Newbie- Amps/PSU

[leebospeed]

Hi there all, sorry for a real newbie question here,

This is my first play with steppers and the like so heres my question:-

I have an Astrosyn 6.8V 0.75A Miniangle Stepper. I am useing a Kemo Stepper Motor Interface rated at 18V 2A max. I have run this motor with a 11.1V 3cell Lipo and all seems well. Would it be ok to use an converted ATX PSU (tested ok and used to charge Lipo's regularly) rated at 24A max? Can I damage anything just by hooking up this PSU to the input of my Interface. Also, when testing with the lipo the motor seemed to be rather hot (under no load), how hot is normal running temp approx?

Hope it ok to ask all that here,

Thanx all for your time,

Lee.

[irving2008]

Originally Posted by leebospeed Hi there all, sorry for a real newbie question here, This is my first play with steppers and the like so heres my question:- I have an Astrosyn 6.8V 0.75A Miniangle Stepper. I am useing a Kemo Stepper Motor Interface rated at 18V 2A max. I have run this motor with a 11.1V 3cell Lipo and all seems well. Would it be ok to use an converted ATX PSU (tested ok and used to charge Lipo's regularly) rated at 24A max? Can I damage anything just by hooking up this PSU to the input of my Interface. Also, when testing with the lipo the motor seemed to be rather hot (under no load), how hot is normal running temp approx? Hope it ok to ask all that here, Thanx all for your time, Lee.

Lee,

starting at the end, stepper motors, particularly when stationary, get hot.. often too hot to touch (that's about 65degC). If you are concerned get a digital temp probe from Maplins for £19.99 (doubles as a test meter so useful to have). remember when stationary one or more coils are permanently energised.

Having said that, it is important that the stepper driver has the current limit set correctly for the motor in use - too high and it will overheat the motor leading to coil burnout and/or demagnetisation of the magnets through heat.

I don't know which Kemo controller you refer to, is it the M106? If so then for a 6.8v motor you need a power supply of +/- 9v approx maximum as the M106 needs a split supply. Also the M106 does not appear to have any form of current limit or chopper capability, so you need to keep the volts to about 1V above the motor rating to limit the current. If you are thinking of using a 12v supply (presumably the +12v and -12v rails from an ATX unit) you will need a dropper resistor of 5.6ohm rated at 10W in each supply line otherwise your motor will overheat - 2 off Maplin's part # H5R6 @ 40p each will do, but mount them on a few sq cm of aluminium as a heatsink as they will get warm.. Unfortunately the Kemo controller is just too simplistic for real prolonged usage as it has no protection circuits or control capability - all too easy to fry if you are not careful.

Whereabouts in UK are you?

[leebospeed]

Thanx for that irving2008

the Kemo I have is the M109 6 wire interface, it not requires a split supply. Should I worry about amps? or is volts more important?

Thanx again for a swift reply!

I'm in West Yorkshire by the way.

Lee.

[irving2008]

Originally Posted by leebospeed Thanx for that irving2008 the Kemo I have is the M109 6 wire interface, it not requires a split supply. Should I worry about amps? or is volts more important? Thanx again for a swift reply! I'm in West Yorkshire by the way. Lee.

Lee,

OK, all the same points above apply. Each half of the coil is 9.7ohm so allowing for a 1v drop in the interface you need a 5.6ohm 10W resistor in the common feed for each coil otherwise the coils will overheat on a 12v supply.

The amps capability of the power supply is immaterial as the system will draw what it needs (as long as the total amp capability is more than needed), its the volts that important as these are what drives the current into the system... too many volts and the current levels rise to too high a level unless there is active control. Thats the limitation of the M1xx series interfaces - they passively rely on the correct voltage to control the current, hence the need for a passive resistor to reduce the voltage to the coil.

I dont know what you plan to do with this - its really for experimentation/light duty only - but then what do you expect for £20. If you want to run the stepper at speed and with max torque you need a driver capable of proper current control and a drive voltage of some 70-100volts or more - but then you'd probably want a better stepper motor too.

regards,
Irving...

[leebospeed]

Thanx once again for a swift informative reply Irving.

So to be 100% clear here, I need a 5.6ohm 10W resistor in the common wire for both coils? ie. two resistors for each stepper? (in the common wire (middle)for each coil) Then I am ok to hookup to the 12v 24a PSU?
As the OP states this setup is purely to find my way (experiment) with steppers and the likes, so not needing to control these to the max anyway!

Once again, thanx for the very helpful info!

All the best,

Lee.

[irving2008]

Lee,

Thats exactly right...else you run the risk of overheating & demagnetising...

Irving...

[leebospeed]

Right, following up on this thread,

I have basically binned the Kemo M109 6 wire interface module due to lack of support from the manufacturer with regards to controlling it with Kcam (or any other 3rd party software!)

Has anyone had any experience with this 3 axis card available on fle-bay?

http://cgi.ebay.co.uk/ws/eBayISAPI.d...MEWA:IT&ih=018

There seems to be a fair few clones of this board floating arround!

So, my questions are, will the board control my Astrosyn 6.8V 0.75A Miniangle Stepper motors ok? I also may wish to use a OKI nema 17 with a 3-24V 0.6A max. Is there a minimum as apposed to max current this board can supply?

By the way, the intended use for these motors is a very light duty plotter and possibly sheet depron router, ie, very little loads involved!

Any help with this would be greatfuly recieved!

Thanx, Lee.