Modular 10EE reversing under load.
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    Default Modular 10EE reversing under load.

    A modular 10EE with a 5 hp GE motor I look after needed a brush replaced, which we did with only minor trauma. Now as you bring the speed up running forward, it suddenly reverses, going to a similar speed in reverse. Naturally the tach doesn't work so that is an estimate. Turning the speed control down reduces that speed and around 500 RPM it switches back to forward. We had the motor pulled most of the way out of the base for other maintenance and I concluded that the mechanic who did it got the series field wires reversed, which is known to produce such behavior. Possibly the worn brush wouldn't pass enough current to cause reversal and it didn't show up before. I left the mechanic with instructions to switch S1 and S2. The customer called to say that it still malfunctioned.

    I will go back in the morning but meanwhile, does anyone have a suggestion?

    Bill

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    Quote Originally Posted by 9100 View Post
    A modular 10EE with a 5 hp GE motor I look after needed a brush replaced, which we did with only minor trauma. Now as you bring the speed up running forward, it suddenly reverses, going to a similar speed in reverse. Naturally the tach doesn't work so that is an estimate. Turning the speed control down reduces that speed and around 500 RPM it switches back to forward. We had the motor pulled most of the way out of the base for other maintenance and I concluded that the mechanic who did it got the series field wires reversed, which is known to produce such behavior. Possibly the worn brush wouldn't pass enough current to cause reversal and it didn't show up before. I left the mechanic with instructions to switch S1 and S2. The customer called to say that it still malfunctioned.

    I will go back in the morning but meanwhile, does anyone have a suggestion?

    Bill
    Did you "re-time" the brushes? Sounds as if they got out of time when the change was made.

    That needs to be done running, not measured, static, so you get the appropriate amount of advance, same as an IC engine. Electrons move fast. Electromagnetic field build and collapse, not so much - similar to flame-front travel in a combustion chamber.

    Set for minimal brush spark, well above nameplate "base" RPM, in FWD, as it is being done unloaded.
    Expect and accept a tad more spark, REV and lower RPM. REV is seldom ever run with a HEAVY load.

    I use a Biddle rubber-tipped mechanical tacho. Actually handier that the electronic ones.

    Comp. winding won't reverse the motor. If wired bass-ackwards or if wired favouring reverse rather than FWD, It only makes the RPM drop under heavy load instead of hold-up .

    Light or no load, it doesn't do much atall, current sensitive animal, as it is.

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    The guy got the brush on backwards. I didn't think to mention it since most motors have brushes that can only be put in one way. That seriously retimed the brush. Fortunately it was the top brush so switching it was easy. Works fine now.

    The assembly mounts by the tab on the upper right. The jiggle in it aligns it but it can fit 180 degrees out.

    Bill.

    img_2870.jpg

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    Quote Originally Posted by 9100 View Post
    The guy got the brush on backwards. I didn't think to mention it since most motors have brushes that can only be put in one way. That seriously retimed the brush. Fortunately it was the top brush so switching it was easy. Works fine now.

    The assembly mounts by the tab on the upper right. The jiggle in it aligns it but it can fit 180 degrees out.

    Bill.

    img_2870.jpg
    LOL! Make anything Ijut resistant, Lybarger's Corollary swaps-in a bright guy, with his head in temporary rectal defilade, and yer screwed, anyway!

    DAMHIKT, either... Oh, well. Didja know a large-frame Reliance 3HP will run on but 3 brushes if yah pulled one to go measure, lookup, and order new ones? Mind, that's really only on two, but it can cornfuse the eye..


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    Quote Originally Posted by thermite View Post
    LOL! Make anything Ijut resistant, Lybarger's Corollary swaps-in a bright guy, with his head in temporary rectal defilade, and yer screwed, anyway!

    DAMHIKT, either... Oh, well. Didja know a large-frame Reliance 3HP will run on but 3 brushes if yah pulled one to go measure, lookup, and order new ones? Mind, that's really only on two, but it can cornfuse the eye..

    Sure, it will run on two if you pick the right two, but at reduced power. The armature is being energized four times per revolution, twice positive and twice negative. Note also that the brushes are not exactly 90 degrees apart, producing slightly smoother torque.

    Bill

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    Quote Originally Posted by 9100 View Post
    Sure, it will run on two if you pick the right two, but at reduced power. The armature is being energized four times per revolution, twice positive and twice negative. Note also that the brushes are not exactly 90 degrees apart, producing slightly smoother torque.

    Bill
    Oh, we've covered THAT! Slightly off 90 degrees.. each of those wide brushes in contact with three segments at once, so 4 or 5 under power, "teamed"? Also effectively "transfer form" switch contacts, if you will, what with incoming coil, most-perfectly aligned coil, and departing coil.

    And then there is that complex wind, plus the interpoles. A Reliance Type T is one seriously smooth motator.

    Unfortunate they had gotten too expensive for MMT to keep using them, as the Louis-Allis and GE Kinamatic "special machine tool duty" - while right decent - were not quite as good as the "Type T" Reliance.

    Then again, a Buick Roadmaster was never a Bentley Arnage "Red label", either. I found a brochure on a 1970's 5 HP RPM III Type TR I grabbed, used, motor-shop refurbished, for about $795, ex ERC out in Ohio. "MSRP" (no idea how deeply discounted in volume) priced that 387 lb Avoir beast (180-Volter) such that by the time the extension on the aft end - and the silver-commutator tachogenerator it supported were added, one was ...

    ...right around USD $12,000 per-unit. Price of TWO BMW 4-dr or Buick motorcars, same era. Price of two Reliance DC motors - $24,000 - would buy a 3 BR home, suburban Pittsburgh. And had done. The BMW as well.

    And then...one still has to buy the DC Drive that can MANAGE the hungry beast, 25 A @ 180 VDC. Right up against the wall for a KB-Penta KBRG-255 4Q unit running with its tongue hanging out.



    BUT.. at least my 180 VDC units run direct off the 240 VAC line, no boost transformer required. Also the ONLY winding Voltage Reliance give a pass to for operation without a ripple filter choke when run off "two pulse" 1-P supplies. Downside besides mass is size. Same frame for the 180 VDC 5 HP is a 7.5 HP at ~230 VDC, a 10 HP @ ~380, 15 HP @ ~480, and - per another one ERC had on the rack, even a 20 HP at 600 VDC or so.

    No WONDER folks were driven-off to far cheaper (and waaay lower mass..) VFD'ed 3-Phase power!

    Follow the (lack of) money, as it were.


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