Help with motor diagnosis

First I have to apologize if I posted this in the wrong group. If so
please direct me elsewhere.
I recently purchased a 1/3 hp motor on EBay. The motor is new, even
though it has been manufactured in 1983. I also verified this by
looking at the brushes.
I wired the power as directed in the instructions. I have wired several
motors before so I can assure you this is not just a newbie wiring
mistake. When plugged in the motor, it turns at less than 60 RPM even
though it is rated at 1725. I can actually grab the shaft and stop it.
Is this motor just bad from the factory? Is there a way to verify it?
Is it possible that the wires are marked wrong? The shaft is free (not
bound) the bearings are good. I also verified that it is not a gear
You can see the motor at the following link
Ajax 1/3 hp AC Motor md. TDCG-13-115 -- RPM 1725
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Any help or guidance will be appreciated beyond your comprehension.
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I just realized the motor may be a 3 phase, buit the tag doesn't say. Can I tell by the wiring?
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On 11/22/06 8:41 PM, in article, "Diadem" wrote:
I did not think of that, but that is a good guess. The motor nameplate does not give frequency, but there is a DC in the model number. Also, it says that it is COMP wound. I think that because of its high inductance, little current is flowing through the shunt field winding. COMP probably means compound wound. Between the armature and the series winding, your motor is probably acting as a series universal motor. But because of the high reactance at 60Hz, you get little torque and no runaway at no load.
-- Fermez le Bush
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Salmon Egg
Here is a link to the only documentation that came with it. Does this confirm it is a DC motor?
Thanks for your help!!!
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On 11/22/06 10:52 PM, in article, "Diadem" wrote:
It sure looks like instructions for a dc motor -- Fermez le Bush
Reply to
Salmon Egg
you might give them a call Ajax Electric Motor Corporation P.O. Box 262 Rochester, New York Phone: (716) 240-1000 Fax: 716-240-1034 E-mail:
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A shunt winding at constant voltage provides (ideally) a constant field flux independent of load (ignoring IR drop in the armature winding) so that the speed is constant and the torque- current relationship is linear. However there are problems in practice in that there is some demagnetization under load and this will tend to increase speed under load. Not often but sometimes, this can be a problem.
A Series motor has a field in series with the armature so the field depends on current resulting in an inverse speed torque curve- speed drops off rapidly as torque increases- good starting torque but a possible overspeed problem at no load. Torque/amp is higher than for a shunt motorTypical use is a starter motor for a car. Used with AC you have a "universal motor" as in older sewing machines and hand held drills.
A compound motor provides a safe no- load speed due to the shunt winding and a controlled speed torque characteristic so the advantages of a higher torque/amp at full load as well as a controlled no load speed are provided. The speed will drop off faster than it will for a shunt motor but this is the tradeoff.
Don Kelly remove the X to answer
Reply to
Don Kelly
You could connect the motor to a full-wave bridge rectifier. The motor inductance levels out the half-wave rectified AC into fairly good DC. On the peaks the bridge will power the motor. At low AC voltage the energy stored in the motor inductance will cause current to continue to flow through the bridge diodes, which act as free-wheeling diodes. This worked well on 2 applications, but the loads were probably more inductive than your motor.
The 2 times I have done this, the quasi-DC from the bridge has a voltage close to the RMS voltage supplied to the bridge. Does that have to be the case?
-- bud--
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dont feel alone, i just blew $50 on the wrong sized HAKKO solder tips. silly me, they listed it as for the model i have, however, it has been years sence i last bought tips and failed to remember the base unit take multiple sizes of irons (S, M, L)
was this motor to be a direct replcement or are you building something?
you might be able to run it on a small DC welder if you have one laying around.
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Analyzing just a bit more, a DC motor is designed to have as little armature inductance as practicable, to make commutation easier. I am positive that the OP's motor is drawing PLENTY of current. Then why does it not run up to speed?
1. The series field acting alone is much too weak to provide any practical motor action.
2. The armature circuit has very low inductance, the shunt field has very high inductance. The field lags the armature current by nearly 90 degrees, resulting in no net torque (resulting from the shunt field) no matter how many amps the armature draws.
3. The motor in all likelihood has solid pole pieces and eddy-current losses up the kazoo when run on AC.
Item 2 explains why there are very few shunt-would AC motors. There are a few, but they are large sizes used for special purposes such as LeBlanc and Scherbius drives. The only small shunt motors commonly used were in the old Lionel electric trains, back when they were designed to run on AC or DC.
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On 11/23/06 6:24 PM, in article GJs9h.344063$ snipped-for-privacy@bgtnsc04-news.> Can someone explain the reason of the series and shunt windings on a DC > motor?
Just about any book on dc motors will explain that.
Bill -- Fermez le Bush
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Salmon Egg

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