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Topic: Regulate the voltage with a A4988 (Read 391 times) previous topic - next topic

Ant_Wan_Kenobi

Jun 21, 2019, 04:41 pm Last Edit: Jun 21, 2019, 05:47 pm by Ant_Wan_Kenobi
Hey !
I'd like to control a stepper motor (working at 2.8V and 2A/phase) with a A4988, I have a 12V 5A external power supply to power everything.
I found a lot of threads showing how to control the current you give to the motor but not about the voltage.
So here is my question:
Can I reduce the voltage (12V) of my power supply to 2.8V for my stepper motor ?
Can it be handled on the board or must I buy a buck converter ?
Thx !

wvmarle

You regulate the voltage by regulating the current. There's a little pot on the board to do just that. Remember to add a heat sink if you want more than 1A of current.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

MorganS

The A4988 is a sort of buck converter. That is why we love it. You don't need to add any components.
"The problem is in the code you didn't post."

groundFungus

#3
Jun 23, 2019, 04:36 pm Last Edit: Jun 23, 2019, 04:36 pm by groundFungus
The voltage to the stepper is not relevant.  The current to the coils is relevant.  An A4988 controls the current (as set by the user).  Even with a heat sink and fan cooling, 2A is on the ragged edge for for an A4988.

Ant_Wan_Kenobi

Hey, thanks for your answers that helped me out !
I choose an other stepper motor:
- it's cheaper,
- has the same torque for smaller,
- is 1.7A (further from the A4988 limit),
- is 12V.
Thx !

wvmarle

I hope you realise the nonsensical ratings the seller gives you?

1.7A current. Sensible.
30Ω winding resistance. Well, sounds a bit high but within the realm of possibilities.
12V supply. Unusual for steppers that are indeed current driven.

But... since when does 30 * 1.7 equal 12?

Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

MarkT

Hey !
I'd like to control a stepper motor (working at 2.8V and 2A/phase) with a A4988, I have a 12V 5A external power supply to power everything.
I found a lot of threads showing how to control the current you give to the motor but not about the voltage.
You don't control the voltage, you control the current.   There's no way you can control both, the load won't cooperate.
Quote
So here is my question:
Can I reduce the voltage (12V) of my power supply to 2.8V for my stepper motor ?
No, it won't work, the A4988 needs at least 8V to function at all.
Quote
Can it be handled on the board or must I buy a buck converter ?
Thx !
Absolutely nothing needs doing.  You might want to _increase_ the supply voltage for better performance, however.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

Ant_Wan_Kenobi

I hope you realise the nonsensical ratings the seller gives you?

1.7A current. Sensible.
30Ω winding resistance. Well, sounds a bit high but within the realm of possibilities.
12V supply. Unusual for steppers that are indeed current driven.

But... since when does 30 * 1.7 equal 12?


Yes, I made myself the same reflexion...
What would you suggest ? Should I look for an other stepper motor with correct ratings ?

wvmarle

I've learned to ignore the nonsense written in e-bay and similar ads, instead look up the datasheet of the part.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

Ant_Wan_Kenobi

I've learned to ignore the nonsense written in e-bay and similar ads, instead look up the datasheet of the part.
Turned out the 1.7 Amps were actually 0.4 Amps.
The stepper motor's ref was hidden on a picture: 42SHD0001-24B.
Looked on an other website that had the same motor and turns out its current is 0.4A (0.4*30 = 12).
Thx !

wvmarle

This are much more typical stepper specifications: coil resistance 2.1Ω and rated current 1.33A, that comes to a voltage of 2.8V which is also very typical for steppers.

And that's also why they're rated 5-24V and you need a stepper driver (which acts like a buck converter, using the stepper's coil instead of a fixed inductor). Without stepper driver the coils would indeed burn out pretty quickly.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

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