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H bridge for Bipolar Stepper Driver

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tdport

New Member
Hello, I am planning on attempting to build a bipolar stepper driver. I was looking into the wiring diagrams for Bipolar Parallel of an 8 wire motor and I am having trouble understanding how to drive the A, A-, B and B-. I was originally intending on using 4 MOSFETS and a PIC18, but I realize now that the bipolar stepper is going to need more complicated circuitry. I only need to drive in one direction. I am not familiar with an H bridge and my MOSFET are for 30V and 25Amps as I am driving 4 stepper from the 4 MOSFET system. All will move in unison. If you have any suggestions or ideas on how I can make this project come together I appreciate it. Have a nice day.
 

Sceadwian

Banned
If it's not too late see if you can get unipolar steppers, it simplifies things dramatically.
 

tdport

New Member
Nice job on the H-bridge work. I tried to meet with a prof at GT today to get some tips but he was out of the office. It looks doable and quite simple from the picture. I am posting a schematic I found that seems to be more complicated for the H-bridge. I also am adding the motor description .pdf. Could you elaborate further on where the A, A-, B, and B- are connected into the H-bridge. I imagine one H-bridge is for A and the other is for B connections. I don't know if it is better. I understand there are PNP and NPN transistor, but are MOSFETS of a different category completely or are there PNP... MOSFETS as well?

I need to get something straight:
these motors are 8 wire 4 phase steppers. It is 6.3 Amps per phase. I am intending on running all 4 motors from one driver. Does that mean that each MOSFET must be able to release 25 amps? Then these diodes will also need to be able to withstand the 25 amps without breaking down correct? Are you using a special type of diode or any will do?

Also: I am going to try to do the wiring to the motors this weekend as they are 10 feet away from where I can put the driver. It is an 8 wire stepper but will be in bipolar parallel configuration. Does this mean that only 4 wires are necessary to the stepper motor. That is my assumption based on the wiring diagram?

I am sorry to bombard you with so many questions, my final one is I have a solder-less breadboard and I was wondering if you think the breadboard would be able to handle the 25 amp loads? It is a 3,200 point breadboard with 4 Power supply connections. Thanks for all your help.
 

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tdport

New Member
If it's not too late see if you can get unipolar steppers, it simplifies things dramatically.
I am needing over 25 lb/in rolling torque and I was told there is at least a 1/3 drop of torque from the beginning if I do unipolar. What is you opinion?
 

Sceadwian

Banned
You can wire those any way you please, each pair of wires is a coil.
Stepper Motor wiring
Sorry, I'm not used to seeing those, most of the steppers I get are 5/6 wire unipolar or 4 wire bipolar. If you noticed the only difference between the steppers is how their coils are connected you can wire the ones you have any way you want. The only way I've ever wired them is like a 5 wire stepper, where the common is fed VCC and you use 4 fets to ground each of the phases of the stepper in pairs to drive it. As far as exactly how much torque you'll get out of each possible setup I'm not sure, as long as they're driven with the same relative current the torque should be the same.
 

tdport

New Member
Torque

I have received two very different responses on this issue of torque.
1. I was told months back that as long as I am above the rated torque the stepper will move. If the volts are not high enough then at a certain pulses per second my torque will degrade. This seems to ring true to me and I hope this is right.

2. I was told today from another stepper supplier that I will not have enough torque from the beginning because my voltage is too low.

My understanding was the higher the voltage the faster you can send pulses to the stepper and the coils still fully charge. If you send pulses slow to a stepper motor then it will have full torque whether the voltage is 2 time or 10 times above the rated voltage as long as the coils are filling up.

My certain situation. The rated voltage is 2.3Volts. I am supplying 12Volts. I will only be running around 300-600 pulses per second in full step mode.
 

Sceadwian

Banned
Higher voltage is better, but if you don't limit the current that things gonna go up in flames. Sure it'll be fine under low or no load situations, but if the stepper shaft is ever stalled somehow poof. Being a mechanical device you can certifiably guarantee that it's going to undergo greater load than it was designed for at some point in it's life.
 
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tdport

New Member
resistors

I have run into another problem in my pursuit to drive these stepper motors. The drive I found that would work for my application requires a resistor to be placed between the motor coil and driver to limit the max amperage passing through. The figures I have come up with are I need a 1.5 Ohm resistor rated at 76 watts. That is crazy- and I need 8 because it takes 2 per motor. Is there a better way to do this like: 1 power resistor between the power supply and the 4 drivers?
 

Sceadwian

Banned
Use a power supply for the stepper motors that can only put out the max current your motor can take.
 
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