sae8425
Aluminum
- Joined
- Mar 30, 2011
- Location
- western pa
This, my first post, is rather lengthy. Given the issues raised I couldn’t condense it any further without impacting on the necessary background information. So, grab a beer/coffee and have a (hopefully) good read.
I’ve looked around some of the previous forum threads, and if all of this has been discussed before I apologize for bringing up discussed matters, but I haven’t yet come across any wholly relevant postings.
I need to install a phase conversion system to run some machinery on my rural homestead.
I currently have an ABB Type CSP 15 kVA (ie. 125 Amp) transformer supplying a 100 Amp service, which I can upgrade to a 125 Amp service. But prior to the most recent mains distribution box upgrade, there was a 60 Amp service, and I’m fairly certain the utility didn’t upgrade the supply cables when the 100 Amp service was installed back in the early 1990’s. This serves both the house and my workshop. So, when I’m welding at 250 Amps, my girlfriend isn’t able to cook a chicken in the oven. And the electric water heater is only turned on when I’m not out in the workshop. No air conditioning, and we heat with wood. The only other ‘biggish’ house electrical loads that can come one while I’m in the workshop are the microwave and toaster. So; house covered.
Down the road (18 to 24 months) I will have 2 x 200 Amp services installed on the property, which will give me a dedicated 200 Amp supply for my workshop (and allow my girlfriend to shower while I’m welding!).
But, I need 3 phase today, and so I (and she) have to live with the limitations of the 15 kVA supply.
Right now, my hardest starting, and biggest power drawing 3 phase items are:
Sullair 5 hp rotary screw air compressor
Hypertherm Powermax 1250 Plasma Cutter – 37 Amp @ 230 volts 3 phase input (12KW output)
ESAB Migmaster 250 Pro welder
Summit 19 x 54 engine lathe – 5 hp clutch start
I work alone, and while the air compressor is able to automatically cycle on and off, I would rarely have but one other 3 phase piece of equipment turned on at the same time.
From time to time I will want to have the Mig welder and the plasma cutter turned on at the same time, but one would be ‘idling’ while the other was being used. I can’t cut with my left hand and weld with my right hand!
And I could also see the Mig welder and/or plasma cutter being used while something was suspended on my powered crane hoist.
I’ve talked to all the usual (and some of the less well known) suppliers in the phase conversion industry.
I’ve poured over specs sheets, and spent countless hours on the internet trolling through forums and websites searching for answers to my questions, and (hopefully) gaining an insight that will prevent me wasting money.
I thought I was making progress until I talked with Larry Katz at Kay Industries (ie. PhaseMaster) recently. To say that his comments have confused and troubled me would be an understatement!
While Mr. Katz seems (I studied electronics years ago, but my memory is somewhat hazy) to truly understand the physics behind and complexities of phase conversion, his sizing recommendations seem to fly in the face of convention and widely accepted guidelines.
He is adamant that I could successfully run (at the same time) my Hypertherm plasma cutter, the ESAB welder, and the 5 hp Sullair air compressor on a PhaseMaster MA-1B 7.5 hp RPC. Furthermore, even with the lathe also running at the same time, he simply can’t see any need for a converter any bigger than a PhaseMaster MA-2 10 hp RPC. And even this size of RPC he isn’t absolutely convinced is really essential.
He also said that if I configured the Sullair 5 hp air compressor motor to idle under no load (rather than cycle on/off), that this extra electrical potential could be harnessed to allow the lathe to also start on a 7.5 hp RPC without any problems whatsoever (with everything else mentioned above also running), and thereby absolutely negating the need for a 10 hp RPC.
Nobody else that I’ve talked to, or sizing guidelines that I’ve seen, recommends an RPC that’s remotely as small as 7.5 hp for my purposes. Only a few have even said that a 10 hp RPC will suffice. Most seem to say that to be ‘safe’ I should get at least a 15 hp RPC, and to be ‘really safe’ a 20 hp RPC would be a prudent choice.
Even on this forum, back in 2005, bnelson commented that a PhaseMaster 25 hp MA-5 simply wasn’t big enough to start a 25 hp Sullair air compressor (he said that a PhaseMaster MA-8 was the minimum size required). See:
http://www.practicalmachinist.com/v...ers-vfd/phasemaster-rpc-toggle-switch-102694/
The MA-8 is a 50 hp (largest single motor) 885 lb RPC. And the sizing advice given by bnelson in the thread mentioned seems to be in agreement with virtually all of the published/spoken words I have knowledge of.
Except for the guidance provided by Larry Katz of PhaseMaster! I don’t understand why the sizing advice provided by PhaseMaster is so divergent from that of virtually the whole of the RPC industry. Any ideas?
When you look at RPC weights and motor frame sizes used, you soon realize that many firms are ‘skimping on iron’ when it comes to sizing their RPC units. But PhaseMaster certainly isn’t guilty of this practice. The MA-4 20 hp unit uses a 324T frame and weighs 423 lbs. This is, in fact, heavier than some 40 hp RPC’s being sold.
Gary Werner of Smith Motor Works talks about the differences between low and high resistance rotors, and claims that low resistance rotors are a better ‘fit’ for phase conversion. Can anyone elaborate on this claim?
And many manufacturers are claiming to use rotors that are specially produced by Baldor, but I’ve yet to see any actual details about what makes these rotors better suited for making an RPC with. What are the differences?
PhaseMaster provides the least technical details of any RPC manufacturer that I know of, yet, by all accounts they do produce a very high quality product that seems to be well regarded by users and website contributors.
But Mr. Katz contends that ‘real’ understanding of the physics of electrical motors seems to be in very short supply when he looks around the RPC industry, and that the PhaseMaster RPC’s are so conservatively rated that ‘normal’ sizing guidelines simply don’t apply. Listening to him explain various considerations is addictive; but, his comments certainly haven’t provided me with the ‘killer insight’ about RPC’s that I’m trying to acquire.
Mr. Katz claims that I am way over-thinking/researching this whole issue, and that I should just buy an MA-1B and get on with my life. But since I can’t see where his 2 + 2 = 4 regarding RPC sizing, I can’t just let this go.
When almost everyone else is saying to get a much bigger RPC, I’m a bit like a rabbit in the headlights. Frozen.
One potential way around the inrush current issue (which is a total non-issue according to Mr. Katz) with the 100 Amp supply, might be to use a pony motor started RPC. A neighboring farmer who is soon to retire, has offered me his self-made phase converter, which is based on a GE 30 hp, 975 rpm, 854 lb, 405S frame motor.
I’ve watched him start this with a 1 hp single phase pony motor on countless occasions without any flicker or dimming of his workshop or house lights. He says that it’s served him well for 30 years on a 100 Amp service.
Oh it takes that 1 hp motor about 8 to 10 seconds to get that 30 hp rotor spun up to speed before electricity can be applied to the windings, but other than the slow (non-connected) initial run up, I can’t see any downsides to this approach. But perhaps I’m missing something. If so, what is the ‘hidden’ downside to this approach?
The farmer says that the weight of the rotor, combined with the very slow rotor speed makes for a virtually unstoppable RPC that helps to ‘cushion’ the mains supply from the 3 phase loads it serves. He has about the biggest drill press I’ve ever seen with an old 286 frame 10 hp motor on it and it starts almost instantaneously.
And he has a 15 hp DSG gap bed lathe with a 40" face plate on it that I’ve watched start turning a 1000 lb piece of steel with no discernible effect (ie. lights dimming/flickering) being observed in the workshop/house.
But this is a really ‘low-buck’ setup that would need to be balanced with capacitors, bleed resistors, etc.
So; might any forum member be able to better explain Mr. Katz’s PhaseMaster sizing recommendations?
Should I be more cautious and shop around for a ‘name brand’ capacitor start RPC in the 15-20 hp range to use on my 100 Amp service (which I can upgrade to a 125 Amp service if necessary)? Would a 20 hp capacitor start RPC even start on a 100 Amp service? Jason Smith, of Smith Motor Works, has told me that a 256 frame 20 hp motor will start on a 100 Amp service; but what about a 324T frame MA-4 20 hp PhaseMaster RPC? Too big?
Or should I buy the home made 30 Hp pony started idler/RPC off my neighbor, and do the balancing needed?
I am also concerned about the effect a large capacitor start RPC might have on my neighbors electrical supply What is the largest capacitor start RPC that I could safely start without causing problems in the local electrical system (in this rural area all the houses have individual transformers and all are fairly long distances apart if it makes any difference)?
My preference is to spend my time making other things rather than designing RPC systems. Self start would be nice, but if the inrush current issue is almost always going to be my main supply side limitation, I will invest the time necessary to make a well configured pony start system.
Many thanks for anyone that takes the time to digest all of this and offer a response.
I’ve looked around some of the previous forum threads, and if all of this has been discussed before I apologize for bringing up discussed matters, but I haven’t yet come across any wholly relevant postings.
I need to install a phase conversion system to run some machinery on my rural homestead.
I currently have an ABB Type CSP 15 kVA (ie. 125 Amp) transformer supplying a 100 Amp service, which I can upgrade to a 125 Amp service. But prior to the most recent mains distribution box upgrade, there was a 60 Amp service, and I’m fairly certain the utility didn’t upgrade the supply cables when the 100 Amp service was installed back in the early 1990’s. This serves both the house and my workshop. So, when I’m welding at 250 Amps, my girlfriend isn’t able to cook a chicken in the oven. And the electric water heater is only turned on when I’m not out in the workshop. No air conditioning, and we heat with wood. The only other ‘biggish’ house electrical loads that can come one while I’m in the workshop are the microwave and toaster. So; house covered.
Down the road (18 to 24 months) I will have 2 x 200 Amp services installed on the property, which will give me a dedicated 200 Amp supply for my workshop (and allow my girlfriend to shower while I’m welding!).
But, I need 3 phase today, and so I (and she) have to live with the limitations of the 15 kVA supply.
Right now, my hardest starting, and biggest power drawing 3 phase items are:
Sullair 5 hp rotary screw air compressor
Hypertherm Powermax 1250 Plasma Cutter – 37 Amp @ 230 volts 3 phase input (12KW output)
ESAB Migmaster 250 Pro welder
Summit 19 x 54 engine lathe – 5 hp clutch start
I work alone, and while the air compressor is able to automatically cycle on and off, I would rarely have but one other 3 phase piece of equipment turned on at the same time.
From time to time I will want to have the Mig welder and the plasma cutter turned on at the same time, but one would be ‘idling’ while the other was being used. I can’t cut with my left hand and weld with my right hand!
And I could also see the Mig welder and/or plasma cutter being used while something was suspended on my powered crane hoist.
I’ve talked to all the usual (and some of the less well known) suppliers in the phase conversion industry.
I’ve poured over specs sheets, and spent countless hours on the internet trolling through forums and websites searching for answers to my questions, and (hopefully) gaining an insight that will prevent me wasting money.
I thought I was making progress until I talked with Larry Katz at Kay Industries (ie. PhaseMaster) recently. To say that his comments have confused and troubled me would be an understatement!
While Mr. Katz seems (I studied electronics years ago, but my memory is somewhat hazy) to truly understand the physics behind and complexities of phase conversion, his sizing recommendations seem to fly in the face of convention and widely accepted guidelines.
He is adamant that I could successfully run (at the same time) my Hypertherm plasma cutter, the ESAB welder, and the 5 hp Sullair air compressor on a PhaseMaster MA-1B 7.5 hp RPC. Furthermore, even with the lathe also running at the same time, he simply can’t see any need for a converter any bigger than a PhaseMaster MA-2 10 hp RPC. And even this size of RPC he isn’t absolutely convinced is really essential.
He also said that if I configured the Sullair 5 hp air compressor motor to idle under no load (rather than cycle on/off), that this extra electrical potential could be harnessed to allow the lathe to also start on a 7.5 hp RPC without any problems whatsoever (with everything else mentioned above also running), and thereby absolutely negating the need for a 10 hp RPC.
Nobody else that I’ve talked to, or sizing guidelines that I’ve seen, recommends an RPC that’s remotely as small as 7.5 hp for my purposes. Only a few have even said that a 10 hp RPC will suffice. Most seem to say that to be ‘safe’ I should get at least a 15 hp RPC, and to be ‘really safe’ a 20 hp RPC would be a prudent choice.
Even on this forum, back in 2005, bnelson commented that a PhaseMaster 25 hp MA-5 simply wasn’t big enough to start a 25 hp Sullair air compressor (he said that a PhaseMaster MA-8 was the minimum size required). See:
http://www.practicalmachinist.com/v...ers-vfd/phasemaster-rpc-toggle-switch-102694/
The MA-8 is a 50 hp (largest single motor) 885 lb RPC. And the sizing advice given by bnelson in the thread mentioned seems to be in agreement with virtually all of the published/spoken words I have knowledge of.
Except for the guidance provided by Larry Katz of PhaseMaster! I don’t understand why the sizing advice provided by PhaseMaster is so divergent from that of virtually the whole of the RPC industry. Any ideas?
When you look at RPC weights and motor frame sizes used, you soon realize that many firms are ‘skimping on iron’ when it comes to sizing their RPC units. But PhaseMaster certainly isn’t guilty of this practice. The MA-4 20 hp unit uses a 324T frame and weighs 423 lbs. This is, in fact, heavier than some 40 hp RPC’s being sold.
Gary Werner of Smith Motor Works talks about the differences between low and high resistance rotors, and claims that low resistance rotors are a better ‘fit’ for phase conversion. Can anyone elaborate on this claim?
And many manufacturers are claiming to use rotors that are specially produced by Baldor, but I’ve yet to see any actual details about what makes these rotors better suited for making an RPC with. What are the differences?
PhaseMaster provides the least technical details of any RPC manufacturer that I know of, yet, by all accounts they do produce a very high quality product that seems to be well regarded by users and website contributors.
But Mr. Katz contends that ‘real’ understanding of the physics of electrical motors seems to be in very short supply when he looks around the RPC industry, and that the PhaseMaster RPC’s are so conservatively rated that ‘normal’ sizing guidelines simply don’t apply. Listening to him explain various considerations is addictive; but, his comments certainly haven’t provided me with the ‘killer insight’ about RPC’s that I’m trying to acquire.
Mr. Katz claims that I am way over-thinking/researching this whole issue, and that I should just buy an MA-1B and get on with my life. But since I can’t see where his 2 + 2 = 4 regarding RPC sizing, I can’t just let this go.
When almost everyone else is saying to get a much bigger RPC, I’m a bit like a rabbit in the headlights. Frozen.
One potential way around the inrush current issue (which is a total non-issue according to Mr. Katz) with the 100 Amp supply, might be to use a pony motor started RPC. A neighboring farmer who is soon to retire, has offered me his self-made phase converter, which is based on a GE 30 hp, 975 rpm, 854 lb, 405S frame motor.
I’ve watched him start this with a 1 hp single phase pony motor on countless occasions without any flicker or dimming of his workshop or house lights. He says that it’s served him well for 30 years on a 100 Amp service.
Oh it takes that 1 hp motor about 8 to 10 seconds to get that 30 hp rotor spun up to speed before electricity can be applied to the windings, but other than the slow (non-connected) initial run up, I can’t see any downsides to this approach. But perhaps I’m missing something. If so, what is the ‘hidden’ downside to this approach?
The farmer says that the weight of the rotor, combined with the very slow rotor speed makes for a virtually unstoppable RPC that helps to ‘cushion’ the mains supply from the 3 phase loads it serves. He has about the biggest drill press I’ve ever seen with an old 286 frame 10 hp motor on it and it starts almost instantaneously.
And he has a 15 hp DSG gap bed lathe with a 40" face plate on it that I’ve watched start turning a 1000 lb piece of steel with no discernible effect (ie. lights dimming/flickering) being observed in the workshop/house.
But this is a really ‘low-buck’ setup that would need to be balanced with capacitors, bleed resistors, etc.
So; might any forum member be able to better explain Mr. Katz’s PhaseMaster sizing recommendations?
Should I be more cautious and shop around for a ‘name brand’ capacitor start RPC in the 15-20 hp range to use on my 100 Amp service (which I can upgrade to a 125 Amp service if necessary)? Would a 20 hp capacitor start RPC even start on a 100 Amp service? Jason Smith, of Smith Motor Works, has told me that a 256 frame 20 hp motor will start on a 100 Amp service; but what about a 324T frame MA-4 20 hp PhaseMaster RPC? Too big?
Or should I buy the home made 30 Hp pony started idler/RPC off my neighbor, and do the balancing needed?
I am also concerned about the effect a large capacitor start RPC might have on my neighbors electrical supply What is the largest capacitor start RPC that I could safely start without causing problems in the local electrical system (in this rural area all the houses have individual transformers and all are fairly long distances apart if it makes any difference)?
My preference is to spend my time making other things rather than designing RPC systems. Self start would be nice, but if the inrush current issue is almost always going to be my main supply side limitation, I will invest the time necessary to make a well configured pony start system.
Many thanks for anyone that takes the time to digest all of this and offer a response.
