Another 3 phase Question

[outlawspeeder]

What are you looking to power outlaw?

K&T #3 model K New 10HP motor.

SO I think I am back to a VFD. For the cost of a DPS.. A couple of bucks more I get soft start and something that is known..

Thanks' for everyone's input.

[rdfeil]

It is not that static converters do not work. To a large degree, they do. But it is the use of the word "digital" that brings up such concern. I would not do business with them. PERIOD!

That is why I said "almost" snake oil

[The Metal Butcher]

K&T #3 model K New 10HP motor.

SO I think I am back to a VFD. For the cost of a DPS.. A couple of bucks more I get soft start and something that is known..

Thanks' for everyone's input.

I thought it might be.

Let me give you another suggestion. Clutch machines are easy to start. I don't think your 5hp could get it. Start caps could though. But your 5hp could run it. So, you could have two options. Add some start caps that come online when starting and run it single phase. You'd have, ~7hp then? Still plenty. Or add some start caps and hook it to your RPC. The RPC will run it plenty fine. I know dad's 7.5 is rated for 22hp running. So 5, maybe 15. It would do it. That's a cheap, cheap solution and requires minimal electrical mods.

[Fasttrack]

I thought it might be.

Let me give you another suggestion. Clutch machines are easy to start. I don't think your 5hp could get it. Start caps could though. But your 5hp could run it. So, you could have two options. Add some start caps that come online when starting and run it single phase. You'd have, ~7hp then? Still plenty. Or add some start caps and hook it to your RPC. The RPC will run it plenty fine. I know dad's 7.5 is rated for 22hp running. So 5, maybe 15. It would do it. That's a cheap, cheap solution and requires minimal electrical mods.

And it's worth asking, how often will you really be using all 10 horses? In a non-production environment ... well I'm willing to bet that many of us on this forum rarely run their machines at full power. I'd suggest trying it with the 5 HP RPC and see what happens. You might be surprised.

Of course, I don't know how your RPC is built or what kind of overload protection it has. I suppose you'd be pretty p*ssed at me if you tried it and then let the confetti out of a capacitor or the magic smoke out of the idler...

[Sparky_NY]

K&T #3 model K New 10HP motor.

SO I think I am back to a VFD. For the cost of a DPS.. A couple of bucks more I get soft start and something that is known..

Thanks' for everyone's input.

A short while ago I started a thread on a real cheap 10HP single phase VFD that I bought on amazon. It worked great and was real cheap ! Might be of interest to you.

https://bbs.homeshopmachinist.net/forum/general/1959697-replacing-a-bad-yaskawa-vfd-with-a-cheap-import-10hp-single-phase

[gellfex]

A short while ago I started a thread on a real cheap 10HP single phase VFD that I bought on amazon. It worked great and was real cheap ! Might be of interest to you.
https://bbs.homeshopmachinist.net/fo...p-single-phase

Given the prices of VFDs today phase converters make little sense. I disassembled my RPC a few years ago after getting my 4th VFD. But my biggest motor is 2hp.

[J Tiers]

Given the prices of VFDs today phase converters make little sense. I disassembled my RPC a few years ago after getting my 4th VFD. But my biggest motor is 2hp.

Maybe....

An RPC is "stone hammer simple", almost literally bulletproof, and can sit there working fine for decades. The parts involved are likewise simple, and the most basic version requires nothing other than a large motor and some wiring.

While VFDs are reliable devices (if made by reputable companies), they are definitely not as reliable as motors. The MTBF has to be lower due to the large number of parts.

If you need variable speed, your other options beside a VFD are limited. But if you only want reasonable 3 phase created, an RPC is the simplest and generally most reliable method.

If you have a number of machines, and/or machines with several motors, the provision of VFDs for each motor or machine will almost certainly total up to more cost than a single RPC, possibly even if it is bought brand new at "retail". Clearly true if motor etc is sourced used.

So, the decision is not a "slam dunk". It depends on what you want, and what you wish to spend. Saying that "it makes little sense" to have an RPC or even a static converter is probably taking the logic to an unjustified extreme.

The ability to use a 3 phase machine is, however. a big advantage, no matter what means is used to get 3 phase compatibility. Most hobby types cannot and need to factor in replacement of the motor and other modifications. That leads to them turning down machines having that "disadvantage". The prices of machinery in the hobby market often reflects that.

[gellfex]

If you need variable speed, your other options beside a VFD are limited.

This is what brought me to VFDs when I'd built a perfectly good RPC. Only my pedestal buffer doesn't really benefit from variable speed, and I'm sure someone would debate even that. DP, lathe and mill are all a joy with a VFD.

[J Tiers]

It's pretty much "whatever floats your watch". Some demand it, others are "Meh".

Not having continuously variable speed does not bother me at all on lathe or mills. One lathe has it, and I don't use it that much even there (watchmaker's lathe).

[PStechPaul]

"Digital" might just mean that it uses fingers (or toes) to operate. So Mozart used a "digital" piano!

This device is probably just a capacitor in a fancy enclosure. But it could be made like a Phase Perfect. For that design, a 3 HP rating would only need a PWM output for one (third) phase and 1 HP, so it could be pretty small.

[J Tiers]

True, but the lack of any heatsink, and the statement of "no high frequencies" seem to suggest it is not. As I mentioned, if the bottom of the case is a "coldplate", then the heatsink would be whatever you bolt the case down to, and you'd need to use heat conductive grease between the base and mounting surface.

But, the descriptions seem to make that unlikely.

There is another possible explanation, which is a "digitally switched" or "time delayed" capacitor... Charged up during the single phase maximum, and then discharged through the third wire at the appropriate time for correct phase. With multiple SCRs, both polarities can be supplied.

That might do a reasonably credible job of supplying appropriate voltage to the third wire. It would also partly explain the power level distinction, since the capacitor value would affect the waveform supplied to the motor, due to resonance effects.

I've never tried that, and it might work. No clue of anyone is doing that, but if not, you saw it here first! (and now it is no longer patentable, as I "disclosed" the basic idea, so one "skilled in the art" can make one).

I did also have a thought that it might make a 3rd phase with plain "modified sine wave" (square wave, actually) output. That would be at 60 Hz, and might get away with only the most minimal heatsinking.

But, it would require a DC bus, and there is not much room in there for a bus capacitor. It would, however, explain the "digital" description, while not particularly explaining the power range, which is suspiciously similar to most "static converters".



it's fairly expensive for a static converter, so one wonders if they just make an outrageous profit, or if there is something in there to justify a higher cost.

[macona]

Id say its just a static phase converter with an electronic circuit to control the relays instead of a mechanical relay. The faq says its normal not to have all three phases at the terminals when the motor is not running, so static phase converter.

[J Tiers]

Id say its just a static phase converter with an electronic circuit to control the relays instead of a mechanical relay. The faq says its normal not to have all three phases at the terminals when the motor is not running, so static phase converter.

That is the most likely.

The other ideas are basically assuming that there must be SOME reason for the cost. But there need not be any such reason..... other than extracting the most $$ from the customer.

[Tundra Twin Track]

[QUOTE=Fasttrack;n1964141]

And it's worth asking, how often will you really be using all 10 horses? In a non-production environment ... well I'm willing to bet that many of us on this forum rarely run their machines at full power. I'd suggest trying it with the 5 HP RPC and see what happens. You might be surprised.

I have a 18x60 lathe that came with 10hp 3ph from factory switched to 5hp 1ph 10 yrs ago and has performed flawless.I’ve taken some heavy cuts and never tripped the overload breaker yet,not a clutch style lathe motor does forward&reverse.

[outlawspeeder]

I will most likely never use the full 10HP. The VFD is sitting on the floor in front of me. I was reading the book on how to set it up.

How much do I have to worry about dust and the VFD? Is there an easy box to put the VFD inside?