 1-3 and 2-3 respectively. That was the cause of this symptom on my old RPC. i |
#4
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25 hp Phase converter
On Mon, 14 Jan 2008 08:30:03 -0500, "Dixon"
wrote: Ive been using a 25 hp phase converter for several years now and it's worked perfectly except with no load there is "ghost voltage" on the generated leg. As soon as a load is applied, the voltage is quite even. The ghost voltage is twenty or thirty volts higher on the generated leg and is no problem for motors but cnc equipt is very sensitive. To be safe I would turn on a bridgeport or band saw before applying power to a cnc. I just bought a new 30 hp cnc safe converter for around $1900.SNIP Dixon Hey Dixon, Glad you brought that up. I had real 3 phase in my last shop, but made a converter when I moved. It had really (still has really) flaky traces, although under load it is only a 20 volt spread. Anyway, it runs all the "straight" three phase stuff just fine, that is until I hooked it up to the CNC lathe. The only thing on the CNC lathe that RUNS 3 phase is the spindle motor which is controlled by a plain old motor-starter panel that is just switched on and off by the computer. But when they built the whole thong (OEM), they "balanced" the three phase across all the goodies in the box. so it ran OK for about a minute, and poooofffff....something went. It had never occurred to me to re-lug everything across just the "hot terminal", or simpler yet, start the mill or another lathe or the grinder!! That might have save me! Anilam wants $9,000 for an upgrade!! Take care. Brian Lawson, Bothwell, Ontario. |
#5
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25 hp Phase converter
"Robert Swinney" wrote in message ... There is no such thing as "ghost voltage" from a rotary phase converter. A RPC is an electrical network consisting of : 2 three-phase motors or 1 single-phase motor and 1 or more 3-phase motors running from a common source. That source may be 3-phase or single phase and 1 of the motors (the idler) can be single phase. The usual RPC consists of a single-phase motor and a three-phase motor (load) connected across a single-phase supply with appropriate "balancing" and starting capacitors. See www.metalwebnews.com for some good articles on RPCs. Bob Swinney Bob, over time I have read many of your posts and they all were well done and made a lot of sense---until now. WTF are you talking about! I certainly appreciate you trying to help me, but are you kidding? I've had close to thirty years experience with phase converters and diesel, real three phase power, and I've never heard such a convoluted explaination of a phase converter. I'm sorry, but your explaination sounds like a story one would come up with when coming home at 5 A.M. and the wife is unexpectedly awake when you try to sneak into bed! Dixon |
#6
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25 hp Phase converter
"Robert Swinney" wrote: There is no such thing as "ghost voltage" from a rotary phase converter. (clip) ^^^^^^^^^^^^^^^^^^^^ I don't believe in ghosts, either, but are we just quibbling about words here? The OP described a voltage imbalance which evidently has a high output impedance, so that as soon as it encounters a load the value becomes negligible. Why do you object to calling it "ghost voltage?" Your description of how phase converters are configured doesn't answer the question for me. If you can clarify, I'd appreciate it. Thanks. |
#7
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25 hp Phase converter
"Robert Swinney" wrote in message ... There is no such thing as "ghost voltage" from a rotary phase converter. A RPC is an electrical network consisting of : 2 three-phase motors or 1 single-phase motor and 1 or more 3-phase motors running from a common source. That source may be 3-phase or single phase and 1 of the motors (the idler) can be single phase. The usual RPC consists of a single-phase motor and a three-phase motor (load) connected across a single-phase supply with appropriate "balancing" and starting capacitors. See www.metalwebnews.com for some good articles on RPCs. Bob Swinney Hi Bob I especially liked the referenced article titled "Induction Motors and Phase Converters. I have read it many times and am still learning things about 3 phase motors from the information included therein. Jerry |
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