Amperage for power supply

[Curtis Erpeldin]

I am trying to figure out the power supply I will need to run four identical stepper motors in bipolar parallel mode. The amp rating/phase of a single motor is 5 amps when used in bipolar parallel mode. My drivers are Gecko G201's. In the 201 manual it says I will need 67% of the rated phase amperage from my power supply. Since I'm running four motors, does this mean I need a power supply rated at 13.4 amps? (.67 * 5 * 4). I've already calculated the voltage of the power supply from the Gecko formula: 32 * sq rt mH to be about 40 volts (32 * sq rt of 1.65mH). This is less than 25 times the rated voltage (1.9v) of the motor, so I think I'm OK with a 40volt power supply. So should I stay at or under 13.4 amps for the current supply? As you may guess, I know next to nothing about electronics. I'm just trying to plug in the specs from my various components to determine the power supply I need. Thanks for any help.

CE

[ger21]

I'd go with a 15 amp supply. It doesn't hurt to have a little extra if needed. But if you could get a 12a supply for a lot cheaper, it would probably be OK, as it's unlikely that all 4 motors will be drawing full current at the same time.

[gfc62]

Originally Posted by Curtis Erpeldin ...So should I stay at or under 13.4 amps for the current supply? As you may guess, I know next to nothing about electronics. I'm just trying to plug in the specs from my various components to determine the power supply I need. Thanks for any help.... CE

It's OK to think about staying at or under a voltage rating but when you ask about staying under an amperage rating you should rethink the question and remind yourself about the difference between voltage and amperage.

The hydraulic analogy of electricity isn't a perfect metaphor but can be used effectively here. If someone told you they were about to quadruple the water pressure serving your house, your experience and common sense would cause you to doubt this decision; too much pressure can clearly cause problems.

If instead you were told that the potential flow rate of water into your house would quadruple, let's say the water mains were enlarged, you'd likely figure out that this was no problem since your existing pipes will throttle the flow rate of the incoming water, allowing each plumbing circuit to take advantage of the maximum flow it can handle.

Voltage is like water pressure, amperage is like water flow. Too much voltage or pressure is problematic. Too much flow or amperage isn't since the plumbing or electrical system can only draw what it needs.

Buying a too-high amperage power supply will only cost you more money, it won't cause any problems. Round up a bit on amp ratings if you can afford to.

[Curtis Erpeldin]

Thanks to both of you for your advice. Now another related question. What's the difference between a regulated and unregulated power supply given the same voltage and amperage rating and how would that affect the motors?CE

[gfc62]

Originally Posted by Curtis Erpeldin Thanks to both of you for your advice. Now another related question. What's the difference between a regulated and unregulated power supply given the same voltage and amperage rating and how would that affect the motors?CE

The easy answer is that motors don't like regulated power supplies so don't spend money on one.

A regulated supply attempts to maintain a constant voltage output regardless of the load. These are needed for electronic components that are voltage sensitive. Some power supplies (like many of the Antek units) provide both unregulated output for the motors and a lower voltage (5V or 12V) output for any controlling electronics.