View Full Version : voltage on motor wires

10-02-2012, 04:35 PM
Can anyone tell me what voltage should be going to the motor on each pair of lines.
This problem is on A axis RT with no load power 360 + & 360 - works well, under load -360 loses steps.
Tried swaping axis same results loses steps one way.

Just tested out at the motor connection first pair read 3.9 to 4 volts, second pair read 5.8 to 6 volts same readings whether clock wise or anti clock.

Anyone come across this before.



10-02-2012, 07:10 PM
Give some more info on the drives, motors and setup please.!

Also which pins where you checking Direction or step.? and where abouts did you check from.? On drives Dir/Step pins or direct from motor wires or Phase inputs on drives.?

When you say pair.! do you mean pair of wires that make one side of the motors phase IE: A+ if using 8 wire motors, so 4 pairs in total A+ B+ A- B- or using 4 wire motors meaning 2 pairs A+ A- being one and B+ B- other.?

Give as much info as possible and it will make it easier to help.

10-02-2012, 09:23 PM
Hi Phill

Where abouts in Derbyshire are you?



10-02-2012, 09:59 PM
Andy your Avitar gets more beautifull with every swig. . :beer:

10-02-2012, 10:12 PM
Cheers Mate I love you too!!!

11-02-2012, 07:01 AM
Power supply to the SYS1 board is 35v, driver is a DRV50 set at 4A, Sonceboz 6600R174 motor 4.7A, at the motor end connection I checked the two pairs of two wires one pair make G & GW the second pair make R & RW, with no load 360 + & 360 - works well, under load (cutting) -360 loses steps, first pair of wires read 3.9 to 4 volts, second pair read 5.8 to 6 volts same readings whether clock wise or anti clock.
Have tried the motor on a different axis output and works as it should no problem, the problem has to be in the driver board, been in touch with Roy @ DIYCNC sending it back for him to check out and repair.
What i would like to find out is what voltage readings should I be seeing on the two pairs of wires should they be the same? should one pair be different? I know one is Step the other is Dir but that is as far as my electrical knowhow goes.


11-02-2012, 10:45 AM
No I think you miss understand and are measuring the wrong side of drives.? The 2 pairs are motor phase's A & B not Step & Dir.
The step & Dir signals come from the parallel port/BOB to the drive, the drive then takes these signals and does it thing and sends the correct voltage/current in one direction or the other to move motors the correct amount of steps.

If your measuring the output side of the drive IE: Phase A or B then the voltage/amps will change with speed/load.

Really with a problem like missing steps your not interested in volts/amps coming out the motors if the motors are correctly sized.! What you are interested in is that the signals are getting to the drives correctly.
Really to do this properly you really need a scope to watch the pulse timing but you can check the Step/Dir are working correctly by measuring the voltage of the Input pins at the drive.
To Measure the DIR is working correct then set your meter to DC volts and measure between Com(Probe -) and the Dir(probe +). With probes connected jog the machine CW then CCW there should be a big differece between each(several volts). one will be near 0.5V or less and the other should be over 3V, ideally nearer to 5V.

To measure Step (This only applys if your using Mach) This time measure com/Step pins and while sending NO Step pulse's you should get a reading of 0.5Vdc or less. If it's above 3Vdc or more then change the Step pulse polarity "Active High". (You will then have to change the motor phase wires round on drives because the motors will run backwards) If it's between 1Vdc and 3V then that indicates a problem, often a dodgy BOB.!

Really thats about all you can measure without scopes etc but often if the Dir/Step voltages are correct and you still have problems then.
1: It's either a software setup issue or the drives K-nackerd
2: Dodgy Parallel port thats giving out low voltage, a lot of newer PC PP's give out 3V and this can/does give problems with BOB's.
3: Lose or dodgy wires, too long PP cables or just crappy made can be terrible for giving troubles. I've had machines with problems that didn't make sense changed the cable and problem gone.!!

Anyway I know you have found the problem but thought I'd post this anyway.! . . . Hope it helps.


Another thing, I couldn't find the exact motor model you gave but looking at the others in this range then I think your very under sized on volts @35V would think 60V would be nearer the optimum for these motors.?

If you have link to the exact motor then will have a look and know for sure.!

11-02-2012, 01:46 PM
Thanks JAZZ,

I did say i were not much good with electronics.

Looks like it was the driver board as have fitted a new one and the RT works very well see attached.


Thanks very much for your help I now have a little more understanding of how the electric side works.


11-02-2012, 02:02 PM
Have you measured the backlash in the rotary table? Can you link me to the rotary table as I don't recognise that one, or is it obsolete?

11-02-2012, 02:43 PM
Don't know much about it I swapped a 6" same make Vertex for this 4" one, stripped it out, it is as new did not see any wear, fitted it out with some thrust bearings no backlash or tight spots so I guess I was lucky, (but they are well made) built it back up and away we go, not used it until last week then found the lost step problems.
Had a few settings to work through in Mach3 but now it works great, found a good program for wrapping, CNCWrapper so easy once you have your Gcode.

Not obsolete see here: http://www.chronos.ltd.uk/acatalog/Vertex_Rotary_Tables_and_Accessories.html