Buck/Boost to Phase Perfect
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    Default Buck/Boost to Phase Perfect

    Alright, I've got a 240/32 buck boost transformer, 1.5kVa. I wired it according to the schematics from GE (the manufacturer) to reduce to 218V from 240. It worked in that voltage is going down from 241-243V to 216V, and after the Phase Perfect I'm seeing the two legs and the manufactured leg within a few volts of each other (like 216V/217V/218V).

    However... my three legs are 120V/95V/195V to ground, respectively.

    Is this normal or do I need to switch some things around? The CNC is down for repair so I've got some time to screw around with it right now.

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    It's normal. What you have is good to go.

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    Quote Originally Posted by Rick Finsta View Post
    Alright, I've got a 240/32 buck boost transformer, 1.5kVa. I wired it according to the schematics from GE (the manufacturer) to reduce to 218V from 240. It worked in that voltage is going down from 241-243V to 216V, and after the Phase Perfect I'm seeing the two legs and the manufactured leg within a few volts of each other (like 216V/217V/218V).

    However... my three legs are 120V/95V/195V to ground, respectively.

    Is this normal or do I need to switch some things around? The CNC is down for repair so I've got some time to screw around with it right now.
    A Phase-Perfect's output is "Delta", so yes - not balanced with respect to Earth, only with respect to each other.

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    Yeah I knew about the high leg (used to be 118/122/208 after the PP) I just didn't quite get why the numbers don't seem to have changed the same degree. Electricity is magic!

    Also... these transformers are loud. I'm gonna have to start playing music in the shop!

    Appreciate the responses.

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    Quote Originally Posted by Rick Finsta View Post
    Yeah I knew about the high leg (used to be 118/122/208 after the PP) I just didn't quite get why the numbers don't seem to have changed the same degree. Electricity is magic!

    Also... these transformers are loud. I'm gonna have to start playing music in the shop!

    Appreciate the responses.
    "Magic" also meaning it doesn't take a huge spend on conduit and good wire (five-each 100 foot rolls THHN/THWN #4) to put most of this stuff (Diesel Gen set, RPC, Phase-Perfect, transformers...) off in a place where the sound is less obtrusive.

    Doesn't take much spend on some baffling in between to help even more.

    Call me old-fashioned - I am - but I have never had much tolerance for the distraction of "most" music in a workplace, when wheeling a fast touring car, nor left-seating an aircraft.

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    After a couple of years my PP and transformer went outside. They are noisy.

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    Quote Originally Posted by DavidScott View Post
    After a couple of years my PP and transformer went outside. They are noisy.
    It does not take rocket science nor huge coin to protect them from snakes, rodents, insects, dust, pollen, excess / condensing moisture - the weather in general.

    The space freed-up is not huge - I was up for "stacking" P-P & RPC, both, in a corner - but at least serves me for one more tool storage drawer stack for goods that I do NOT want outdoors.

    Perhaps I am the "lone ranger" on this... or maybe not so much... but I know that when the time comes, a complicated electrical system in a garage/shop/annex is NOT a plus to quick nor top-dollar sale of the facility.

    Ergo a vote for 100% surface-mount conduit and outlets, any of RPC, P-P, transformers, and switchgear racked and even wheeled so it can all be easily severed, removed, sold-off, donated, scrapped, or transferred to your own NEXT facility with minimal fuss.

    Leaving the space clean, clear, and problem-free for the next owner to do as THEY please has monetary advantage.

    "plan ahea "


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    Okay, so while waiting on parts still for my machine I am getting some testing done and after a few hours or so the transformer kicked the 60A breaker feeding the sub panel as well as the 50A breaker in the sub that is feeding the transformer (and subsequently, the Phase Perfect). I double checked the wiring but now it will kick the breakers as soon as I power it up.

    If this happened right away I would have thought it was an inrush issue, but it ran for hours before this occurred, and now it is instantaneous. I'm thinking the transformer may be fried?

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    Disconnect the wiring at the input to the phase perfect and then see if the transformer input breaker holds, recheck the transformer bank output voltage, if it holds on.

    SAF Ω

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    Quote Originally Posted by Rick Finsta View Post
    Okay, so while waiting on parts still for my machine I am getting some testing done and after a few hours or so the transformer kicked the 60A breaker feeding the sub panel as well as the 50A breaker in the sub that is feeding the transformer (and subsequently, the Phase Perfect). I double checked the wiring but now it will kick the breakers as soon as I power it up.

    If this happened right away I would have thought it was an inrush issue, but it ran for hours before this occurred, and now it is instantaneous. I'm thinking the transformer may be fried?
    NO LOAD on the P-P while you await parts for a downed machine-tool as is meant to be its primary if not also ONLY load? And the breakers are tripping?

    Sounds more as if you've borked the P-P than the buck/boost.

    Unless you under-spec'ed the buck/boost on KVA?

    What size P-P?

    Hang on... My 10 HP P-P wants a 55A upstream breaker, IIRC. Or at least it would for full-load delivery. Check your manual. we may have the same sizes and such.

    Worst-case you are bucking 13% with a 10% rated transformer. That is "worst case", but I'd want a 1.5 KVA or 2 KVA, not a 1.2 KVA. Better disconnect and check that buck trans for a fault, after all?

    You shouldn't be seeing this "at once" on an UNloaded P-P otherwise. They are not pussycats, but still.. nothing like the "starting" load of a 3-P motor-as-idler that doesn't KNOW in advance it is only going to "idle" after start-me time.

    Or IS it loaded? The machine just not "fully" active and making chips?

    P-P's manual have a different arrangement of a P-P when used "dedicated" and possibly serving as the motor's starter instead of as a general-purpose 3-Phase "mothership", all-comers, at-start or switched on/off, later.

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    I pulled the transformer out of the circuit and the PP works fine, everything else checks out. Looks like the transformer is bad? It was used when I got it.

    I can try what SAF recommends but I've quadruple checked my wiring and everything looks correct (plus it was working for several hours before it stopped). Transformer is a 1.5kVa unit.

    It is a PT-380 (30hp) but it is only hooked up to run maximum ~25A on the output side (input breaker and wiring sizing). I only have 100A service to the house, and this subpanel is only fed by a 60A breaker. According to Phase Technology the PP doesn't care what it is rated for it will only need as much input rating as you need output. I am set up for maximum of like 15kVa I think? I'd have to go back and look at my notes but I ran them by my electrician after posting here and everything checked out.

    The thing is, the tranformer draws immediately, but the PP doesn't engage and start drawing more than a few mA until after about 5-10 seconds when the contactor engages.

    I will look into how one goes about testing a transformer, I suppose?

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    Quote Originally Posted by Rick Finsta View Post
    I will look into how one goes about testing a transformer, I suppose?
    Be rude of me to chuckle, Rick.. But you just DID "test a transformer". "Destructively, even!"

    It would now be a waste of yer time to bother to "look into it", most of those "dry type" units for indoor OR outdoor use being potted in waxy-stuff and sand grains or wotever to save on wax or wotever-it-is as they are.

    I'd suggest it gives you a wider margin, lower nose, cooler operation to use a buck/boost with a KVA rating good for closer to the rated 30 HP, even if you won't "go there".. intentionally. For now. But maybe someday-later-on?

    Five KVA mebbe? They are common enough, used, to not cost a lot more.

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    Thing is I never even put a load on that transformer since I installed it after my machine screen went down. It only ever idled the CNC machine; never even ran the spindle or jogged and axis.

    *sigh*

    Maybe I need to change my job title to "Destroyer of Pixies, Liberator of the Smoke."

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    Default Buck Boost Sizing

    Quote Originally Posted by Rick Finsta View Post
    Thing is I never even put a load on that transformer since I installed it after my machine screen went down. It only ever idled the CNC machine; never even ran the spindle or jogged and axis.

    *sigh*

    Maybe I need to change my job title to "Destroyer of Pixies, Liberator of the Smoke."
    How about Green Horn Electrical Engineer?

    Your math is off, and that unit is woefully undersized, for using on the input to the phase perfect. It's capacity is only rated for 5A @240V , likely why it gave up the smoke.

    For the 25A capacity you say you need, a 7.5 KVA unit would be required.
    For the 80A rating of your 30HP PP, you would require a 20KVA unit.

    Try this calculator to check your math.

    SAF Ω

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    SAF it is hooked up as an autotransformer in single phase so Schneider tells me to use their 2S46F which is 2kVA based on the maximum 15kVA I rated the circuit but honestly more than that "real" 7.5hp mill VMC should ever draw.

    I originally considered putting an isolation transformer on the three phase side of the PP but they are pretty expensive and it would take up a lot of room.

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    Quote Originally Posted by Rick Finsta View Post
    SAF it is hooked up as an autotransformer in single phase so Schneider tells me to use their 2S46F which is 2kVA based on the maximum 15kVA I rated the circuit but honestly more than that "real" 7.5hp mill VMC should ever draw.

    I originally considered putting an isolation transformer on the three phase side of the PP but they are pretty expensive and it would take up a lot of room.
    Well I did that... but I only have a 10 HP P-P.

    The Delta to Wye was what I wanted, and the 27 KVA only because it also serves the 10 HP RPC, which can be bumped-up to over 20 HP with supplementary idlers. No, not both at once. Salvaged Square-D 60 A "transfer" switch. Two, actually.

    Unless your 3-P side drive-isolation transformer had a goodly selection of adusting taps, you'd now need TWO buck-boost, minimum.

    So what could perhaps do you more good is full-isolation on the Single-Phase LINE side.

    IF you did have a full isolation, especially if the chosen transformer also had adjusting taps, the "buck/boost" can be lighter goods, if even still needed at all. Parallel the primaries, then series aid or series buck (out of phase), their secondary sides.

    NOW your math (and Schneider's math) is a closer fit to what yer actually doing with yer loads.

    But the "real reason" is that you've built yerself a "drive isolation" transformer into the deal.

    The line-side noise others are "now and then, not always" reporting as walking back upline off their P-P's into the shop/residence "local grid" and hammering everything under-roof from stereo systems to fridge-freezers to microwaves then hits a bit of an attenuating barrier with the isolation transformer's acting as fair-decent low-pass filter(s). Not perfect, but good news, and IF P-P noise still a problem, what's left "above" it is easier to tame.

    Used 1-P transformers are bulky but not terribly dear. NONE of these goods actually have to live right in the shop space, given the way electricity will follow a Copper wire as well as it does. so ...

    It's on MY "To Do" list, but I'm not sayin' "JFDI".

    I'm more into tests and experiments than making of chips, so my whole rig (including a Diesel gen set..) is more of a flexible lab for my playtoys than any sort of earner of crust, but still..

    With the first-go at buck-boost now toast, yer back to Day One, blank drawing board, so it might be worth a thought - and some scouting as to costs?

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    There is a local guy selling an 18kVA UPS so I may just say "Screw it" and go that route. That thing could power my machine for like 15 minutes at full tilt during a blackout and completely isolates the input and output through double-conversion. We used these on scientific instruments in my past life where inductive loads in the building were frying sensitive equipment.

    That sucker weighs 1400lb with the batteries!

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    Quote Originally Posted by Rick Finsta View Post
    There is a local guy selling an 18kVA UPS so I may just say "Screw it" and go that route. That thing could power my machine for like 15 minutes at full tilt during a blackout and completely isolates the input and output through double-conversion. We used these on scientific instruments in my past life where inductive loads in the building were frying sensitive equipment.

    That sucker weighs 1400lb with the batteries!
    Small ones can be that light, yes. Some are also ugly as sin on their synthetic Sine-wave outputs to BE that light as well.



    Dominant Carrier Global TELCO pensioner here. (C&W, and "nailed up" - government and Fortune 400, mostly..)

    Need I say more?



    Well.. "maybe".

    Here's a "rule of thumb" lotta folk are not aware of.

    Take my gen set. A NATO/OTAN surplus Fermont-integrated rig, the MEP-803A utilizes a Marathon head switch-selectable as to 120 or 240 single-phase or 208 Wye 3-phase I can throttle up to 220 Wye, leg-to-leg, given leg-to-neutral ain't even used, ergo "so what" it is over-volted.

    A Lister-Petter/Cummins-Onan 4-banger liquid-cooled Diesel of about 12 or 14 normally-aspirated HP earns a 10 KVA rating at 8,000 feet above mean sea level.

    The bottom line is generally considered a 12 KVA at my 356 ft AMSL, and known to be able to stand up easily to 15 KVA peak loading.

    Where "stand up" does NOT mean there is no sag when a heavy load comes online, nor any shortage of overshoot when it drops-off.

    Not even close to as stable as a major-utility power grid, distributed small and "local" or not. "Broader Shoulders" up the backline of it.

    So.. run a 10 HP load? Well. "Sort-of".

    I'm "all manual", and one pair of hands and eyes, so one machine at a go. Also max one motor load is only 7.5 HP. Bogging down to start? No Big deal. So all that works "well enough".

    Thing is, few are aware it really needs a factor of TEN - around 60 or 70 KVA - to run more demanding loads.

    Such as a "roughly" 10 HP CNC machine tool and its complexity.

    Stability under rapidly changing load thing, yah?

    Similar strictures apply to your proposed but "nominal" 18 KVA UPS.

    It probably won't be stout enough to do what you think it will.

    Not for machine-tools that have BOTH of gnarly motive power demands AND finicky "brains", anyway.

    And batteries? Talk about a pain in the ass!

    Had to keep HSBC, MoD, DoD online yah, yah JF "Deal Wit Dat".

    Here? Power is out? See to it the steaks stay frozen, residence is comfy, any season of the year, and otherwise JF go do sumthin' else, is all.

    Costs too much to make chips "regardless"? Just take a break and do not.

    Can't pay the bills yah hafta make so great an investment yer actually SUBSIDIZING 'em, can yah?

    Remember - I'm a for-the-fun-of-f**king-around sorta half-vast "Redneck R&D lab".

    Not a bizness.

    See Kalifornios relocating to less flammable locations with more reliable mains power. ELSE go on the dole - and still be short-served, even hungry.


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