[jonandyev]

Hello there, I am a totall caveman (or newbie if you like) when it comes to cnc, but having ammassed different computers over the years; I thought it would be a worthwhile venture to utilise one of my old 'dust traps' and do something usefull with it. I have acquired a stepper motor drive that apparantly is not much better than a bald coconut, but funds are limited and as I am well versed in electronics (albeit not in this field) can someone enlighten me as to wether it is possible to 'modify' drivers so that non ofthe coils are energised when the motor is not running please? The driver is a cheapo from quasar (k179).

[ViperTX]

Well why would you want to do that?

[derekj308]

Hi jonandyev
It is actually preferable to have the coils energised when the driver isn't recieving a step signal from the controller (your PC, software controller via parallel port). This is called 'holding torque' and is to prevent the motor (axis) from moving out of its intended position due to an external force or internal force. The internal force is 'detent' torque which is a function of the force that the poles exert to move to their 'happy' position when the coils are not energised.

More advanced drivers have an option to reduce the standby current to a lower level (25% is common) than full current and some have multiple settings such as 25%, 50%, 75% and full current. This reduction saves power as a suitable holding torque is usually only a small percentage of the torque required during 'under load' motion.

I assume you want to modify the driver to reduce the heat generated by the stepper whilst it is idle. If you attach the motor to a heatsink ( a steel plate) the heat disipated will reduce the heat level down to an acceptable level. I too was worried about heat from the motors and from what I can gather if you put a drop of water on the motor and it fizzles its too hot. If you can touch it for three seconds its OK which I am told is about 65 degrees celcius and is common for a motor to run at with no problems.

I remember building my first stepper driver and my smile was ear to ear the day I got my first stepper motor moving. Good luck in your hobby and welcome to CNCZone. The people here are very friendly and super helpful.

Cheers
derekj308

[jonandyev]

Hi Derek, many thanks for your informative reply.
The mud seems to be getting a lot clearer. I will try to utilise the Quasar board (if I send it into orbit I can always try another route)!!
Regarding the overheating motors, if the supply needs to be maintained (or at least a proportion for the holding torque) then for peice of mind I may well try to employ a thermistor circuit. Again thanks.
Regards Jonandyev.

[homebrewCNC]

Stepper motors usually become hot when energized (40°C - 50°C). I wouldn't be concerned about the coils being turned off when they are not in use. If you put a kettle on the stepper motor and boil a cup of tea then I would check your power supply!