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Thread: B&A Precision

  1. #5501
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    Interesting.

    I don't think my RPC effects my power bill much at all. I heat my house and shop with electricity and that shows well on the power bill.

    One single day of heating my shop (20KW heater) is notable on my power bill. A month with RPC idling VS not much use at all doesn't change the numbers one bit.

    I have to run RPC just to use the bridgeport or just the auto bandsaw by itself. Virtually nil power use, but that RPC is still spinning.

    I think Philabuster's right on with his 400 Watts. 1.5 amps is not accounting for $1400 in power usage.

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    On a related note of PRC's hopefully not furthering off-topic discussion, I have 3 RPC's in my garage shop, I just went and checked my idling loads.
    (small scale shop, not out there every day, sometimes not even every week)

    10hp idling, about 10amps
    10hp and 20hp idling together, about 15amps
    60hp, 20hp, and 10hp, all idling together, about 30amps.

    I do run all 3 of them together when running the Okuma CNC lathe, she's a power hog. Especially when ripping off 30+ cubic inches a minute of 4140 at about 20 HRC, and 4340 at about 37 HRC. No problems at all running that and the Sharp CNC mill (fairly small load) and the Bridgeport. Or any other combination of smaller manual machines.

    The Phase Perfect units draw near nothing when idling, IIRC. I looked into them for that reason, but decided the up-front cost would be quite a while getting back at my average hrs/wk of usage. If it were a full-time thing, that'd be a different story.

    30amps, 10hrs/day, $0.16/kwhr, 20days/mo, equates to about $230/mo idling cost. Maybe your electric rates are higher, Ox?

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    My 20 hp RPC doesn't affect my bill a noticeable amount. I cannot imagine an idling RPC costing 1k a month.

    How many transformers does your (Ox) RPC feed, and do they stay energized all the time?

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    Quote Originally Posted by Fish On View Post
    My 20 hp RPC doesn't affect my bill a noticeable amount. I cannot imagine an idling RPC costing 1k a month.

    How many transformers does your (Ox) RPC feed, and do they stay energized all the time?

    Yes - that is true as well.
    I have several and they aint small.

    But - if you wunna figger it out per hour, in my case - you need to figger 24 x 30 / month @ $.13 (?) = which comes out to 10.7A static load.

    I'm sure that X's are a fair amount of my equazsion as well - you are correct.
    I knew this and just wasn't thinkin' at the time...

    Sorry Tom.

    If I ever re-doo things - I would like to have 2 lines of buss, one for 240 and one for 480, and only have one X.



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    Think Snow Eh!
    Ox

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    Quote Originally Posted by pianoman8t8 View Post
    On a related note of PRC's hopefully not furthering off-topic discussion, I have 3 RPC's in my garage shop, I just went and checked my idling loads.
    (small scale shop, not out there every day, sometimes not even every week)

    10hp idling, about 10amps
    10hp and 20hp idling together, about 15amps
    60hp, 20hp, and 10hp, all idling together, about 30amps.

    I do run all 3 of them together when running the Okuma CNC lathe, she's a power hog. Especially when ripping off 30+ cubic inches a minute of 4140 at about 20 HRC, and 4340 at about 37 HRC. No problems at all running that and the Sharp CNC mill (fairly small load) and the Bridgeport. Or any other combination of smaller manual machines.

    The Phase Perfect units draw near nothing when idling, IIRC. I looked into them for that reason, but decided the up-front cost would be quite a while getting back at my average hrs/wk of usage. If it were a full-time thing, that'd be a different story.

    30amps, 10hrs/day, $0.16/kwhr, 20days/mo, equates to about $230/mo idling cost. Maybe your electric rates are higher, Ox?
    Current by itself means nothing. An idling motor has a near zero power factor. Watts = volts x amps x power factor.

    Tom

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    My concern of PP vs RPC, is the RPC is even more limiting of what you'll be able to run on your 1ph Amps available.
    The PP has capacitors that allow it to start high loads at something like 400% its normal rating, without trying to draw 400% straight off your main line...
    That said, the harmonics thing still is bothering me a bit but haven't spent any more time on it, still haven't heard back from PP on their newest 3rd gen units either and how what improvements were made regarding that filtering, I know filter caps are now supposed to be much easier to replace.
    I think the master/slave units like yours might have had some issues anyhow, that design is gone, higher HP models are all 1 unit now, but I'd still rather have 2-3 smaller independent units than 1 big one.

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    Quote Originally Posted by TDegenhart View Post
    Current by itself means nothing. An idling motor has a near zero power factor. Watts = volts x amps x power factor.

    Tom

    I know that we have had discussion about this regarding what kind of metering devise is used, as that can apparently make all the diff in the world.

    ???


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    Ox

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    Quote Originally Posted by SND View Post
    My concern of PP vs RPC, is the RPC is even more limiting of what you'll be able to run on your 1ph Amps available.
    The PP has capacitors that allow it to start high loads at something like 400% its normal rating, without trying to draw 400% straight off your main line... Not true, see below
    That said, the harmonics thing still is bothering me a bit but haven't spent any more time on it, still haven't heard back from PP on their newest 3rd gen units either and how what improvements were made regarding that filtering, I know filter caps are now supposed to be much easier to replace.
    I think the master/slave units like yours might have had some issues anyhow, that design is gone, higher HP models are all 1 unit now, but I'd still rather have 2-3 smaller independent units than 1 big one.
    ..................
    I may be wrong, and if so, I trust someone will correct me. It is my understanding that the two supply lines simply go through the PP and that the third phase is created, somewhat like a rotary and that the third phase is created by switching electronics much the same as a VFD or drive work. (I later verified this is true)

    A typical large motor draws 6x running rated current at startup and for a "normal" starting load, the the inrush time is about 6-8 electrical cycles or about .12 seconds. An inertia load can lengthen this time out to several seconds. This does not include such loads as a conveyor.

    consider a 10 hp motor, 7.5 kw and 230 volts has a full load current of 28 amp per phase. The starting current would then be 168 amps per phase. The single phase line current into the convertor would then will be 168 x 1.732 = 290 amp. When rotary convertor is used, the normal rules of starter and overload relay apply, the size of the starter according to the hp of the motor and the OL relay heaters or settings according to the needed protection of the motor. NEMA class overload relays and heaters are available in three classes; class 10, 4-10 sec , class 20, 6-20 sec and class 30, 9-30 seconds.

    Application of the PP is different in that inrush on starting is limited to 4 seconds at the published max current. The published max current is less than the standard 6x rating, more in the 5-5 1/2 range. The application here should be by an (I^2)t rating rather raw numbers. (I^2)t is a value that is normally used for short term overcurrent conditions such as thermal ratings of overload relays, fuses and such. It reflects the short term heating effects. Using data from a PP PT410R, max current is 90 amps at 4 sec. The (I^2)t rating is 90^2 x 4 = 32,400 amp sq sec. If the application as only 70 amp max, the max time would be 32400/4900 = 6.6 sec. Of course, verify this through PT before using it as gospel.

    Since these units are normally oversized, that normally is not a problem but it is a limitation that is not shared by a RPC. Also, unlike a VFD, these is no built in load limitation since since the two feeds go directly to the load motor.

    To the question of the capacitors holding enough charge to limit the incoming load, that is not true. The caps are there for smoothing the ripple so that the switching units can produce a sine wave. They do not act as a long duration battery.

    Tom

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    I like to think of it like this-

    Our CNC's all use servo and spindle drives that rectify 3 phase into DC then chop it back up and spit it out as AC for the motors. If you feed many of them single phase power into the drives (might need a trick or two) they will run fine to 50-75% of their ratings.

    So with an RPC, regardless of how shitty the generated leg is, it's still feeding those needed pixies into the drives to be chopped up and turned into whatever the drive needs.

    The control itself runs on DC power rectified from TWO legs of the power coming in.

    So, I don't see much point spending a fortune on another box filled with switching transistors and capacitors when my machines already have them. Sure, maybe the PP can be more efficient, but I refuse to believe it is anywhere near as reliable/resilient as an RPC.

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    Quote Originally Posted by Garwood View Post
    I like to think of it like this-

    Our CNC's all use servo and spindle drives that rectify 3 phase into DC then chop it back up and spit it out as AC for the motors. If you feed many of them single phase power into the drives (might need a trick or two) they will run fine to 50-75% of their ratings.

    So with an RPC, regardless of how shitty the generated leg is, it's still feeding those needed pixies into the drives to be chopped up and turned into whatever the drive needs.

    The control itself runs on DC power rectified from TWO legs of the power coming in.

    So, I don't see much point spending a fortune on another box filled with switching transistors and capacitors when my machines already have them. Sure, maybe the PP can be more efficient, but I refuse to believe it is anywhere near as reliable/resilient as an RPC.
    I agree with that. Knowing the little bit that I do about IGBT's. I will take that big-ole' 3-ph motor any day for longevity! (and lack of switching noise)

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    Quote Originally Posted by Ox View Post
    Yes - that is true as well.
    I have several and they aint small.

    But - if you wunna figger it out per hour, in my case - you need to figger 24 x 30 / month @ $.13 (?) = which comes out to 10.7A static load.

    I'm sure that X's are a fair amount of my equazsion as well - you are correct.
    I knew this and just wasn't thinkin' at the time...

    Sorry Tom.

    If I ever re-doo things - I would like to have 2 lines of buss, one for 240 and one for 480, and only have one X.



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    Ox
    Just a minor correction, you neglected to include the watts used. Using Philibuster's 400 watts then the calculation is

    400/1000(Kw) x 24 (hrs) x 30 (days) x .13 ($/Kw-Hr) = $37/month.

    Your RPC is larger so use $50/month just to run the RPC motor. Probably another $50/month per transformer.

    Is there a reason you run these 23/7 or just ???

    Tom

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    Hopefully I have something running overnight, or at least maybe a few hours after I walk out, but even if I don't - my electrics stay up, etc.
    Also - I'm already here 14 hrs generally anyhow, so the down time is less anyhow.


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    Ox

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    Worst thing about buying used machine tools: there is a weird smell in here!
    Its not bad. It just smells like somebody else's shop. I dumped a gal of command-clean in the sump. Should clear up in a week or so.

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    Quote Originally Posted by wheelieking71 View Post
    Worst thing about buying used machine tools: there is a weird smell in here!
    Its not bad. It just smells like somebody else's shop. I dumped a gal of command-clean in the sump. Should clear up in a week or so.
    Id'nt funny? My Doosan mill was the same way.....................after fresh coolant and a complete wipe down, she stank just like the rest of the iron in my place in a week's time..................................

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    Used machine tools are almost never in operation until the day they are sold. Someone make a conscious decision to separate themselves, and the first thing that gets neglected is the coolant.

    That smell is the Square Inch Dealer's dirty deeds (RIP Frank).


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