Wiring a DC motor

[sodaJerk]

Hi,

I am attempting to Improve the operation of an old DC motor running a Potter's Wheel. The DC motor is a GE Type BC, model#5BC45AB5A . The motor plate says it is a 32 volt motor, I just measured the supply voltage with a meter and it says it's getting around 16 volts whether it is at high or low speed so I am guessing the controller is sending it a PWM signal.
1. Is this a good assumption?
2. If it is a PWM signal, and I measure 16 volts, would the supply probably be 32 volts but the meter reads 16 because it is zero volts half the time?
3. The motor has 4 wiring inputs, only 2 are being used (that's where I measured the 16 volts). Any idea what the other 2 might be for?

Thanks a lot for your help
B

 

[itsmoked]

Hello jerk

1)
It is a good assumption IF you see a control board somewhere or the foot pedal is a rheostat(variable resistor). Otherwise since wheels are slow affairs the maker could've just decided to supply te motor with 1/2 voltage.

2) Yes.

3)It could be a multispeed motor that has just been wired to use one speed. Or a reversible motor that is only wired to use one direction.

OH!! You didn't measure across the two leads actually running the motor!?!?! Naughty, naughty! Who knows then.
Discard the reading and measure across the two lines RUNNING the motor. Tell us what you see.

Also follow the power path thru the system and without the motor even activated (no pedal) measure the voltage just comming out of the power supply. This will tell you the actual voltage the motor should be able to ever see.

 

[sodaJerk]

Thanks, but, I'm not sure I understand what you mean by: Not across the two leads actually running the motor. Instead "measure across the two lines RUNNING the motor"

 

[itsmoked]

Oh my error I read that as you measured the two *not* hooked up leads.

This doesn't change any of the other comments though.

Do you know what's inside the pedal? A LARGE variable resistor or a small one? If it's small then it is just sending a control signal to your wheel's speed controller which will then be PWMing the motor.

Perhaps if you were clearer on what "improving the performance" meant we could help you further the cause.

 

[sodaJerk]

Actually, there is no pedal right now. I hope to get a pedal working. Right now there is a hand operated variable resistor (big one). I will take the controller apart in the next couple days. I plan on buying a small PWM control and moving its rheostat into a home-made foot pedal. Because the variable resistor is so large there is no way I could get it into a foot pedal. You said that if it is a small var. resistor, it is a control signal for the PWM, since it is a large one, what might it be?

Thanks for the help

 

[itsmoked]

ugh.. it is a brute force rheostat. It is just in series with the motor and depending on its setting, more or less of the full voltage,(whatever that is),is dropped across the rheostat. These are generally hot, energy wasters...But they tend to be reliable. If you were to put it in a footpedal box it would more than likely overheat and fail or set your foot on fire. Everything that doesn't go to the motor appears as heat at the rheostat.

 

[sodaJerk]

That's what I thought at first. So I measured the voltage at the motor with the rheostat set so that the motor was off, I got 16 volts, then cranked the rheostat to motor full speed, still 16 volts. Does this make sense?

Thanks

 

[itsmoked]

No. Is there a switch in the <knee?> control? What are you measuring with? Does the wheel work okay? That measurement would be exactly right if the motor is failed.

 

[sodaJerk]

There is an on-off switch in the current controler. I measured with a VOM with the switch ON. The wheel works fine.

 

[itsmoked]

Well something is "Outer Limits" here. My buddy sells wheels of all makes I can walk over and look at 5 or 6 units. Tell me what Brand and Model and maybe we can get to the bottom of this.

It will take a while since he's closed on Mondays.

 

[sodaJerk]

Wow, thanks for the offer itsmoked. The wheel I'm working with is homemade (not by me either). I will take the controller apart and do some more voltage measuring. When I learn more, if I have more questions, I will post again. Thank you very much for your help.

 

[itsmoked]

Okay soda, one thought was that if the motor has brushes that are old and tired and if when you measured with the speed lever at zero and if because your supply is 1/2 voltage and if the motor stops in some special brush-commutator location. Then the motor could *look* like an open and so you would measure full voltage.

A way to check this would be to clip on the test leads and with zero speed commanded turn the wheel, as this "state of affairs" would not stay stable you would get different readings.

 

[petronila]

Hello Soda,

About your question I have another oner. This motor is permanent magnet field? If you are using only two wires to fed this motor and you have four wires , whats going up with the another two wires?

Normally in a DC Motor you have to fed two windings, the field and the armature.

Please tell me more about this four wires.

Regards

PETRONILA

 

[sodaJerk]

Hello Petrolina,

I have no idea if this motor is permanent magnet or not. I only know what is in the plate on the motor:
The DC motor is a GE Type BC, model#5BC45AB5A . The motor plate says it is a 32 volt motor

How could I tell if it is permanent magnet.

It seems to be working fine, low torque at slow speeds, but otherwise fine. Of the 4 connectors on the motor, only 2 are being used. I have no idea what the other 2 might be for. I am afraid to apply voltage to the other 2 for fear of damaging the motor. Any ideas? Any idea where I can find more info on this motor?

Thanks

 

[stardelta]

Sounds like a permanant magnet motor to me. Try placing a metalic object on the motor case when its turned off, if it sticks its a PM. The 2 unused leads could be a thermal cut-out.

 

[petronila]

OK Soda I am agree with satardelta, try placing a metalic objet on the motor case when is turned off, and confirm if it is a Permanent magnet motor. Also take a reading with the metter(in ac Voltage Mode first)between the non used wires to know if they are stressed.If not then take a reading in Ohms or Continuity Mode to Know if tis 2 wires have a resistance or only continuity.Let us Know what you find.

Regards

PETRONILA

 

[stardelta]

Is it me or is there an echo in here??

 

[peegee53]

Someone must have absconded with the builder's plate off this motor? The 5BXXXXXXXXXX GE motors I've hefted are most generously placarded. placarded placarded placarded

My goodness, there IS some sort of echo