Thread: Power supply for stepper motor

1. Power supply for stepper motor

Hello,

Can anyone explain to me how to calculate the supply voltage and the current needed for stepper motor ? Or maybe a link ?

I have 3 stepper motors rated at :
- 5,2V and 1A per phase for one
- 2,6V and 1,2A per phase for the 2 others

I need the formulas for an unregulated PSU as my driver cards use chopper mode. They use LMD18245T rated at 55V/3A.

Thank you for all the help you can give me !

Gaelle

2. Download 'Step motor basics.pdf' at www.geckodrive.com/support.cfm That white paper explains most of what you'll need to know to get started using stepper motors.

I know that you've written that you're not using Gecko stepper drivers, but I've used this general forumla to size power supplies for several years:

AMPS = SUM(amps required for all motors) X 0.66

Voltage = Minimum, 10X motor's rated voltage, Maximum, 20X motor's rated voltage

In your case: 1A + 1.2A + 1.2A = 3.4A and 3.4A X 0.66 = 2.24A, 5.2V X 10 = 50.2 V, 2.6V X 20 = 52V. So, a power supply that produces at least 2.25A at 50VDC would be my starting point.

If I were building my own power supply, I could buy a toroidal transformer (AVEL Y236654, \$46.10 from www.partsExpress.com), a 10A 100V bridge rectifier (less than \$10), and a computer grade 63V 15,000 uF can-style capacitor (about \$35). Or, I would buy a complete unit from AnTek, such at the PS-3N50 for \$85 (www.toroid-transformer.com).

3. Thank you Richards !

If I buy the PS-3N50 i would have 6A. You said that my rated current is 2.25A. This 6A is not too much ?

Best regards.

Gaelle

4. No, the power supply can supply more current than the motor requires. The motor will only 'pull' as much current as it needs from the power supply. Think of the current capacity of the power supply as money in the bank. As long as you draw less money from the bank account than the amount of money that you have in the account, everything is fine; however, if you tried to withdraw more money from the account than the amount of money that you had available, the transaction would fail. That's basically how power supplies and motors work. As long as the power supply can generate more power (current) than the motor needs, everything works fine; however, if the motor tries to draw more current than the power supply can generate, the power supply will overheat and eventually fail.

To keep size and cost reasonable, I try to size a power supply to generate between 150% and 200% of the required current. (If I know exactly how much current the circuit requires and if that current requirement is constant, then I'll sometimes install a power supply that 'only' supplies 125% of the required current.) In most cases, having 50% to 100% margin means that the power supply will run much cooler, and, in cases like this, when a variety of off-the-shelf power supplies are similar in size and cost, be safe and buy one with extra current capability.

5. Thank you for your explanation ! I'll go to buy all what I need §

Bye

6. Originally Posted by Richards
Voltage = Minimum, 10X motor's rated voltage, Maximum, 20X motor's rated voltage

In your case: 1A + 1.2A + 1.2A = 3.4A and 3.4A X 0.66 = 2.24A, 5.2V X 10 = 50.2 V, 2.6V X 20 = 52V. So, a power supply that produces at least 2.25A at 50VDC would be my starting point.

If I were building my own power supply, I could buy a toroidal transformer (AVEL Y236654, \$46.10 from www.partsExpress.com).
Hi. Thanks for the info...

Regarding the Volts. How did you get to the 10x and 20x? (is that for all steppers?)

I have 3 Nema17 steppers that I am building a power supply for. It is rated at 5V and 1.2A.

To be honest I am finding it hard to think that you can give it 50V without burning it.. LOL

I using a HobbyCNC Pro stepper driver board and they suggest 24v min for the power supply.

Any more advice to help me understand the concept?

Thanks.

7. Chopper drives use a high voltage to 'force' current into the motor. The motor never actually sees the higher voltage because it is 'chopped' as soon as internal feedback sensors detect that the voltage/current is rising. Here is a quote from the Gecko G202 manual:

PLEASE READ FIRST BEFORE USING THE G202
Before you start, you must have a suitable step motor, a DC power supply suitable for the motor and a current set resistor. The motor’s rated phase current must be between 0.3 Amp and 7 Amps. The power supply voltage must be between 4 times and 20 times the motor’s rated voltage. The current set resistor may be a 1/4 Watt, 5% part. Finally have a STEP and DIRECTION pulse source available.

Of course, the 4X to 20X applies to Gecko products. Other stepper drive manufacturers have their own limits. Personally, I've found that a 10X to 15X multiplier works very well with my applications. It is a good compromise between heat and speed. I use Gecko G202 and G203 stepper drivers with Oriental Motor PK29x drives.

8. Originally Posted by Richards
Chopper drives use a high voltage to 'force' current into the motor. The motor never actually sees the higher voltage because it is 'chopped' as soon as internal feedback sensors detect that the voltage/current is rising. Here is a quote from the Gecko G202 manual:

PLEASE READ FIRST BEFORE USING THE G202
Before you start, you must have a suitable step motor, a DC power supply suitable for the motor and a current set resistor. The motor’s rated phase current must be between 0.3 Amp and 7 Amps. The power supply voltage must be between 4 times and 20 times the motor’s rated voltage. The current set resistor may be a 1/4 Watt, 5% part. Finally have a STEP and DIRECTION pulse source available.

Of course, the 4X to 20X applies to Gecko products. Other stepper drive manufacturers have their own limits. Personally, I've found that a 10X to 15X multiplier works very well with my applications. It is a good compromise between heat and speed. I use Gecko G202 and G203 stepper drivers with Oriental Motor PK29x drives.
Its starting to get clear now...

Thanks for the info.