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Baldor 3-phase motor for RPC

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  • J Tiers
    replied
    Originally posted by Fear View Post

    I've checked the wiring to the field coils of the motor so many times. It is definitely wired for 240vac.
    Excess current, and bogging down can be from many causes. Among them are the following reasonably common causes in RPCs.

    1) Start caps not disconnecting. Contactor or control system fault. Usually, if run for long, start caps will fail spectacularly or at the least become very hot. I think that it was mentioned that some already failed, probably from the bad timer board. Others may be damaged or open due to overheating even though not "exploded".

    2) Idler motor loaded down with too much "balance" capacitance. Remove ALL balance capacitors, and check operation with ONLY start caps. It should work, with possibly a slightly low generated leg.

    3) Idler started with a load on it. Output contactor (if present) may have failed, or control for it may be defective. Load machine simply left on. Disconnect all loads and try again, then if OK, check load machines or contactor.

    4) Motor wired for correct voltage, but has at least one reversed coil in one of the phases. Triple check the coils both for voltage configuration, AND for correct polarity, correct as needed

    5) Motor actually has a shorted turn in a coil. Check for possible heating in one specific area of the winding. If tested too much or for too long, one portion of winding may become discolored. Shorted turns are difficult to find without specialized equipment. They are not too common unless motor is known to be abused, electrically or physically, both of which leave traces, either discoloration from overheating, or evidence of physical damage due to impacts, etc. No cure for this, get a different motor.

    A useful test is to disconnect everything from the motor, get the motor rolling over, and connect two wires to 240V power. The idler should accelerate and run. If it does on both L1/L2, and L2/L3 pairs, then shorted turns are not the issue, and problem is in "control box".

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  • PStechPaul
    replied
    Can you connect 240 VAC to T1 and T2, and then spin the rotor using an electric drill or other means to get at least 3000 RPM? Once up to near synchronous speed, it should run on single phase. Repeat the test for T2-T3, and T3-T1, to make sure all three windings are OK. Could be a reversed winding or mislabeled connections.

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  • Fear
    replied
    Originally posted by PStechPaul View Post
    I just hope we can get Fear's RPC working. I'm really curious about why it has presented so many confusing symptoms and still won't properly generate the third phase. It may be that a two pole motor has to spin a lot faster than a four pole, and it needs to be running at least about 80% of synchronous speed before the third phase is sufficiently generated. Another thought is that perhaps the motor is actually wired for 480 VAC in which case it will bog down on 240 and cause problems as he has experienced.
    I've checked the wiring to the field coils of the motor so many times. It is definitely wired for 240vac.

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  • PStechPaul
    replied
    I just hope we can get Fear's RPC working. I'm really curious about why it has presented so many confusing symptoms and still won't properly generate the third phase. It may be that a two pole motor has to spin a lot faster than a four pole, and it needs to be running at least about 80% of synchronous speed before the third phase is sufficiently generated. Another thought is that perhaps the motor is actually wired for 480 VAC in which case it will bog down on 240 and cause problems as he has experienced.

    Leave a comment:


  • The Metal Butcher
    replied
    Originally posted by Fear View Post
    I don't know how to type the upside-down lower case "h" for microfarad so I've just been using MFD.

    How come most schematics for homemade RPCs show run caps between L1&L3 and L2&L3? Isn't it going to balance out (as in literally balance, like minimal vibration) if caps are spread more uniformly?
    To get mu on a windows computer hold down alt, and with it held, type 230 on your NUMPAD (it must be using a numpad) and you'll get your ยต.

    Leave a comment:


  • J Tiers
    replied
    Originally posted by Jim Stewart View Post


    Well, Paul, perhaps you haven't been dealing with old electronics - by "old" I mean from the twenties and thirties.

    My first radio receiver was an RME (Radio Manufacturing Engineers) superhet, manufactured in '36 or thereabouts. The dial was calibrated in Kilocycles and the manual used MFD throughout. Tubes with grid caps on top. So MFD does have historical precedence.

    -js
    Absolutely correct. And marked on old components as well. Old can be the 50's or possibly 60's, not just 30's.

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  • Jim Stewart
    replied
    Originally posted by PStechPaul View Post

    [rant] Microfarads are "uF", whereas "mF" is millifarads, so 1000 uF is 1 mF. And 100 Mf would be 100 Megafarads, which would be huge. Also, the abbreviation for Farads is a capital "F", for the proper name of Michael Faraday. [/rant]

    Well, Paul, perhaps you haven't been dealing with old electronics - by "old" I mean from the twenties and thirties.

    My first radio receiver was an RME (Radio Manufacturing Engineers) superhet, manufactured in '36 or thereabouts. The dial was calibrated in Kilocycles and the manual used MFD throughout. Tubes with grid caps on top. So MFD does have historical precedence.

    BTW, for anyone who still cares about this, ยต is in the extended ASCII character set. Windows has it in the character map tool.

    -js

    Leave a comment:


  • J Tiers
    replied
    Originally posted by Fear View Post

    How come most schematics for homemade RPCs show run caps between L1&L3 and L2&L3? Isn't it going to balance out (as in literally balance, like minimal vibration) if caps are spread more uniformly?
    because the run caps are there to cancel motor inductance, they do not have to be from one line specifically the way start caps must be. There can be an imbalance of run caps on the two incoming lines to make adjustments to the phase, since the act of "almost fully" compensating for inductance still makes a bit of change to phase.

    The motor itself produces correct phase even with NO "balance" capacitors. That is due to the location of the windings in the motor, which is acting as a generator for the "generated phase". They are already properly located mechanically to give the 120 degree phasing.

    But you cannot make a total compensation for inductance or the voltage gets out of hand. That not-quite-complete compensation leaves some inductance uncompensated, which causes a slight phase lag of current. The extra capacitance to one or the other of the incoming lines "pulls" the phase slightly, so that it gives a good compromise overall. It is essentially a "final tweak" of the unit.

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  • nickel-city-fab
    replied
    Originally posted by Fear View Post
    I don't know how to type the upside-down lower case "h" for microfarad so I've just been using MFD.

    How come most schematics for homemade RPCs show run caps between L1&L3 and L2&L3? Isn't it going to balance out (as in literally balance, like minimal vibration) if caps are spread more uniformly?
    Dunno how to help with the rest of it, but you can use a lower case "u" instead of an upside-down lower case "h"

    Leave a comment:


  • Fear
    replied
    I don't know how to type the upside-down lower case "h" for microfarad so I've just been using MFD.

    How come most schematics for homemade RPCs show run caps between L1&L3 and L2&L3? Isn't it going to balance out (as in literally balance, like minimal vibration) if caps are spread more uniformly?

    Leave a comment:


  • Rich Carlstedt
    replied
    Originally posted by PStechPaul View Post

    [rant] Microfarads are "uF", whereas "mF" is millifarads, so 1000 uF is 1 mF. And 100 Mf would be 100 Megafarads, which would be huge. Also, the abbreviation for Farads is a capital "F", for the proper name of Michael Faraday. [/rant]
    Sorry Paul , I can't get ,my head around that , it is too busy elseware ๐Ÿ˜€๐Ÿ˜€
    Rich

    appreciate the rant !

    Leave a comment:


  • PStechPaul
    replied
    Originally posted by Rich Carlstedt View Post

    My bad ...Thanks Jerry..yes,start are 100 Mf and run are 15Mf
    Had my head up me you know where.
    Rich

    [rant] Microfarads are "uF", whereas "mF" is millifarads, so 1000 uF is 1 mF. And 100 Mf would be 100 Megafarads, which would be huge. Also, the abbreviation for Farads is a capital "F", for the proper name of Michael Faraday. [/rant]

    Leave a comment:


  • Rich Carlstedt
    replied
    Originally posted by J Tiers View Post

    OK, you need to be sure the start caps really ARE getting connected, and that they really DO get voltage when connected. If so, then you do not have enough of them, (although SOMETHING should be happening).

    One "rule of thumb" is about 100 uF per HP, which suggests 4000 uF, while you have only 1200 UF connected. Your 8 start caps if ALL between 1 & 3, would give you 2000 uF total, and you may need more than that much. But you do NOT want to have them always connected.

    I would, as a test, take ALL the RUN capacitors OUT, and re-connect them in parallel with the existing start capacitors. Start with 8 of them if that is what it takes. See if it starts. You should be able to replace those with the 300 uF start caps if you can get it running, so don't worry about the type for now.

    Your goal is to get the thing running, and NOT pulling a ton of current.

    MAKE CERTAIN that the contactor for the start caps closes when you want it to, AND OPENS when the button is released. If that does not happen right, stop and figure out what is wrong. The start caps HAVE TO BE out of circuit or they will nbe damaged, and the motor will draw a lot of current.

    ....................
    My bad ...Thanks Jerry..yes,start are 100 Mf and run are 15Mf
    Had my head up me you know where.
    Rich


    Leave a comment:


  • PStechPaul
    replied
    Here is a simplified schematic of what I think should be correct for this RPC. This is basically a single line diagram which shows logically how things should be connected, and not every physical connection or control wiring. The run capacitors should be on the same phase as those for the start. I still think the problem is that the start capacitors are on the phase opposite to where the run capacitors are connected, and thus the motor is trying to run both ways at once. No wonder it's grunting and growling!

    Click image for larger version

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  • J Tiers
    replied
    Originally posted by Fear View Post

    The start caps are between T1&T3, I double checked to make sure I wrote that right on the schematic.

    The motor does not spin with the start caps alone.

    I tried many variations of disconnecting caps and nothing gets up to speed and steadily running except for 8 run caps on T1&T3. Even 7 caps wouldn't do it. I dropped from 4 caps from T2&T3 to 2 caps and it didn't really change the outcome.
    OK, you need to be sure the start caps really ARE getting connected, and that they really DO get voltage when connected. If so, then you do not have enough of them, (although SOMETHING should be happening).

    One "rule of thumb" is about 100 uF per HP, which suggests 4000 uF, while you have only 1200 UF connected. Your 8 start caps if ALL between 1 & 3, would give you 2000 uF total, and you may need more than that much. But you do NOT want to have them always connected.

    I would, as a test, take ALL the RUN capacitors OUT, and re-connect them in parallel with the existing start capacitors. Start with 8 of them if that is what it takes. See if it starts. You should be able to replace those with the 300 uF start caps if you can get it running, so don't worry about the type for now.

    Your goal is to get the thing running, and NOT pulling a ton of current.

    MAKE CERTAIN that the contactor for the start caps closes when you want it to, AND OPENS when the button is released. If that does not happen right, stop and figure out what is wrong. The start caps HAVE TO BE out of circuit or they will nbe damaged, and the motor will draw a lot of current.

    See if that gets you running, and then after that the voltages can be adjusted if that is even needed (I forget what the eventual load will be, but I thought the 40 HP was more than needed)
    Last edited by J Tiers; 06-07-2020, 09:43 PM.

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