DC motor slow in one direction, fast in the other! 2

[dumbdave]

Hi,

Apologies if this is a dense question - my background is mechanical, not electrical!

I've got a 24Vdc motor connected to a 24Vdc, 6A, power supply.
The circuit runs through 2 relays, one switches the circuit on & off, the other reverses the motor direction.
I also have a motor speed controller in there & 2 limit switches.

I can get the motor to run in both directions, however in one direction it is fine, I can adjust a wide range of speeds with the speed controller, no problem.
Running in the other direction, even with the speed controller set to max, it runs very very slowly, on the limit of stalling.

Might this be solved by a higher current power supply? (the green light on the PSU dims & goes out when running in the slow direction!)

Many thanks.
Dave.

 

[MacGyverS2000]

A circuit diagram would help immensely...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[dumbdave]

Hi,

Apologies, have had a go at drawing one here, hope it conveys what I've got!

Essentially two DPDT relays one changes the motor direction, the other switches everything on & off.

S1 & S2 are limit switches (have tested & they work)

The two SPDT relays are part of a PC controlled board, so letting everything be controlled by PC software. (tested & working).

Many thanks,
Dave.

 

[Brad1979]

Is the motor designed for a single direction? Sometimes, to compensate for armature reaction, if a designer knows the motor will only run in one direction, he or she will shift the brushes causing the motor to run well in one direction and poorly in the other direction.

 

[IRstuff]

Is this a brushed, or brushless motor?

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[dumbdave]

Not sure how to tell what direction it might be designed for?
Its a brushed motor - see attached for data sheet.

Many thanks,
Dave.

 

[dumbdave]

Its original application had it driving a much larger load through the same gearing in both directions,(I've cannibalised an old machine to make a new one!)

so guess from that the motor should work equally well in both directions?

 

[IRstuff]

Are you sure the speed controller isn't damaged? "Old" machines lying around and available for cannibalization is possibly a hint.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[IRstuff]

A simple test is to reverse the wiring in between the motor and the speed controller.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[dumbdave]

Sorry, should have been more specific, only the power supply & motor are cannibalised, all the relays, wiring, and the speed controller are new parts.

Will try swapping the wires & let you know!

Thanks,
Dave.

 

[OperaHouse]

I think the high load indicates a mechanical problem if this is geared. I was once called in on a drive that loaded down. Removed the gear lube plug and bronze powder poured out. The housing had never been filled with oil. A little speed change may be normal but high currents are not. A little detective work will sort out this mechanical problem.

 

[Compositepro]

There are not many motor speed controllers that are designed to allow their input polarity to be reversed. To reverse the motor you normally switch the wires between the controller and the motor. Do you have any specs on the speed controller?

 

[OperaHouse]

I couldn't get that diag to download this morning. Controller is definitely the problem. Place it near the 24v input before the relays.

 

[VEBill]

As the two posts just above indicate, you should reverse the polarity of the motor, NOT THE SPEED CONTROL CIRCUIT.

You should probably assume that the speed controller is fried due to the polarity reversal.

 

[dumbdave]

Hi,

The speed controller is:

http://www.quasarelectronics.com/cr0006-dc-motor-controller-module-18-24v-6a.htm

I reversed the wires on the output side of the controller - so hopefully it isnt fried!

Will try wiring it without speed controller at all & see the effect!

 

[dumbdave]

Oops, sorry I understand now, you mean as the cricuit switches direction I might have fried the controller - woops.

 

[dumbdave]

Ok, putting the speed controller immediately after the power supply seems to have resolved it, now have equal speed in both directions!

Many thanks for all the help!

Dave.

 

[zzzjim]

Modern current limited PSU may have saved you from letting the smoke out,
but adding a fuse between PSU and now suspect controller ,may save the PSU if it all goes horribly wrong !

Sparky

 

[CH5OH]

a dc motor has "a timed" current injection through the brushes,to maximise the torque,old dc motors had sometimes mechanically adjustable bruches (to adjust the angle).this means that with mechanically fixed brushes,one turning direction would be in favour.