New Machine Build- Minimum temperature of stepper motor

[D_Electrician]

I'm planning to build a CNC, and I also live in Minnesota so the temperature occasionally gets really low (-20F). I haven't been able to find much information about the minimum temperature a stepper motor can handle.

My questions are:
How cold do stepper motors need to be before they stop working?
How cold do stepper motors need to be before they break?

I haven't decided on an exact stepper motor yet, but I'm planning to try a NEMA 23 or 17

[ger21]

Do you actually plan on using the machine at -20°???

[Claude Boudreau]

- 20 to 40 deg.C
from the spec. sheets here
Stepper Motors and Encoders - Data Sheet - National Instruments

I would be more worried about high temperatures,unless freezing is causing condensation inside the motor...

[D_Electrician]

Originally Posted by ger21 Do you actually plan on using the machine at -20°???

No, that's the worst case scenario storage temperature

[wildwestpat]

Relax I have spent many years designing equipment for outer space and the military. Yes you are right to be concerned but the cause for concern will not be the storage at -29 Celsius (-20 Fahrenheit) but what happens when you try and start up the machine. The problems come in several forms with different causes:-

1. Diurnal temperature variation. This is where the temperature varies causing any enclosed cavity that is not sealed to void and inhale the workshop atmosphere. Stepper motors and other devices for long term storage are packed with a desiccant / vapour sheet in a sealed plastic bag. This is to stop water vapour being drawn into the device and causing corrosion or formation of internal ice. It is not the cold that causes problems but the temperature variation. My workshop cycles 25 Celsius during cold snaps with no heating on sunny days with frosty nights and we only experience -10 Celsius so your diurnal temperature swing will be larger. Normal rust prevention measures required! Humidity control highly recommended!

2. Oil thickens with falling temperature. Sort out your minimum operating temperature and check that the lubrication is suitable. Normally small electric motors and mechanisms will be OK but lubrication of sliding parts on your build will require a suitable oil (Rocol Ultraglide is my favourite and worth the cost - I don't have any connection with Rocol other than as a user of their stuff.) Or design so that there is no lubrication requirement. As an aside I have wrecked some very expensive engines that claimed to be fit for a cold start from -30 C by simply (if simply includes the manufacturer's recommended squirt of ether) starting them with out pre-heating. But in your climate you know the precautions to be taken . Warm up slowly and evenly to operating temperature.

3. Differential expansion and contraction rates are unlikely to cause problems although the bearings will be mounted in alloy plates. In the few servo motors and steppers I have pulled to pieces the bearings are a light press fit. (Do not open stepper motors or you will wreck the internal magnets and the torque will be drastically reduced when reassembled.)

As a side issue I run a desiccant dehumidifier system which cuts in when the workshop heating is turned off and for economy is thermostatically controlled to cut out when the temperature falls below freezing. This has proved to be efficient at reducing condensation and uses a lot less electricity than over night heating. Compressor type dehumidifiers are less effective than the desiccant type under low temperature conditions. Unfortunately most of them smell and you need to arrange for the control to switch off the heating element prior to turning off the power. This is a simple modification but must be done by a competent person.

Have fun with the build and size the motors when you have worked out the mass of the parts to be moved and the acceleration / speeds you want. Don't forget that steppers lose torque when you invoke micro-stepping.

Regards - Pat

[RomanLini]

I don't like the idea of a delicate precision machine getting even "storage" temperatures of -29'C.

Depending on the alignment of linear bearings and bedways etc the metal contraction can cause a lot of force and pull things out of alignment or crack bearings on linear shafts with really high point loads at low temps etc.

I think stepper motor storage temperature is the least of your worries...

You might want to make the whole machine from steel so the contraction of the machine and bearings etc are all constant. If you have steel linear bearing rails on an aluminium plate (or even wood) you will have some serious issues...