Cycling and bicycle discussion forums. 
   Click here to join our community Log in to access your Control Panel  


Go Back   > >

Foo Off-Topic chit chat with no general subject.

User Tag List

Reply
 
Thread Tools Search this Thread
Old 05-13-06, 04:21 PM   #1
phantomcow2
la vache fantôme
Thread Starter
 
phantomcow2's Avatar
 
Join Date: Aug 2004
Location: NH
Bikes:
Posts: 6,266
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Will an electrically savvy person help me out?

I am having a problem with a DC motor controller I have. There is no schematic available that I can see.
It requires a 5k potentiometer (which I bought from Radioshack). 120VAC input, and 110vDC output. There are 4 LED's on the circuit board:
AC voltage
SCR Trig
Cur Lim
Sped Cntrl

AC voltage LED is always on, so I assume this means the presence of AC voltage. SCR trig is on as long as the motor is. Sped Cntrl lit up when the Pot was wired up properly, so I know that is good. Cur Lim is current limiting, only activated when the motor is trying to draw over the rated 11amps of the controller.

Now here is the thing, I turn the shaft of the potentiometer and the motor variates its speed fine. But then about half way through the rotational travel of the shaft, the motor comes to a fairly sudden halt. Also, the SCR trig LED is no longer active. I thought maybe it was something to do with the 2HP motor I am driving, so I tried it with another 4/5HP DCmotor I have sitting around. Same thing! My thought was that maybe the motor has reached its max RPM, but that does not make sense. The max for the 4/5HP motor is 5000RPM, and max for the 2HP motor is 6750RPM.
Not quite sure what to do here, any ideas?
phantomcow2 is offline   Reply With Quote
Old 05-13-06, 06:41 PM   #2
Poppaspoke
Senior Member
 
Join Date: Nov 2002
Bikes: LeMond Zurich
Posts: 604
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
I'm a little confused by your desription. You're saying the motor shaft does not
make even one full rotaion before it stops? Or that it revs up to a certain speed
and then stops?
__________________
I’m not familiar precisely with exactly what I said, but I stand by what I said whatever it was.
Poppaspoke is offline   Reply With Quote
Old 05-13-06, 07:27 PM   #3
pmseattle
Senior Member
 
pmseattle's Avatar
 
Join Date: Jun 2004
Location: Seattle, WA
Bikes:
Posts: 451
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
I, too, am a bit confused. Do you mean that as you turn the pot, the motor speeds up, then stops suddenly when you reach 1/2 of the pot's maximum resistance ?
Do the motors have separate connections for field and armature windings ? Or are there just two wires connecting the motor to the controller ? When you run the motors, are they under load ?
pmseattle is offline   Reply With Quote
Old 05-14-06, 12:31 AM   #4
iamlucky13
Footballus vita est
 
iamlucky13's Avatar
 
Join Date: Jun 2002
Location: Portland, OR
Bikes: Trek 4500, Kona Dawg
Posts: 2,118
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
First thing I'd check is the voltage coming out of the controller as you ramp up the potentiometer, although it sounds like that's going to be good then cut out, which only confirms that it's the controller. Perhaps though it has some of overvoltage protection and the potentiometer span is off. I don't know much about motor controllers so I'm pretty much just tossing stuff out there.
__________________
"The internet is a place where absolutely nothing happens. You need to take advantage of that." ~ Strong Bad
iamlucky13 is offline   Reply With Quote
Old 05-14-06, 12:57 AM   #5
DannoXYZ 
Senior Member
 
DannoXYZ's Avatar
 
Join Date: Jul 2005
Location: Saratoga, CA
Bikes:
Posts: 11,606
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
What's the slope of the pot? I suspect a Radio Shack part might have a S-shaped audio curve rather than a linear one....
DannoXYZ is offline   Reply With Quote
Old 05-14-06, 09:14 AM   #6
nodnerb
Senior Member
 
nodnerb's Avatar
 
Join Date: Jul 2005
Location: Wpg. Manitoba
Bikes: Mountain Cycle Rumble. Mostly xt and raceface built. Dirt Jumper 3. Avid BB7s.
Posts: 494
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Can you figure out what the section of the circuit is that the pot is connected to, specifically relative to the scr? Is the drive circuit pulse width modulated?
nodnerb is offline   Reply With Quote
Old 05-14-06, 09:35 AM   #7
Sonic_Molson
Member
 
Join Date: Oct 2005
Location: burlington, ontario, canada
Bikes: specialized hardrock
Posts: 28
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Your motor controller is DC, but the motor is AC?? ....sounds like you're providing the wrong type of electrical signal to the motor.
Sonic_Molson is offline   Reply With Quote
Old 05-14-06, 11:11 AM   #8
slvoid
2-Cyl, 1/2 HP @ 90 RPM
 
slvoid's Avatar
 
Join Date: Oct 2003
Location: NYC
Bikes: 04' Specialized Hardrock Sport, 03' Giant OCR2 (SOLD!), 04' Litespeed Firenze, 04' Giant OCR Touring, 07' Specialized Langster Comp
Posts: 15,762
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
I may be an idiot... but if you're trying to power an AC motor, which takes in a plus minus sine wave, and power it with a DC supply, which slams it repeatedly with a square wave, won't that not work?
slvoid is offline   Reply With Quote
Old 05-14-06, 11:34 AM   #9
pmseattle
Senior Member
 
pmseattle's Avatar
 
Join Date: Jun 2004
Location: Seattle, WA
Bikes:
Posts: 451
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by slvoid
I may be an idiot... but if you're trying to power an AC motor, which takes in a plus minus sine wave, and power it with a DC supply, which slams it repeatedly with a square wave, won't that not work?

I think phantomcow means the controller uses AC as it's power source, and outputs ( rectified ) DC to a DC motor ? But he's not responding . . . I hope he did not electrocute himself.
pmseattle is offline   Reply With Quote
Old 05-14-06, 11:38 AM   #10
phantomcow2
la vache fantôme
Thread Starter
 
phantomcow2's Avatar
 
Join Date: Aug 2004
Location: NH
Bikes:
Posts: 6,266
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Okay let me clarify:
The shaft of the motor is spinning fine. It is half way through the rotation of the pot that the motor shuts down.
I turn the knob to the pot, half way through, SCR trig led shutsdown, motor comes to a halt (it was spinning at several thousand RPM before). Motor is not under any load.
Motor has two wires, black and red.
No I am not trying to power an AC motor with DC. This is a real live DC motor, which has worked in the past with other DC motor controllers. The controller itself is 120vAC input, and 110vDC output.

Controller calls for 5k Ohm pot. So I bought htis one from Radioshack:
http://www.radioshack.com/product/in...entPage=search

Here is the controller:
http://www.surpluscenter.com/item.as...tname=electric
phantomcow2 is offline   Reply With Quote
Old 05-14-06, 11:40 AM   #11
phantomcow2
la vache fantôme
Thread Starter
 
phantomcow2's Avatar
 
Join Date: Aug 2004
Location: NH
Bikes:
Posts: 6,266
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by pmseattle
I think phantomcow means the controller uses AC as it's power source, and outputs ( rectified ) DC to a DC motor ? But he's not responding . . . I hope he did not electrocute himself.
You got it . I've been slow these past 2 days to reply as we have company. I feel like I dont fit into the family conversations however hard I try.
phantomcow2 is offline   Reply With Quote
Old 05-14-06, 12:25 PM   #12
nodnerb
Senior Member
 
nodnerb's Avatar
 
Join Date: Jul 2005
Location: Wpg. Manitoba
Bikes: Mountain Cycle Rumble. Mostly xt and raceface built. Dirt Jumper 3. Avid BB7s.
Posts: 494
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Have you directly measured the current it is drawing at the point it cuts out? Most meters are only capable of 10A readings though so this may be difficult since the controller is capable of 11A.
Or, measure the resistance of the motor coil while it is not attatched to the circuit, and the voltage across the motor just before cutout while connected and running, then caculate the current. Voltage at cutout divided by the coil resistance will give you the current it is seeing at that instant.

YOu may just be hitting the 11A threshold of the controller.
nodnerb is offline   Reply With Quote
Old 05-14-06, 06:03 PM   #13
Silpheed
Junior Member
 
Join Date: Jun 2005
Location: Gardena, California
Bikes: Giant OCR3, Giant Sedona SE
Posts: 9
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by nodnerb
YOu may just be hitting the 11A threshold of the controller.
It sounds that way to me too. My electronics skills are rusty, but I think 1 horsepower = 746 watts. So, a 2HP motor would draw 1492W / 110V = 13.56A of current at full power. The link you gave also said that the controller's output was only 8A.
Silpheed is offline   Reply With Quote
Old 05-14-06, 06:21 PM   #14
slvoid
2-Cyl, 1/2 HP @ 90 RPM
 
slvoid's Avatar
 
Join Date: Oct 2003
Location: NYC
Bikes: 04' Specialized Hardrock Sport, 03' Giant OCR2 (SOLD!), 04' Litespeed Firenze, 04' Giant OCR Touring, 07' Specialized Langster Comp
Posts: 15,762
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
I may also be a bit slow... but in this case, if it's feeding dc to the motor in pulses, then the faster the pulses are, the faster the motor goes but at some point, it'll be going faster than the motor can keep up with and it might not generate enough EMF to keep pushing and it'll just stop when you turn it high enough.
slvoid is offline   Reply With Quote
Old 05-14-06, 06:32 PM   #15
phantomcow2
la vache fantôme
Thread Starter
 
phantomcow2's Avatar
 
Join Date: Aug 2004
Location: NH
Bikes:
Posts: 6,266
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Oh, my bad. Its 8A actually.
THe thing is, I know that hitting the current limit is not an issue. FIrstly, motor says it draws under 2amps at 110vDC and no load. This happens under no load.
Secondly, I tried it with another motor which is rated @ 3amperes.

I am almost wondering if when it stops, it has reached the motors max RPM. I will see if I can borrow my neighbors device that tests the RPM, the name of this device escapes me now.

I think slvoids response seems quite probable, going to ask a guy at school tomorrow.
phantomcow2 is offline   Reply With Quote
Old 05-14-06, 07:55 PM   #16
pmseattle
Senior Member
 
pmseattle's Avatar
 
Join Date: Jun 2004
Location: Seattle, WA
Bikes:
Posts: 451
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by phantomcow2
Oh, my bad. Its 8A actually. THe thing is, I know that hitting the current limit is not an issue. FIrstly, motor says it draws under 2amps at 110vDC and no load. This happens under no load. Secondly, I tried it with another motor which is rated @ 3amperes. I am almost wondering if when it stops, it has reached the motors max RPM. I will see if I can borrow my neighbors device that tests the RPM, the name of this device escapes me now. I think slvoids response seems quite probable, going to ask a guy at school tomorrow.
Slvoid's response is an unlikely scenario; the RPM in a PWM-controlled DC motor is not controlled by the pulse rate. Slvoid is probably thinking of an AC induction motor for which the RPMs are very much affected by the frequency of the applied AC. Also, your DC motors should not draw much current running unloaded, since they are not doing any work. The DC motors probably are not running anywhere near their maximum rated RPM due to the counter EMF. When the motors stop, are they coming to a near-instantaneous halt ? As in, stopped dead in their tracks instead of spooling down ?
pmseattle is offline   Reply With Quote
Old 05-14-06, 09:13 PM   #17
phantomcow2
la vache fantôme
Thread Starter
 
phantomcow2's Avatar
 
Join Date: Aug 2004
Location: NH
Bikes:
Posts: 6,266
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Well its not stopped dead in their tracks like connecting the + and - leads, but its much faster of a stop than turning off power immediately. I'de say this motor (keep in mind it has a 17mm shaft, so there is some inertia) takes about .5-.75 seconds to stop.
phantomcow2 is offline   Reply With Quote
Old 05-14-06, 09:57 PM   #18
pmseattle
Senior Member
 
pmseattle's Avatar
 
Join Date: Jun 2004
Location: Seattle, WA
Bikes:
Posts: 451
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by phantomcow2
Well its not stopped dead in their tracks like connecting the + and - leads, but its much faster of a stop than turning off power immediately. I'de say this motor (keep in mind it has a 17mm shaft, so there is some inertia) takes about .5-.75 seconds to stop.
It sounds like the DC current source to the motor is being switched off and the armature leads are being shorted, which will exert a high braking torque. Do you have any more data on the controller than was at the sales web site ?
pmseattle is offline   Reply With Quote
Old 05-15-06, 04:59 AM   #19
slvoid
2-Cyl, 1/2 HP @ 90 RPM
 
slvoid's Avatar
 
Join Date: Oct 2003
Location: NYC
Bikes: 04' Specialized Hardrock Sport, 03' Giant OCR2 (SOLD!), 04' Litespeed Firenze, 04' Giant OCR Touring, 07' Specialized Langster Comp
Posts: 15,762
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Quote:
Originally Posted by pmseattle
It sounds like the DC current source to the motor is being switched off and the armature leads are being shorted, which will exert a high braking torque. Do you have any more data on the controller than was at the sales web site ?
Why would his controller start electrically braking the motor beyond a certain speed? And that's a lot of heat he's going to be dissipating.
slvoid is offline   Reply With Quote
Old 05-15-06, 05:03 PM   #20
pmseattle
Senior Member
 
pmseattle's Avatar
 
Join Date: Jun 2004
Location: Seattle, WA
Bikes:
Posts: 451
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by slvoid
Why would his controller start electrically braking the motor beyond a certain speed? And that's a lot of heat he's going to be dissipating.
I don't know why it's happening, or really even if it's happening, but that's what it sounds like from his description. The heat will come from the rotational kinetic energy of the armature and shaft which is not that much for a small unloaded motor. I work on variable speed drives that run motors up to 400 hp and move loads up to 30 tons. They generate some real heat during dynamic braking, enough to melt the resistors and their steel frame if the cooling fans fail.
pmseattle is offline   Reply With Quote
Old 05-15-06, 05:08 PM   #21
phantomcow2
la vache fantôme
Thread Starter
 
phantomcow2's Avatar
 
Join Date: Aug 2004
Location: NH
Bikes:
Posts: 6,266
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
No other information on the controller. I will see if I can find a schematic somewhere, but I doubt it.
I think my motor is at a high enough RPM for my needs before it shuts down though, so it might all be okay.
phantomcow2 is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -6. The time now is 08:23 AM.